YQ Connector: support managed ClickHouse

Со стороны dqrun можно обратиться к инстансу коннектора, который работает на streaming стенде, и извлечь данные из облачного CH.

1 files changed, 18297 insertions, 0 deletions

diff --git a/contrib/libs/clang14/lib/Sema/SemaDeclCXX.cpp b/contrib/libs/clang14/lib/Sema/SemaDeclCXX.cpp
new file mode 100644
index 0000000000..16cdb7e577
--- /dev/null
+++ b/contrib/libs/clang14/lib/Sema/SemaDeclCXX.cpp
@@ -0,0 +1,18297 @@
+//===------ SemaDeclCXX.cpp - Semantic Analysis for C++ Declarations ------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements semantic analysis for C++ declarations.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/AST/ASTConsumer.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/ASTLambda.h"
+#include "clang/AST/ASTMutationListener.h"
+#include "clang/AST/CXXInheritance.h"
+#include "clang/AST/CharUnits.h"
+#include "clang/AST/ComparisonCategories.h"
+#include "clang/AST/EvaluatedExprVisitor.h"
+#include "clang/AST/ExprCXX.h"
+#include "clang/AST/RecordLayout.h"
+#include "clang/AST/RecursiveASTVisitor.h"
+#include "clang/AST/StmtVisitor.h"
+#include "clang/AST/TypeLoc.h"
+#include "clang/AST/TypeOrdering.h"
+#include "clang/Basic/AttributeCommonInfo.h"
+#include "clang/Basic/PartialDiagnostic.h"
+#include "clang/Basic/Specifiers.h"
+#include "clang/Basic/TargetInfo.h"
+#include "clang/Lex/LiteralSupport.h"
+#include "clang/Lex/Preprocessor.h"
+#include "clang/Sema/CXXFieldCollector.h"
+#include "clang/Sema/DeclSpec.h"
+#include "clang/Sema/Initialization.h"
+#include "clang/Sema/Lookup.h"
+#include "clang/Sema/ParsedTemplate.h"
+#include "clang/Sema/Scope.h"
+#include "clang/Sema/ScopeInfo.h"
+#include "clang/Sema/SemaInternal.h"
+#include "clang/Sema/Template.h"
+#include "llvm/ADT/ScopeExit.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/StringExtras.h"
+#include <map>
+#include <set>
+
+using namespace clang;
+
+//===----------------------------------------------------------------------===//
+// CheckDefaultArgumentVisitor
+//===----------------------------------------------------------------------===//
+
+namespace {
+/// CheckDefaultArgumentVisitor - C++ [dcl.fct.default] Traverses
+/// the default argument of a parameter to determine whether it
+/// contains any ill-formed subexpressions. For example, this will
+/// diagnose the use of local variables or parameters within the
+/// default argument expression.
+class CheckDefaultArgumentVisitor
+    : public ConstStmtVisitor<CheckDefaultArgumentVisitor, bool> {
+  Sema &S;
+  const Expr *DefaultArg;
+
+public:
+  CheckDefaultArgumentVisitor(Sema &S, const Expr *DefaultArg)
+      : S(S), DefaultArg(DefaultArg) {}
+
+  bool VisitExpr(const Expr *Node);
+  bool VisitDeclRefExpr(const DeclRefExpr *DRE);
+  bool VisitCXXThisExpr(const CXXThisExpr *ThisE);
+  bool VisitLambdaExpr(const LambdaExpr *Lambda);
+  bool VisitPseudoObjectExpr(const PseudoObjectExpr *POE);
+};
+
+/// VisitExpr - Visit all of the children of this expression.
+bool CheckDefaultArgumentVisitor::VisitExpr(const Expr *Node) {
+  bool IsInvalid = false;
+  for (const Stmt *SubStmt : Node->children())
+    IsInvalid |= Visit(SubStmt);
+  return IsInvalid;
+}
+
+/// VisitDeclRefExpr - Visit a reference to a declaration, to
+/// determine whether this declaration can be used in the default
+/// argument expression.
+bool CheckDefaultArgumentVisitor::VisitDeclRefExpr(const DeclRefExpr *DRE) {
+  const NamedDecl *Decl = DRE->getDecl();
+  if (const auto *Param = dyn_cast<ParmVarDecl>(Decl)) {
+    // C++ [dcl.fct.default]p9:
+    //   [...] parameters of a function shall not be used in default
+    //   argument expressions, even if they are not evaluated. [...]
+    //
+    // C++17 [dcl.fct.default]p9 (by CWG 2082):
+    //   [...] A parameter shall not appear as a potentially-evaluated
+    //   expression in a default argument. [...]
+    //
+    if (DRE->isNonOdrUse() != NOUR_Unevaluated)
+      return S.Diag(DRE->getBeginLoc(),
+                    diag::err_param_default_argument_references_param)
+             << Param->getDeclName() << DefaultArg->getSourceRange();
+  } else if (const auto *VDecl = dyn_cast<VarDecl>(Decl)) {
+    // C++ [dcl.fct.default]p7:
+    //   Local variables shall not be used in default argument
+    //   expressions.
+    //
+    // C++17 [dcl.fct.default]p7 (by CWG 2082):
+    //   A local variable shall not appear as a potentially-evaluated
+    //   expression in a default argument.
+    //
+    // C++20 [dcl.fct.default]p7 (DR as part of P0588R1, see also CWG 2346):
+    //   Note: A local variable cannot be odr-used (6.3) in a default argument.
+    //
+    if (VDecl->isLocalVarDecl() && !DRE->isNonOdrUse())
+      return S.Diag(DRE->getBeginLoc(),
+                    diag::err_param_default_argument_references_local)
+             << VDecl->getDeclName() << DefaultArg->getSourceRange();
+  }
+
+  return false;
+}
+
+/// VisitCXXThisExpr - Visit a C++ "this" expression.
+bool CheckDefaultArgumentVisitor::VisitCXXThisExpr(const CXXThisExpr *ThisE) {
+  // C++ [dcl.fct.default]p8:
+  //   The keyword this shall not be used in a default argument of a
+  //   member function.
+  return S.Diag(ThisE->getBeginLoc(),
+                diag::err_param_default_argument_references_this)
+         << ThisE->getSourceRange();
+}
+
+bool CheckDefaultArgumentVisitor::VisitPseudoObjectExpr(
+    const PseudoObjectExpr *POE) {
+  bool Invalid = false;
+  for (const Expr *E : POE->semantics()) {
+    // Look through bindings.
+    if (const auto *OVE = dyn_cast<OpaqueValueExpr>(E)) {
+      E = OVE->getSourceExpr();
+      assert(E && "pseudo-object binding without source expression?");
+    }
+
+    Invalid |= Visit(E);
+  }
+  return Invalid;
+}
+
+bool CheckDefaultArgumentVisitor::VisitLambdaExpr(const LambdaExpr *Lambda) {
+  // C++11 [expr.lambda.prim]p13:
+  //   A lambda-expression appearing in a default argument shall not
+  //   implicitly or explicitly capture any entity.
+  if (Lambda->capture_begin() == Lambda->capture_end())
+    return false;
+
+  return S.Diag(Lambda->getBeginLoc(), diag::err_lambda_capture_default_arg);
+}
+} // namespace
+
+void
+Sema::ImplicitExceptionSpecification::CalledDecl(SourceLocation CallLoc,
+                                                 const CXXMethodDecl *Method) {
+  // If we have an MSAny spec already, don't bother.
+  if (!Method || ComputedEST == EST_MSAny)
+    return;
+
+  const FunctionProtoType *Proto
+    = Method->getType()->getAs<FunctionProtoType>();
+  Proto = Self->ResolveExceptionSpec(CallLoc, Proto);
+  if (!Proto)
+    return;
+
+  ExceptionSpecificationType EST = Proto->getExceptionSpecType();
+
+  // If we have a throw-all spec at this point, ignore the function.
+  if (ComputedEST == EST_None)
+    return;
+
+  if (EST == EST_None && Method->hasAttr<NoThrowAttr>())
+    EST = EST_BasicNoexcept;
+
+  switch (EST) {
+  case EST_Unparsed:
+  case EST_Uninstantiated:
+  case EST_Unevaluated:
+    llvm_unreachable("should not see unresolved exception specs here");
+
+  // If this function can throw any exceptions, make a note of that.
+  case EST_MSAny:
+  case EST_None:
+    // FIXME: Whichever we see last of MSAny and None determines our result.
+    // We should make a consistent, order-independent choice here.
+    ClearExceptions();
+    ComputedEST = EST;
+    return;
+  case EST_NoexceptFalse:
+    ClearExceptions();
+    ComputedEST = EST_None;
+    return;
+  // FIXME: If the call to this decl is using any of its default arguments, we
+  // need to search them for potentially-throwing calls.
+  // If this function has a basic noexcept, it doesn't affect the outcome.
+  case EST_BasicNoexcept:
+  case EST_NoexceptTrue:
+  case EST_NoThrow:
+    return;
+  // If we're still at noexcept(true) and there's a throw() callee,
+  // change to that specification.
+  case EST_DynamicNone:
+    if (ComputedEST == EST_BasicNoexcept)
+      ComputedEST = EST_DynamicNone;
+    return;
+  case EST_DependentNoexcept:
+    llvm_unreachable(
+        "should not generate implicit declarations for dependent cases");
+  case EST_Dynamic:
+    break;
+  }
+  assert(EST == EST_Dynamic && "EST case not considered earlier.");
+  assert(ComputedEST != EST_None &&
+         "Shouldn't collect exceptions when throw-all is guaranteed.");
+  ComputedEST = EST_Dynamic;
+  // Record the exceptions in this function's exception specification.
+  for (const auto &E : Proto->exceptions())
+    if (ExceptionsSeen.insert(Self->Context.getCanonicalType(E)).second)
+      Exceptions.push_back(E);
+}
+
+void Sema::ImplicitExceptionSpecification::CalledStmt(Stmt *S) {
+  if (!S || ComputedEST == EST_MSAny)
+    return;
+
+  // FIXME:
+  //
+  // C++0x [except.spec]p14:
+  //   [An] implicit exception-specification specifies the type-id T if and
+  // only if T is allowed by the exception-specification of a function directly
+  // invoked by f's implicit definition; f shall allow all exceptions if any
+  // function it directly invokes allows all exceptions, and f shall allow no
+  // exceptions if every function it directly invokes allows no exceptions.
+  //
+  // Note in particular that if an implicit exception-specification is generated
+  // for a function containing a throw-expression, that specification can still
+  // be noexcept(true).
+  //
+  // Note also that 'directly invoked' is not defined in the standard, and there
+  // is no indication that we should only consider potentially-evaluated calls.
+  //
+  // Ultimately we should implement the intent of the standard: the exception
+  // specification should be the set of exceptions which can be thrown by the
+  // implicit definition. For now, we assume that any non-nothrow expression can
+  // throw any exception.
+
+  if (Self->canThrow(S))
+    ComputedEST = EST_None;
+}
+
+ExprResult Sema::ConvertParamDefaultArgument(ParmVarDecl *Param, Expr *Arg,
+                                             SourceLocation EqualLoc) {
+  if (RequireCompleteType(Param->getLocation(), Param->getType(),
+                          diag::err_typecheck_decl_incomplete_type))
+    return true;
+
+  // C++ [dcl.fct.default]p5
+  //   A default argument expression is implicitly converted (clause
+  //   4) to the parameter type. The default argument expression has
+  //   the same semantic constraints as the initializer expression in
+  //   a declaration of a variable of the parameter type, using the
+  //   copy-initialization semantics (8.5).
+  InitializedEntity Entity = InitializedEntity::InitializeParameter(Context,
+                                                                    Param);
+  InitializationKind Kind = InitializationKind::CreateCopy(Param->getLocation(),
+                                                           EqualLoc);
+  InitializationSequence InitSeq(*this, Entity, Kind, Arg);
+  ExprResult Result = InitSeq.Perform(*this, Entity, Kind, Arg);
+  if (Result.isInvalid())
+    return true;
+  Arg = Result.getAs<Expr>();
+
+  CheckCompletedExpr(Arg, EqualLoc);
+  Arg = MaybeCreateExprWithCleanups(Arg);
+
+  return Arg;
+}
+
+void Sema::SetParamDefaultArgument(ParmVarDecl *Param, Expr *Arg,
+                                   SourceLocation EqualLoc) {
+  // Add the default argument to the parameter
+  Param->setDefaultArg(Arg);
+
+  // We have already instantiated this parameter; provide each of the
+  // instantiations with the uninstantiated default argument.
+  UnparsedDefaultArgInstantiationsMap::iterator InstPos
+    = UnparsedDefaultArgInstantiations.find(Param);
+  if (InstPos != UnparsedDefaultArgInstantiations.end()) {
+    for (unsigned I = 0, N = InstPos->second.size(); I != N; ++I)
+      InstPos->second[I]->setUninstantiatedDefaultArg(Arg);
+
+    // We're done tracking this parameter's instantiations.
+    UnparsedDefaultArgInstantiations.erase(InstPos);
+  }
+}
+
+/// ActOnParamDefaultArgument - Check whether the default argument
+/// provided for a function parameter is well-formed. If so, attach it
+/// to the parameter declaration.
+void
+Sema::ActOnParamDefaultArgument(Decl *param, SourceLocation EqualLoc,
+                                Expr *DefaultArg) {
+  if (!param || !DefaultArg)
+    return;
+
+  ParmVarDecl *Param = cast<ParmVarDecl>(param);
+  UnparsedDefaultArgLocs.erase(Param);
+
+  auto Fail = [&] {
+    Param->setInvalidDecl();
+    Param->setDefaultArg(new (Context) OpaqueValueExpr(
+        EqualLoc, Param->getType().getNonReferenceType(), VK_PRValue));
+  };
+
+  // Default arguments are only permitted in C++
+  if (!getLangOpts().CPlusPlus) {
+    Diag(EqualLoc, diag::err_param_default_argument)
+      << DefaultArg->getSourceRange();
+    return Fail();
+  }
+
+  // Check for unexpanded parameter packs.
+  if (DiagnoseUnexpandedParameterPack(DefaultArg, UPPC_DefaultArgument)) {
+    return Fail();
+  }
+
+  // C++11 [dcl.fct.default]p3
+  //   A default argument expression [...] shall not be specified for a
+  //   parameter pack.
+  if (Param->isParameterPack()) {
+    Diag(EqualLoc, diag::err_param_default_argument_on_parameter_pack)
+        << DefaultArg->getSourceRange();
+    // Recover by discarding the default argument.
+    Param->setDefaultArg(nullptr);
+    return;
+  }
+
+  ExprResult Result = ConvertParamDefaultArgument(Param, DefaultArg, EqualLoc);
+  if (Result.isInvalid())
+    return Fail();
+
+  DefaultArg = Result.getAs<Expr>();
+
+  // Check that the default argument is well-formed
+  CheckDefaultArgumentVisitor DefaultArgChecker(*this, DefaultArg);
+  if (DefaultArgChecker.Visit(DefaultArg))
+    return Fail();
+
+  SetParamDefaultArgument(Param, DefaultArg, EqualLoc);
+}
+
+/// ActOnParamUnparsedDefaultArgument - We've seen a default
+/// argument for a function parameter, but we can't parse it yet
+/// because we're inside a class definition. Note that this default
+/// argument will be parsed later.
+void Sema::ActOnParamUnparsedDefaultArgument(Decl *param,
+                                             SourceLocation EqualLoc,
+                                             SourceLocation ArgLoc) {
+  if (!param)
+    return;
+
+  ParmVarDecl *Param = cast<ParmVarDecl>(param);
+  Param->setUnparsedDefaultArg();
+  UnparsedDefaultArgLocs[Param] = ArgLoc;
+}
+
+/// ActOnParamDefaultArgumentError - Parsing or semantic analysis of
+/// the default argument for the parameter param failed.
+void Sema::ActOnParamDefaultArgumentError(Decl *param,
+                                          SourceLocation EqualLoc) {
+  if (!param)
+    return;
+
+  ParmVarDecl *Param = cast<ParmVarDecl>(param);
+  Param->setInvalidDecl();
+  UnparsedDefaultArgLocs.erase(Param);
+  Param->setDefaultArg(new (Context) OpaqueValueExpr(
+      EqualLoc, Param->getType().getNonReferenceType(), VK_PRValue));
+}
+
+/// CheckExtraCXXDefaultArguments - Check for any extra default
+/// arguments in the declarator, which is not a function declaration
+/// or definition and therefore is not permitted to have default
+/// arguments. This routine should be invoked for every declarator
+/// that is not a function declaration or definition.
+void Sema::CheckExtraCXXDefaultArguments(Declarator &D) {
+  // C++ [dcl.fct.default]p3
+  //   A default argument expression shall be specified only in the
+  //   parameter-declaration-clause of a function declaration or in a
+  //   template-parameter (14.1). It shall not be specified for a
+  //   parameter pack. If it is specified in a
+  //   parameter-declaration-clause, it shall not occur within a
+  //   declarator or abstract-declarator of a parameter-declaration.
+  bool MightBeFunction = D.isFunctionDeclarationContext();
+  for (unsigned i = 0, e = D.getNumTypeObjects(); i != e; ++i) {
+    DeclaratorChunk &chunk = D.getTypeObject(i);
+    if (chunk.Kind == DeclaratorChunk::Function) {
+      if (MightBeFunction) {
+        // This is a function declaration. It can have default arguments, but
+        // keep looking in case its return type is a function type with default
+        // arguments.
+        MightBeFunction = false;
+        continue;
+      }
+      for (unsigned argIdx = 0, e = chunk.Fun.NumParams; argIdx != e;
+           ++argIdx) {
+        ParmVarDecl *Param = cast<ParmVarDecl>(chunk.Fun.Params[argIdx].Param);
+        if (Param->hasUnparsedDefaultArg()) {
+          std::unique_ptr<CachedTokens> Toks =
+              std::move(chunk.Fun.Params[argIdx].DefaultArgTokens);
+          SourceRange SR;
+          if (Toks->size() > 1)
+            SR = SourceRange((*Toks)[1].getLocation(),
+                             Toks->back().getLocation());
+          else
+            SR = UnparsedDefaultArgLocs[Param];
+          Diag(Param->getLocation(), diag::err_param_default_argument_nonfunc)
+            << SR;
+        } else if (Param->getDefaultArg()) {
+          Diag(Param->getLocation(), diag::err_param_default_argument_nonfunc)
+            << Param->getDefaultArg()->getSourceRange();
+          Param->setDefaultArg(nullptr);
+        }
+      }
+    } else if (chunk.Kind != DeclaratorChunk::Paren) {
+      MightBeFunction = false;
+    }
+  }
+}
+
+static bool functionDeclHasDefaultArgument(const FunctionDecl *FD) {
+  return llvm::any_of(FD->parameters(), [](ParmVarDecl *P) {
+    return P->hasDefaultArg() && !P->hasInheritedDefaultArg();
+  });
+}
+
+/// MergeCXXFunctionDecl - Merge two declarations of the same C++
+/// function, once we already know that they have the same
+/// type. Subroutine of MergeFunctionDecl. Returns true if there was an
+/// error, false otherwise.
+bool Sema::MergeCXXFunctionDecl(FunctionDecl *New, FunctionDecl *Old,
+                                Scope *S) {
+  bool Invalid = false;
+
+  // The declaration context corresponding to the scope is the semantic
+  // parent, unless this is a local function declaration, in which case
+  // it is that surrounding function.
+  DeclContext *ScopeDC = New->isLocalExternDecl()
+                             ? New->getLexicalDeclContext()
+                             : New->getDeclContext();
+
+  // Find the previous declaration for the purpose of default arguments.
+  FunctionDecl *PrevForDefaultArgs = Old;
+  for (/**/; PrevForDefaultArgs;
+       // Don't bother looking back past the latest decl if this is a local
+       // extern declaration; nothing else could work.
+       PrevForDefaultArgs = New->isLocalExternDecl()
+                                ? nullptr
+                                : PrevForDefaultArgs->getPreviousDecl()) {
+    // Ignore hidden declarations.
+    if (!LookupResult::isVisible(*this, PrevForDefaultArgs))
+      continue;
+
+    if (S && !isDeclInScope(PrevForDefaultArgs, ScopeDC, S) &&
+        !New->isCXXClassMember()) {
+      // Ignore default arguments of old decl if they are not in
+      // the same scope and this is not an out-of-line definition of
+      // a member function.
+      continue;
+    }
+
+    if (PrevForDefaultArgs->isLocalExternDecl() != New->isLocalExternDecl()) {
+      // If only one of these is a local function declaration, then they are
+      // declared in different scopes, even though isDeclInScope may think
+      // they're in the same scope. (If both are local, the scope check is
+      // sufficient, and if neither is local, then they are in the same scope.)
+      continue;
+    }
+
+    // We found the right previous declaration.
+    break;
+  }
+
+  // C++ [dcl.fct.default]p4:
+  //   For non-template functions, default arguments can be added in
+  //   later declarations of a function in the same
+  //   scope. Declarations in different scopes have completely
+  //   distinct sets of default arguments. That is, declarations in
+  //   inner scopes do not acquire default arguments from
+  //   declarations in outer scopes, and vice versa. In a given
+  //   function declaration, all parameters subsequent to a
+  //   parameter with a default argument shall have default
+  //   arguments supplied in this or previous declarations. A
+  //   default argument shall not be redefined by a later
+  //   declaration (not even to the same value).
+  //
+  // C++ [dcl.fct.default]p6:
+  //   Except for member functions of class templates, the default arguments
+  //   in a member function definition that appears outside of the class
+  //   definition are added to the set of default arguments provided by the
+  //   member function declaration in the class definition.
+  for (unsigned p = 0, NumParams = PrevForDefaultArgs
+                                       ? PrevForDefaultArgs->getNumParams()
+                                       : 0;
+       p < NumParams; ++p) {
+    ParmVarDecl *OldParam = PrevForDefaultArgs->getParamDecl(p);
+    ParmVarDecl *NewParam = New->getParamDecl(p);
+
+    bool OldParamHasDfl = OldParam ? OldParam->hasDefaultArg() : false;
+    bool NewParamHasDfl = NewParam->hasDefaultArg();
+
+    if (OldParamHasDfl && NewParamHasDfl) {
+      unsigned DiagDefaultParamID =
+        diag::err_param_default_argument_redefinition;
+
+      // MSVC accepts that default parameters be redefined for member functions
+      // of template class. The new default parameter's value is ignored.
+      Invalid = true;
+      if (getLangOpts().MicrosoftExt) {
+        CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(New);
+        if (MD && MD->getParent()->getDescribedClassTemplate()) {
+          // Merge the old default argument into the new parameter.
+          NewParam->setHasInheritedDefaultArg();
+          if (OldParam->hasUninstantiatedDefaultArg())
+            NewParam->setUninstantiatedDefaultArg(
+                                      OldParam->getUninstantiatedDefaultArg());
+          else
+            NewParam->setDefaultArg(OldParam->getInit());
+          DiagDefaultParamID = diag::ext_param_default_argument_redefinition;
+          Invalid = false;
+        }
+      }
+
+      // FIXME: If we knew where the '=' was, we could easily provide a fix-it
+      // hint here. Alternatively, we could walk the type-source information
+      // for NewParam to find the last source location in the type... but it
+      // isn't worth the effort right now. This is the kind of test case that
+      // is hard to get right:
+      //   int f(int);
+      //   void g(int (*fp)(int) = f);
+      //   void g(int (*fp)(int) = &f);
+      Diag(NewParam->getLocation(), DiagDefaultParamID)
+        << NewParam->getDefaultArgRange();
+
+      // Look for the function declaration where the default argument was
+      // actually written, which may be a declaration prior to Old.
+      for (auto Older = PrevForDefaultArgs;
+           OldParam->hasInheritedDefaultArg(); /**/) {
+        Older = Older->getPreviousDecl();
+        OldParam = Older->getParamDecl(p);
+      }
+
+      Diag(OldParam->getLocation(), diag::note_previous_definition)
+        << OldParam->getDefaultArgRange();
+    } else if (OldParamHasDfl) {
+      // Merge the old default argument into the new parameter unless the new
+      // function is a friend declaration in a template class. In the latter
+      // case the default arguments will be inherited when the friend
+      // declaration will be instantiated.
+      if (New->getFriendObjectKind() == Decl::FOK_None ||
+          !New->getLexicalDeclContext()->isDependentContext()) {
+        // It's important to use getInit() here;  getDefaultArg()
+        // strips off any top-level ExprWithCleanups.
+        NewParam->setHasInheritedDefaultArg();
+        if (OldParam->hasUnparsedDefaultArg())
+          NewParam->setUnparsedDefaultArg();
+        else if (OldParam->hasUninstantiatedDefaultArg())
+          NewParam->setUninstantiatedDefaultArg(
+                                       OldParam->getUninstantiatedDefaultArg());
+        else
+          NewParam->setDefaultArg(OldParam->getInit());
+      }
+    } else if (NewParamHasDfl) {
+      if (New->getDescribedFunctionTemplate()) {
+        // Paragraph 4, quoted above, only applies to non-template functions.
+        Diag(NewParam->getLocation(),
+             diag::err_param_default_argument_template_redecl)
+          << NewParam->getDefaultArgRange();
+        Diag(PrevForDefaultArgs->getLocation(),
+             diag::note_template_prev_declaration)
+            << false;
+      } else if (New->getTemplateSpecializationKind()
+                   != TSK_ImplicitInstantiation &&
+                 New->getTemplateSpecializationKind() != TSK_Undeclared) {
+        // C++ [temp.expr.spec]p21:
+        //   Default function arguments shall not be specified in a declaration
+        //   or a definition for one of the following explicit specializations:
+        //     - the explicit specialization of a function template;
+        //     - the explicit specialization of a member function template;
+        //     - the explicit specialization of a member function of a class
+        //       template where the class template specialization to which the
+        //       member function specialization belongs is implicitly
+        //       instantiated.
+        Diag(NewParam->getLocation(), diag::err_template_spec_default_arg)
+          << (New->getTemplateSpecializationKind() ==TSK_ExplicitSpecialization)
+          << New->getDeclName()
+          << NewParam->getDefaultArgRange();
+      } else if (New->getDeclContext()->isDependentContext()) {
+        // C++ [dcl.fct.default]p6 (DR217):
+        //   Default arguments for a member function of a class template shall
+        //   be specified on the initial declaration of the member function
+        //   within the class template.
+        //
+        // Reading the tea leaves a bit in DR217 and its reference to DR205
+        // leads me to the conclusion that one cannot add default function
+        // arguments for an out-of-line definition of a member function of a
+        // dependent type.
+        int WhichKind = 2;
+        if (CXXRecordDecl *Record
+              = dyn_cast<CXXRecordDecl>(New->getDeclContext())) {
+          if (Record->getDescribedClassTemplate())
+            WhichKind = 0;
+          else if (isa<ClassTemplatePartialSpecializationDecl>(Record))
+            WhichKind = 1;
+          else
+            WhichKind = 2;
+        }
+
+        Diag(NewParam->getLocation(),
+             diag::err_param_default_argument_member_template_redecl)
+          << WhichKind
+          << NewParam->getDefaultArgRange();
+      }
+    }
+  }
+
+  // DR1344: If a default argument is added outside a class definition and that
+  // default argument makes the function a special member function, the program
+  // is ill-formed. This can only happen for constructors.
+  if (isa<CXXConstructorDecl>(New) &&
+      New->getMinRequiredArguments() < Old->getMinRequiredArguments()) {
+    CXXSpecialMember NewSM = getSpecialMember(cast<CXXMethodDecl>(New)),
+                     OldSM = getSpecialMember(cast<CXXMethodDecl>(Old));
+    if (NewSM != OldSM) {
+      ParmVarDecl *NewParam = New->getParamDecl(New->getMinRequiredArguments());
+      assert(NewParam->hasDefaultArg());
+      Diag(NewParam->getLocation(), diag::err_default_arg_makes_ctor_special)
+        << NewParam->getDefaultArgRange() << NewSM;
+      Diag(Old->getLocation(), diag::note_previous_declaration);
+    }
+  }
+
+  const FunctionDecl *Def;
+  // C++11 [dcl.constexpr]p1: If any declaration of a function or function
+  // template has a constexpr specifier then all its declarations shall
+  // contain the constexpr specifier.
+  if (New->getConstexprKind() != Old->getConstexprKind()) {
+    Diag(New->getLocation(), diag::err_constexpr_redecl_mismatch)
+        << New << static_cast<int>(New->getConstexprKind())
+        << static_cast<int>(Old->getConstexprKind());
+    Diag(Old->getLocation(), diag::note_previous_declaration);
+    Invalid = true;
+  } else if (!Old->getMostRecentDecl()->isInlined() && New->isInlined() &&
+             Old->isDefined(Def) &&
+             // If a friend function is inlined but does not have 'inline'
+             // specifier, it is a definition. Do not report attribute conflict
+             // in this case, redefinition will be diagnosed later.
+             (New->isInlineSpecified() ||
+              New->getFriendObjectKind() == Decl::FOK_None)) {
+    // C++11 [dcl.fcn.spec]p4:
+    //   If the definition of a function appears in a translation unit before its
+    //   first declaration as inline, the program is ill-formed.
+    Diag(New->getLocation(), diag::err_inline_decl_follows_def) << New;
+    Diag(Def->getLocation(), diag::note_previous_definition);
+    Invalid = true;
+  }
+
+  // C++17 [temp.deduct.guide]p3:
+  //   Two deduction guide declarations in the same translation unit
+  //   for the same class template shall not have equivalent
+  //   parameter-declaration-clauses.
+  if (isa<CXXDeductionGuideDecl>(New) &&
+      !New->isFunctionTemplateSpecialization() && isVisible(Old)) {
+    Diag(New->getLocation(), diag::err_deduction_guide_redeclared);
+    Diag(Old->getLocation(), diag::note_previous_declaration);
+  }
+
+  // C++11 [dcl.fct.default]p4: If a friend declaration specifies a default
+  // argument expression, that declaration shall be a definition and shall be
+  // the only declaration of the function or function template in the
+  // translation unit.
+  if (Old->getFriendObjectKind() == Decl::FOK_Undeclared &&
+      functionDeclHasDefaultArgument(Old)) {
+    Diag(New->getLocation(), diag::err_friend_decl_with_def_arg_redeclared);
+    Diag(Old->getLocation(), diag::note_previous_declaration);
+    Invalid = true;
+  }
+
+  // C++11 [temp.friend]p4 (DR329):
+  //   When a function is defined in a friend function declaration in a class
+  //   template, the function is instantiated when the function is odr-used.
+  //   The same restrictions on multiple declarations and definitions that
+  //   apply to non-template function declarations and definitions also apply
+  //   to these implicit definitions.
+  const FunctionDecl *OldDefinition = nullptr;
+  if (New->isThisDeclarationInstantiatedFromAFriendDefinition() &&
+      Old->isDefined(OldDefinition, true))
+    CheckForFunctionRedefinition(New, OldDefinition);
+
+  return Invalid;
+}
+
+NamedDecl *
+Sema::ActOnDecompositionDeclarator(Scope *S, Declarator &D,
+                                   MultiTemplateParamsArg TemplateParamLists) {
+  assert(D.isDecompositionDeclarator());
+  const DecompositionDeclarator &Decomp = D.getDecompositionDeclarator();
+
+  // The syntax only allows a decomposition declarator as a simple-declaration,
+  // a for-range-declaration, or a condition in Clang, but we parse it in more
+  // cases than that.
+  if (!D.mayHaveDecompositionDeclarator()) {
+    Diag(Decomp.getLSquareLoc(), diag::err_decomp_decl_context)
+      << Decomp.getSourceRange();
+    return nullptr;
+  }
+
+  if (!TemplateParamLists.empty()) {
+    // FIXME: There's no rule against this, but there are also no rules that
+    // would actually make it usable, so we reject it for now.
+    Diag(TemplateParamLists.front()->getTemplateLoc(),
+         diag::err_decomp_decl_template);
+    return nullptr;
+  }
+
+  Diag(Decomp.getLSquareLoc(),
+       !getLangOpts().CPlusPlus17
+           ? diag::ext_decomp_decl
+           : D.getContext() == DeclaratorContext::Condition
+                 ? diag::ext_decomp_decl_cond
+                 : diag::warn_cxx14_compat_decomp_decl)
+      << Decomp.getSourceRange();
+
+  // The semantic context is always just the current context.
+  DeclContext *const DC = CurContext;
+
+  // C++17 [dcl.dcl]/8:
+  //   The decl-specifier-seq shall contain only the type-specifier auto
+  //   and cv-qualifiers.
+  // C++2a [dcl.dcl]/8:
+  //   If decl-specifier-seq contains any decl-specifier other than static,
+  //   thread_local, auto, or cv-qualifiers, the program is ill-formed.
+  auto &DS = D.getDeclSpec();
+  {
+    SmallVector<StringRef, 8> BadSpecifiers;
+    SmallVector<SourceLocation, 8> BadSpecifierLocs;
+    SmallVector<StringRef, 8> CPlusPlus20Specifiers;
+    SmallVector<SourceLocation, 8> CPlusPlus20SpecifierLocs;
+    if (auto SCS = DS.getStorageClassSpec()) {
+      if (SCS == DeclSpec::SCS_static) {
+        CPlusPlus20Specifiers.push_back(DeclSpec::getSpecifierName(SCS));
+        CPlusPlus20SpecifierLocs.push_back(DS.getStorageClassSpecLoc());
+      } else {
+        BadSpecifiers.push_back(DeclSpec::getSpecifierName(SCS));
+        BadSpecifierLocs.push_back(DS.getStorageClassSpecLoc());
+      }
+    }
+    if (auto TSCS = DS.getThreadStorageClassSpec()) {
+      CPlusPlus20Specifiers.push_back(DeclSpec::getSpecifierName(TSCS));
+      CPlusPlus20SpecifierLocs.push_back(DS.getThreadStorageClassSpecLoc());
+    }
+    if (DS.hasConstexprSpecifier()) {
+      BadSpecifiers.push_back(
+          DeclSpec::getSpecifierName(DS.getConstexprSpecifier()));
+      BadSpecifierLocs.push_back(DS.getConstexprSpecLoc());
+    }
+    if (DS.isInlineSpecified()) {
+      BadSpecifiers.push_back("inline");
+      BadSpecifierLocs.push_back(DS.getInlineSpecLoc());
+    }
+    if (!BadSpecifiers.empty()) {
+      auto &&Err = Diag(BadSpecifierLocs.front(), diag::err_decomp_decl_spec);
+      Err << (int)BadSpecifiers.size()
+          << llvm::join(BadSpecifiers.begin(), BadSpecifiers.end(), " ");
+      // Don't add FixItHints to remove the specifiers; we do still respect
+      // them when building the underlying variable.
+      for (auto Loc : BadSpecifierLocs)
+        Err << SourceRange(Loc, Loc);
+    } else if (!CPlusPlus20Specifiers.empty()) {
+      auto &&Warn = Diag(CPlusPlus20SpecifierLocs.front(),
+                         getLangOpts().CPlusPlus20
+                             ? diag::warn_cxx17_compat_decomp_decl_spec
+                             : diag::ext_decomp_decl_spec);
+      Warn << (int)CPlusPlus20Specifiers.size()
+           << llvm::join(CPlusPlus20Specifiers.begin(),
+                         CPlusPlus20Specifiers.end(), " ");
+      for (auto Loc : CPlusPlus20SpecifierLocs)
+        Warn << SourceRange(Loc, Loc);
+    }
+    // We can't recover from it being declared as a typedef.
+    if (DS.getStorageClassSpec() == DeclSpec::SCS_typedef)
+      return nullptr;
+  }
+
+  // C++2a [dcl.struct.bind]p1:
+  //   A cv that includes volatile is deprecated
+  if ((DS.getTypeQualifiers() & DeclSpec::TQ_volatile) &&
+      getLangOpts().CPlusPlus20)
+    Diag(DS.getVolatileSpecLoc(),
+         diag::warn_deprecated_volatile_structured_binding);
+
+  TypeSourceInfo *TInfo = GetTypeForDeclarator(D, S);
+  QualType R = TInfo->getType();
+
+  if (DiagnoseUnexpandedParameterPack(D.getIdentifierLoc(), TInfo,
+                                      UPPC_DeclarationType))
+    D.setInvalidType();
+
+  // The syntax only allows a single ref-qualifier prior to the decomposition
+  // declarator. No other declarator chunks are permitted. Also check the type
+  // specifier here.
+  if (DS.getTypeSpecType() != DeclSpec::TST_auto ||
+      D.hasGroupingParens() || D.getNumTypeObjects() > 1 ||
+      (D.getNumTypeObjects() == 1 &&
+       D.getTypeObject(0).Kind != DeclaratorChunk::Reference)) {
+    Diag(Decomp.getLSquareLoc(),
+         (D.hasGroupingParens() ||
+          (D.getNumTypeObjects() &&
+           D.getTypeObject(0).Kind == DeclaratorChunk::Paren))
+             ? diag::err_decomp_decl_parens
+             : diag::err_decomp_decl_type)
+        << R;
+
+    // In most cases, there's no actual problem with an explicitly-specified
+    // type, but a function type won't work here, and ActOnVariableDeclarator
+    // shouldn't be called for such a type.
+    if (R->isFunctionType())
+      D.setInvalidType();
+  }
+
+  // Build the BindingDecls.
+  SmallVector<BindingDecl*, 8> Bindings;
+
+  // Build the BindingDecls.
+  for (auto &B : D.getDecompositionDeclarator().bindings()) {
+    // Check for name conflicts.
+    DeclarationNameInfo NameInfo(B.Name, B.NameLoc);
+    LookupResult Previous(*this, NameInfo, LookupOrdinaryName,
+                          ForVisibleRedeclaration);
+    LookupName(Previous, S,
+               /*CreateBuiltins*/DC->getRedeclContext()->isTranslationUnit());
+
+    // It's not permitted to shadow a template parameter name.
+    if (Previous.isSingleResult() &&
+        Previous.getFoundDecl()->isTemplateParameter()) {
+      DiagnoseTemplateParameterShadow(D.getIdentifierLoc(),
+                                      Previous.getFoundDecl());
+      Previous.clear();
+    }
+
+    auto *BD = BindingDecl::Create(Context, DC, B.NameLoc, B.Name);
+
+    // Find the shadowed declaration before filtering for scope.
+    NamedDecl *ShadowedDecl = D.getCXXScopeSpec().isEmpty()
+                                  ? getShadowedDeclaration(BD, Previous)
+                                  : nullptr;
+
+    bool ConsiderLinkage = DC->isFunctionOrMethod() &&
+                           DS.getStorageClassSpec() == DeclSpec::SCS_extern;
+    FilterLookupForScope(Previous, DC, S, ConsiderLinkage,
+                         /*AllowInlineNamespace*/false);
+
+    if (!Previous.empty()) {
+      auto *Old = Previous.getRepresentativeDecl();
+      Diag(B.NameLoc, diag::err_redefinition) << B.Name;
+      Diag(Old->getLocation(), diag::note_previous_definition);
+    } else if (ShadowedDecl && !D.isRedeclaration()) {
+      CheckShadow(BD, ShadowedDecl, Previous);
+    }
+    PushOnScopeChains(BD, S, true);
+    Bindings.push_back(BD);
+    ParsingInitForAutoVars.insert(BD);
+  }
+
+  // There are no prior lookup results for the variable itself, because it
+  // is unnamed.
+  DeclarationNameInfo NameInfo((IdentifierInfo *)nullptr,
+                               Decomp.getLSquareLoc());
+  LookupResult Previous(*this, NameInfo, LookupOrdinaryName,
+                        ForVisibleRedeclaration);
+
+  // Build the variable that holds the non-decomposed object.
+  bool AddToScope = true;
+  NamedDecl *New =
+      ActOnVariableDeclarator(S, D, DC, TInfo, Previous,
+                              MultiTemplateParamsArg(), AddToScope, Bindings);
+  if (AddToScope) {
+    S->AddDecl(New);
+    CurContext->addHiddenDecl(New);
+  }
+
+  if (isInOpenMPDeclareTargetContext())
+    checkDeclIsAllowedInOpenMPTarget(nullptr, New);
+
+  return New;
+}
+
+static bool checkSimpleDecomposition(
+    Sema &S, ArrayRef<BindingDecl *> Bindings, ValueDecl *Src,
+    QualType DecompType, const llvm::APSInt &NumElems, QualType ElemType,
+    llvm::function_ref<ExprResult(SourceLocation, Expr *, unsigned)> GetInit) {
+  if ((int64_t)Bindings.size() != NumElems) {
+    S.Diag(Src->getLocation(), diag::err_decomp_decl_wrong_number_bindings)
+        << DecompType << (unsigned)Bindings.size()
+        << (unsigned)NumElems.getLimitedValue(UINT_MAX)
+        << toString(NumElems, 10) << (NumElems < Bindings.size());
+    return true;
+  }
+
+  unsigned I = 0;
+  for (auto *B : Bindings) {
+    SourceLocation Loc = B->getLocation();
+    ExprResult E = S.BuildDeclRefExpr(Src, DecompType, VK_LValue, Loc);
+    if (E.isInvalid())
+      return true;
+    E = GetInit(Loc, E.get(), I++);
+    if (E.isInvalid())
+      return true;
+    B->setBinding(ElemType, E.get());
+  }
+
+  return false;
+}
+
+static bool checkArrayLikeDecomposition(Sema &S,
+                                        ArrayRef<BindingDecl *> Bindings,
+                                        ValueDecl *Src, QualType DecompType,
+                                        const llvm::APSInt &NumElems,
+                                        QualType ElemType) {
+  return checkSimpleDecomposition(
+      S, Bindings, Src, DecompType, NumElems, ElemType,
+      [&](SourceLocation Loc, Expr *Base, unsigned I) -> ExprResult {
+        ExprResult E = S.ActOnIntegerConstant(Loc, I);
+        if (E.isInvalid())
+          return ExprError();
+        return S.CreateBuiltinArraySubscriptExpr(Base, Loc, E.get(), Loc);
+      });
+}
+
+static bool checkArrayDecomposition(Sema &S, ArrayRef<BindingDecl*> Bindings,
+                                    ValueDecl *Src, QualType DecompType,
+                                    const ConstantArrayType *CAT) {
+  return checkArrayLikeDecomposition(S, Bindings, Src, DecompType,
+                                     llvm::APSInt(CAT->getSize()),
+                                     CAT->getElementType());
+}
+
+static bool checkVectorDecomposition(Sema &S, ArrayRef<BindingDecl*> Bindings,
+                                     ValueDecl *Src, QualType DecompType,
+                                     const VectorType *VT) {
+  return checkArrayLikeDecomposition(
+      S, Bindings, Src, DecompType, llvm::APSInt::get(VT->getNumElements()),
+      S.Context.getQualifiedType(VT->getElementType(),
+                                 DecompType.getQualifiers()));
+}
+
+static bool checkComplexDecomposition(Sema &S,
+                                      ArrayRef<BindingDecl *> Bindings,
+                                      ValueDecl *Src, QualType DecompType,
+                                      const ComplexType *CT) {
+  return checkSimpleDecomposition(
+      S, Bindings, Src, DecompType, llvm::APSInt::get(2),
+      S.Context.getQualifiedType(CT->getElementType(),
+                                 DecompType.getQualifiers()),
+      [&](SourceLocation Loc, Expr *Base, unsigned I) -> ExprResult {
+        return S.CreateBuiltinUnaryOp(Loc, I ? UO_Imag : UO_Real, Base);
+      });
+}
+
+static std::string printTemplateArgs(const PrintingPolicy &PrintingPolicy,
+                                     TemplateArgumentListInfo &Args,
+                                     const TemplateParameterList *Params) {
+  SmallString<128> SS;
+  llvm::raw_svector_ostream OS(SS);
+  bool First = true;
+  unsigned I = 0;
+  for (auto &Arg : Args.arguments()) {
+    if (!First)
+      OS << ", ";
+    Arg.getArgument().print(PrintingPolicy, OS,
+                            TemplateParameterList::shouldIncludeTypeForArgument(
+                                PrintingPolicy, Params, I));
+    First = false;
+    I++;
+  }
+  return std::string(OS.str());
+}
+
+static bool lookupStdTypeTraitMember(Sema &S, LookupResult &TraitMemberLookup,
+                                     SourceLocation Loc, StringRef Trait,
+                                     TemplateArgumentListInfo &Args,
+                                     unsigned DiagID) {
+  auto DiagnoseMissing = [&] {
+    if (DiagID)
+      S.Diag(Loc, DiagID) << printTemplateArgs(S.Context.getPrintingPolicy(),
+                                               Args, /*Params*/ nullptr);
+    return true;
+  };
+
+  // FIXME: Factor out duplication with lookupPromiseType in SemaCoroutine.
+  NamespaceDecl *Std = S.getStdNamespace();
+  if (!Std)
+    return DiagnoseMissing();
+
+  // Look up the trait itself, within namespace std. We can diagnose various
+  // problems with this lookup even if we've been asked to not diagnose a
+  // missing specialization, because this can only fail if the user has been
+  // declaring their own names in namespace std or we don't support the
+  // standard library implementation in use.
+  LookupResult Result(S, &S.PP.getIdentifierTable().get(Trait),
+                      Loc, Sema::LookupOrdinaryName);
+  if (!S.LookupQualifiedName(Result, Std))
+    return DiagnoseMissing();
+  if (Result.isAmbiguous())
+    return true;
+
+  ClassTemplateDecl *TraitTD = Result.getAsSingle<ClassTemplateDecl>();
+  if (!TraitTD) {
+    Result.suppressDiagnostics();
+    NamedDecl *Found = *Result.begin();
+    S.Diag(Loc, diag::err_std_type_trait_not_class_template) << Trait;
+    S.Diag(Found->getLocation(), diag::note_declared_at);
+    return true;
+  }
+
+  // Build the template-id.
+  QualType TraitTy = S.CheckTemplateIdType(TemplateName(TraitTD), Loc, Args);
+  if (TraitTy.isNull())
+    return true;
+  if (!S.isCompleteType(Loc, TraitTy)) {
+    if (DiagID)
+      S.RequireCompleteType(
+          Loc, TraitTy, DiagID,
+          printTemplateArgs(S.Context.getPrintingPolicy(), Args,
+                            TraitTD->getTemplateParameters()));
+    return true;
+  }
+
+  CXXRecordDecl *RD = TraitTy->getAsCXXRecordDecl();
+  assert(RD && "specialization of class template is not a class?");
+
+  // Look up the member of the trait type.
+  S.LookupQualifiedName(TraitMemberLookup, RD);
+  return TraitMemberLookup.isAmbiguous();
+}
+
+static TemplateArgumentLoc
+getTrivialIntegralTemplateArgument(Sema &S, SourceLocation Loc, QualType T,
+                                   uint64_t I) {
+  TemplateArgument Arg(S.Context, S.Context.MakeIntValue(I, T), T);
+  return S.getTrivialTemplateArgumentLoc(Arg, T, Loc);
+}
+
+static TemplateArgumentLoc
+getTrivialTypeTemplateArgument(Sema &S, SourceLocation Loc, QualType T) {
+  return S.getTrivialTemplateArgumentLoc(TemplateArgument(T), QualType(), Loc);
+}
+
+namespace { enum class IsTupleLike { TupleLike, NotTupleLike, Error }; }
+
+static IsTupleLike isTupleLike(Sema &S, SourceLocation Loc, QualType T,
+                               llvm::APSInt &Size) {
+  EnterExpressionEvaluationContext ContextRAII(
+      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+
+  DeclarationName Value = S.PP.getIdentifierInfo("value");
+  LookupResult R(S, Value, Loc, Sema::LookupOrdinaryName);
+
+  // Form template argument list for tuple_size<T>.
+  TemplateArgumentListInfo Args(Loc, Loc);
+  Args.addArgument(getTrivialTypeTemplateArgument(S, Loc, T));
+
+  // If there's no tuple_size specialization or the lookup of 'value' is empty,
+  // it's not tuple-like.
+  if (lookupStdTypeTraitMember(S, R, Loc, "tuple_size", Args, /*DiagID*/ 0) ||
+      R.empty())
+    return IsTupleLike::NotTupleLike;
+
+  // If we get this far, we've committed to the tuple interpretation, but
+  // we can still fail if there actually isn't a usable ::value.
+
+  struct ICEDiagnoser : Sema::VerifyICEDiagnoser {
+    LookupResult &R;
+    TemplateArgumentListInfo &Args;
+    ICEDiagnoser(LookupResult &R, TemplateArgumentListInfo &Args)
+        : R(R), Args(Args) {}
+    Sema::SemaDiagnosticBuilder diagnoseNotICE(Sema &S,
+                                               SourceLocation Loc) override {
+      return S.Diag(Loc, diag::err_decomp_decl_std_tuple_size_not_constant)
+             << printTemplateArgs(S.Context.getPrintingPolicy(), Args,
+                                  /*Params*/ nullptr);
+    }
+  } Diagnoser(R, Args);
+
+  ExprResult E =
+      S.BuildDeclarationNameExpr(CXXScopeSpec(), R, /*NeedsADL*/false);
+  if (E.isInvalid())
+    return IsTupleLike::Error;
+
+  E = S.VerifyIntegerConstantExpression(E.get(), &Size, Diagnoser);
+  if (E.isInvalid())
+    return IsTupleLike::Error;
+
+  return IsTupleLike::TupleLike;
+}
+
+/// \return std::tuple_element<I, T>::type.
+static QualType getTupleLikeElementType(Sema &S, SourceLocation Loc,
+                                        unsigned I, QualType T) {
+  // Form template argument list for tuple_element<I, T>.
+  TemplateArgumentListInfo Args(Loc, Loc);
+  Args.addArgument(
+      getTrivialIntegralTemplateArgument(S, Loc, S.Context.getSizeType(), I));
+  Args.addArgument(getTrivialTypeTemplateArgument(S, Loc, T));
+
+  DeclarationName TypeDN = S.PP.getIdentifierInfo("type");
+  LookupResult R(S, TypeDN, Loc, Sema::LookupOrdinaryName);
+  if (lookupStdTypeTraitMember(
+          S, R, Loc, "tuple_element", Args,
+          diag::err_decomp_decl_std_tuple_element_not_specialized))
+    return QualType();
+
+  auto *TD = R.getAsSingle<TypeDecl>();
+  if (!TD) {
+    R.suppressDiagnostics();
+    S.Diag(Loc, diag::err_decomp_decl_std_tuple_element_not_specialized)
+        << printTemplateArgs(S.Context.getPrintingPolicy(), Args,
+                             /*Params*/ nullptr);
+    if (!R.empty())
+      S.Diag(R.getRepresentativeDecl()->getLocation(), diag::note_declared_at);
+    return QualType();
+  }
+
+  return S.Context.getTypeDeclType(TD);
+}
+
+namespace {
+struct InitializingBinding {
+  Sema &S;
+  InitializingBinding(Sema &S, BindingDecl *BD) : S(S) {
+    Sema::CodeSynthesisContext Ctx;
+    Ctx.Kind = Sema::CodeSynthesisContext::InitializingStructuredBinding;
+    Ctx.PointOfInstantiation = BD->getLocation();
+    Ctx.Entity = BD;
+    S.pushCodeSynthesisContext(Ctx);
+  }
+  ~InitializingBinding() {
+    S.popCodeSynthesisContext();
+  }
+};
+}
+
+static bool checkTupleLikeDecomposition(Sema &S,
+                                        ArrayRef<BindingDecl *> Bindings,
+                                        VarDecl *Src, QualType DecompType,
+                                        const llvm::APSInt &TupleSize) {
+  if ((int64_t)Bindings.size() != TupleSize) {
+    S.Diag(Src->getLocation(), diag::err_decomp_decl_wrong_number_bindings)
+        << DecompType << (unsigned)Bindings.size()
+        << (unsigned)TupleSize.getLimitedValue(UINT_MAX)
+        << toString(TupleSize, 10) << (TupleSize < Bindings.size());
+    return true;
+  }
+
+  if (Bindings.empty())
+    return false;
+
+  DeclarationName GetDN = S.PP.getIdentifierInfo("get");
+
+  // [dcl.decomp]p3:
+  //   The unqualified-id get is looked up in the scope of E by class member
+  //   access lookup ...
+  LookupResult MemberGet(S, GetDN, Src->getLocation(), Sema::LookupMemberName);
+  bool UseMemberGet = false;
+  if (S.isCompleteType(Src->getLocation(), DecompType)) {
+    if (auto *RD = DecompType->getAsCXXRecordDecl())
+      S.LookupQualifiedName(MemberGet, RD);
+    if (MemberGet.isAmbiguous())
+      return true;
+    //   ... and if that finds at least one declaration that is a function
+    //   template whose first template parameter is a non-type parameter ...
+    for (NamedDecl *D : MemberGet) {
+      if (FunctionTemplateDecl *FTD =
+              dyn_cast<FunctionTemplateDecl>(D->getUnderlyingDecl())) {
+        TemplateParameterList *TPL = FTD->getTemplateParameters();
+        if (TPL->size() != 0 &&
+            isa<NonTypeTemplateParmDecl>(TPL->getParam(0))) {
+          //   ... the initializer is e.get<i>().
+          UseMemberGet = true;
+          break;
+        }
+      }
+    }
+  }
+
+  unsigned I = 0;
+  for (auto *B : Bindings) {
+    InitializingBinding InitContext(S, B);
+    SourceLocation Loc = B->getLocation();
+
+    ExprResult E = S.BuildDeclRefExpr(Src, DecompType, VK_LValue, Loc);
+    if (E.isInvalid())
+      return true;
+
+    //   e is an lvalue if the type of the entity is an lvalue reference and
+    //   an xvalue otherwise
+    if (!Src->getType()->isLValueReferenceType())
+      E = ImplicitCastExpr::Create(S.Context, E.get()->getType(), CK_NoOp,
+                                   E.get(), nullptr, VK_XValue,
+                                   FPOptionsOverride());
+
+    TemplateArgumentListInfo Args(Loc, Loc);
+    Args.addArgument(
+        getTrivialIntegralTemplateArgument(S, Loc, S.Context.getSizeType(), I));
+
+    if (UseMemberGet) {
+      //   if [lookup of member get] finds at least one declaration, the
+      //   initializer is e.get<i-1>().
+      E = S.BuildMemberReferenceExpr(E.get(), DecompType, Loc, false,
+                                     CXXScopeSpec(), SourceLocation(), nullptr,
+                                     MemberGet, &Args, nullptr);
+      if (E.isInvalid())
+        return true;
+
+      E = S.BuildCallExpr(nullptr, E.get(), Loc, None, Loc);
+    } else {
+      //   Otherwise, the initializer is get<i-1>(e), where get is looked up
+      //   in the associated namespaces.
+      Expr *Get = UnresolvedLookupExpr::Create(
+          S.Context, nullptr, NestedNameSpecifierLoc(), SourceLocation(),
+          DeclarationNameInfo(GetDN, Loc), /*RequiresADL*/true, &Args,
+          UnresolvedSetIterator(), UnresolvedSetIterator());
+
+      Expr *Arg = E.get();
+      E = S.BuildCallExpr(nullptr, Get, Loc, Arg, Loc);
+    }
+    if (E.isInvalid())
+      return true;
+    Expr *Init = E.get();
+
+    //   Given the type T designated by std::tuple_element<i - 1, E>::type,
+    QualType T = getTupleLikeElementType(S, Loc, I, DecompType);
+    if (T.isNull())
+      return true;
+
+    //   each vi is a variable of type "reference to T" initialized with the
+    //   initializer, where the reference is an lvalue reference if the
+    //   initializer is an lvalue and an rvalue reference otherwise
+    QualType RefType =
+        S.BuildReferenceType(T, E.get()->isLValue(), Loc, B->getDeclName());
+    if (RefType.isNull())
+      return true;
+    auto *RefVD = VarDecl::Create(
+        S.Context, Src->getDeclContext(), Loc, Loc,
+        B->getDeclName().getAsIdentifierInfo(), RefType,
+        S.Context.getTrivialTypeSourceInfo(T, Loc), Src->getStorageClass());
+    RefVD->setLexicalDeclContext(Src->getLexicalDeclContext());
+    RefVD->setTSCSpec(Src->getTSCSpec());
+    RefVD->setImplicit();
+    if (Src->isInlineSpecified())
+      RefVD->setInlineSpecified();
+    RefVD->getLexicalDeclContext()->addHiddenDecl(RefVD);
+
+    InitializedEntity Entity = InitializedEntity::InitializeBinding(RefVD);
+    InitializationKind Kind = InitializationKind::CreateCopy(Loc, Loc);
+    InitializationSequence Seq(S, Entity, Kind, Init);
+    E = Seq.Perform(S, Entity, Kind, Init);
+    if (E.isInvalid())
+      return true;
+    E = S.ActOnFinishFullExpr(E.get(), Loc, /*DiscardedValue*/ false);
+    if (E.isInvalid())
+      return true;
+    RefVD->setInit(E.get());
+    S.CheckCompleteVariableDeclaration(RefVD);
+
+    E = S.BuildDeclarationNameExpr(CXXScopeSpec(),
+                                   DeclarationNameInfo(B->getDeclName(), Loc),
+                                   RefVD);
+    if (E.isInvalid())
+      return true;
+
+    B->setBinding(T, E.get());
+    I++;
+  }
+
+  return false;
+}
+
+/// Find the base class to decompose in a built-in decomposition of a class type.
+/// This base class search is, unfortunately, not quite like any other that we
+/// perform anywhere else in C++.
+static DeclAccessPair findDecomposableBaseClass(Sema &S, SourceLocation Loc,
+                                                const CXXRecordDecl *RD,
+                                                CXXCastPath &BasePath) {
+  auto BaseHasFields = [](const CXXBaseSpecifier *Specifier,
+                          CXXBasePath &Path) {
+    return Specifier->getType()->getAsCXXRecordDecl()->hasDirectFields();
+  };
+
+  const CXXRecordDecl *ClassWithFields = nullptr;
+  AccessSpecifier AS = AS_public;
+  if (RD->hasDirectFields())
+    // [dcl.decomp]p4:
+    //   Otherwise, all of E's non-static data members shall be public direct
+    //   members of E ...
+    ClassWithFields = RD;
+  else {
+    //   ... or of ...
+    CXXBasePaths Paths;
+    Paths.setOrigin(const_cast<CXXRecordDecl*>(RD));
+    if (!RD->lookupInBases(BaseHasFields, Paths)) {
+      // If no classes have fields, just decompose RD itself. (This will work
+      // if and only if zero bindings were provided.)
+      return DeclAccessPair::make(const_cast<CXXRecordDecl*>(RD), AS_public);
+    }
+
+    CXXBasePath *BestPath = nullptr;
+    for (auto &P : Paths) {
+      if (!BestPath)
+        BestPath = &P;
+      else if (!S.Context.hasSameType(P.back().Base->getType(),
+                                      BestPath->back().Base->getType())) {
+        //   ... the same ...
+        S.Diag(Loc, diag::err_decomp_decl_multiple_bases_with_members)
+          << false << RD << BestPath->back().Base->getType()
+          << P.back().Base->getType();
+        return DeclAccessPair();
+      } else if (P.Access < BestPath->Access) {
+        BestPath = &P;
+      }
+    }
+
+    //   ... unambiguous ...
+    QualType BaseType = BestPath->back().Base->getType();
+    if (Paths.isAmbiguous(S.Context.getCanonicalType(BaseType))) {
+      S.Diag(Loc, diag::err_decomp_decl_ambiguous_base)
+        << RD << BaseType << S.getAmbiguousPathsDisplayString(Paths);
+      return DeclAccessPair();
+    }
+
+    //   ... [accessible, implied by other rules] base class of E.
+    S.CheckBaseClassAccess(Loc, BaseType, S.Context.getRecordType(RD),
+                           *BestPath, diag::err_decomp_decl_inaccessible_base);
+    AS = BestPath->Access;
+
+    ClassWithFields = BaseType->getAsCXXRecordDecl();
+    S.BuildBasePathArray(Paths, BasePath);
+  }
+
+  // The above search did not check whether the selected class itself has base
+  // classes with fields, so check that now.
+  CXXBasePaths Paths;
+  if (ClassWithFields->lookupInBases(BaseHasFields, Paths)) {
+    S.Diag(Loc, diag::err_decomp_decl_multiple_bases_with_members)
+      << (ClassWithFields == RD) << RD << ClassWithFields
+      << Paths.front().back().Base->getType();
+    return DeclAccessPair();
+  }
+
+  return DeclAccessPair::make(const_cast<CXXRecordDecl*>(ClassWithFields), AS);
+}
+
+static bool checkMemberDecomposition(Sema &S, ArrayRef<BindingDecl*> Bindings,
+                                     ValueDecl *Src, QualType DecompType,
+                                     const CXXRecordDecl *OrigRD) {
+  if (S.RequireCompleteType(Src->getLocation(), DecompType,
+                            diag::err_incomplete_type))
+    return true;
+
+  CXXCastPath BasePath;
+  DeclAccessPair BasePair =
+      findDecomposableBaseClass(S, Src->getLocation(), OrigRD, BasePath);
+  const CXXRecordDecl *RD = cast_or_null<CXXRecordDecl>(BasePair.getDecl());
+  if (!RD)
+    return true;
+  QualType BaseType = S.Context.getQualifiedType(S.Context.getRecordType(RD),
+                                                 DecompType.getQualifiers());
+
+  auto DiagnoseBadNumberOfBindings = [&]() -> bool {
+    unsigned NumFields = llvm::count_if(
+        RD->fields(), [](FieldDecl *FD) { return !FD->isUnnamedBitfield(); });
+    assert(Bindings.size() != NumFields);
+    S.Diag(Src->getLocation(), diag::err_decomp_decl_wrong_number_bindings)
+        << DecompType << (unsigned)Bindings.size() << NumFields << NumFields
+        << (NumFields < Bindings.size());
+    return true;
+  };
+
+  //   all of E's non-static data members shall be [...] well-formed
+  //   when named as e.name in the context of the structured binding,
+  //   E shall not have an anonymous union member, ...
+  unsigned I = 0;
+  for (auto *FD : RD->fields()) {
+    if (FD->isUnnamedBitfield())
+      continue;
+
+    // All the non-static data members are required to be nameable, so they
+    // must all have names.
+    if (!FD->getDeclName()) {
+      if (RD->isLambda()) {
+        S.Diag(Src->getLocation(), diag::err_decomp_decl_lambda);
+        S.Diag(RD->getLocation(), diag::note_lambda_decl);
+        return true;
+      }
+
+      if (FD->isAnonymousStructOrUnion()) {
+        S.Diag(Src->getLocation(), diag::err_decomp_decl_anon_union_member)
+          << DecompType << FD->getType()->isUnionType();
+        S.Diag(FD->getLocation(), diag::note_declared_at);
+        return true;
+      }
+
+      // FIXME: Are there any other ways we could have an anonymous member?
+    }
+
+    // We have a real field to bind.
+    if (I >= Bindings.size())
+      return DiagnoseBadNumberOfBindings();
+    auto *B = Bindings[I++];
+    SourceLocation Loc = B->getLocation();
+
+    // The field must be accessible in the context of the structured binding.
+    // We already checked that the base class is accessible.
+    // FIXME: Add 'const' to AccessedEntity's classes so we can remove the
+    // const_cast here.
+    S.CheckStructuredBindingMemberAccess(
+        Loc, const_cast<CXXRecordDecl *>(OrigRD),
+        DeclAccessPair::make(FD, CXXRecordDecl::MergeAccess(
+                                     BasePair.getAccess(), FD->getAccess())));
+
+    // Initialize the binding to Src.FD.
+    ExprResult E = S.BuildDeclRefExpr(Src, DecompType, VK_LValue, Loc);
+    if (E.isInvalid())
+      return true;
+    E = S.ImpCastExprToType(E.get(), BaseType, CK_UncheckedDerivedToBase,
+                            VK_LValue, &BasePath);
+    if (E.isInvalid())
+      return true;
+    E = S.BuildFieldReferenceExpr(E.get(), /*IsArrow*/ false, Loc,
+                                  CXXScopeSpec(), FD,
+                                  DeclAccessPair::make(FD, FD->getAccess()),
+                                  DeclarationNameInfo(FD->getDeclName(), Loc));
+    if (E.isInvalid())
+      return true;
+
+    // If the type of the member is T, the referenced type is cv T, where cv is
+    // the cv-qualification of the decomposition expression.
+    //
+    // FIXME: We resolve a defect here: if the field is mutable, we do not add
+    // 'const' to the type of the field.
+    Qualifiers Q = DecompType.getQualifiers();
+    if (FD->isMutable())
+      Q.removeConst();
+    B->setBinding(S.BuildQualifiedType(FD->getType(), Loc, Q), E.get());
+  }
+
+  if (I != Bindings.size())
+    return DiagnoseBadNumberOfBindings();
+
+  return false;
+}
+
+void Sema::CheckCompleteDecompositionDeclaration(DecompositionDecl *DD) {
+  QualType DecompType = DD->getType();
+
+  // If the type of the decomposition is dependent, then so is the type of
+  // each binding.
+  if (DecompType->isDependentType()) {
+    for (auto *B : DD->bindings())
+      B->setType(Context.DependentTy);
+    return;
+  }
+
+  DecompType = DecompType.getNonReferenceType();
+  ArrayRef<BindingDecl*> Bindings = DD->bindings();
+
+  // C++1z [dcl.decomp]/2:
+  //   If E is an array type [...]
+  // As an extension, we also support decomposition of built-in complex and
+  // vector types.
+  if (auto *CAT = Context.getAsConstantArrayType(DecompType)) {
+    if (checkArrayDecomposition(*this, Bindings, DD, DecompType, CAT))
+      DD->setInvalidDecl();
+    return;
+  }
+  if (auto *VT = DecompType->getAs<VectorType>()) {
+    if (checkVectorDecomposition(*this, Bindings, DD, DecompType, VT))
+      DD->setInvalidDecl();
+    return;
+  }
+  if (auto *CT = DecompType->getAs<ComplexType>()) {
+    if (checkComplexDecomposition(*this, Bindings, DD, DecompType, CT))
+      DD->setInvalidDecl();
+    return;
+  }
+
+  // C++1z [dcl.decomp]/3:
+  //   if the expression std::tuple_size<E>::value is a well-formed integral
+  //   constant expression, [...]
+  llvm::APSInt TupleSize(32);
+  switch (isTupleLike(*this, DD->getLocation(), DecompType, TupleSize)) {
+  case IsTupleLike::Error:
+    DD->setInvalidDecl();
+    return;
+
+  case IsTupleLike::TupleLike:
+    if (checkTupleLikeDecomposition(*this, Bindings, DD, DecompType, TupleSize))
+      DD->setInvalidDecl();
+    return;
+
+  case IsTupleLike::NotTupleLike:
+    break;
+  }
+
+  // C++1z [dcl.dcl]/8:
+  //   [E shall be of array or non-union class type]
+  CXXRecordDecl *RD = DecompType->getAsCXXRecordDecl();
+  if (!RD || RD->isUnion()) {
+    Diag(DD->getLocation(), diag::err_decomp_decl_unbindable_type)
+        << DD << !RD << DecompType;
+    DD->setInvalidDecl();
+    return;
+  }
+
+  // C++1z [dcl.decomp]/4:
+  //   all of E's non-static data members shall be [...] direct members of
+  //   E or of the same unambiguous public base class of E, ...
+  if (checkMemberDecomposition(*this, Bindings, DD, DecompType, RD))
+    DD->setInvalidDecl();
+}
+
+/// Merge the exception specifications of two variable declarations.
+///
+/// This is called when there's a redeclaration of a VarDecl. The function
+/// checks if the redeclaration might have an exception specification and
+/// validates compatibility and merges the specs if necessary.
+void Sema::MergeVarDeclExceptionSpecs(VarDecl *New, VarDecl *Old) {
+  // Shortcut if exceptions are disabled.
+  if (!getLangOpts().CXXExceptions)
+    return;
+
+  assert(Context.hasSameType(New->getType(), Old->getType()) &&
+         "Should only be called if types are otherwise the same.");
+
+  QualType NewType = New->getType();
+  QualType OldType = Old->getType();
+
+  // We're only interested in pointers and references to functions, as well
+  // as pointers to member functions.
+  if (const ReferenceType *R = NewType->getAs<ReferenceType>()) {
+    NewType = R->getPointeeType();
+    OldType = OldType->castAs<ReferenceType>()->getPointeeType();
+  } else if (const PointerType *P = NewType->getAs<PointerType>()) {
+    NewType = P->getPointeeType();
+    OldType = OldType->castAs<PointerType>()->getPointeeType();
+  } else if (const MemberPointerType *M = NewType->getAs<MemberPointerType>()) {
+    NewType = M->getPointeeType();
+    OldType = OldType->castAs<MemberPointerType>()->getPointeeType();
+  }
+
+  if (!NewType->isFunctionProtoType())
+    return;
+
+  // There's lots of special cases for functions. For function pointers, system
+  // libraries are hopefully not as broken so that we don't need these
+  // workarounds.
+  if (CheckEquivalentExceptionSpec(
+        OldType->getAs<FunctionProtoType>(), Old->getLocation(),
+        NewType->getAs<FunctionProtoType>(), New->getLocation())) {
+    New->setInvalidDecl();
+  }
+}
+
+/// CheckCXXDefaultArguments - Verify that the default arguments for a
+/// function declaration are well-formed according to C++
+/// [dcl.fct.default].
+void Sema::CheckCXXDefaultArguments(FunctionDecl *FD) {
+  unsigned NumParams = FD->getNumParams();
+  unsigned ParamIdx = 0;
+
+  // This checking doesn't make sense for explicit specializations; their
+  // default arguments are determined by the declaration we're specializing,
+  // not by FD.
+  if (FD->getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
+    return;
+  if (auto *FTD = FD->getDescribedFunctionTemplate())
+    if (FTD->isMemberSpecialization())
+      return;
+
+  // Find first parameter with a default argument
+  for (; ParamIdx < NumParams; ++ParamIdx) {
+    ParmVarDecl *Param = FD->getParamDecl(ParamIdx);
+    if (Param->hasDefaultArg())
+      break;
+  }
+
+  // C++20 [dcl.fct.default]p4:
+  //   In a given function declaration, each parameter subsequent to a parameter
+  //   with a default argument shall have a default argument supplied in this or
+  //   a previous declaration, unless the parameter was expanded from a
+  //   parameter pack, or shall be a function parameter pack.
+  for (; ParamIdx < NumParams; ++ParamIdx) {
+    ParmVarDecl *Param = FD->getParamDecl(ParamIdx);
+    if (!Param->hasDefaultArg() && !Param->isParameterPack() &&
+        !(CurrentInstantiationScope &&
+          CurrentInstantiationScope->isLocalPackExpansion(Param))) {
+      if (Param->isInvalidDecl())
+        /* We already complained about this parameter. */;
+      else if (Param->getIdentifier())
+        Diag(Param->getLocation(),
+             diag::err_param_default_argument_missing_name)
+          << Param->getIdentifier();
+      else
+        Diag(Param->getLocation(),
+             diag::err_param_default_argument_missing);
+    }
+  }
+}
+
+/// Check that the given type is a literal type. Issue a diagnostic if not,
+/// if Kind is Diagnose.
+/// \return \c true if a problem has been found (and optionally diagnosed).
+template <typename... Ts>
+static bool CheckLiteralType(Sema &SemaRef, Sema::CheckConstexprKind Kind,
+                             SourceLocation Loc, QualType T, unsigned DiagID,
+                             Ts &&...DiagArgs) {
+  if (T->isDependentType())
+    return false;
+
+  switch (Kind) {
+  case Sema::CheckConstexprKind::Diagnose:
+    return SemaRef.RequireLiteralType(Loc, T, DiagID,
+                                      std::forward<Ts>(DiagArgs)...);
+
+  case Sema::CheckConstexprKind::CheckValid:
+    return !T->isLiteralType(SemaRef.Context);
+  }
+
+  llvm_unreachable("unknown CheckConstexprKind");
+}
+
+/// Determine whether a destructor cannot be constexpr due to
+static bool CheckConstexprDestructorSubobjects(Sema &SemaRef,
+                                               const CXXDestructorDecl *DD,
+                                               Sema::CheckConstexprKind Kind) {
+  auto Check = [&](SourceLocation Loc, QualType T, const FieldDecl *FD) {
+    const CXXRecordDecl *RD =
+        T->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
+    if (!RD || RD->hasConstexprDestructor())
+      return true;
+
+    if (Kind == Sema::CheckConstexprKind::Diagnose) {
+      SemaRef.Diag(DD->getLocation(), diag::err_constexpr_dtor_subobject)
+          << static_cast<int>(DD->getConstexprKind()) << !FD
+          << (FD ? FD->getDeclName() : DeclarationName()) << T;
+      SemaRef.Diag(Loc, diag::note_constexpr_dtor_subobject)
+          << !FD << (FD ? FD->getDeclName() : DeclarationName()) << T;
+    }
+    return false;
+  };
+
+  const CXXRecordDecl *RD = DD->getParent();
+  for (const CXXBaseSpecifier &B : RD->bases())
+    if (!Check(B.getBaseTypeLoc(), B.getType(), nullptr))
+      return false;
+  for (const FieldDecl *FD : RD->fields())
+    if (!Check(FD->getLocation(), FD->getType(), FD))
+      return false;
+  return true;
+}
+
+/// Check whether a function's parameter types are all literal types. If so,
+/// return true. If not, produce a suitable diagnostic and return false.
+static bool CheckConstexprParameterTypes(Sema &SemaRef,
+                                         const FunctionDecl *FD,
+                                         Sema::CheckConstexprKind Kind) {
+  unsigned ArgIndex = 0;
+  const auto *FT = FD->getType()->castAs<FunctionProtoType>();
+  for (FunctionProtoType::param_type_iterator i = FT->param_type_begin(),
+                                              e = FT->param_type_end();
+       i != e; ++i, ++ArgIndex) {
+    const ParmVarDecl *PD = FD->getParamDecl(ArgIndex);
+    SourceLocation ParamLoc = PD->getLocation();
+    if (CheckLiteralType(SemaRef, Kind, ParamLoc, *i,
+                         diag::err_constexpr_non_literal_param, ArgIndex + 1,
+                         PD->getSourceRange(), isa<CXXConstructorDecl>(FD),
+                         FD->isConsteval()))
+      return false;
+  }
+  return true;
+}
+
+/// Check whether a function's return type is a literal type. If so, return
+/// true. If not, produce a suitable diagnostic and return false.
+static bool CheckConstexprReturnType(Sema &SemaRef, const FunctionDecl *FD,
+                                     Sema::CheckConstexprKind Kind) {
+  if (CheckLiteralType(SemaRef, Kind, FD->getLocation(), FD->getReturnType(),
+                       diag::err_constexpr_non_literal_return,
+                       FD->isConsteval()))
+    return false;
+  return true;
+}
+
+/// Get diagnostic %select index for tag kind for
+/// record diagnostic message.
+/// WARNING: Indexes apply to particular diagnostics only!
+///
+/// \returns diagnostic %select index.
+static unsigned getRecordDiagFromTagKind(TagTypeKind Tag) {
+  switch (Tag) {
+  case TTK_Struct: return 0;
+  case TTK_Interface: return 1;
+  case TTK_Class:  return 2;
+  default: llvm_unreachable("Invalid tag kind for record diagnostic!");
+  }
+}
+
+static bool CheckConstexprFunctionBody(Sema &SemaRef, const FunctionDecl *Dcl,
+                                       Stmt *Body,
+                                       Sema::CheckConstexprKind Kind);
+
+// Check whether a function declaration satisfies the requirements of a
+// constexpr function definition or a constexpr constructor definition. If so,
+// return true. If not, produce appropriate diagnostics (unless asked not to by
+// Kind) and return false.
+//
+// This implements C++11 [dcl.constexpr]p3,4, as amended by DR1360.
+bool Sema::CheckConstexprFunctionDefinition(const FunctionDecl *NewFD,
+                                            CheckConstexprKind Kind) {
+  const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(NewFD);
+  if (MD && MD->isInstance()) {
+    // C++11 [dcl.constexpr]p4:
+    //  The definition of a constexpr constructor shall satisfy the following
+    //  constraints:
+    //  - the class shall not have any virtual base classes;
+    //
+    // FIXME: This only applies to constructors and destructors, not arbitrary
+    // member functions.
+    const CXXRecordDecl *RD = MD->getParent();
+    if (RD->getNumVBases()) {
+      if (Kind == CheckConstexprKind::CheckValid)
+        return false;
+
+      Diag(NewFD->getLocation(), diag::err_constexpr_virtual_base)
+        << isa<CXXConstructorDecl>(NewFD)
+        << getRecordDiagFromTagKind(RD->getTagKind()) << RD->getNumVBases();
+      for (const auto &I : RD->vbases())
+        Diag(I.getBeginLoc(), diag::note_constexpr_virtual_base_here)
+            << I.getSourceRange();
+      return false;
+    }
+  }
+
+  if (!isa<CXXConstructorDecl>(NewFD)) {
+    // C++11 [dcl.constexpr]p3:
+    //  The definition of a constexpr function shall satisfy the following
+    //  constraints:
+    // - it shall not be virtual; (removed in C++20)
+    const CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(NewFD);
+    if (Method && Method->isVirtual()) {
+      if (getLangOpts().CPlusPlus20) {
+        if (Kind == CheckConstexprKind::Diagnose)
+          Diag(Method->getLocation(), diag::warn_cxx17_compat_constexpr_virtual);
+      } else {
+        if (Kind == CheckConstexprKind::CheckValid)
+          return false;
+
+        Method = Method->getCanonicalDecl();
+        Diag(Method->getLocation(), diag::err_constexpr_virtual);
+
+        // If it's not obvious why this function is virtual, find an overridden
+        // function which uses the 'virtual' keyword.
+        const CXXMethodDecl *WrittenVirtual = Method;
+        while (!WrittenVirtual->isVirtualAsWritten())
+          WrittenVirtual = *WrittenVirtual->begin_overridden_methods();
+        if (WrittenVirtual != Method)
+          Diag(WrittenVirtual->getLocation(),
+               diag::note_overridden_virtual_function);
+        return false;
+      }
+    }
+
+    // - its return type shall be a literal type;
+    if (!CheckConstexprReturnType(*this, NewFD, Kind))
+      return false;
+  }
+
+  if (auto *Dtor = dyn_cast<CXXDestructorDecl>(NewFD)) {
+    // A destructor can be constexpr only if the defaulted destructor could be;
+    // we don't need to check the members and bases if we already know they all
+    // have constexpr destructors.
+    if (!Dtor->getParent()->defaultedDestructorIsConstexpr()) {
+      if (Kind == CheckConstexprKind::CheckValid)
+        return false;
+      if (!CheckConstexprDestructorSubobjects(*this, Dtor, Kind))
+        return false;
+    }
+  }
+
+  // - each of its parameter types shall be a literal type;
+  if (!CheckConstexprParameterTypes(*this, NewFD, Kind))
+    return false;
+
+  Stmt *Body = NewFD->getBody();
+  assert(Body &&
+         "CheckConstexprFunctionDefinition called on function with no body");
+  return CheckConstexprFunctionBody(*this, NewFD, Body, Kind);
+}
+
+/// Check the given declaration statement is legal within a constexpr function
+/// body. C++11 [dcl.constexpr]p3,p4, and C++1y [dcl.constexpr]p3.
+///
+/// \return true if the body is OK (maybe only as an extension), false if we
+///         have diagnosed a problem.
+static bool CheckConstexprDeclStmt(Sema &SemaRef, const FunctionDecl *Dcl,
+                                   DeclStmt *DS, SourceLocation &Cxx1yLoc,
+                                   Sema::CheckConstexprKind Kind) {
+  // C++11 [dcl.constexpr]p3 and p4:
+  //  The definition of a constexpr function(p3) or constructor(p4) [...] shall
+  //  contain only
+  for (const auto *DclIt : DS->decls()) {
+    switch (DclIt->getKind()) {
+    case Decl::StaticAssert:
+    case Decl::Using:
+    case Decl::UsingShadow:
+    case Decl::UsingDirective:
+    case Decl::UnresolvedUsingTypename:
+    case Decl::UnresolvedUsingValue:
+    case Decl::UsingEnum:
+      //   - static_assert-declarations
+      //   - using-declarations,
+      //   - using-directives,
+      //   - using-enum-declaration
+      continue;
+
+    case Decl::Typedef:
+    case Decl::TypeAlias: {
+      //   - typedef declarations and alias-declarations that do not define
+      //     classes or enumerations,
+      const auto *TN = cast<TypedefNameDecl>(DclIt);
+      if (TN->getUnderlyingType()->isVariablyModifiedType()) {
+        // Don't allow variably-modified types in constexpr functions.
+        if (Kind == Sema::CheckConstexprKind::Diagnose) {
+          TypeLoc TL = TN->getTypeSourceInfo()->getTypeLoc();
+          SemaRef.Diag(TL.getBeginLoc(), diag::err_constexpr_vla)
+            << TL.getSourceRange() << TL.getType()
+            << isa<CXXConstructorDecl>(Dcl);
+        }
+        return false;
+      }
+      continue;
+    }
+
+    case Decl::Enum:
+    case Decl::CXXRecord:
+      // C++1y allows types to be defined, not just declared.
+      if (cast<TagDecl>(DclIt)->isThisDeclarationADefinition()) {
+        if (Kind == Sema::CheckConstexprKind::Diagnose) {
+          SemaRef.Diag(DS->getBeginLoc(),
+                       SemaRef.getLangOpts().CPlusPlus14
+                           ? diag::warn_cxx11_compat_constexpr_type_definition
+                           : diag::ext_constexpr_type_definition)
+              << isa<CXXConstructorDecl>(Dcl);
+        } else if (!SemaRef.getLangOpts().CPlusPlus14) {
+          return false;
+        }
+      }
+      continue;
+
+    case Decl::EnumConstant:
+    case Decl::IndirectField:
+    case Decl::ParmVar:
+      // These can only appear with other declarations which are banned in
+      // C++11 and permitted in C++1y, so ignore them.
+      continue;
+
+    case Decl::Var:
+    case Decl::Decomposition: {
+      // C++1y [dcl.constexpr]p3 allows anything except:
+      //   a definition of a variable of non-literal type or of static or
+      //   thread storage duration or [before C++2a] for which no
+      //   initialization is performed.
+      const auto *VD = cast<VarDecl>(DclIt);
+      if (VD->isThisDeclarationADefinition()) {
+        if (VD->isStaticLocal()) {
+          if (Kind == Sema::CheckConstexprKind::Diagnose) {
+            SemaRef.Diag(VD->getLocation(),
+                         diag::err_constexpr_local_var_static)
+              << isa<CXXConstructorDecl>(Dcl)
+              << (VD->getTLSKind() == VarDecl::TLS_Dynamic);
+          }
+          return false;
+        }
+        if (CheckLiteralType(SemaRef, Kind, VD->getLocation(), VD->getType(),
+                             diag::err_constexpr_local_var_non_literal_type,
+                             isa<CXXConstructorDecl>(Dcl)))
+          return false;
+        if (!VD->getType()->isDependentType() &&
+            !VD->hasInit() && !VD->isCXXForRangeDecl()) {
+          if (Kind == Sema::CheckConstexprKind::Diagnose) {
+            SemaRef.Diag(
+                VD->getLocation(),
+                SemaRef.getLangOpts().CPlusPlus20
+                    ? diag::warn_cxx17_compat_constexpr_local_var_no_init
+                    : diag::ext_constexpr_local_var_no_init)
+                << isa<CXXConstructorDecl>(Dcl);
+          } else if (!SemaRef.getLangOpts().CPlusPlus20) {
+            return false;
+          }
+          continue;
+        }
+      }
+      if (Kind == Sema::CheckConstexprKind::Diagnose) {
+        SemaRef.Diag(VD->getLocation(),
+                     SemaRef.getLangOpts().CPlusPlus14
+                      ? diag::warn_cxx11_compat_constexpr_local_var
+                      : diag::ext_constexpr_local_var)
+          << isa<CXXConstructorDecl>(Dcl);
+      } else if (!SemaRef.getLangOpts().CPlusPlus14) {
+        return false;
+      }
+      continue;
+    }
+
+    case Decl::NamespaceAlias:
+    case Decl::Function:
+      // These are disallowed in C++11 and permitted in C++1y. Allow them
+      // everywhere as an extension.
+      if (!Cxx1yLoc.isValid())
+        Cxx1yLoc = DS->getBeginLoc();
+      continue;
+
+    default:
+      if (Kind == Sema::CheckConstexprKind::Diagnose) {
+        SemaRef.Diag(DS->getBeginLoc(), diag::err_constexpr_body_invalid_stmt)
+            << isa<CXXConstructorDecl>(Dcl) << Dcl->isConsteval();
+      }
+      return false;
+    }
+  }
+
+  return true;
+}
+
+/// Check that the given field is initialized within a constexpr constructor.
+///
+/// \param Dcl The constexpr constructor being checked.
+/// \param Field The field being checked. This may be a member of an anonymous
+///        struct or union nested within the class being checked.
+/// \param Inits All declarations, including anonymous struct/union members and
+///        indirect members, for which any initialization was provided.
+/// \param Diagnosed Whether we've emitted the error message yet. Used to attach
+///        multiple notes for different members to the same error.
+/// \param Kind Whether we're diagnosing a constructor as written or determining
+///        whether the formal requirements are satisfied.
+/// \return \c false if we're checking for validity and the constructor does
+///         not satisfy the requirements on a constexpr constructor.
+static bool CheckConstexprCtorInitializer(Sema &SemaRef,
+                                          const FunctionDecl *Dcl,
+                                          FieldDecl *Field,
+                                          llvm::SmallSet<Decl*, 16> &Inits,
+                                          bool &Diagnosed,
+                                          Sema::CheckConstexprKind Kind) {
+  // In C++20 onwards, there's nothing to check for validity.
+  if (Kind == Sema::CheckConstexprKind::CheckValid &&
+      SemaRef.getLangOpts().CPlusPlus20)
+    return true;
+
+  if (Field->isInvalidDecl())
+    return true;
+
+  if (Field->isUnnamedBitfield())
+    return true;
+
+  // Anonymous unions with no variant members and empty anonymous structs do not
+  // need to be explicitly initialized. FIXME: Anonymous structs that contain no
+  // indirect fields don't need initializing.
+  if (Field->isAnonymousStructOrUnion() &&
+      (Field->getType()->isUnionType()
+           ? !Field->getType()->getAsCXXRecordDecl()->hasVariantMembers()
+           : Field->getType()->getAsCXXRecordDecl()->isEmpty()))
+    return true;
+
+  if (!Inits.count(Field)) {
+    if (Kind == Sema::CheckConstexprKind::Diagnose) {
+      if (!Diagnosed) {
+        SemaRef.Diag(Dcl->getLocation(),
+                     SemaRef.getLangOpts().CPlusPlus20
+                         ? diag::warn_cxx17_compat_constexpr_ctor_missing_init
+                         : diag::ext_constexpr_ctor_missing_init);
+        Diagnosed = true;
+      }
+      SemaRef.Diag(Field->getLocation(),
+                   diag::note_constexpr_ctor_missing_init);
+    } else if (!SemaRef.getLangOpts().CPlusPlus20) {
+      return false;
+    }
+  } else if (Field->isAnonymousStructOrUnion()) {
+    const RecordDecl *RD = Field->getType()->castAs<RecordType>()->getDecl();
+    for (auto *I : RD->fields())
+      // If an anonymous union contains an anonymous struct of which any member
+      // is initialized, all members must be initialized.
+      if (!RD->isUnion() || Inits.count(I))
+        if (!CheckConstexprCtorInitializer(SemaRef, Dcl, I, Inits, Diagnosed,
+                                           Kind))
+          return false;
+  }
+  return true;
+}
+
+/// Check the provided statement is allowed in a constexpr function
+/// definition.
+static bool
+CheckConstexprFunctionStmt(Sema &SemaRef, const FunctionDecl *Dcl, Stmt *S,
+                           SmallVectorImpl<SourceLocation> &ReturnStmts,
+                           SourceLocation &Cxx1yLoc, SourceLocation &Cxx2aLoc,
+                           Sema::CheckConstexprKind Kind) {
+  // - its function-body shall be [...] a compound-statement that contains only
+  switch (S->getStmtClass()) {
+  case Stmt::NullStmtClass:
+    //   - null statements,
+    return true;
+
+  case Stmt::DeclStmtClass:
+    //   - static_assert-declarations
+    //   - using-declarations,
+    //   - using-directives,
+    //   - typedef declarations and alias-declarations that do not define
+    //     classes or enumerations,
+    if (!CheckConstexprDeclStmt(SemaRef, Dcl, cast<DeclStmt>(S), Cxx1yLoc, Kind))
+      return false;
+    return true;
+
+  case Stmt::ReturnStmtClass:
+    //   - and exactly one return statement;
+    if (isa<CXXConstructorDecl>(Dcl)) {
+      // C++1y allows return statements in constexpr constructors.
+      if (!Cxx1yLoc.isValid())
+        Cxx1yLoc = S->getBeginLoc();
+      return true;
+    }
+
+    ReturnStmts.push_back(S->getBeginLoc());
+    return true;
+
+  case Stmt::AttributedStmtClass:
+    // Attributes on a statement don't affect its formal kind and hence don't
+    // affect its validity in a constexpr function.
+    return CheckConstexprFunctionStmt(SemaRef, Dcl,
+                                      cast<AttributedStmt>(S)->getSubStmt(),
+                                      ReturnStmts, Cxx1yLoc, Cxx2aLoc, Kind);
+
+  case Stmt::CompoundStmtClass: {
+    // C++1y allows compound-statements.
+    if (!Cxx1yLoc.isValid())
+      Cxx1yLoc = S->getBeginLoc();
+
+    CompoundStmt *CompStmt = cast<CompoundStmt>(S);
+    for (auto *BodyIt : CompStmt->body()) {
+      if (!CheckConstexprFunctionStmt(SemaRef, Dcl, BodyIt, ReturnStmts,
+                                      Cxx1yLoc, Cxx2aLoc, Kind))
+        return false;
+    }
+    return true;
+  }
+
+  case Stmt::IfStmtClass: {
+    // C++1y allows if-statements.
+    if (!Cxx1yLoc.isValid())
+      Cxx1yLoc = S->getBeginLoc();
+
+    IfStmt *If = cast<IfStmt>(S);
+    if (!CheckConstexprFunctionStmt(SemaRef, Dcl, If->getThen(), ReturnStmts,
+                                    Cxx1yLoc, Cxx2aLoc, Kind))
+      return false;
+    if (If->getElse() &&
+        !CheckConstexprFunctionStmt(SemaRef, Dcl, If->getElse(), ReturnStmts,
+                                    Cxx1yLoc, Cxx2aLoc, Kind))
+      return false;
+    return true;
+  }
+
+  case Stmt::WhileStmtClass:
+  case Stmt::DoStmtClass:
+  case Stmt::ForStmtClass:
+  case Stmt::CXXForRangeStmtClass:
+  case Stmt::ContinueStmtClass:
+    // C++1y allows all of these. We don't allow them as extensions in C++11,
+    // because they don't make sense without variable mutation.
+    if (!SemaRef.getLangOpts().CPlusPlus14)
+      break;
+    if (!Cxx1yLoc.isValid())
+      Cxx1yLoc = S->getBeginLoc();
+    for (Stmt *SubStmt : S->children())
+      if (SubStmt &&
+          !CheckConstexprFunctionStmt(SemaRef, Dcl, SubStmt, ReturnStmts,
+                                      Cxx1yLoc, Cxx2aLoc, Kind))
+        return false;
+    return true;
+
+  case Stmt::SwitchStmtClass:
+  case Stmt::CaseStmtClass:
+  case Stmt::DefaultStmtClass:
+  case Stmt::BreakStmtClass:
+    // C++1y allows switch-statements, and since they don't need variable
+    // mutation, we can reasonably allow them in C++11 as an extension.
+    if (!Cxx1yLoc.isValid())
+      Cxx1yLoc = S->getBeginLoc();
+    for (Stmt *SubStmt : S->children())
+      if (SubStmt &&
+          !CheckConstexprFunctionStmt(SemaRef, Dcl, SubStmt, ReturnStmts,
+                                      Cxx1yLoc, Cxx2aLoc, Kind))
+        return false;
+    return true;
+
+  case Stmt::GCCAsmStmtClass:
+  case Stmt::MSAsmStmtClass:
+    // C++2a allows inline assembly statements.
+  case Stmt::CXXTryStmtClass:
+    if (Cxx2aLoc.isInvalid())
+      Cxx2aLoc = S->getBeginLoc();
+    for (Stmt *SubStmt : S->children()) {
+      if (SubStmt &&
+          !CheckConstexprFunctionStmt(SemaRef, Dcl, SubStmt, ReturnStmts,
+                                      Cxx1yLoc, Cxx2aLoc, Kind))
+        return false;
+    }
+    return true;
+
+  case Stmt::CXXCatchStmtClass:
+    // Do not bother checking the language mode (already covered by the
+    // try block check).
+    if (!CheckConstexprFunctionStmt(SemaRef, Dcl,
+                                    cast<CXXCatchStmt>(S)->getHandlerBlock(),
+                                    ReturnStmts, Cxx1yLoc, Cxx2aLoc, Kind))
+      return false;
+    return true;
+
+  default:
+    if (!isa<Expr>(S))
+      break;
+
+    // C++1y allows expression-statements.
+    if (!Cxx1yLoc.isValid())
+      Cxx1yLoc = S->getBeginLoc();
+    return true;
+  }
+
+  if (Kind == Sema::CheckConstexprKind::Diagnose) {
+    SemaRef.Diag(S->getBeginLoc(), diag::err_constexpr_body_invalid_stmt)
+        << isa<CXXConstructorDecl>(Dcl) << Dcl->isConsteval();
+  }
+  return false;
+}
+
+/// Check the body for the given constexpr function declaration only contains
+/// the permitted types of statement. C++11 [dcl.constexpr]p3,p4.
+///
+/// \return true if the body is OK, false if we have found or diagnosed a
+/// problem.
+static bool CheckConstexprFunctionBody(Sema &SemaRef, const FunctionDecl *Dcl,
+                                       Stmt *Body,
+                                       Sema::CheckConstexprKind Kind) {
+  SmallVector<SourceLocation, 4> ReturnStmts;
+
+  if (isa<CXXTryStmt>(Body)) {
+    // C++11 [dcl.constexpr]p3:
+    //  The definition of a constexpr function shall satisfy the following
+    //  constraints: [...]
+    // - its function-body shall be = delete, = default, or a
+    //   compound-statement
+    //
+    // C++11 [dcl.constexpr]p4:
+    //  In the definition of a constexpr constructor, [...]
+    // - its function-body shall not be a function-try-block;
+    //
+    // This restriction is lifted in C++2a, as long as inner statements also
+    // apply the general constexpr rules.
+    switch (Kind) {
+    case Sema::CheckConstexprKind::CheckValid:
+      if (!SemaRef.getLangOpts().CPlusPlus20)
+        return false;
+      break;
+
+    case Sema::CheckConstexprKind::Diagnose:
+      SemaRef.Diag(Body->getBeginLoc(),
+           !SemaRef.getLangOpts().CPlusPlus20
+               ? diag::ext_constexpr_function_try_block_cxx20
+               : diag::warn_cxx17_compat_constexpr_function_try_block)
+          << isa<CXXConstructorDecl>(Dcl);
+      break;
+    }
+  }
+
+  // - its function-body shall be [...] a compound-statement that contains only
+  //   [... list of cases ...]
+  //
+  // Note that walking the children here is enough to properly check for
+  // CompoundStmt and CXXTryStmt body.
+  SourceLocation Cxx1yLoc, Cxx2aLoc;
+  for (Stmt *SubStmt : Body->children()) {
+    if (SubStmt &&
+        !CheckConstexprFunctionStmt(SemaRef, Dcl, SubStmt, ReturnStmts,
+                                    Cxx1yLoc, Cxx2aLoc, Kind))
+      return false;
+  }
+
+  if (Kind == Sema::CheckConstexprKind::CheckValid) {
+    // If this is only valid as an extension, report that we don't satisfy the
+    // constraints of the current language.
+    if ((Cxx2aLoc.isValid() && !SemaRef.getLangOpts().CPlusPlus20) ||
+        (Cxx1yLoc.isValid() && !SemaRef.getLangOpts().CPlusPlus17))
+      return false;
+  } else if (Cxx2aLoc.isValid()) {
+    SemaRef.Diag(Cxx2aLoc,
+         SemaRef.getLangOpts().CPlusPlus20
+           ? diag::warn_cxx17_compat_constexpr_body_invalid_stmt
+           : diag::ext_constexpr_body_invalid_stmt_cxx20)
+      << isa<CXXConstructorDecl>(Dcl);
+  } else if (Cxx1yLoc.isValid()) {
+    SemaRef.Diag(Cxx1yLoc,
+         SemaRef.getLangOpts().CPlusPlus14
+           ? diag::warn_cxx11_compat_constexpr_body_invalid_stmt
+           : diag::ext_constexpr_body_invalid_stmt)
+      << isa<CXXConstructorDecl>(Dcl);
+  }
+
+  if (const CXXConstructorDecl *Constructor
+        = dyn_cast<CXXConstructorDecl>(Dcl)) {
+    const CXXRecordDecl *RD = Constructor->getParent();
+    // DR1359:
+    // - every non-variant non-static data member and base class sub-object
+    //   shall be initialized;
+    // DR1460:
+    // - if the class is a union having variant members, exactly one of them
+    //   shall be initialized;
+    if (RD->isUnion()) {
+      if (Constructor->getNumCtorInitializers() == 0 &&
+          RD->hasVariantMembers()) {
+        if (Kind == Sema::CheckConstexprKind::Diagnose) {
+          SemaRef.Diag(
+              Dcl->getLocation(),
+              SemaRef.getLangOpts().CPlusPlus20
+                  ? diag::warn_cxx17_compat_constexpr_union_ctor_no_init
+                  : diag::ext_constexpr_union_ctor_no_init);
+        } else if (!SemaRef.getLangOpts().CPlusPlus20) {
+          return false;
+        }
+      }
+    } else if (!Constructor->isDependentContext() &&
+               !Constructor->isDelegatingConstructor()) {
+      assert(RD->getNumVBases() == 0 && "constexpr ctor with virtual bases");
+
+      // Skip detailed checking if we have enough initializers, and we would
+      // allow at most one initializer per member.
+      bool AnyAnonStructUnionMembers = false;
+      unsigned Fields = 0;
+      for (CXXRecordDecl::field_iterator I = RD->field_begin(),
+           E = RD->field_end(); I != E; ++I, ++Fields) {
+        if (I->isAnonymousStructOrUnion()) {
+          AnyAnonStructUnionMembers = true;
+          break;
+        }
+      }
+      // DR1460:
+      // - if the class is a union-like class, but is not a union, for each of
+      //   its anonymous union members having variant members, exactly one of
+      //   them shall be initialized;
+      if (AnyAnonStructUnionMembers ||
+          Constructor->getNumCtorInitializers() != RD->getNumBases() + Fields) {
+        // Check initialization of non-static data members. Base classes are
+        // always initialized so do not need to be checked. Dependent bases
+        // might not have initializers in the member initializer list.
+        llvm::SmallSet<Decl*, 16> Inits;
+        for (const auto *I: Constructor->inits()) {
+          if (FieldDecl *FD = I->getMember())
+            Inits.insert(FD);
+          else if (IndirectFieldDecl *ID = I->getIndirectMember())
+            Inits.insert(ID->chain_begin(), ID->chain_end());
+        }
+
+        bool Diagnosed = false;
+        for (auto *I : RD->fields())
+          if (!CheckConstexprCtorInitializer(SemaRef, Dcl, I, Inits, Diagnosed,
+                                             Kind))
+            return false;
+      }
+    }
+  } else {
+    if (ReturnStmts.empty()) {
+      // C++1y doesn't require constexpr functions to contain a 'return'
+      // statement. We still do, unless the return type might be void, because
+      // otherwise if there's no return statement, the function cannot
+      // be used in a core constant expression.
+      bool OK = SemaRef.getLangOpts().CPlusPlus14 &&
+                (Dcl->getReturnType()->isVoidType() ||
+                 Dcl->getReturnType()->isDependentType());
+      switch (Kind) {
+      case Sema::CheckConstexprKind::Diagnose:
+        SemaRef.Diag(Dcl->getLocation(),
+                     OK ? diag::warn_cxx11_compat_constexpr_body_no_return
+                        : diag::err_constexpr_body_no_return)
+            << Dcl->isConsteval();
+        if (!OK)
+          return false;
+        break;
+
+      case Sema::CheckConstexprKind::CheckValid:
+        // The formal requirements don't include this rule in C++14, even
+        // though the "must be able to produce a constant expression" rules
+        // still imply it in some cases.
+        if (!SemaRef.getLangOpts().CPlusPlus14)
+          return false;
+        break;
+      }
+    } else if (ReturnStmts.size() > 1) {
+      switch (Kind) {
+      case Sema::CheckConstexprKind::Diagnose:
+        SemaRef.Diag(
+            ReturnStmts.back(),
+            SemaRef.getLangOpts().CPlusPlus14
+                ? diag::warn_cxx11_compat_constexpr_body_multiple_return
+                : diag::ext_constexpr_body_multiple_return);
+        for (unsigned I = 0; I < ReturnStmts.size() - 1; ++I)
+          SemaRef.Diag(ReturnStmts[I],
+                       diag::note_constexpr_body_previous_return);
+        break;
+
+      case Sema::CheckConstexprKind::CheckValid:
+        if (!SemaRef.getLangOpts().CPlusPlus14)
+          return false;
+        break;
+      }
+    }
+  }
+
+  // C++11 [dcl.constexpr]p5:
+  //   if no function argument values exist such that the function invocation
+  //   substitution would produce a constant expression, the program is
+  //   ill-formed; no diagnostic required.
+  // C++11 [dcl.constexpr]p3:
+  //   - every constructor call and implicit conversion used in initializing the
+  //     return value shall be one of those allowed in a constant expression.
+  // C++11 [dcl.constexpr]p4:
+  //   - every constructor involved in initializing non-static data members and
+  //     base class sub-objects shall be a constexpr constructor.
+  //
+  // Note that this rule is distinct from the "requirements for a constexpr
+  // function", so is not checked in CheckValid mode.
+  SmallVector<PartialDiagnosticAt, 8> Diags;
+  if (Kind == Sema::CheckConstexprKind::Diagnose &&
+      !Expr::isPotentialConstantExpr(Dcl, Diags)) {
+    SemaRef.Diag(Dcl->getLocation(),
+                 diag::ext_constexpr_function_never_constant_expr)
+        << isa<CXXConstructorDecl>(Dcl) << Dcl->isConsteval();
+    for (size_t I = 0, N = Diags.size(); I != N; ++I)
+      SemaRef.Diag(Diags[I].first, Diags[I].second);
+    // Don't return false here: we allow this for compatibility in
+    // system headers.
+  }
+
+  return true;
+}
+
+/// Get the class that is directly named by the current context. This is the
+/// class for which an unqualified-id in this scope could name a constructor
+/// or destructor.
+///
+/// If the scope specifier denotes a class, this will be that class.
+/// If the scope specifier is empty, this will be the class whose
+/// member-specification we are currently within. Otherwise, there
+/// is no such class.
+CXXRecordDecl *Sema::getCurrentClass(Scope *, const CXXScopeSpec *SS) {
+  assert(getLangOpts().CPlusPlus && "No class names in C!");
+
+  if (SS && SS->isInvalid())
+    return nullptr;
+
+  if (SS && SS->isNotEmpty()) {
+    DeclContext *DC = computeDeclContext(*SS, true);
+    return dyn_cast_or_null<CXXRecordDecl>(DC);
+  }
+
+  return dyn_cast_or_null<CXXRecordDecl>(CurContext);
+}
+
+/// isCurrentClassName - Determine whether the identifier II is the
+/// name of the class type currently being defined. In the case of
+/// nested classes, this will only return true if II is the name of
+/// the innermost class.
+bool Sema::isCurrentClassName(const IdentifierInfo &II, Scope *S,
+                              const CXXScopeSpec *SS) {
+  CXXRecordDecl *CurDecl = getCurrentClass(S, SS);
+  return CurDecl && &II == CurDecl->getIdentifier();
+}
+
+/// Determine whether the identifier II is a typo for the name of
+/// the class type currently being defined. If so, update it to the identifier
+/// that should have been used.
+bool Sema::isCurrentClassNameTypo(IdentifierInfo *&II, const CXXScopeSpec *SS) {
+  assert(getLangOpts().CPlusPlus && "No class names in C!");
+
+  if (!getLangOpts().SpellChecking)
+    return false;
+
+  CXXRecordDecl *CurDecl;
+  if (SS && SS->isSet() && !SS->isInvalid()) {
+    DeclContext *DC = computeDeclContext(*SS, true);
+    CurDecl = dyn_cast_or_null<CXXRecordDecl>(DC);
+  } else
+    CurDecl = dyn_cast_or_null<CXXRecordDecl>(CurContext);
+
+  if (CurDecl && CurDecl->getIdentifier() && II != CurDecl->getIdentifier() &&
+      3 * II->getName().edit_distance(CurDecl->getIdentifier()->getName())
+          < II->getLength()) {
+    II = CurDecl->getIdentifier();
+    return true;
+  }
+
+  return false;
+}
+
+/// Determine whether the given class is a base class of the given
+/// class, including looking at dependent bases.
+static bool findCircularInheritance(const CXXRecordDecl *Class,
+                                    const CXXRecordDecl *Current) {
+  SmallVector<const CXXRecordDecl*, 8> Queue;
+
+  Class = Class->getCanonicalDecl();
+  while (true) {
+    for (const auto &I : Current->bases()) {
+      CXXRecordDecl *Base = I.getType()->getAsCXXRecordDecl();
+      if (!Base)
+        continue;
+
+      Base = Base->getDefinition();
+      if (!Base)
+        continue;
+
+      if (Base->getCanonicalDecl() == Class)
+        return true;
+
+      Queue.push_back(Base);
+    }
+
+    if (Queue.empty())
+      return false;
+
+    Current = Queue.pop_back_val();
+  }
+
+  return false;
+}
+
+/// Check the validity of a C++ base class specifier.
+///
+/// \returns a new CXXBaseSpecifier if well-formed, emits diagnostics
+/// and returns NULL otherwise.
+CXXBaseSpecifier *
+Sema::CheckBaseSpecifier(CXXRecordDecl *Class,
+                         SourceRange SpecifierRange,
+                         bool Virtual, AccessSpecifier Access,
+                         TypeSourceInfo *TInfo,
+                         SourceLocation EllipsisLoc) {
+  QualType BaseType = TInfo->getType();
+  if (BaseType->containsErrors()) {
+    // Already emitted a diagnostic when parsing the error type.
+    return nullptr;
+  }
+  // C++ [class.union]p1:
+  //   A union shall not have base classes.
+  if (Class->isUnion()) {
+    Diag(Class->getLocation(), diag::err_base_clause_on_union)
+      << SpecifierRange;
+    return nullptr;
+  }
+
+  if (EllipsisLoc.isValid() &&
+      !TInfo->getType()->containsUnexpandedParameterPack()) {
+    Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
+      << TInfo->getTypeLoc().getSourceRange();
+    EllipsisLoc = SourceLocation();
+  }
+
+  SourceLocation BaseLoc = TInfo->getTypeLoc().getBeginLoc();
+
+  if (BaseType->isDependentType()) {
+    // Make sure that we don't have circular inheritance among our dependent
+    // bases. For non-dependent bases, the check for completeness below handles
+    // this.
+    if (CXXRecordDecl *BaseDecl = BaseType->getAsCXXRecordDecl()) {
+      if (BaseDecl->getCanonicalDecl() == Class->getCanonicalDecl() ||
+          ((BaseDecl = BaseDecl->getDefinition()) &&
+           findCircularInheritance(Class, BaseDecl))) {
+        Diag(BaseLoc, diag::err_circular_inheritance)
+          << BaseType << Context.getTypeDeclType(Class);
+
+        if (BaseDecl->getCanonicalDecl() != Class->getCanonicalDecl())
+          Diag(BaseDecl->getLocation(), diag::note_previous_decl)
+            << BaseType;
+
+        return nullptr;
+      }
+    }
+
+    // Make sure that we don't make an ill-formed AST where the type of the
+    // Class is non-dependent and its attached base class specifier is an
+    // dependent type, which violates invariants in many clang code paths (e.g.
+    // constexpr evaluator). If this case happens (in errory-recovery mode), we
+    // explicitly mark the Class decl invalid. The diagnostic was already
+    // emitted.
+    if (!Class->getTypeForDecl()->isDependentType())
+      Class->setInvalidDecl();
+    return new (Context) CXXBaseSpecifier(SpecifierRange, Virtual,
+                                          Class->getTagKind() == TTK_Class,
+                                          Access, TInfo, EllipsisLoc);
+  }
+
+  // Base specifiers must be record types.
+  if (!BaseType->isRecordType()) {
+    Diag(BaseLoc, diag::err_base_must_be_class) << SpecifierRange;
+    return nullptr;
+  }
+
+  // C++ [class.union]p1:
+  //   A union shall not be used as a base class.
+  if (BaseType->isUnionType()) {
+    Diag(BaseLoc, diag::err_union_as_base_class) << SpecifierRange;
+    return nullptr;
+  }
+
+  // For the MS ABI, propagate DLL attributes to base class templates.
+  if (Context.getTargetInfo().getCXXABI().isMicrosoft()) {
+    if (Attr *ClassAttr = getDLLAttr(Class)) {
+      if (auto *BaseTemplate = dyn_cast_or_null<ClassTemplateSpecializationDecl>(
+              BaseType->getAsCXXRecordDecl())) {
+        propagateDLLAttrToBaseClassTemplate(Class, ClassAttr, BaseTemplate,
+                                            BaseLoc);
+      }
+    }
+  }
+
+  // C++ [class.derived]p2:
+  //   The class-name in a base-specifier shall not be an incompletely
+  //   defined class.
+  if (RequireCompleteType(BaseLoc, BaseType,
+                          diag::err_incomplete_base_class, SpecifierRange)) {
+    Class->setInvalidDecl();
+    return nullptr;
+  }
+
+  // If the base class is polymorphic or isn't empty, the new one is/isn't, too.
+  RecordDecl *BaseDecl = BaseType->castAs<RecordType>()->getDecl();
+  assert(BaseDecl && "Record type has no declaration");
+  BaseDecl = BaseDecl->getDefinition();
+  assert(BaseDecl && "Base type is not incomplete, but has no definition");
+  CXXRecordDecl *CXXBaseDecl = cast<CXXRecordDecl>(BaseDecl);
+  assert(CXXBaseDecl && "Base type is not a C++ type");
+
+  // Microsoft docs say:
+  // "If a base-class has a code_seg attribute, derived classes must have the
+  // same attribute."
+  const auto *BaseCSA = CXXBaseDecl->getAttr<CodeSegAttr>();
+  const auto *DerivedCSA = Class->getAttr<CodeSegAttr>();
+  if ((DerivedCSA || BaseCSA) &&
+      (!BaseCSA || !DerivedCSA || BaseCSA->getName() != DerivedCSA->getName())) {
+    Diag(Class->getLocation(), diag::err_mismatched_code_seg_base);
+    Diag(CXXBaseDecl->getLocation(), diag::note_base_class_specified_here)
+      << CXXBaseDecl;
+    return nullptr;
+  }
+
+  // A class which contains a flexible array member is not suitable for use as a
+  // base class:
+  //   - If the layout determines that a base comes before another base,
+  //     the flexible array member would index into the subsequent base.
+  //   - If the layout determines that base comes before the derived class,
+  //     the flexible array member would index into the derived class.
+  if (CXXBaseDecl->hasFlexibleArrayMember()) {
+    Diag(BaseLoc, diag::err_base_class_has_flexible_array_member)
+      << CXXBaseDecl->getDeclName();
+    return nullptr;
+  }
+
+  // C++ [class]p3:
+  //   If a class is marked final and it appears as a base-type-specifier in
+  //   base-clause, the program is ill-formed.
+  if (FinalAttr *FA = CXXBaseDecl->getAttr<FinalAttr>()) {
+    Diag(BaseLoc, diag::err_class_marked_final_used_as_base)
+      << CXXBaseDecl->getDeclName()
+      << FA->isSpelledAsSealed();
+    Diag(CXXBaseDecl->getLocation(), diag::note_entity_declared_at)
+        << CXXBaseDecl->getDeclName() << FA->getRange();
+    return nullptr;
+  }
+
+  if (BaseDecl->isInvalidDecl())
+    Class->setInvalidDecl();
+
+  // Create the base specifier.
+  return new (Context) CXXBaseSpecifier(SpecifierRange, Virtual,
+                                        Class->getTagKind() == TTK_Class,
+                                        Access, TInfo, EllipsisLoc);
+}
+
+/// ActOnBaseSpecifier - Parsed a base specifier. A base specifier is
+/// one entry in the base class list of a class specifier, for
+/// example:
+///    class foo : public bar, virtual private baz {
+/// 'public bar' and 'virtual private baz' are each base-specifiers.
+BaseResult
+Sema::ActOnBaseSpecifier(Decl *classdecl, SourceRange SpecifierRange,
+                         ParsedAttributes &Attributes,
+                         bool Virtual, AccessSpecifier Access,
+                         ParsedType basetype, SourceLocation BaseLoc,
+                         SourceLocation EllipsisLoc) {
+  if (!classdecl)
+    return true;
+
+  AdjustDeclIfTemplate(classdecl);
+  CXXRecordDecl *Class = dyn_cast<CXXRecordDecl>(classdecl);
+  if (!Class)
+    return true;
+
+  // We haven't yet attached the base specifiers.
+  Class->setIsParsingBaseSpecifiers();
+
+  // We do not support any C++11 attributes on base-specifiers yet.
+  // Diagnose any attributes we see.
+  for (const ParsedAttr &AL : Attributes) {
+    if (AL.isInvalid() || AL.getKind() == ParsedAttr::IgnoredAttribute)
+      continue;
+    Diag(AL.getLoc(), AL.getKind() == ParsedAttr::UnknownAttribute
+                          ? (unsigned)diag::warn_unknown_attribute_ignored
+                          : (unsigned)diag::err_base_specifier_attribute)
+        << AL << AL.getRange();
+  }
+
+  TypeSourceInfo *TInfo = nullptr;
+  GetTypeFromParser(basetype, &TInfo);
+
+  if (EllipsisLoc.isInvalid() &&
+      DiagnoseUnexpandedParameterPack(SpecifierRange.getBegin(), TInfo,
+                                      UPPC_BaseType))
+    return true;
+
+  if (CXXBaseSpecifier *BaseSpec = CheckBaseSpecifier(Class, SpecifierRange,
+                                                      Virtual, Access, TInfo,
+                                                      EllipsisLoc))
+    return BaseSpec;
+  else
+    Class->setInvalidDecl();
+
+  return true;
+}
+
+/// Use small set to collect indirect bases.  As this is only used
+/// locally, there's no need to abstract the small size parameter.
+typedef llvm::SmallPtrSet<QualType, 4> IndirectBaseSet;
+
+/// Recursively add the bases of Type.  Don't add Type itself.
+static void
+NoteIndirectBases(ASTContext &Context, IndirectBaseSet &Set,
+                  const QualType &Type)
+{
+  // Even though the incoming type is a base, it might not be
+  // a class -- it could be a template parm, for instance.
+  if (auto Rec = Type->getAs<RecordType>()) {
+    auto Decl = Rec->getAsCXXRecordDecl();
+
+    // Iterate over its bases.
+    for (const auto &BaseSpec : Decl->bases()) {
+      QualType Base = Context.getCanonicalType(BaseSpec.getType())
+        .getUnqualifiedType();
+      if (Set.insert(Base).second)
+        // If we've not already seen it, recurse.
+        NoteIndirectBases(Context, Set, Base);
+    }
+  }
+}
+
+/// Performs the actual work of attaching the given base class
+/// specifiers to a C++ class.
+bool Sema::AttachBaseSpecifiers(CXXRecordDecl *Class,
+                                MutableArrayRef<CXXBaseSpecifier *> Bases) {
+ if (Bases.empty())
+    return false;
+
+  // Used to keep track of which base types we have already seen, so
+  // that we can properly diagnose redundant direct base types. Note
+  // that the key is always the unqualified canonical type of the base
+  // class.
+  std::map<QualType, CXXBaseSpecifier*, QualTypeOrdering> KnownBaseTypes;
+
+  // Used to track indirect bases so we can see if a direct base is
+  // ambiguous.
+  IndirectBaseSet IndirectBaseTypes;
+
+  // Copy non-redundant base specifiers into permanent storage.
+  unsigned NumGoodBases = 0;
+  bool Invalid = false;
+  for (unsigned idx = 0; idx < Bases.size(); ++idx) {
+    QualType NewBaseType
+      = Context.getCanonicalType(Bases[idx]->getType());
+    NewBaseType = NewBaseType.getLocalUnqualifiedType();
+
+    CXXBaseSpecifier *&KnownBase = KnownBaseTypes[NewBaseType];
+    if (KnownBase) {
+      // C++ [class.mi]p3:
+      //   A class shall not be specified as a direct base class of a
+      //   derived class more than once.
+      Diag(Bases[idx]->getBeginLoc(), diag::err_duplicate_base_class)
+          << KnownBase->getType() << Bases[idx]->getSourceRange();
+
+      // Delete the duplicate base class specifier; we're going to
+      // overwrite its pointer later.
+      Context.Deallocate(Bases[idx]);
+
+      Invalid = true;
+    } else {
+      // Okay, add this new base class.
+      KnownBase = Bases[idx];
+      Bases[NumGoodBases++] = Bases[idx];
+
+      if (NewBaseType->isDependentType())
+        continue;
+      // Note this base's direct & indirect bases, if there could be ambiguity.
+      if (Bases.size() > 1)
+        NoteIndirectBases(Context, IndirectBaseTypes, NewBaseType);
+
+      if (const RecordType *Record = NewBaseType->getAs<RecordType>()) {
+        const CXXRecordDecl *RD = cast<CXXRecordDecl>(Record->getDecl());
+        if (Class->isInterface() &&
+              (!RD->isInterfaceLike() ||
+               KnownBase->getAccessSpecifier() != AS_public)) {
+          // The Microsoft extension __interface does not permit bases that
+          // are not themselves public interfaces.
+          Diag(KnownBase->getBeginLoc(), diag::err_invalid_base_in_interface)
+              << getRecordDiagFromTagKind(RD->getTagKind()) << RD
+              << RD->getSourceRange();
+          Invalid = true;
+        }
+        if (RD->hasAttr<WeakAttr>())
+          Class->addAttr(WeakAttr::CreateImplicit(Context));
+      }
+    }
+  }
+
+  // Attach the remaining base class specifiers to the derived class.
+  Class->setBases(Bases.data(), NumGoodBases);
+
+  // Check that the only base classes that are duplicate are virtual.
+  for (unsigned idx = 0; idx < NumGoodBases; ++idx) {
+    // Check whether this direct base is inaccessible due to ambiguity.
+    QualType BaseType = Bases[idx]->getType();
+
+    // Skip all dependent types in templates being used as base specifiers.
+    // Checks below assume that the base specifier is a CXXRecord.
+    if (BaseType->isDependentType())
+      continue;
+
+    CanQualType CanonicalBase = Context.getCanonicalType(BaseType)
+      .getUnqualifiedType();
+
+    if (IndirectBaseTypes.count(CanonicalBase)) {
+      CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
+                         /*DetectVirtual=*/true);
+      bool found
+        = Class->isDerivedFrom(CanonicalBase->getAsCXXRecordDecl(), Paths);
+      assert(found);
+      (void)found;
+
+      if (Paths.isAmbiguous(CanonicalBase))
+        Diag(Bases[idx]->getBeginLoc(), diag::warn_inaccessible_base_class)
+            << BaseType << getAmbiguousPathsDisplayString(Paths)
+            << Bases[idx]->getSourceRange();
+      else
+        assert(Bases[idx]->isVirtual());
+    }
+
+    // Delete the base class specifier, since its data has been copied
+    // into the CXXRecordDecl.
+    Context.Deallocate(Bases[idx]);
+  }
+
+  return Invalid;
+}
+
+/// ActOnBaseSpecifiers - Attach the given base specifiers to the
+/// class, after checking whether there are any duplicate base
+/// classes.
+void Sema::ActOnBaseSpecifiers(Decl *ClassDecl,
+                               MutableArrayRef<CXXBaseSpecifier *> Bases) {
+  if (!ClassDecl || Bases.empty())
+    return;
+
+  AdjustDeclIfTemplate(ClassDecl);
+  AttachBaseSpecifiers(cast<CXXRecordDecl>(ClassDecl), Bases);
+}
+
+/// Determine whether the type \p Derived is a C++ class that is
+/// derived from the type \p Base.
+bool Sema::IsDerivedFrom(SourceLocation Loc, QualType Derived, QualType Base) {
+  if (!getLangOpts().CPlusPlus)
+    return false;
+
+  CXXRecordDecl *DerivedRD = Derived->getAsCXXRecordDecl();
+  if (!DerivedRD)
+    return false;
+
+  CXXRecordDecl *BaseRD = Base->getAsCXXRecordDecl();
+  if (!BaseRD)
+    return false;
+
+  // If either the base or the derived type is invalid, don't try to
+  // check whether one is derived from the other.
+  if (BaseRD->isInvalidDecl() || DerivedRD->isInvalidDecl())
+    return false;
+
+  // FIXME: In a modules build, do we need the entire path to be visible for us
+  // to be able to use the inheritance relationship?
+  if (!isCompleteType(Loc, Derived) && !DerivedRD->isBeingDefined())
+    return false;
+
+  return DerivedRD->isDerivedFrom(BaseRD);
+}
+
+/// Determine whether the type \p Derived is a C++ class that is
+/// derived from the type \p Base.
+bool Sema::IsDerivedFrom(SourceLocation Loc, QualType Derived, QualType Base,
+                         CXXBasePaths &Paths) {
+  if (!getLangOpts().CPlusPlus)
+    return false;
+
+  CXXRecordDecl *DerivedRD = Derived->getAsCXXRecordDecl();
+  if (!DerivedRD)
+    return false;
+
+  CXXRecordDecl *BaseRD = Base->getAsCXXRecordDecl();
+  if (!BaseRD)
+    return false;
+
+  if (!isCompleteType(Loc, Derived) && !DerivedRD->isBeingDefined())
+    return false;
+
+  return DerivedRD->isDerivedFrom(BaseRD, Paths);
+}
+
+static void BuildBasePathArray(const CXXBasePath &Path,
+                               CXXCastPath &BasePathArray) {
+  // We first go backward and check if we have a virtual base.
+  // FIXME: It would be better if CXXBasePath had the base specifier for
+  // the nearest virtual base.
+  unsigned Start = 0;
+  for (unsigned I = Path.size(); I != 0; --I) {
+    if (Path[I - 1].Base->isVirtual()) {
+      Start = I - 1;
+      break;
+    }
+  }
+
+  // Now add all bases.
+  for (unsigned I = Start, E = Path.size(); I != E; ++I)
+    BasePathArray.push_back(const_cast<CXXBaseSpecifier*>(Path[I].Base));
+}
+
+
+void Sema::BuildBasePathArray(const CXXBasePaths &Paths,
+                              CXXCastPath &BasePathArray) {
+  assert(BasePathArray.empty() && "Base path array must be empty!");
+  assert(Paths.isRecordingPaths() && "Must record paths!");
+  return ::BuildBasePathArray(Paths.front(), BasePathArray);
+}
+/// CheckDerivedToBaseConversion - Check whether the Derived-to-Base
+/// conversion (where Derived and Base are class types) is
+/// well-formed, meaning that the conversion is unambiguous (and
+/// that all of the base classes are accessible). Returns true
+/// and emits a diagnostic if the code is ill-formed, returns false
+/// otherwise. Loc is the location where this routine should point to
+/// if there is an error, and Range is the source range to highlight
+/// if there is an error.
+///
+/// If either InaccessibleBaseID or AmbiguousBaseConvID are 0, then the
+/// diagnostic for the respective type of error will be suppressed, but the
+/// check for ill-formed code will still be performed.
+bool
+Sema::CheckDerivedToBaseConversion(QualType Derived, QualType Base,
+                                   unsigned InaccessibleBaseID,
+                                   unsigned AmbiguousBaseConvID,
+                                   SourceLocation Loc, SourceRange Range,
+                                   DeclarationName Name,
+                                   CXXCastPath *BasePath,
+                                   bool IgnoreAccess) {
+  // First, determine whether the path from Derived to Base is
+  // ambiguous. This is slightly more expensive than checking whether
+  // the Derived to Base conversion exists, because here we need to
+  // explore multiple paths to determine if there is an ambiguity.
+  CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
+                     /*DetectVirtual=*/false);
+  bool DerivationOkay = IsDerivedFrom(Loc, Derived, Base, Paths);
+  if (!DerivationOkay)
+    return true;
+
+  const CXXBasePath *Path = nullptr;
+  if (!Paths.isAmbiguous(Context.getCanonicalType(Base).getUnqualifiedType()))
+    Path = &Paths.front();
+
+  // For MSVC compatibility, check if Derived directly inherits from Base. Clang
+  // warns about this hierarchy under -Winaccessible-base, but MSVC allows the
+  // user to access such bases.
+  if (!Path && getLangOpts().MSVCCompat) {
+    for (const CXXBasePath &PossiblePath : Paths) {
+      if (PossiblePath.size() == 1) {
+        Path = &PossiblePath;
+        if (AmbiguousBaseConvID)
+          Diag(Loc, diag::ext_ms_ambiguous_direct_base)
+              << Base << Derived << Range;
+        break;
+      }
+    }
+  }
+
+  if (Path) {
+    if (!IgnoreAccess) {
+      // Check that the base class can be accessed.
+      switch (
+          CheckBaseClassAccess(Loc, Base, Derived, *Path, InaccessibleBaseID)) {
+      case AR_inaccessible:
+        return true;
+      case AR_accessible:
+      case AR_dependent:
+      case AR_delayed:
+        break;
+      }
+    }
+
+    // Build a base path if necessary.
+    if (BasePath)
+      ::BuildBasePathArray(*Path, *BasePath);
+    return false;
+  }
+
+  if (AmbiguousBaseConvID) {
+    // We know that the derived-to-base conversion is ambiguous, and
+    // we're going to produce a diagnostic. Perform the derived-to-base
+    // search just one more time to compute all of the possible paths so
+    // that we can print them out. This is more expensive than any of
+    // the previous derived-to-base checks we've done, but at this point
+    // performance isn't as much of an issue.
+    Paths.clear();
+    Paths.setRecordingPaths(true);
+    bool StillOkay = IsDerivedFrom(Loc, Derived, Base, Paths);
+    assert(StillOkay && "Can only be used with a derived-to-base conversion");
+    (void)StillOkay;
+
+    // Build up a textual representation of the ambiguous paths, e.g.,
+    // D -> B -> A, that will be used to illustrate the ambiguous
+    // conversions in the diagnostic. We only print one of the paths
+    // to each base class subobject.
+    std::string PathDisplayStr = getAmbiguousPathsDisplayString(Paths);
+
+    Diag(Loc, AmbiguousBaseConvID)
+    << Derived << Base << PathDisplayStr << Range << Name;
+  }
+  return true;
+}
+
+bool
+Sema::CheckDerivedToBaseConversion(QualType Derived, QualType Base,
+                                   SourceLocation Loc, SourceRange Range,
+                                   CXXCastPath *BasePath,
+                                   bool IgnoreAccess) {
+  return CheckDerivedToBaseConversion(
+      Derived, Base, diag::err_upcast_to_inaccessible_base,
+      diag::err_ambiguous_derived_to_base_conv, Loc, Range, DeclarationName(),
+      BasePath, IgnoreAccess);
+}
+
+
+/// Builds a string representing ambiguous paths from a
+/// specific derived class to different subobjects of the same base
+/// class.
+///
+/// This function builds a string that can be used in error messages
+/// to show the different paths that one can take through the
+/// inheritance hierarchy to go from the derived class to different
+/// subobjects of a base class. The result looks something like this:
+/// @code
+/// struct D -> struct B -> struct A
+/// struct D -> struct C -> struct A
+/// @endcode
+std::string Sema::getAmbiguousPathsDisplayString(CXXBasePaths &Paths) {
+  std::string PathDisplayStr;
+  std::set<unsigned> DisplayedPaths;
+  for (CXXBasePaths::paths_iterator Path = Paths.begin();
+       Path != Paths.end(); ++Path) {
+    if (DisplayedPaths.insert(Path->back().SubobjectNumber).second) {
+      // We haven't displayed a path to this particular base
+      // class subobject yet.
+      PathDisplayStr += "\n    ";
+      PathDisplayStr += Context.getTypeDeclType(Paths.getOrigin()).getAsString();
+      for (CXXBasePath::const_iterator Element = Path->begin();
+           Element != Path->end(); ++Element)
+        PathDisplayStr += " -> " + Element->Base->getType().getAsString();
+    }
+  }
+
+  return PathDisplayStr;
+}
+
+//===----------------------------------------------------------------------===//
+// C++ class member Handling
+//===----------------------------------------------------------------------===//
+
+/// ActOnAccessSpecifier - Parsed an access specifier followed by a colon.
+bool Sema::ActOnAccessSpecifier(AccessSpecifier Access, SourceLocation ASLoc,
+                                SourceLocation ColonLoc,
+                                const ParsedAttributesView &Attrs) {
+  assert(Access != AS_none && "Invalid kind for syntactic access specifier!");
+  AccessSpecDecl *ASDecl = AccessSpecDecl::Create(Context, Access, CurContext,
+                                                  ASLoc, ColonLoc);
+  CurContext->addHiddenDecl(ASDecl);
+  return ProcessAccessDeclAttributeList(ASDecl, Attrs);
+}
+
+/// CheckOverrideControl - Check C++11 override control semantics.
+void Sema::CheckOverrideControl(NamedDecl *D) {
+  if (D->isInvalidDecl())
+    return;
+
+  // We only care about "override" and "final" declarations.
+  if (!D->hasAttr<OverrideAttr>() && !D->hasAttr<FinalAttr>())
+    return;
+
+  CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(D);
+
+  // We can't check dependent instance methods.
+  if (MD && MD->isInstance() &&
+      (MD->getParent()->hasAnyDependentBases() ||
+       MD->getType()->isDependentType()))
+    return;
+
+  if (MD && !MD->isVirtual()) {
+    // If we have a non-virtual method, check if if hides a virtual method.
+    // (In that case, it's most likely the method has the wrong type.)
+    SmallVector<CXXMethodDecl *, 8> OverloadedMethods;
+    FindHiddenVirtualMethods(MD, OverloadedMethods);
+
+    if (!OverloadedMethods.empty()) {
+      if (OverrideAttr *OA = D->getAttr<OverrideAttr>()) {
+        Diag(OA->getLocation(),
+             diag::override_keyword_hides_virtual_member_function)
+          << "override" << (OverloadedMethods.size() > 1);
+      } else if (FinalAttr *FA = D->getAttr<FinalAttr>()) {
+        Diag(FA->getLocation(),
+             diag::override_keyword_hides_virtual_member_function)
+          << (FA->isSpelledAsSealed() ? "sealed" : "final")
+          << (OverloadedMethods.size() > 1);
+      }
+      NoteHiddenVirtualMethods(MD, OverloadedMethods);
+      MD->setInvalidDecl();
+      return;
+    }
+    // Fall through into the general case diagnostic.
+    // FIXME: We might want to attempt typo correction here.
+  }
+
+  if (!MD || !MD->isVirtual()) {
+    if (OverrideAttr *OA = D->getAttr<OverrideAttr>()) {
+      Diag(OA->getLocation(),
+           diag::override_keyword_only_allowed_on_virtual_member_functions)
+        << "override" << FixItHint::CreateRemoval(OA->getLocation());
+      D->dropAttr<OverrideAttr>();
+    }
+    if (FinalAttr *FA = D->getAttr<FinalAttr>()) {
+      Diag(FA->getLocation(),
+           diag::override_keyword_only_allowed_on_virtual_member_functions)
+        << (FA->isSpelledAsSealed() ? "sealed" : "final")
+        << FixItHint::CreateRemoval(FA->getLocation());
+      D->dropAttr<FinalAttr>();
+    }
+    return;
+  }
+
+  // C++11 [class.virtual]p5:
+  //   If a function is marked with the virt-specifier override and
+  //   does not override a member function of a base class, the program is
+  //   ill-formed.
+  bool HasOverriddenMethods = MD->size_overridden_methods() != 0;
+  if (MD->hasAttr<OverrideAttr>() && !HasOverriddenMethods)
+    Diag(MD->getLocation(), diag::err_function_marked_override_not_overriding)
+      << MD->getDeclName();
+}
+
+void Sema::DiagnoseAbsenceOfOverrideControl(NamedDecl *D, bool Inconsistent) {
+  if (D->isInvalidDecl() || D->hasAttr<OverrideAttr>())
+    return;
+  CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(D);
+  if (!MD || MD->isImplicit() || MD->hasAttr<FinalAttr>())
+    return;
+
+  SourceLocation Loc = MD->getLocation();
+  SourceLocation SpellingLoc = Loc;
+  if (getSourceManager().isMacroArgExpansion(Loc))
+    SpellingLoc = getSourceManager().getImmediateExpansionRange(Loc).getBegin();
+  SpellingLoc = getSourceManager().getSpellingLoc(SpellingLoc);
+  if (SpellingLoc.isValid() && getSourceManager().isInSystemHeader(SpellingLoc))
+      return;
+
+  if (MD->size_overridden_methods() > 0) {
+    auto EmitDiag = [&](unsigned DiagInconsistent, unsigned DiagSuggest) {
+      unsigned DiagID =
+          Inconsistent && !Diags.isIgnored(DiagInconsistent, MD->getLocation())
+              ? DiagInconsistent
+              : DiagSuggest;
+      Diag(MD->getLocation(), DiagID) << MD->getDeclName();
+      const CXXMethodDecl *OMD = *MD->begin_overridden_methods();
+      Diag(OMD->getLocation(), diag::note_overridden_virtual_function);
+    };
+    if (isa<CXXDestructorDecl>(MD))
+      EmitDiag(
+          diag::warn_inconsistent_destructor_marked_not_override_overriding,
+          diag::warn_suggest_destructor_marked_not_override_overriding);
+    else
+      EmitDiag(diag::warn_inconsistent_function_marked_not_override_overriding,
+               diag::warn_suggest_function_marked_not_override_overriding);
+  }
+}
+
+/// CheckIfOverriddenFunctionIsMarkedFinal - Checks whether a virtual member
+/// function overrides a virtual member function marked 'final', according to
+/// C++11 [class.virtual]p4.
+bool Sema::CheckIfOverriddenFunctionIsMarkedFinal(const CXXMethodDecl *New,
+                                                  const CXXMethodDecl *Old) {
+  FinalAttr *FA = Old->getAttr<FinalAttr>();
+  if (!FA)
+    return false;
+
+  Diag(New->getLocation(), diag::err_final_function_overridden)
+    << New->getDeclName()
+    << FA->isSpelledAsSealed();
+  Diag(Old->getLocation(), diag::note_overridden_virtual_function);
+  return true;
+}
+
+static bool InitializationHasSideEffects(const FieldDecl &FD) {
+  const Type *T = FD.getType()->getBaseElementTypeUnsafe();
+  // FIXME: Destruction of ObjC lifetime types has side-effects.
+  if (const CXXRecordDecl *RD = T->getAsCXXRecordDecl())
+    return !RD->isCompleteDefinition() ||
+           !RD->hasTrivialDefaultConstructor() ||
+           !RD->hasTrivialDestructor();
+  return false;
+}
+
+static const ParsedAttr *getMSPropertyAttr(const ParsedAttributesView &list) {
+  ParsedAttributesView::const_iterator Itr =
+      llvm::find_if(list, [](const ParsedAttr &AL) {
+        return AL.isDeclspecPropertyAttribute();
+      });
+  if (Itr != list.end())
+    return &*Itr;
+  return nullptr;
+}
+
+// Check if there is a field shadowing.
+void Sema::CheckShadowInheritedFields(const SourceLocation &Loc,
+                                      DeclarationName FieldName,
+                                      const CXXRecordDecl *RD,
+                                      bool DeclIsField) {
+  if (Diags.isIgnored(diag::warn_shadow_field, Loc))
+    return;
+
+  // To record a shadowed field in a base
+  std::map<CXXRecordDecl*, NamedDecl*> Bases;
+  auto FieldShadowed = [&](const CXXBaseSpecifier *Specifier,
+                           CXXBasePath &Path) {
+    const auto Base = Specifier->getType()->getAsCXXRecordDecl();
+    // Record an ambiguous path directly
+    if (Bases.find(Base) != Bases.end())
+      return true;
+    for (const auto Field : Base->lookup(FieldName)) {
+      if ((isa<FieldDecl>(Field) || isa<IndirectFieldDecl>(Field)) &&
+          Field->getAccess() != AS_private) {
+        assert(Field->getAccess() != AS_none);
+        assert(Bases.find(Base) == Bases.end());
+        Bases[Base] = Field;
+        return true;
+      }
+    }
+    return false;
+  };
+
+  CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
+                     /*DetectVirtual=*/true);
+  if (!RD->lookupInBases(FieldShadowed, Paths))
+    return;
+
+  for (const auto &P : Paths) {
+    auto Base = P.back().Base->getType()->getAsCXXRecordDecl();
+    auto It = Bases.find(Base);
+    // Skip duplicated bases
+    if (It == Bases.end())
+      continue;
+    auto BaseField = It->second;
+    assert(BaseField->getAccess() != AS_private);
+    if (AS_none !=
+        CXXRecordDecl::MergeAccess(P.Access, BaseField->getAccess())) {
+      Diag(Loc, diag::warn_shadow_field)
+        << FieldName << RD << Base << DeclIsField;
+      Diag(BaseField->getLocation(), diag::note_shadow_field);
+      Bases.erase(It);
+    }
+  }
+}
+
+/// ActOnCXXMemberDeclarator - This is invoked when a C++ class member
+/// declarator is parsed. 'AS' is the access specifier, 'BW' specifies the
+/// bitfield width if there is one, 'InitExpr' specifies the initializer if
+/// one has been parsed, and 'InitStyle' is set if an in-class initializer is
+/// present (but parsing it has been deferred).
+NamedDecl *
+Sema::ActOnCXXMemberDeclarator(Scope *S, AccessSpecifier AS, Declarator &D,
+                               MultiTemplateParamsArg TemplateParameterLists,
+                               Expr *BW, const VirtSpecifiers &VS,
+                               InClassInitStyle InitStyle) {
+  const DeclSpec &DS = D.getDeclSpec();
+  DeclarationNameInfo NameInfo = GetNameForDeclarator(D);
+  DeclarationName Name = NameInfo.getName();
+  SourceLocation Loc = NameInfo.getLoc();
+
+  // For anonymous bitfields, the location should point to the type.
+  if (Loc.isInvalid())
+    Loc = D.getBeginLoc();
+
+  Expr *BitWidth = static_cast<Expr*>(BW);
+
+  assert(isa<CXXRecordDecl>(CurContext));
+  assert(!DS.isFriendSpecified());
+
+  bool isFunc = D.isDeclarationOfFunction();
+  const ParsedAttr *MSPropertyAttr =
+      getMSPropertyAttr(D.getDeclSpec().getAttributes());
+
+  if (cast<CXXRecordDecl>(CurContext)->isInterface()) {
+    // The Microsoft extension __interface only permits public member functions
+    // and prohibits constructors, destructors, operators, non-public member
+    // functions, static methods and data members.
+    unsigned InvalidDecl;
+    bool ShowDeclName = true;
+    if (!isFunc &&
+        (DS.getStorageClassSpec() == DeclSpec::SCS_typedef || MSPropertyAttr))
+      InvalidDecl = 0;
+    else if (!isFunc)
+      InvalidDecl = 1;
+    else if (AS != AS_public)
+      InvalidDecl = 2;
+    else if (DS.getStorageClassSpec() == DeclSpec::SCS_static)
+      InvalidDecl = 3;
+    else switch (Name.getNameKind()) {
+      case DeclarationName::CXXConstructorName:
+        InvalidDecl = 4;
+        ShowDeclName = false;
+        break;
+
+      case DeclarationName::CXXDestructorName:
+        InvalidDecl = 5;
+        ShowDeclName = false;
+        break;
+
+      case DeclarationName::CXXOperatorName:
+      case DeclarationName::CXXConversionFunctionName:
+        InvalidDecl = 6;
+        break;
+
+      default:
+        InvalidDecl = 0;
+        break;
+    }
+
+    if (InvalidDecl) {
+      if (ShowDeclName)
+        Diag(Loc, diag::err_invalid_member_in_interface)
+          << (InvalidDecl-1) << Name;
+      else
+        Diag(Loc, diag::err_invalid_member_in_interface)
+          << (InvalidDecl-1) << "";
+      return nullptr;
+    }
+  }
+
+  // C++ 9.2p6: A member shall not be declared to have automatic storage
+  // duration (auto, register) or with the extern storage-class-specifier.
+  // C++ 7.1.1p8: The mutable specifier can be applied only to names of class
+  // data members and cannot be applied to names declared const or static,
+  // and cannot be applied to reference members.
+  switch (DS.getStorageClassSpec()) {
+  case DeclSpec::SCS_unspecified:
+  case DeclSpec::SCS_typedef:
+  case DeclSpec::SCS_static:
+    break;
+  case DeclSpec::SCS_mutable:
+    if (isFunc) {
+      Diag(DS.getStorageClassSpecLoc(), diag::err_mutable_function);
+
+      // FIXME: It would be nicer if the keyword was ignored only for this
+      // declarator. Otherwise we could get follow-up errors.
+      D.getMutableDeclSpec().ClearStorageClassSpecs();
+    }
+    break;
+  default:
+    Diag(DS.getStorageClassSpecLoc(),
+         diag::err_storageclass_invalid_for_member);
+    D.getMutableDeclSpec().ClearStorageClassSpecs();
+    break;
+  }
+
+  bool isInstField = ((DS.getStorageClassSpec() == DeclSpec::SCS_unspecified ||
+                       DS.getStorageClassSpec() == DeclSpec::SCS_mutable) &&
+                      !isFunc);
+
+  if (DS.hasConstexprSpecifier() && isInstField) {
+    SemaDiagnosticBuilder B =
+        Diag(DS.getConstexprSpecLoc(), diag::err_invalid_constexpr_member);
+    SourceLocation ConstexprLoc = DS.getConstexprSpecLoc();
+    if (InitStyle == ICIS_NoInit) {
+      B << 0 << 0;
+      if (D.getDeclSpec().getTypeQualifiers() & DeclSpec::TQ_const)
+        B << FixItHint::CreateRemoval(ConstexprLoc);
+      else {
+        B << FixItHint::CreateReplacement(ConstexprLoc, "const");
+        D.getMutableDeclSpec().ClearConstexprSpec();
+        const char *PrevSpec;
+        unsigned DiagID;
+        bool Failed = D.getMutableDeclSpec().SetTypeQual(
+            DeclSpec::TQ_const, ConstexprLoc, PrevSpec, DiagID, getLangOpts());
+        (void)Failed;
+        assert(!Failed && "Making a constexpr member const shouldn't fail");
+      }
+    } else {
+      B << 1;
+      const char *PrevSpec;
+      unsigned DiagID;
+      if (D.getMutableDeclSpec().SetStorageClassSpec(
+          *this, DeclSpec::SCS_static, ConstexprLoc, PrevSpec, DiagID,
+          Context.getPrintingPolicy())) {
+        assert(DS.getStorageClassSpec() == DeclSpec::SCS_mutable &&
+               "This is the only DeclSpec that should fail to be applied");
+        B << 1;
+      } else {
+        B << 0 << FixItHint::CreateInsertion(ConstexprLoc, "static ");
+        isInstField = false;
+      }
+    }
+  }
+
+  NamedDecl *Member;
+  if (isInstField) {
+    CXXScopeSpec &SS = D.getCXXScopeSpec();
+
+    // Data members must have identifiers for names.
+    if (!Name.isIdentifier()) {
+      Diag(Loc, diag::err_bad_variable_name)
+        << Name;
+      return nullptr;
+    }
+
+    IdentifierInfo *II = Name.getAsIdentifierInfo();
+
+    // Member field could not be with "template" keyword.
+    // So TemplateParameterLists should be empty in this case.
+    if (TemplateParameterLists.size()) {
+      TemplateParameterList* TemplateParams = TemplateParameterLists[0];
+      if (TemplateParams->size()) {
+        // There is no such thing as a member field template.
+        Diag(D.getIdentifierLoc(), diag::err_template_member)
+            << II
+            << SourceRange(TemplateParams->getTemplateLoc(),
+                TemplateParams->getRAngleLoc());
+      } else {
+        // There is an extraneous 'template<>' for this member.
+        Diag(TemplateParams->getTemplateLoc(),
+            diag::err_template_member_noparams)
+            << II
+            << SourceRange(TemplateParams->getTemplateLoc(),
+                TemplateParams->getRAngleLoc());
+      }
+      return nullptr;
+    }
+
+    if (SS.isSet() && !SS.isInvalid()) {
+      // The user provided a superfluous scope specifier inside a class
+      // definition:
+      //
+      // class X {
+      //   int X::member;
+      // };
+      if (DeclContext *DC = computeDeclContext(SS, false))
+        diagnoseQualifiedDeclaration(SS, DC, Name, D.getIdentifierLoc(),
+                                     D.getName().getKind() ==
+                                         UnqualifiedIdKind::IK_TemplateId);
+      else
+        Diag(D.getIdentifierLoc(), diag::err_member_qualification)
+          << Name << SS.getRange();
+
+      SS.clear();
+    }
+
+    if (MSPropertyAttr) {
+      Member = HandleMSProperty(S, cast<CXXRecordDecl>(CurContext), Loc, D,
+                                BitWidth, InitStyle, AS, *MSPropertyAttr);
+      if (!Member)
+        return nullptr;
+      isInstField = false;
+    } else {
+      Member = HandleField(S, cast<CXXRecordDecl>(CurContext), Loc, D,
+                                BitWidth, InitStyle, AS);
+      if (!Member)
+        return nullptr;
+    }
+
+    CheckShadowInheritedFields(Loc, Name, cast<CXXRecordDecl>(CurContext));
+  } else {
+    Member = HandleDeclarator(S, D, TemplateParameterLists);
+    if (!Member)
+      return nullptr;
+
+    // Non-instance-fields can't have a bitfield.
+    if (BitWidth) {
+      if (Member->isInvalidDecl()) {
+        // don't emit another diagnostic.
+      } else if (isa<VarDecl>(Member) || isa<VarTemplateDecl>(Member)) {
+        // C++ 9.6p3: A bit-field shall not be a static member.
+        // "static member 'A' cannot be a bit-field"
+        Diag(Loc, diag::err_static_not_bitfield)
+          << Name << BitWidth->getSourceRange();
+      } else if (isa<TypedefDecl>(Member)) {
+        // "typedef member 'x' cannot be a bit-field"
+        Diag(Loc, diag::err_typedef_not_bitfield)
+          << Name << BitWidth->getSourceRange();
+      } else {
+        // A function typedef ("typedef int f(); f a;").
+        // C++ 9.6p3: A bit-field shall have integral or enumeration type.
+        Diag(Loc, diag::err_not_integral_type_bitfield)
+          << Name << cast<ValueDecl>(Member)->getType()
+          << BitWidth->getSourceRange();
+      }
+
+      BitWidth = nullptr;
+      Member->setInvalidDecl();
+    }
+
+    NamedDecl *NonTemplateMember = Member;
+    if (FunctionTemplateDecl *FunTmpl = dyn_cast<FunctionTemplateDecl>(Member))
+      NonTemplateMember = FunTmpl->getTemplatedDecl();
+    else if (VarTemplateDecl *VarTmpl = dyn_cast<VarTemplateDecl>(Member))
+      NonTemplateMember = VarTmpl->getTemplatedDecl();
+
+    Member->setAccess(AS);
+
+    // If we have declared a member function template or static data member
+    // template, set the access of the templated declaration as well.
+    if (NonTemplateMember != Member)
+      NonTemplateMember->setAccess(AS);
+
+    // C++ [temp.deduct.guide]p3:
+    //   A deduction guide [...] for a member class template [shall be
+    //   declared] with the same access [as the template].
+    if (auto *DG = dyn_cast<CXXDeductionGuideDecl>(NonTemplateMember)) {
+      auto *TD = DG->getDeducedTemplate();
+      // Access specifiers are only meaningful if both the template and the
+      // deduction guide are from the same scope.
+      if (AS != TD->getAccess() &&
+          TD->getDeclContext()->getRedeclContext()->Equals(
+              DG->getDeclContext()->getRedeclContext())) {
+        Diag(DG->getBeginLoc(), diag::err_deduction_guide_wrong_access);
+        Diag(TD->getBeginLoc(), diag::note_deduction_guide_template_access)
+            << TD->getAccess();
+        const AccessSpecDecl *LastAccessSpec = nullptr;
+        for (const auto *D : cast<CXXRecordDecl>(CurContext)->decls()) {
+          if (const auto *AccessSpec = dyn_cast<AccessSpecDecl>(D))
+            LastAccessSpec = AccessSpec;
+        }
+        assert(LastAccessSpec && "differing access with no access specifier");
+        Diag(LastAccessSpec->getBeginLoc(), diag::note_deduction_guide_access)
+            << AS;
+      }
+    }
+  }
+
+  if (VS.isOverrideSpecified())
+    Member->addAttr(OverrideAttr::Create(Context, VS.getOverrideLoc(),
+                                         AttributeCommonInfo::AS_Keyword));
+  if (VS.isFinalSpecified())
+    Member->addAttr(FinalAttr::Create(
+        Context, VS.getFinalLoc(), AttributeCommonInfo::AS_Keyword,
+        static_cast<FinalAttr::Spelling>(VS.isFinalSpelledSealed())));
+
+  if (VS.getLastLocation().isValid()) {
+    // Update the end location of a method that has a virt-specifiers.
+    if (CXXMethodDecl *MD = dyn_cast_or_null<CXXMethodDecl>(Member))
+      MD->setRangeEnd(VS.getLastLocation());
+  }
+
+  CheckOverrideControl(Member);
+
+  assert((Name || isInstField) && "No identifier for non-field ?");
+
+  if (isInstField) {
+    FieldDecl *FD = cast<FieldDecl>(Member);
+    FieldCollector->Add(FD);
+
+    if (!Diags.isIgnored(diag::warn_unused_private_field, FD->getLocation())) {
+      // Remember all explicit private FieldDecls that have a name, no side
+      // effects and are not part of a dependent type declaration.
+      if (!FD->isImplicit() && FD->getDeclName() &&
+          FD->getAccess() == AS_private &&
+          !FD->hasAttr<UnusedAttr>() &&
+          !FD->getParent()->isDependentContext() &&
+          !InitializationHasSideEffects(*FD))
+        UnusedPrivateFields.insert(FD);
+    }
+  }
+
+  return Member;
+}
+
+namespace {
+  class UninitializedFieldVisitor
+      : public EvaluatedExprVisitor<UninitializedFieldVisitor> {
+    Sema &S;
+    // List of Decls to generate a warning on.  Also remove Decls that become
+    // initialized.
+    llvm::SmallPtrSetImpl<ValueDecl*> &Decls;
+    // List of base classes of the record.  Classes are removed after their
+    // initializers.
+    llvm::SmallPtrSetImpl<QualType> &BaseClasses;
+    // Vector of decls to be removed from the Decl set prior to visiting the
+    // nodes.  These Decls may have been initialized in the prior initializer.
+    llvm::SmallVector<ValueDecl*, 4> DeclsToRemove;
+    // If non-null, add a note to the warning pointing back to the constructor.
+    const CXXConstructorDecl *Constructor;
+    // Variables to hold state when processing an initializer list.  When
+    // InitList is true, special case initialization of FieldDecls matching
+    // InitListFieldDecl.
+    bool InitList;
+    FieldDecl *InitListFieldDecl;
+    llvm::SmallVector<unsigned, 4> InitFieldIndex;
+
+  public:
+    typedef EvaluatedExprVisitor<UninitializedFieldVisitor> Inherited;
+    UninitializedFieldVisitor(Sema &S,
+                              llvm::SmallPtrSetImpl<ValueDecl*> &Decls,
+                              llvm::SmallPtrSetImpl<QualType> &BaseClasses)
+      : Inherited(S.Context), S(S), Decls(Decls), BaseClasses(BaseClasses),
+        Constructor(nullptr), InitList(false), InitListFieldDecl(nullptr) {}
+
+    // Returns true if the use of ME is not an uninitialized use.
+    bool IsInitListMemberExprInitialized(MemberExpr *ME,
+                                         bool CheckReferenceOnly) {
+      llvm::SmallVector<FieldDecl*, 4> Fields;
+      bool ReferenceField = false;
+      while (ME) {
+        FieldDecl *FD = dyn_cast<FieldDecl>(ME->getMemberDecl());
+        if (!FD)
+          return false;
+        Fields.push_back(FD);
+        if (FD->getType()->isReferenceType())
+          ReferenceField = true;
+        ME = dyn_cast<MemberExpr>(ME->getBase()->IgnoreParenImpCasts());
+      }
+
+      // Binding a reference to an uninitialized field is not an
+      // uninitialized use.
+      if (CheckReferenceOnly && !ReferenceField)
+        return true;
+
+      llvm::SmallVector<unsigned, 4> UsedFieldIndex;
+      // Discard the first field since it is the field decl that is being
+      // initialized.
+      for (const FieldDecl *FD : llvm::drop_begin(llvm::reverse(Fields)))
+        UsedFieldIndex.push_back(FD->getFieldIndex());
+
+      for (auto UsedIter = UsedFieldIndex.begin(),
+                UsedEnd = UsedFieldIndex.end(),
+                OrigIter = InitFieldIndex.begin(),
+                OrigEnd = InitFieldIndex.end();
+           UsedIter != UsedEnd && OrigIter != OrigEnd; ++UsedIter, ++OrigIter) {
+        if (*UsedIter < *OrigIter)
+          return true;
+        if (*UsedIter > *OrigIter)
+          break;
+      }
+
+      return false;
+    }
+
+    void HandleMemberExpr(MemberExpr *ME, bool CheckReferenceOnly,
+                          bool AddressOf) {
+      if (isa<EnumConstantDecl>(ME->getMemberDecl()))
+        return;
+
+      // FieldME is the inner-most MemberExpr that is not an anonymous struct
+      // or union.
+      MemberExpr *FieldME = ME;
+
+      bool AllPODFields = FieldME->getType().isPODType(S.Context);
+
+      Expr *Base = ME;
+      while (MemberExpr *SubME =
+                 dyn_cast<MemberExpr>(Base->IgnoreParenImpCasts())) {
+
+        if (isa<VarDecl>(SubME->getMemberDecl()))
+          return;
+
+        if (FieldDecl *FD = dyn_cast<FieldDecl>(SubME->getMemberDecl()))
+          if (!FD->isAnonymousStructOrUnion())
+            FieldME = SubME;
+
+        if (!FieldME->getType().isPODType(S.Context))
+          AllPODFields = false;
+
+        Base = SubME->getBase();
+      }
+
+      if (!isa<CXXThisExpr>(Base->IgnoreParenImpCasts())) {
+        Visit(Base);
+        return;
+      }
+
+      if (AddressOf && AllPODFields)
+        return;
+
+      ValueDecl* FoundVD = FieldME->getMemberDecl();
+
+      if (ImplicitCastExpr *BaseCast = dyn_cast<ImplicitCastExpr>(Base)) {
+        while (isa<ImplicitCastExpr>(BaseCast->getSubExpr())) {
+          BaseCast = cast<ImplicitCastExpr>(BaseCast->getSubExpr());
+        }
+
+        if (BaseCast->getCastKind() == CK_UncheckedDerivedToBase) {
+          QualType T = BaseCast->getType();
+          if (T->isPointerType() &&
+              BaseClasses.count(T->getPointeeType())) {
+            S.Diag(FieldME->getExprLoc(), diag::warn_base_class_is_uninit)
+                << T->getPointeeType() << FoundVD;
+          }
+        }
+      }
+
+      if (!Decls.count(FoundVD))
+        return;
+
+      const bool IsReference = FoundVD->getType()->isReferenceType();
+
+      if (InitList && !AddressOf && FoundVD == InitListFieldDecl) {
+        // Special checking for initializer lists.
+        if (IsInitListMemberExprInitialized(ME, CheckReferenceOnly)) {
+          return;
+        }
+      } else {
+        // Prevent double warnings on use of unbounded references.
+        if (CheckReferenceOnly && !IsReference)
+          return;
+      }
+
+      unsigned diag = IsReference
+          ? diag::warn_reference_field_is_uninit
+          : diag::warn_field_is_uninit;
+      S.Diag(FieldME->getExprLoc(), diag) << FoundVD;
+      if (Constructor)
+        S.Diag(Constructor->getLocation(),
+               diag::note_uninit_in_this_constructor)
+          << (Constructor->isDefaultConstructor() && Constructor->isImplicit());
+
+    }
+
+    void HandleValue(Expr *E, bool AddressOf) {
+      E = E->IgnoreParens();
+
+      if (MemberExpr *ME = dyn_cast<MemberExpr>(E)) {
+        HandleMemberExpr(ME, false /*CheckReferenceOnly*/,
+                         AddressOf /*AddressOf*/);
+        return;
+      }
+
+      if (ConditionalOperator *CO = dyn_cast<ConditionalOperator>(E)) {
+        Visit(CO->getCond());
+        HandleValue(CO->getTrueExpr(), AddressOf);
+        HandleValue(CO->getFalseExpr(), AddressOf);
+        return;
+      }
+
+      if (BinaryConditionalOperator *BCO =
+              dyn_cast<BinaryConditionalOperator>(E)) {
+        Visit(BCO->getCond());
+        HandleValue(BCO->getFalseExpr(), AddressOf);
+        return;
+      }
+
+      if (OpaqueValueExpr *OVE = dyn_cast<OpaqueValueExpr>(E)) {
+        HandleValue(OVE->getSourceExpr(), AddressOf);
+        return;
+      }
+
+      if (BinaryOperator *BO = dyn_cast<BinaryOperator>(E)) {
+        switch (BO->getOpcode()) {
+        default:
+          break;
+        case(BO_PtrMemD):
+        case(BO_PtrMemI):
+          HandleValue(BO->getLHS(), AddressOf);
+          Visit(BO->getRHS());
+          return;
+        case(BO_Comma):
+          Visit(BO->getLHS());
+          HandleValue(BO->getRHS(), AddressOf);
+          return;
+        }
+      }
+
+      Visit(E);
+    }
+
+    void CheckInitListExpr(InitListExpr *ILE) {
+      InitFieldIndex.push_back(0);
+      for (auto Child : ILE->children()) {
+        if (InitListExpr *SubList = dyn_cast<InitListExpr>(Child)) {
+          CheckInitListExpr(SubList);
+        } else {
+          Visit(Child);
+        }
+        ++InitFieldIndex.back();
+      }
+      InitFieldIndex.pop_back();
+    }
+
+    void CheckInitializer(Expr *E, const CXXConstructorDecl *FieldConstructor,
+                          FieldDecl *Field, const Type *BaseClass) {
+      // Remove Decls that may have been initialized in the previous
+      // initializer.
+      for (ValueDecl* VD : DeclsToRemove)
+        Decls.erase(VD);
+      DeclsToRemove.clear();
+
+      Constructor = FieldConstructor;
+      InitListExpr *ILE = dyn_cast<InitListExpr>(E);
+
+      if (ILE && Field) {
+        InitList = true;
+        InitListFieldDecl = Field;
+        InitFieldIndex.clear();
+        CheckInitListExpr(ILE);
+      } else {
+        InitList = false;
+        Visit(E);
+      }
+
+      if (Field)
+        Decls.erase(Field);
+      if (BaseClass)
+        BaseClasses.erase(BaseClass->getCanonicalTypeInternal());
+    }
+
+    void VisitMemberExpr(MemberExpr *ME) {
+      // All uses of unbounded reference fields will warn.
+      HandleMemberExpr(ME, true /*CheckReferenceOnly*/, false /*AddressOf*/);
+    }
+
+    void VisitImplicitCastExpr(ImplicitCastExpr *E) {
+      if (E->getCastKind() == CK_LValueToRValue) {
+        HandleValue(E->getSubExpr(), false /*AddressOf*/);
+        return;
+      }
+
+      Inherited::VisitImplicitCastExpr(E);
+    }
+
+    void VisitCXXConstructExpr(CXXConstructExpr *E) {
+      if (E->getConstructor()->isCopyConstructor()) {
+        Expr *ArgExpr = E->getArg(0);
+        if (InitListExpr *ILE = dyn_cast<InitListExpr>(ArgExpr))
+          if (ILE->getNumInits() == 1)
+            ArgExpr = ILE->getInit(0);
+        if (ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(ArgExpr))
+          if (ICE->getCastKind() == CK_NoOp)
+            ArgExpr = ICE->getSubExpr();
+        HandleValue(ArgExpr, false /*AddressOf*/);
+        return;
+      }
+      Inherited::VisitCXXConstructExpr(E);
+    }
+
+    void VisitCXXMemberCallExpr(CXXMemberCallExpr *E) {
+      Expr *Callee = E->getCallee();
+      if (isa<MemberExpr>(Callee)) {
+        HandleValue(Callee, false /*AddressOf*/);
+        for (auto Arg : E->arguments())
+          Visit(Arg);
+        return;
+      }
+
+      Inherited::VisitCXXMemberCallExpr(E);
+    }
+
+    void VisitCallExpr(CallExpr *E) {
+      // Treat std::move as a use.
+      if (E->isCallToStdMove()) {
+        HandleValue(E->getArg(0), /*AddressOf=*/false);
+        return;
+      }
+
+      Inherited::VisitCallExpr(E);
+    }
+
+    void VisitCXXOperatorCallExpr(CXXOperatorCallExpr *E) {
+      Expr *Callee = E->getCallee();
+
+      if (isa<UnresolvedLookupExpr>(Callee))
+        return Inherited::VisitCXXOperatorCallExpr(E);
+
+      Visit(Callee);
+      for (auto Arg : E->arguments())
+        HandleValue(Arg->IgnoreParenImpCasts(), false /*AddressOf*/);
+    }
+
+    void VisitBinaryOperator(BinaryOperator *E) {
+      // If a field assignment is detected, remove the field from the
+      // uninitiailized field set.
+      if (E->getOpcode() == BO_Assign)
+        if (MemberExpr *ME = dyn_cast<MemberExpr>(E->getLHS()))
+          if (FieldDecl *FD = dyn_cast<FieldDecl>(ME->getMemberDecl()))
+            if (!FD->getType()->isReferenceType())
+              DeclsToRemove.push_back(FD);
+
+      if (E->isCompoundAssignmentOp()) {
+        HandleValue(E->getLHS(), false /*AddressOf*/);
+        Visit(E->getRHS());
+        return;
+      }
+
+      Inherited::VisitBinaryOperator(E);
+    }
+
+    void VisitUnaryOperator(UnaryOperator *E) {
+      if (E->isIncrementDecrementOp()) {
+        HandleValue(E->getSubExpr(), false /*AddressOf*/);
+        return;
+      }
+      if (E->getOpcode() == UO_AddrOf) {
+        if (MemberExpr *ME = dyn_cast<MemberExpr>(E->getSubExpr())) {
+          HandleValue(ME->getBase(), true /*AddressOf*/);
+          return;
+        }
+      }
+
+      Inherited::VisitUnaryOperator(E);
+    }
+  };
+
+  // Diagnose value-uses of fields to initialize themselves, e.g.
+  //   foo(foo)
+  // where foo is not also a parameter to the constructor.
+  // Also diagnose across field uninitialized use such as
+  //   x(y), y(x)
+  // TODO: implement -Wuninitialized and fold this into that framework.
+  static void DiagnoseUninitializedFields(
+      Sema &SemaRef, const CXXConstructorDecl *Constructor) {
+
+    if (SemaRef.getDiagnostics().isIgnored(diag::warn_field_is_uninit,
+                                           Constructor->getLocation())) {
+      return;
+    }
+
+    if (Constructor->isInvalidDecl())
+      return;
+
+    const CXXRecordDecl *RD = Constructor->getParent();
+
+    if (RD->isDependentContext())
+      return;
+
+    // Holds fields that are uninitialized.
+    llvm::SmallPtrSet<ValueDecl*, 4> UninitializedFields;
+
+    // At the beginning, all fields are uninitialized.
+    for (auto *I : RD->decls()) {
+      if (auto *FD = dyn_cast<FieldDecl>(I)) {
+        UninitializedFields.insert(FD);
+      } else if (auto *IFD = dyn_cast<IndirectFieldDecl>(I)) {
+        UninitializedFields.insert(IFD->getAnonField());
+      }
+    }
+
+    llvm::SmallPtrSet<QualType, 4> UninitializedBaseClasses;
+    for (auto I : RD->bases())
+      UninitializedBaseClasses.insert(I.getType().getCanonicalType());
+
+    if (UninitializedFields.empty() && UninitializedBaseClasses.empty())
+      return;
+
+    UninitializedFieldVisitor UninitializedChecker(SemaRef,
+                                                   UninitializedFields,
+                                                   UninitializedBaseClasses);
+
+    for (const auto *FieldInit : Constructor->inits()) {
+      if (UninitializedFields.empty() && UninitializedBaseClasses.empty())
+        break;
+
+      Expr *InitExpr = FieldInit->getInit();
+      if (!InitExpr)
+        continue;
+
+      if (CXXDefaultInitExpr *Default =
+              dyn_cast<CXXDefaultInitExpr>(InitExpr)) {
+        InitExpr = Default->getExpr();
+        if (!InitExpr)
+          continue;
+        // In class initializers will point to the constructor.
+        UninitializedChecker.CheckInitializer(InitExpr, Constructor,
+                                              FieldInit->getAnyMember(),
+                                              FieldInit->getBaseClass());
+      } else {
+        UninitializedChecker.CheckInitializer(InitExpr, nullptr,
+                                              FieldInit->getAnyMember(),
+                                              FieldInit->getBaseClass());
+      }
+    }
+  }
+} // namespace
+
+/// Enter a new C++ default initializer scope. After calling this, the
+/// caller must call \ref ActOnFinishCXXInClassMemberInitializer, even if
+/// parsing or instantiating the initializer failed.
+void Sema::ActOnStartCXXInClassMemberInitializer() {
+  // Create a synthetic function scope to represent the call to the constructor
+  // that notionally surrounds a use of this initializer.
+  PushFunctionScope();
+}
+
+void Sema::ActOnStartTrailingRequiresClause(Scope *S, Declarator &D) {
+  if (!D.isFunctionDeclarator())
+    return;
+  auto &FTI = D.getFunctionTypeInfo();
+  if (!FTI.Params)
+    return;
+  for (auto &Param : ArrayRef<DeclaratorChunk::ParamInfo>(FTI.Params,
+                                                          FTI.NumParams)) {
+    auto *ParamDecl = cast<NamedDecl>(Param.Param);
+    if (ParamDecl->getDeclName())
+      PushOnScopeChains(ParamDecl, S, /*AddToContext=*/false);
+  }
+}
+
+ExprResult Sema::ActOnFinishTrailingRequiresClause(ExprResult ConstraintExpr) {
+  return ActOnRequiresClause(ConstraintExpr);
+}
+
+ExprResult Sema::ActOnRequiresClause(ExprResult ConstraintExpr) {
+  if (ConstraintExpr.isInvalid())
+    return ExprError();
+
+  ConstraintExpr = CorrectDelayedTyposInExpr(ConstraintExpr);
+  if (ConstraintExpr.isInvalid())
+    return ExprError();
+
+  if (DiagnoseUnexpandedParameterPack(ConstraintExpr.get(),
+                                      UPPC_RequiresClause))
+    return ExprError();
+
+  return ConstraintExpr;
+}
+
+/// This is invoked after parsing an in-class initializer for a
+/// non-static C++ class member, and after instantiating an in-class initializer
+/// in a class template. Such actions are deferred until the class is complete.
+void Sema::ActOnFinishCXXInClassMemberInitializer(Decl *D,
+                                                  SourceLocation InitLoc,
+                                                  Expr *InitExpr) {
+  // Pop the notional constructor scope we created earlier.
+  PopFunctionScopeInfo(nullptr, D);
+
+  FieldDecl *FD = dyn_cast<FieldDecl>(D);
+  assert((isa<MSPropertyDecl>(D) || FD->getInClassInitStyle() != ICIS_NoInit) &&
+         "must set init style when field is created");
+
+  if (!InitExpr) {
+    D->setInvalidDecl();
+    if (FD)
+      FD->removeInClassInitializer();
+    return;
+  }
+
+  if (DiagnoseUnexpandedParameterPack(InitExpr, UPPC_Initializer)) {
+    FD->setInvalidDecl();
+    FD->removeInClassInitializer();
+    return;
+  }
+
+  ExprResult Init = InitExpr;
+  if (!FD->getType()->isDependentType() && !InitExpr->isTypeDependent()) {
+    InitializedEntity Entity =
+        InitializedEntity::InitializeMemberFromDefaultMemberInitializer(FD);
+    InitializationKind Kind =
+        FD->getInClassInitStyle() == ICIS_ListInit
+            ? InitializationKind::CreateDirectList(InitExpr->getBeginLoc(),
+                                                   InitExpr->getBeginLoc(),
+                                                   InitExpr->getEndLoc())
+            : InitializationKind::CreateCopy(InitExpr->getBeginLoc(), InitLoc);
+    InitializationSequence Seq(*this, Entity, Kind, InitExpr);
+    Init = Seq.Perform(*this, Entity, Kind, InitExpr);
+    if (Init.isInvalid()) {
+      FD->setInvalidDecl();
+      return;
+    }
+  }
+
+  // C++11 [class.base.init]p7:
+  //   The initialization of each base and member constitutes a
+  //   full-expression.
+  Init = ActOnFinishFullExpr(Init.get(), InitLoc, /*DiscardedValue*/ false);
+  if (Init.isInvalid()) {
+    FD->setInvalidDecl();
+    return;
+  }
+
+  InitExpr = Init.get();
+
+  FD->setInClassInitializer(InitExpr);
+}
+
+/// Find the direct and/or virtual base specifiers that
+/// correspond to the given base type, for use in base initialization
+/// within a constructor.
+static bool FindBaseInitializer(Sema &SemaRef,
+                                CXXRecordDecl *ClassDecl,
+                                QualType BaseType,
+                                const CXXBaseSpecifier *&DirectBaseSpec,
+                                const CXXBaseSpecifier *&VirtualBaseSpec) {
+  // First, check for a direct base class.
+  DirectBaseSpec = nullptr;
+  for (const auto &Base : ClassDecl->bases()) {
+    if (SemaRef.Context.hasSameUnqualifiedType(BaseType, Base.getType())) {
+      // We found a direct base of this type. That's what we're
+      // initializing.
+      DirectBaseSpec = &Base;
+      break;
+    }
+  }
+
+  // Check for a virtual base class.
+  // FIXME: We might be able to short-circuit this if we know in advance that
+  // there are no virtual bases.
+  VirtualBaseSpec = nullptr;
+  if (!DirectBaseSpec || !DirectBaseSpec->isVirtual()) {
+    // We haven't found a base yet; search the class hierarchy for a
+    // virtual base class.
+    CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
+                       /*DetectVirtual=*/false);
+    if (SemaRef.IsDerivedFrom(ClassDecl->getLocation(),
+                              SemaRef.Context.getTypeDeclType(ClassDecl),
+                              BaseType, Paths)) {
+      for (CXXBasePaths::paths_iterator Path = Paths.begin();
+           Path != Paths.end(); ++Path) {
+        if (Path->back().Base->isVirtual()) {
+          VirtualBaseSpec = Path->back().Base;
+          break;
+        }
+      }
+    }
+  }
+
+  return DirectBaseSpec || VirtualBaseSpec;
+}
+
+/// Handle a C++ member initializer using braced-init-list syntax.
+MemInitResult
+Sema::ActOnMemInitializer(Decl *ConstructorD,
+                          Scope *S,
+                          CXXScopeSpec &SS,
+                          IdentifierInfo *MemberOrBase,
+                          ParsedType TemplateTypeTy,
+                          const DeclSpec &DS,
+                          SourceLocation IdLoc,
+                          Expr *InitList,
+                          SourceLocation EllipsisLoc) {
+  return BuildMemInitializer(ConstructorD, S, SS, MemberOrBase, TemplateTypeTy,
+                             DS, IdLoc, InitList,
+                             EllipsisLoc);
+}
+
+/// Handle a C++ member initializer using parentheses syntax.
+MemInitResult
+Sema::ActOnMemInitializer(Decl *ConstructorD,
+                          Scope *S,
+                          CXXScopeSpec &SS,
+                          IdentifierInfo *MemberOrBase,
+                          ParsedType TemplateTypeTy,
+                          const DeclSpec &DS,
+                          SourceLocation IdLoc,
+                          SourceLocation LParenLoc,
+                          ArrayRef<Expr *> Args,
+                          SourceLocation RParenLoc,
+                          SourceLocation EllipsisLoc) {
+  Expr *List = ParenListExpr::Create(Context, LParenLoc, Args, RParenLoc);
+  return BuildMemInitializer(ConstructorD, S, SS, MemberOrBase, TemplateTypeTy,
+                             DS, IdLoc, List, EllipsisLoc);
+}
+
+namespace {
+
+// Callback to only accept typo corrections that can be a valid C++ member
+// initializer: either a non-static field member or a base class.
+class MemInitializerValidatorCCC final : public CorrectionCandidateCallback {
+public:
+  explicit MemInitializerValidatorCCC(CXXRecordDecl *ClassDecl)
+      : ClassDecl(ClassDecl) {}
+
+  bool ValidateCandidate(const TypoCorrection &candidate) override {
+    if (NamedDecl *ND = candidate.getCorrectionDecl()) {
+      if (FieldDecl *Member = dyn_cast<FieldDecl>(ND))
+        return Member->getDeclContext()->getRedeclContext()->Equals(ClassDecl);
+      return isa<TypeDecl>(ND);
+    }
+    return false;
+  }
+
+  std::unique_ptr<CorrectionCandidateCallback> clone() override {
+    return std::make_unique<MemInitializerValidatorCCC>(*this);
+  }
+
+private:
+  CXXRecordDecl *ClassDecl;
+};
+
+}
+
+ValueDecl *Sema::tryLookupCtorInitMemberDecl(CXXRecordDecl *ClassDecl,
+                                             CXXScopeSpec &SS,
+                                             ParsedType TemplateTypeTy,
+                                             IdentifierInfo *MemberOrBase) {
+  if (SS.getScopeRep() || TemplateTypeTy)
+    return nullptr;
+  for (auto *D : ClassDecl->lookup(MemberOrBase))
+    if (isa<FieldDecl>(D) || isa<IndirectFieldDecl>(D))
+      return cast<ValueDecl>(D);
+  return nullptr;
+}
+
+/// Handle a C++ member initializer.
+MemInitResult
+Sema::BuildMemInitializer(Decl *ConstructorD,
+                          Scope *S,
+                          CXXScopeSpec &SS,
+                          IdentifierInfo *MemberOrBase,
+                          ParsedType TemplateTypeTy,
+                          const DeclSpec &DS,
+                          SourceLocation IdLoc,
+                          Expr *Init,
+                          SourceLocation EllipsisLoc) {
+  ExprResult Res = CorrectDelayedTyposInExpr(Init, /*InitDecl=*/nullptr,
+                                             /*RecoverUncorrectedTypos=*/true);
+  if (!Res.isUsable())
+    return true;
+  Init = Res.get();
+
+  if (!ConstructorD)
+    return true;
+
+  AdjustDeclIfTemplate(ConstructorD);
+
+  CXXConstructorDecl *Constructor
+    = dyn_cast<CXXConstructorDecl>(ConstructorD);
+  if (!Constructor) {
+    // The user wrote a constructor initializer on a function that is
+    // not a C++ constructor. Ignore the error for now, because we may
+    // have more member initializers coming; we'll diagnose it just
+    // once in ActOnMemInitializers.
+    return true;
+  }
+
+  CXXRecordDecl *ClassDecl = Constructor->getParent();
+
+  // C++ [class.base.init]p2:
+  //   Names in a mem-initializer-id are looked up in the scope of the
+  //   constructor's class and, if not found in that scope, are looked
+  //   up in the scope containing the constructor's definition.
+  //   [Note: if the constructor's class contains a member with the
+  //   same name as a direct or virtual base class of the class, a
+  //   mem-initializer-id naming the member or base class and composed
+  //   of a single identifier refers to the class member. A
+  //   mem-initializer-id for the hidden base class may be specified
+  //   using a qualified name. ]
+
+  // Look for a member, first.
+  if (ValueDecl *Member = tryLookupCtorInitMemberDecl(
+          ClassDecl, SS, TemplateTypeTy, MemberOrBase)) {
+    if (EllipsisLoc.isValid())
+      Diag(EllipsisLoc, diag::err_pack_expansion_member_init)
+          << MemberOrBase
+          << SourceRange(IdLoc, Init->getSourceRange().getEnd());
+
+    return BuildMemberInitializer(Member, Init, IdLoc);
+  }
+  // It didn't name a member, so see if it names a class.
+  QualType BaseType;
+  TypeSourceInfo *TInfo = nullptr;
+
+  if (TemplateTypeTy) {
+    BaseType = GetTypeFromParser(TemplateTypeTy, &TInfo);
+    if (BaseType.isNull())
+      return true;
+  } else if (DS.getTypeSpecType() == TST_decltype) {
+    BaseType = BuildDecltypeType(DS.getRepAsExpr());
+  } else if (DS.getTypeSpecType() == TST_decltype_auto) {
+    Diag(DS.getTypeSpecTypeLoc(), diag::err_decltype_auto_invalid);
+    return true;
+  } else {
+    LookupResult R(*this, MemberOrBase, IdLoc, LookupOrdinaryName);
+    LookupParsedName(R, S, &SS);
+
+    TypeDecl *TyD = R.getAsSingle<TypeDecl>();
+    if (!TyD) {
+      if (R.isAmbiguous()) return true;
+
+      // We don't want access-control diagnostics here.
+      R.suppressDiagnostics();
+
+      if (SS.isSet() && isDependentScopeSpecifier(SS)) {
+        bool NotUnknownSpecialization = false;
+        DeclContext *DC = computeDeclContext(SS, false);
+        if (CXXRecordDecl *Record = dyn_cast_or_null<CXXRecordDecl>(DC))
+          NotUnknownSpecialization = !Record->hasAnyDependentBases();
+
+        if (!NotUnknownSpecialization) {
+          // When the scope specifier can refer to a member of an unknown
+          // specialization, we take it as a type name.
+          BaseType = CheckTypenameType(ETK_None, SourceLocation(),
+                                       SS.getWithLocInContext(Context),
+                                       *MemberOrBase, IdLoc);
+          if (BaseType.isNull())
+            return true;
+
+          TInfo = Context.CreateTypeSourceInfo(BaseType);
+          DependentNameTypeLoc TL =
+              TInfo->getTypeLoc().castAs<DependentNameTypeLoc>();
+          if (!TL.isNull()) {
+            TL.setNameLoc(IdLoc);
+            TL.setElaboratedKeywordLoc(SourceLocation());
+            TL.setQualifierLoc(SS.getWithLocInContext(Context));
+          }
+
+          R.clear();
+          R.setLookupName(MemberOrBase);
+        }
+      }
+
+      // If no results were found, try to correct typos.
+      TypoCorrection Corr;
+      MemInitializerValidatorCCC CCC(ClassDecl);
+      if (R.empty() && BaseType.isNull() &&
+          (Corr = CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(), S, &SS,
+                              CCC, CTK_ErrorRecovery, ClassDecl))) {
+        if (FieldDecl *Member = Corr.getCorrectionDeclAs<FieldDecl>()) {
+          // We have found a non-static data member with a similar
+          // name to what was typed; complain and initialize that
+          // member.
+          diagnoseTypo(Corr,
+                       PDiag(diag::err_mem_init_not_member_or_class_suggest)
+                         << MemberOrBase << true);
+          return BuildMemberInitializer(Member, Init, IdLoc);
+        } else if (TypeDecl *Type = Corr.getCorrectionDeclAs<TypeDecl>()) {
+          const CXXBaseSpecifier *DirectBaseSpec;
+          const CXXBaseSpecifier *VirtualBaseSpec;
+          if (FindBaseInitializer(*this, ClassDecl,
+                                  Context.getTypeDeclType(Type),
+                                  DirectBaseSpec, VirtualBaseSpec)) {
+            // We have found a direct or virtual base class with a
+            // similar name to what was typed; complain and initialize
+            // that base class.
+            diagnoseTypo(Corr,
+                         PDiag(diag::err_mem_init_not_member_or_class_suggest)
+                           << MemberOrBase << false,
+                         PDiag() /*Suppress note, we provide our own.*/);
+
+            const CXXBaseSpecifier *BaseSpec = DirectBaseSpec ? DirectBaseSpec
+                                                              : VirtualBaseSpec;
+            Diag(BaseSpec->getBeginLoc(), diag::note_base_class_specified_here)
+                << BaseSpec->getType() << BaseSpec->getSourceRange();
+
+            TyD = Type;
+          }
+        }
+      }
+
+      if (!TyD && BaseType.isNull()) {
+        Diag(IdLoc, diag::err_mem_init_not_member_or_class)
+          << MemberOrBase << SourceRange(IdLoc,Init->getSourceRange().getEnd());
+        return true;
+      }
+    }
+
+    if (BaseType.isNull()) {
+      BaseType = Context.getTypeDeclType(TyD);
+      MarkAnyDeclReferenced(TyD->getLocation(), TyD, /*OdrUse=*/false);
+      if (SS.isSet()) {
+        BaseType = Context.getElaboratedType(ETK_None, SS.getScopeRep(),
+                                             BaseType);
+        TInfo = Context.CreateTypeSourceInfo(BaseType);
+        ElaboratedTypeLoc TL = TInfo->getTypeLoc().castAs<ElaboratedTypeLoc>();
+        TL.getNamedTypeLoc().castAs<TypeSpecTypeLoc>().setNameLoc(IdLoc);
+        TL.setElaboratedKeywordLoc(SourceLocation());
+        TL.setQualifierLoc(SS.getWithLocInContext(Context));
+      }
+    }
+  }
+
+  if (!TInfo)
+    TInfo = Context.getTrivialTypeSourceInfo(BaseType, IdLoc);
+
+  return BuildBaseInitializer(BaseType, TInfo, Init, ClassDecl, EllipsisLoc);
+}
+
+MemInitResult
+Sema::BuildMemberInitializer(ValueDecl *Member, Expr *Init,
+                             SourceLocation IdLoc) {
+  FieldDecl *DirectMember = dyn_cast<FieldDecl>(Member);
+  IndirectFieldDecl *IndirectMember = dyn_cast<IndirectFieldDecl>(Member);
+  assert((DirectMember || IndirectMember) &&
+         "Member must be a FieldDecl or IndirectFieldDecl");
+
+  if (DiagnoseUnexpandedParameterPack(Init, UPPC_Initializer))
+    return true;
+
+  if (Member->isInvalidDecl())
+    return true;
+
+  MultiExprArg Args;
+  if (ParenListExpr *ParenList = dyn_cast<ParenListExpr>(Init)) {
+    Args = MultiExprArg(ParenList->getExprs(), ParenList->getNumExprs());
+  } else if (InitListExpr *InitList = dyn_cast<InitListExpr>(Init)) {
+    Args = MultiExprArg(InitList->getInits(), InitList->getNumInits());
+  } else {
+    // Template instantiation doesn't reconstruct ParenListExprs for us.
+    Args = Init;
+  }
+
+  SourceRange InitRange = Init->getSourceRange();
+
+  if (Member->getType()->isDependentType() || Init->isTypeDependent()) {
+    // Can't check initialization for a member of dependent type or when
+    // any of the arguments are type-dependent expressions.
+    DiscardCleanupsInEvaluationContext();
+  } else {
+    bool InitList = false;
+    if (isa<InitListExpr>(Init)) {
+      InitList = true;
+      Args = Init;
+    }
+
+    // Initialize the member.
+    InitializedEntity MemberEntity =
+      DirectMember ? InitializedEntity::InitializeMember(DirectMember, nullptr)
+                   : InitializedEntity::InitializeMember(IndirectMember,
+                                                         nullptr);
+    InitializationKind Kind =
+        InitList ? InitializationKind::CreateDirectList(
+                       IdLoc, Init->getBeginLoc(), Init->getEndLoc())
+                 : InitializationKind::CreateDirect(IdLoc, InitRange.getBegin(),
+                                                    InitRange.getEnd());
+
+    InitializationSequence InitSeq(*this, MemberEntity, Kind, Args);
+    ExprResult MemberInit = InitSeq.Perform(*this, MemberEntity, Kind, Args,
+                                            nullptr);
+    if (!MemberInit.isInvalid()) {
+      // C++11 [class.base.init]p7:
+      //   The initialization of each base and member constitutes a
+      //   full-expression.
+      MemberInit = ActOnFinishFullExpr(MemberInit.get(), InitRange.getBegin(),
+                                       /*DiscardedValue*/ false);
+    }
+
+    if (MemberInit.isInvalid()) {
+      // Args were sensible expressions but we couldn't initialize the member
+      // from them. Preserve them in a RecoveryExpr instead.
+      Init = CreateRecoveryExpr(InitRange.getBegin(), InitRange.getEnd(), Args,
+                                Member->getType())
+                 .get();
+      if (!Init)
+        return true;
+    } else {
+      Init = MemberInit.get();
+    }
+  }
+
+  if (DirectMember) {
+    return new (Context) CXXCtorInitializer(Context, DirectMember, IdLoc,
+                                            InitRange.getBegin(), Init,
+                                            InitRange.getEnd());
+  } else {
+    return new (Context) CXXCtorInitializer(Context, IndirectMember, IdLoc,
+                                            InitRange.getBegin(), Init,
+                                            InitRange.getEnd());
+  }
+}
+
+MemInitResult
+Sema::BuildDelegatingInitializer(TypeSourceInfo *TInfo, Expr *Init,
+                                 CXXRecordDecl *ClassDecl) {
+  SourceLocation NameLoc = TInfo->getTypeLoc().getLocalSourceRange().getBegin();
+  if (!LangOpts.CPlusPlus11)
+    return Diag(NameLoc, diag::err_delegating_ctor)
+      << TInfo->getTypeLoc().getLocalSourceRange();
+  Diag(NameLoc, diag::warn_cxx98_compat_delegating_ctor);
+
+  bool InitList = true;
+  MultiExprArg Args = Init;
+  if (ParenListExpr *ParenList = dyn_cast<ParenListExpr>(Init)) {
+    InitList = false;
+    Args = MultiExprArg(ParenList->getExprs(), ParenList->getNumExprs());
+  }
+
+  SourceRange InitRange = Init->getSourceRange();
+  // Initialize the object.
+  InitializedEntity DelegationEntity = InitializedEntity::InitializeDelegation(
+                                     QualType(ClassDecl->getTypeForDecl(), 0));
+  InitializationKind Kind =
+      InitList ? InitializationKind::CreateDirectList(
+                     NameLoc, Init->getBeginLoc(), Init->getEndLoc())
+               : InitializationKind::CreateDirect(NameLoc, InitRange.getBegin(),
+                                                  InitRange.getEnd());
+  InitializationSequence InitSeq(*this, DelegationEntity, Kind, Args);
+  ExprResult DelegationInit = InitSeq.Perform(*this, DelegationEntity, Kind,
+                                              Args, nullptr);
+  if (!DelegationInit.isInvalid()) {
+    assert((DelegationInit.get()->containsErrors() ||
+            cast<CXXConstructExpr>(DelegationInit.get())->getConstructor()) &&
+           "Delegating constructor with no target?");
+
+    // C++11 [class.base.init]p7:
+    //   The initialization of each base and member constitutes a
+    //   full-expression.
+    DelegationInit = ActOnFinishFullExpr(
+        DelegationInit.get(), InitRange.getBegin(), /*DiscardedValue*/ false);
+  }
+
+  if (DelegationInit.isInvalid()) {
+    DelegationInit =
+        CreateRecoveryExpr(InitRange.getBegin(), InitRange.getEnd(), Args,
+                           QualType(ClassDecl->getTypeForDecl(), 0));
+    if (DelegationInit.isInvalid())
+      return true;
+  } else {
+    // If we are in a dependent context, template instantiation will
+    // perform this type-checking again. Just save the arguments that we
+    // received in a ParenListExpr.
+    // FIXME: This isn't quite ideal, since our ASTs don't capture all
+    // of the information that we have about the base
+    // initializer. However, deconstructing the ASTs is a dicey process,
+    // and this approach is far more likely to get the corner cases right.
+    if (CurContext->isDependentContext())
+      DelegationInit = Init;
+  }
+
+  return new (Context) CXXCtorInitializer(Context, TInfo, InitRange.getBegin(),
+                                          DelegationInit.getAs<Expr>(),
+                                          InitRange.getEnd());
+}
+
+MemInitResult
+Sema::BuildBaseInitializer(QualType BaseType, TypeSourceInfo *BaseTInfo,
+                           Expr *Init, CXXRecordDecl *ClassDecl,
+                           SourceLocation EllipsisLoc) {
+  SourceLocation BaseLoc
+    = BaseTInfo->getTypeLoc().getLocalSourceRange().getBegin();
+
+  if (!BaseType->isDependentType() && !BaseType->isRecordType())
+    return Diag(BaseLoc, diag::err_base_init_does_not_name_class)
+             << BaseType << BaseTInfo->getTypeLoc().getLocalSourceRange();
+
+  // C++ [class.base.init]p2:
+  //   [...] Unless the mem-initializer-id names a nonstatic data
+  //   member of the constructor's class or a direct or virtual base
+  //   of that class, the mem-initializer is ill-formed. A
+  //   mem-initializer-list can initialize a base class using any
+  //   name that denotes that base class type.
+
+  // We can store the initializers in "as-written" form and delay analysis until
+  // instantiation if the constructor is dependent. But not for dependent
+  // (broken) code in a non-template! SetCtorInitializers does not expect this.
+  bool Dependent = CurContext->isDependentContext() &&
+                   (BaseType->isDependentType() || Init->isTypeDependent());
+
+  SourceRange InitRange = Init->getSourceRange();
+  if (EllipsisLoc.isValid()) {
+    // This is a pack expansion.
+    if (!BaseType->containsUnexpandedParameterPack())  {
+      Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
+        << SourceRange(BaseLoc, InitRange.getEnd());
+
+      EllipsisLoc = SourceLocation();
+    }
+  } else {
+    // Check for any unexpanded parameter packs.
+    if (DiagnoseUnexpandedParameterPack(BaseLoc, BaseTInfo, UPPC_Initializer))
+      return true;
+
+    if (DiagnoseUnexpandedParameterPack(Init, UPPC_Initializer))
+      return true;
+  }
+
+  // Check for direct and virtual base classes.
+  const CXXBaseSpecifier *DirectBaseSpec = nullptr;
+  const CXXBaseSpecifier *VirtualBaseSpec = nullptr;
+  if (!Dependent) {
+    if (Context.hasSameUnqualifiedType(QualType(ClassDecl->getTypeForDecl(),0),
+                                       BaseType))
+      return BuildDelegatingInitializer(BaseTInfo, Init, ClassDecl);
+
+    FindBaseInitializer(*this, ClassDecl, BaseType, DirectBaseSpec,
+                        VirtualBaseSpec);
+
+    // C++ [base.class.init]p2:
+    // Unless the mem-initializer-id names a nonstatic data member of the
+    // constructor's class or a direct or virtual base of that class, the
+    // mem-initializer is ill-formed.
+    if (!DirectBaseSpec && !VirtualBaseSpec) {
+      // If the class has any dependent bases, then it's possible that
+      // one of those types will resolve to the same type as
+      // BaseType. Therefore, just treat this as a dependent base
+      // class initialization.  FIXME: Should we try to check the
+      // initialization anyway? It seems odd.
+      if (ClassDecl->hasAnyDependentBases())
+        Dependent = true;
+      else
+        return Diag(BaseLoc, diag::err_not_direct_base_or_virtual)
+          << BaseType << Context.getTypeDeclType(ClassDecl)
+          << BaseTInfo->getTypeLoc().getLocalSourceRange();
+    }
+  }
+
+  if (Dependent) {
+    DiscardCleanupsInEvaluationContext();
+
+    return new (Context) CXXCtorInitializer(Context, BaseTInfo,
+                                            /*IsVirtual=*/false,
+                                            InitRange.getBegin(), Init,
+                                            InitRange.getEnd(), EllipsisLoc);
+  }
+
+  // C++ [base.class.init]p2:
+  //   If a mem-initializer-id is ambiguous because it designates both
+  //   a direct non-virtual base class and an inherited virtual base
+  //   class, the mem-initializer is ill-formed.
+  if (DirectBaseSpec && VirtualBaseSpec)
+    return Diag(BaseLoc, diag::err_base_init_direct_and_virtual)
+      << BaseType << BaseTInfo->getTypeLoc().getLocalSourceRange();
+
+  const CXXBaseSpecifier *BaseSpec = DirectBaseSpec;
+  if (!BaseSpec)
+    BaseSpec = VirtualBaseSpec;
+
+  // Initialize the base.
+  bool InitList = true;
+  MultiExprArg Args = Init;
+  if (ParenListExpr *ParenList = dyn_cast<ParenListExpr>(Init)) {
+    InitList = false;
+    Args = MultiExprArg(ParenList->getExprs(), ParenList->getNumExprs());
+  }
+
+  InitializedEntity BaseEntity =
+    InitializedEntity::InitializeBase(Context, BaseSpec, VirtualBaseSpec);
+  InitializationKind Kind =
+      InitList ? InitializationKind::CreateDirectList(BaseLoc)
+               : InitializationKind::CreateDirect(BaseLoc, InitRange.getBegin(),
+                                                  InitRange.getEnd());
+  InitializationSequence InitSeq(*this, BaseEntity, Kind, Args);
+  ExprResult BaseInit = InitSeq.Perform(*this, BaseEntity, Kind, Args, nullptr);
+  if (!BaseInit.isInvalid()) {
+    // C++11 [class.base.init]p7:
+    //   The initialization of each base and member constitutes a
+    //   full-expression.
+    BaseInit = ActOnFinishFullExpr(BaseInit.get(), InitRange.getBegin(),
+                                   /*DiscardedValue*/ false);
+  }
+
+  if (BaseInit.isInvalid()) {
+    BaseInit = CreateRecoveryExpr(InitRange.getBegin(), InitRange.getEnd(),
+                                  Args, BaseType);
+    if (BaseInit.isInvalid())
+      return true;
+  } else {
+    // If we are in a dependent context, template instantiation will
+    // perform this type-checking again. Just save the arguments that we
+    // received in a ParenListExpr.
+    // FIXME: This isn't quite ideal, since our ASTs don't capture all
+    // of the information that we have about the base
+    // initializer. However, deconstructing the ASTs is a dicey process,
+    // and this approach is far more likely to get the corner cases right.
+    if (CurContext->isDependentContext())
+      BaseInit = Init;
+  }
+
+  return new (Context) CXXCtorInitializer(Context, BaseTInfo,
+                                          BaseSpec->isVirtual(),
+                                          InitRange.getBegin(),
+                                          BaseInit.getAs<Expr>(),
+                                          InitRange.getEnd(), EllipsisLoc);
+}
+
+// Create a static_cast\<T&&>(expr).
+static Expr *CastForMoving(Sema &SemaRef, Expr *E, QualType T = QualType()) {
+  if (T.isNull()) T = E->getType();
+  QualType TargetType = SemaRef.BuildReferenceType(
+      T, /*SpelledAsLValue*/false, SourceLocation(), DeclarationName());
+  SourceLocation ExprLoc = E->getBeginLoc();
+  TypeSourceInfo *TargetLoc = SemaRef.Context.getTrivialTypeSourceInfo(
+      TargetType, ExprLoc);
+
+  return SemaRef.BuildCXXNamedCast(ExprLoc, tok::kw_static_cast, TargetLoc, E,
+                                   SourceRange(ExprLoc, ExprLoc),
+                                   E->getSourceRange()).get();
+}
+
+/// ImplicitInitializerKind - How an implicit base or member initializer should
+/// initialize its base or member.
+enum ImplicitInitializerKind {
+  IIK_Default,
+  IIK_Copy,
+  IIK_Move,
+  IIK_Inherit
+};
+
+static bool
+BuildImplicitBaseInitializer(Sema &SemaRef, CXXConstructorDecl *Constructor,
+                             ImplicitInitializerKind ImplicitInitKind,
+                             CXXBaseSpecifier *BaseSpec,
+                             bool IsInheritedVirtualBase,
+                             CXXCtorInitializer *&CXXBaseInit) {
+  InitializedEntity InitEntity
+    = InitializedEntity::InitializeBase(SemaRef.Context, BaseSpec,
+                                        IsInheritedVirtualBase);
+
+  ExprResult BaseInit;
+
+  switch (ImplicitInitKind) {
+  case IIK_Inherit:
+  case IIK_Default: {
+    InitializationKind InitKind
+      = InitializationKind::CreateDefault(Constructor->getLocation());
+    InitializationSequence InitSeq(SemaRef, InitEntity, InitKind, None);
+    BaseInit = InitSeq.Perform(SemaRef, InitEntity, InitKind, None);
+    break;
+  }
+
+  case IIK_Move:
+  case IIK_Copy: {
+    bool Moving = ImplicitInitKind == IIK_Move;
+    ParmVarDecl *Param = Constructor->getParamDecl(0);
+    QualType ParamType = Param->getType().getNonReferenceType();
+
+    Expr *CopyCtorArg =
+      DeclRefExpr::Create(SemaRef.Context, NestedNameSpecifierLoc(),
+                          SourceLocation(), Param, false,
+                          Constructor->getLocation(), ParamType,
+                          VK_LValue, nullptr);
+
+    SemaRef.MarkDeclRefReferenced(cast<DeclRefExpr>(CopyCtorArg));
+
+    // Cast to the base class to avoid ambiguities.
+    QualType ArgTy =
+      SemaRef.Context.getQualifiedType(BaseSpec->getType().getUnqualifiedType(),
+                                       ParamType.getQualifiers());
+
+    if (Moving) {
+      CopyCtorArg = CastForMoving(SemaRef, CopyCtorArg);
+    }
+
+    CXXCastPath BasePath;
+    BasePath.push_back(BaseSpec);
+    CopyCtorArg = SemaRef.ImpCastExprToType(CopyCtorArg, ArgTy,
+                                            CK_UncheckedDerivedToBase,
+                                            Moving ? VK_XValue : VK_LValue,
+                                            &BasePath).get();
+
+    InitializationKind InitKind
+      = InitializationKind::CreateDirect(Constructor->getLocation(),
+                                         SourceLocation(), SourceLocation());
+    InitializationSequence InitSeq(SemaRef, InitEntity, InitKind, CopyCtorArg);
+    BaseInit = InitSeq.Perform(SemaRef, InitEntity, InitKind, CopyCtorArg);
+    break;
+  }
+  }
+
+  BaseInit = SemaRef.MaybeCreateExprWithCleanups(BaseInit);
+  if (BaseInit.isInvalid())
+    return true;
+
+  CXXBaseInit =
+    new (SemaRef.Context) CXXCtorInitializer(SemaRef.Context,
+               SemaRef.Context.getTrivialTypeSourceInfo(BaseSpec->getType(),
+                                                        SourceLocation()),
+                                             BaseSpec->isVirtual(),
+                                             SourceLocation(),
+                                             BaseInit.getAs<Expr>(),
+                                             SourceLocation(),
+                                             SourceLocation());
+
+  return false;
+}
+
+static bool RefersToRValueRef(Expr *MemRef) {
+  ValueDecl *Referenced = cast<MemberExpr>(MemRef)->getMemberDecl();
+  return Referenced->getType()->isRValueReferenceType();
+}
+
+static bool
+BuildImplicitMemberInitializer(Sema &SemaRef, CXXConstructorDecl *Constructor,
+                               ImplicitInitializerKind ImplicitInitKind,
+                               FieldDecl *Field, IndirectFieldDecl *Indirect,
+                               CXXCtorInitializer *&CXXMemberInit) {
+  if (Field->isInvalidDecl())
+    return true;
+
+  SourceLocation Loc = Constructor->getLocation();
+
+  if (ImplicitInitKind == IIK_Copy || ImplicitInitKind == IIK_Move) {
+    bool Moving = ImplicitInitKind == IIK_Move;
+    ParmVarDecl *Param = Constructor->getParamDecl(0);
+    QualType ParamType = Param->getType().getNonReferenceType();
+
+    // Suppress copying zero-width bitfields.
+    if (Field->isZeroLengthBitField(SemaRef.Context))
+      return false;
+
+    Expr *MemberExprBase =
+      DeclRefExpr::Create(SemaRef.Context, NestedNameSpecifierLoc(),
+                          SourceLocation(), Param, false,
+                          Loc, ParamType, VK_LValue, nullptr);
+
+    SemaRef.MarkDeclRefReferenced(cast<DeclRefExpr>(MemberExprBase));
+
+    if (Moving) {
+      MemberExprBase = CastForMoving(SemaRef, MemberExprBase);
+    }
+
+    // Build a reference to this field within the parameter.
+    CXXScopeSpec SS;
+    LookupResult MemberLookup(SemaRef, Field->getDeclName(), Loc,
+                              Sema::LookupMemberName);
+    MemberLookup.addDecl(Indirect ? cast<ValueDecl>(Indirect)
+                                  : cast<ValueDecl>(Field), AS_public);
+    MemberLookup.resolveKind();
+    ExprResult CtorArg
+      = SemaRef.BuildMemberReferenceExpr(MemberExprBase,
+                                         ParamType, Loc,
+                                         /*IsArrow=*/false,
+                                         SS,
+                                         /*TemplateKWLoc=*/SourceLocation(),
+                                         /*FirstQualifierInScope=*/nullptr,
+                                         MemberLookup,
+                                         /*TemplateArgs=*/nullptr,
+                                         /*S*/nullptr);
+    if (CtorArg.isInvalid())
+      return true;
+
+    // C++11 [class.copy]p15:
+    //   - if a member m has rvalue reference type T&&, it is direct-initialized
+    //     with static_cast<T&&>(x.m);
+    if (RefersToRValueRef(CtorArg.get())) {
+      CtorArg = CastForMoving(SemaRef, CtorArg.get());
+    }
+
+    InitializedEntity Entity =
+        Indirect ? InitializedEntity::InitializeMember(Indirect, nullptr,
+                                                       /*Implicit*/ true)
+                 : InitializedEntity::InitializeMember(Field, nullptr,
+                                                       /*Implicit*/ true);
+
+    // Direct-initialize to use the copy constructor.
+    InitializationKind InitKind =
+      InitializationKind::CreateDirect(Loc, SourceLocation(), SourceLocation());
+
+    Expr *CtorArgE = CtorArg.getAs<Expr>();
+    InitializationSequence InitSeq(SemaRef, Entity, InitKind, CtorArgE);
+    ExprResult MemberInit =
+        InitSeq.Perform(SemaRef, Entity, InitKind, MultiExprArg(&CtorArgE, 1));
+    MemberInit = SemaRef.MaybeCreateExprWithCleanups(MemberInit);
+    if (MemberInit.isInvalid())
+      return true;
+
+    if (Indirect)
+      CXXMemberInit = new (SemaRef.Context) CXXCtorInitializer(
+          SemaRef.Context, Indirect, Loc, Loc, MemberInit.getAs<Expr>(), Loc);
+    else
+      CXXMemberInit = new (SemaRef.Context) CXXCtorInitializer(
+          SemaRef.Context, Field, Loc, Loc, MemberInit.getAs<Expr>(), Loc);
+    return false;
+  }
+
+  assert((ImplicitInitKind == IIK_Default || ImplicitInitKind == IIK_Inherit) &&
+         "Unhandled implicit init kind!");
+
+  QualType FieldBaseElementType =
+    SemaRef.Context.getBaseElementType(Field->getType());
+
+  if (FieldBaseElementType->isRecordType()) {
+    InitializedEntity InitEntity =
+        Indirect ? InitializedEntity::InitializeMember(Indirect, nullptr,
+                                                       /*Implicit*/ true)
+                 : InitializedEntity::InitializeMember(Field, nullptr,
+                                                       /*Implicit*/ true);
+    InitializationKind InitKind =
+      InitializationKind::CreateDefault(Loc);
+
+    InitializationSequence InitSeq(SemaRef, InitEntity, InitKind, None);
+    ExprResult MemberInit =
+      InitSeq.Perform(SemaRef, InitEntity, InitKind, None);
+
+    MemberInit = SemaRef.MaybeCreateExprWithCleanups(MemberInit);
+    if (MemberInit.isInvalid())
+      return true;
+
+    if (Indirect)
+      CXXMemberInit = new (SemaRef.Context) CXXCtorInitializer(SemaRef.Context,
+                                                               Indirect, Loc,
+                                                               Loc,
+                                                               MemberInit.get(),
+                                                               Loc);
+    else
+      CXXMemberInit = new (SemaRef.Context) CXXCtorInitializer(SemaRef.Context,
+                                                               Field, Loc, Loc,
+                                                               MemberInit.get(),
+                                                               Loc);
+    return false;
+  }
+
+  if (!Field->getParent()->isUnion()) {
+    if (FieldBaseElementType->isReferenceType()) {
+      SemaRef.Diag(Constructor->getLocation(),
+                   diag::err_uninitialized_member_in_ctor)
+      << (int)Constructor->isImplicit()
+      << SemaRef.Context.getTagDeclType(Constructor->getParent())
+      << 0 << Field->getDeclName();
+      SemaRef.Diag(Field->getLocation(), diag::note_declared_at);
+      return true;
+    }
+
+    if (FieldBaseElementType.isConstQualified()) {
+      SemaRef.Diag(Constructor->getLocation(),
+                   diag::err_uninitialized_member_in_ctor)
+      << (int)Constructor->isImplicit()
+      << SemaRef.Context.getTagDeclType(Constructor->getParent())
+      << 1 << Field->getDeclName();
+      SemaRef.Diag(Field->getLocation(), diag::note_declared_at);
+      return true;
+    }
+  }
+
+  if (FieldBaseElementType.hasNonTrivialObjCLifetime()) {
+    // ARC and Weak:
+    //   Default-initialize Objective-C pointers to NULL.
+    CXXMemberInit
+      = new (SemaRef.Context) CXXCtorInitializer(SemaRef.Context, Field,
+                                                 Loc, Loc,
+                 new (SemaRef.Context) ImplicitValueInitExpr(Field->getType()),
+                                                 Loc);
+    return false;
+  }
+
+  // Nothing to initialize.
+  CXXMemberInit = nullptr;
+  return false;
+}
+
+namespace {
+struct BaseAndFieldInfo {
+  Sema &S;
+  CXXConstructorDecl *Ctor;
+  bool AnyErrorsInInits;
+  ImplicitInitializerKind IIK;
+  llvm::DenseMap<const void *, CXXCtorInitializer*> AllBaseFields;
+  SmallVector<CXXCtorInitializer*, 8> AllToInit;
+  llvm::DenseMap<TagDecl*, FieldDecl*> ActiveUnionMember;
+
+  BaseAndFieldInfo(Sema &S, CXXConstructorDecl *Ctor, bool ErrorsInInits)
+    : S(S), Ctor(Ctor), AnyErrorsInInits(ErrorsInInits) {
+    bool Generated = Ctor->isImplicit() || Ctor->isDefaulted();
+    if (Ctor->getInheritedConstructor())
+      IIK = IIK_Inherit;
+    else if (Generated && Ctor->isCopyConstructor())
+      IIK = IIK_Copy;
+    else if (Generated && Ctor->isMoveConstructor())
+      IIK = IIK_Move;
+    else
+      IIK = IIK_Default;
+  }
+
+  bool isImplicitCopyOrMove() const {
+    switch (IIK) {
+    case IIK_Copy:
+    case IIK_Move:
+      return true;
+
+    case IIK_Default:
+    case IIK_Inherit:
+      return false;
+    }
+
+    llvm_unreachable("Invalid ImplicitInitializerKind!");
+  }
+
+  bool addFieldInitializer(CXXCtorInitializer *Init) {
+    AllToInit.push_back(Init);
+
+    // Check whether this initializer makes the field "used".
+    if (Init->getInit()->HasSideEffects(S.Context))
+      S.UnusedPrivateFields.remove(Init->getAnyMember());
+
+    return false;
+  }
+
+  bool isInactiveUnionMember(FieldDecl *Field) {
+    RecordDecl *Record = Field->getParent();
+    if (!Record->isUnion())
+      return false;
+
+    if (FieldDecl *Active =
+            ActiveUnionMember.lookup(Record->getCanonicalDecl()))
+      return Active != Field->getCanonicalDecl();
+
+    // In an implicit copy or move constructor, ignore any in-class initializer.
+    if (isImplicitCopyOrMove())
+      return true;
+
+    // If there's no explicit initialization, the field is active only if it
+    // has an in-class initializer...
+    if (Field->hasInClassInitializer())
+      return false;
+    // ... or it's an anonymous struct or union whose class has an in-class
+    // initializer.
+    if (!Field->isAnonymousStructOrUnion())
+      return true;
+    CXXRecordDecl *FieldRD = Field->getType()->getAsCXXRecordDecl();
+    return !FieldRD->hasInClassInitializer();
+  }
+
+  /// Determine whether the given field is, or is within, a union member
+  /// that is inactive (because there was an initializer given for a different
+  /// member of the union, or because the union was not initialized at all).
+  bool isWithinInactiveUnionMember(FieldDecl *Field,
+                                   IndirectFieldDecl *Indirect) {
+    if (!Indirect)
+      return isInactiveUnionMember(Field);
+
+    for (auto *C : Indirect->chain()) {
+      FieldDecl *Field = dyn_cast<FieldDecl>(C);
+      if (Field && isInactiveUnionMember(Field))
+        return true;
+    }
+    return false;
+  }
+};
+}
+
+/// Determine whether the given type is an incomplete or zero-lenfgth
+/// array type.
+static bool isIncompleteOrZeroLengthArrayType(ASTContext &Context, QualType T) {
+  if (T->isIncompleteArrayType())
+    return true;
+
+  while (const ConstantArrayType *ArrayT = Context.getAsConstantArrayType(T)) {
+    if (!ArrayT->getSize())
+      return true;
+
+    T = ArrayT->getElementType();
+  }
+
+  return false;
+}
+
+static bool CollectFieldInitializer(Sema &SemaRef, BaseAndFieldInfo &Info,
+                                    FieldDecl *Field,
+                                    IndirectFieldDecl *Indirect = nullptr) {
+  if (Field->isInvalidDecl())
+    return false;
+
+  // Overwhelmingly common case: we have a direct initializer for this field.
+  if (CXXCtorInitializer *Init =
+          Info.AllBaseFields.lookup(Field->getCanonicalDecl()))
+    return Info.addFieldInitializer(Init);
+
+  // C++11 [class.base.init]p8:
+  //   if the entity is a non-static data member that has a
+  //   brace-or-equal-initializer and either
+  //   -- the constructor's class is a union and no other variant member of that
+  //      union is designated by a mem-initializer-id or
+  //   -- the constructor's class is not a union, and, if the entity is a member
+  //      of an anonymous union, no other member of that union is designated by
+  //      a mem-initializer-id,
+  //   the entity is initialized as specified in [dcl.init].
+  //
+  // We also apply the same rules to handle anonymous structs within anonymous
+  // unions.
+  if (Info.isWithinInactiveUnionMember(Field, Indirect))
+    return false;
+
+  if (Field->hasInClassInitializer() && !Info.isImplicitCopyOrMove()) {
+    ExprResult DIE =
+        SemaRef.BuildCXXDefaultInitExpr(Info.Ctor->getLocation(), Field);
+    if (DIE.isInvalid())
+      return true;
+
+    auto Entity = InitializedEntity::InitializeMember(Field, nullptr, true);
+    SemaRef.checkInitializerLifetime(Entity, DIE.get());
+
+    CXXCtorInitializer *Init;
+    if (Indirect)
+      Init = new (SemaRef.Context)
+          CXXCtorInitializer(SemaRef.Context, Indirect, SourceLocation(),
+                             SourceLocation(), DIE.get(), SourceLocation());
+    else
+      Init = new (SemaRef.Context)
+          CXXCtorInitializer(SemaRef.Context, Field, SourceLocation(),
+                             SourceLocation(), DIE.get(), SourceLocation());
+    return Info.addFieldInitializer(Init);
+  }
+
+  // Don't initialize incomplete or zero-length arrays.
+  if (isIncompleteOrZeroLengthArrayType(SemaRef.Context, Field->getType()))
+    return false;
+
+  // Don't try to build an implicit initializer if there were semantic
+  // errors in any of the initializers (and therefore we might be
+  // missing some that the user actually wrote).
+  if (Info.AnyErrorsInInits)
+    return false;
+
+  CXXCtorInitializer *Init = nullptr;
+  if (BuildImplicitMemberInitializer(Info.S, Info.Ctor, Info.IIK, Field,
+                                     Indirect, Init))
+    return true;
+
+  if (!Init)
+    return false;
+
+  return Info.addFieldInitializer(Init);
+}
+
+bool
+Sema::SetDelegatingInitializer(CXXConstructorDecl *Constructor,
+                               CXXCtorInitializer *Initializer) {
+  assert(Initializer->isDelegatingInitializer());
+  Constructor->setNumCtorInitializers(1);
+  CXXCtorInitializer **initializer =
+    new (Context) CXXCtorInitializer*[1];
+  memcpy(initializer, &Initializer, sizeof (CXXCtorInitializer*));
+  Constructor->setCtorInitializers(initializer);
+
+  if (CXXDestructorDecl *Dtor = LookupDestructor(Constructor->getParent())) {
+    MarkFunctionReferenced(Initializer->getSourceLocation(), Dtor);
+    DiagnoseUseOfDecl(Dtor, Initializer->getSourceLocation());
+  }
+
+  DelegatingCtorDecls.push_back(Constructor);
+
+  DiagnoseUninitializedFields(*this, Constructor);
+
+  return false;
+}
+
+bool Sema::SetCtorInitializers(CXXConstructorDecl *Constructor, bool AnyErrors,
+                               ArrayRef<CXXCtorInitializer *> Initializers) {
+  if (Constructor->isDependentContext()) {
+    // Just store the initializers as written, they will be checked during
+    // instantiation.
+    if (!Initializers.empty()) {
+      Constructor->setNumCtorInitializers(Initializers.size());
+      CXXCtorInitializer **baseOrMemberInitializers =
+        new (Context) CXXCtorInitializer*[Initializers.size()];
+      memcpy(baseOrMemberInitializers, Initializers.data(),
+             Initializers.size() * sizeof(CXXCtorInitializer*));
+      Constructor->setCtorInitializers(baseOrMemberInitializers);
+    }
+
+    // Let template instantiation know whether we had errors.
+    if (AnyErrors)
+      Constructor->setInvalidDecl();
+
+    return false;
+  }
+
+  BaseAndFieldInfo Info(*this, Constructor, AnyErrors);
+
+  // We need to build the initializer AST according to order of construction
+  // and not what user specified in the Initializers list.
+  CXXRecordDecl *ClassDecl = Constructor->getParent()->getDefinition();
+  if (!ClassDecl)
+    return true;
+
+  bool HadError = false;
+
+  for (unsigned i = 0; i < Initializers.size(); i++) {
+    CXXCtorInitializer *Member = Initializers[i];
+
+    if (Member->isBaseInitializer())
+      Info.AllBaseFields[Member->getBaseClass()->getAs<RecordType>()] = Member;
+    else {
+      Info.AllBaseFields[Member->getAnyMember()->getCanonicalDecl()] = Member;
+
+      if (IndirectFieldDecl *F = Member->getIndirectMember()) {
+        for (auto *C : F->chain()) {
+          FieldDecl *FD = dyn_cast<FieldDecl>(C);
+          if (FD && FD->getParent()->isUnion())
+            Info.ActiveUnionMember.insert(std::make_pair(
+                FD->getParent()->getCanonicalDecl(), FD->getCanonicalDecl()));
+        }
+      } else if (FieldDecl *FD = Member->getMember()) {
+        if (FD->getParent()->isUnion())
+          Info.ActiveUnionMember.insert(std::make_pair(
+              FD->getParent()->getCanonicalDecl(), FD->getCanonicalDecl()));
+      }
+    }
+  }
+
+  // Keep track of the direct virtual bases.
+  llvm::SmallPtrSet<CXXBaseSpecifier *, 16> DirectVBases;
+  for (auto &I : ClassDecl->bases()) {
+    if (I.isVirtual())
+      DirectVBases.insert(&I);
+  }
+
+  // Push virtual bases before others.
+  for (auto &VBase : ClassDecl->vbases()) {
+    if (CXXCtorInitializer *Value
+        = Info.AllBaseFields.lookup(VBase.getType()->getAs<RecordType>())) {
+      // [class.base.init]p7, per DR257:
+      //   A mem-initializer where the mem-initializer-id names a virtual base
+      //   class is ignored during execution of a constructor of any class that
+      //   is not the most derived class.
+      if (ClassDecl->isAbstract()) {
+        // FIXME: Provide a fixit to remove the base specifier. This requires
+        // tracking the location of the associated comma for a base specifier.
+        Diag(Value->getSourceLocation(), diag::warn_abstract_vbase_init_ignored)
+          << VBase.getType() << ClassDecl;
+        DiagnoseAbstractType(ClassDecl);
+      }
+
+      Info.AllToInit.push_back(Value);
+    } else if (!AnyErrors && !ClassDecl->isAbstract()) {
+      // [class.base.init]p8, per DR257:
+      //   If a given [...] base class is not named by a mem-initializer-id
+      //   [...] and the entity is not a virtual base class of an abstract
+      //   class, then [...] the entity is default-initialized.
+      bool IsInheritedVirtualBase = !DirectVBases.count(&VBase);
+      CXXCtorInitializer *CXXBaseInit;
+      if (BuildImplicitBaseInitializer(*this, Constructor, Info.IIK,
+                                       &VBase, IsInheritedVirtualBase,
+                                       CXXBaseInit)) {
+        HadError = true;
+        continue;
+      }
+
+      Info.AllToInit.push_back(CXXBaseInit);
+    }
+  }
+
+  // Non-virtual bases.
+  for (auto &Base : ClassDecl->bases()) {
+    // Virtuals are in the virtual base list and already constructed.
+    if (Base.isVirtual())
+      continue;
+
+    if (CXXCtorInitializer *Value
+          = Info.AllBaseFields.lookup(Base.getType()->getAs<RecordType>())) {
+      Info.AllToInit.push_back(Value);
+    } else if (!AnyErrors) {
+      CXXCtorInitializer *CXXBaseInit;
+      if (BuildImplicitBaseInitializer(*this, Constructor, Info.IIK,
+                                       &Base, /*IsInheritedVirtualBase=*/false,
+                                       CXXBaseInit)) {
+        HadError = true;
+        continue;
+      }
+
+      Info.AllToInit.push_back(CXXBaseInit);
+    }
+  }
+
+  // Fields.
+  for (auto *Mem : ClassDecl->decls()) {
+    if (auto *F = dyn_cast<FieldDecl>(Mem)) {
+      // C++ [class.bit]p2:
+      //   A declaration for a bit-field that omits the identifier declares an
+      //   unnamed bit-field. Unnamed bit-fields are not members and cannot be
+      //   initialized.
+      if (F->isUnnamedBitfield())
+        continue;
+
+      // If we're not generating the implicit copy/move constructor, then we'll
+      // handle anonymous struct/union fields based on their individual
+      // indirect fields.
+      if (F->isAnonymousStructOrUnion() && !Info.isImplicitCopyOrMove())
+        continue;
+
+      if (CollectFieldInitializer(*this, Info, F))
+        HadError = true;
+      continue;
+    }
+
+    // Beyond this point, we only consider default initialization.
+    if (Info.isImplicitCopyOrMove())
+      continue;
+
+    if (auto *F = dyn_cast<IndirectFieldDecl>(Mem)) {
+      if (F->getType()->isIncompleteArrayType()) {
+        assert(ClassDecl->hasFlexibleArrayMember() &&
+               "Incomplete array type is not valid");
+        continue;
+      }
+
+      // Initialize each field of an anonymous struct individually.
+      if (CollectFieldInitializer(*this, Info, F->getAnonField(), F))
+        HadError = true;
+
+      continue;
+    }
+  }
+
+  unsigned NumInitializers = Info.AllToInit.size();
+  if (NumInitializers > 0) {
+    Constructor->setNumCtorInitializers(NumInitializers);
+    CXXCtorInitializer **baseOrMemberInitializers =
+      new (Context) CXXCtorInitializer*[NumInitializers];
+    memcpy(baseOrMemberInitializers, Info.AllToInit.data(),
+           NumInitializers * sizeof(CXXCtorInitializer*));
+    Constructor->setCtorInitializers(baseOrMemberInitializers);
+
+    // Constructors implicitly reference the base and member
+    // destructors.
+    MarkBaseAndMemberDestructorsReferenced(Constructor->getLocation(),
+                                           Constructor->getParent());
+  }
+
+  return HadError;
+}
+
+static void PopulateKeysForFields(FieldDecl *Field, SmallVectorImpl<const void*> &IdealInits) {
+  if (const RecordType *RT = Field->getType()->getAs<RecordType>()) {
+    const RecordDecl *RD = RT->getDecl();
+    if (RD->isAnonymousStructOrUnion()) {
+      for (auto *Field : RD->fields())
+        PopulateKeysForFields(Field, IdealInits);
+      return;
+    }
+  }
+  IdealInits.push_back(Field->getCanonicalDecl());
+}
+
+static const void *GetKeyForBase(ASTContext &Context, QualType BaseType) {
+  return Context.getCanonicalType(BaseType).getTypePtr();
+}
+
+static const void *GetKeyForMember(ASTContext &Context,
+                                   CXXCtorInitializer *Member) {
+  if (!Member->isAnyMemberInitializer())
+    return GetKeyForBase(Context, QualType(Member->getBaseClass(), 0));
+
+  return Member->getAnyMember()->getCanonicalDecl();
+}
+
+static void AddInitializerToDiag(const Sema::SemaDiagnosticBuilder &Diag,
+                                 const CXXCtorInitializer *Previous,
+                                 const CXXCtorInitializer *Current) {
+  if (Previous->isAnyMemberInitializer())
+    Diag << 0 << Previous->getAnyMember();
+  else
+    Diag << 1 << Previous->getTypeSourceInfo()->getType();
+
+  if (Current->isAnyMemberInitializer())
+    Diag << 0 << Current->getAnyMember();
+  else
+    Diag << 1 << Current->getTypeSourceInfo()->getType();
+}
+
+static void DiagnoseBaseOrMemInitializerOrder(
+    Sema &SemaRef, const CXXConstructorDecl *Constructor,
+    ArrayRef<CXXCtorInitializer *> Inits) {
+  if (Constructor->getDeclContext()->isDependentContext())
+    return;
+
+  // Don't check initializers order unless the warning is enabled at the
+  // location of at least one initializer.
+  bool ShouldCheckOrder = false;
+  for (unsigned InitIndex = 0; InitIndex != Inits.size(); ++InitIndex) {
+    CXXCtorInitializer *Init = Inits[InitIndex];
+    if (!SemaRef.Diags.isIgnored(diag::warn_initializer_out_of_order,
+                                 Init->getSourceLocation())) {
+      ShouldCheckOrder = true;
+      break;
+    }
+  }
+  if (!ShouldCheckOrder)
+    return;
+
+  // Build the list of bases and members in the order that they'll
+  // actually be initialized.  The explicit initializers should be in
+  // this same order but may be missing things.
+  SmallVector<const void*, 32> IdealInitKeys;
+
+  const CXXRecordDecl *ClassDecl = Constructor->getParent();
+
+  // 1. Virtual bases.
+  for (const auto &VBase : ClassDecl->vbases())
+    IdealInitKeys.push_back(GetKeyForBase(SemaRef.Context, VBase.getType()));
+
+  // 2. Non-virtual bases.
+  for (const auto &Base : ClassDecl->bases()) {
+    if (Base.isVirtual())
+      continue;
+    IdealInitKeys.push_back(GetKeyForBase(SemaRef.Context, Base.getType()));
+  }
+
+  // 3. Direct fields.
+  for (auto *Field : ClassDecl->fields()) {
+    if (Field->isUnnamedBitfield())
+      continue;
+
+    PopulateKeysForFields(Field, IdealInitKeys);
+  }
+
+  unsigned NumIdealInits = IdealInitKeys.size();
+  unsigned IdealIndex = 0;
+
+  // Track initializers that are in an incorrect order for either a warning or
+  // note if multiple ones occur.
+  SmallVector<unsigned> WarnIndexes;
+  // Correlates the index of an initializer in the init-list to the index of
+  // the field/base in the class.
+  SmallVector<std::pair<unsigned, unsigned>, 32> CorrelatedInitOrder;
+
+  for (unsigned InitIndex = 0; InitIndex != Inits.size(); ++InitIndex) {
+    const void *InitKey = GetKeyForMember(SemaRef.Context, Inits[InitIndex]);
+
+    // Scan forward to try to find this initializer in the idealized
+    // initializers list.
+    for (; IdealIndex != NumIdealInits; ++IdealIndex)
+      if (InitKey == IdealInitKeys[IdealIndex])
+        break;
+
+    // If we didn't find this initializer, it must be because we
+    // scanned past it on a previous iteration.  That can only
+    // happen if we're out of order;  emit a warning.
+    if (IdealIndex == NumIdealInits && InitIndex) {
+      WarnIndexes.push_back(InitIndex);
+
+      // Move back to the initializer's location in the ideal list.
+      for (IdealIndex = 0; IdealIndex != NumIdealInits; ++IdealIndex)
+        if (InitKey == IdealInitKeys[IdealIndex])
+          break;
+
+      assert(IdealIndex < NumIdealInits &&
+             "initializer not found in initializer list");
+    }
+    CorrelatedInitOrder.emplace_back(IdealIndex, InitIndex);
+  }
+
+  if (WarnIndexes.empty())
+    return;
+
+  // Sort based on the ideal order, first in the pair.
+  llvm::sort(CorrelatedInitOrder,
+             [](auto &LHS, auto &RHS) { return LHS.first < RHS.first; });
+
+  // Introduce a new scope as SemaDiagnosticBuilder needs to be destroyed to
+  // emit the diagnostic before we can try adding notes.
+  {
+    Sema::SemaDiagnosticBuilder D = SemaRef.Diag(
+        Inits[WarnIndexes.front() - 1]->getSourceLocation(),
+        WarnIndexes.size() == 1 ? diag::warn_initializer_out_of_order
+                                : diag::warn_some_initializers_out_of_order);
+
+    for (unsigned I = 0; I < CorrelatedInitOrder.size(); ++I) {
+      if (CorrelatedInitOrder[I].second == I)
+        continue;
+      // Ideally we would be using InsertFromRange here, but clang doesn't
+      // appear to handle InsertFromRange correctly when the source range is
+      // modified by another fix-it.
+      D << FixItHint::CreateReplacement(
+          Inits[I]->getSourceRange(),
+          Lexer::getSourceText(
+              CharSourceRange::getTokenRange(
+                  Inits[CorrelatedInitOrder[I].second]->getSourceRange()),
+              SemaRef.getSourceManager(), SemaRef.getLangOpts()));
+    }
+
+    // If there is only 1 item out of order, the warning expects the name and
+    // type of each being added to it.
+    if (WarnIndexes.size() == 1) {
+      AddInitializerToDiag(D, Inits[WarnIndexes.front() - 1],
+                           Inits[WarnIndexes.front()]);
+      return;
+    }
+  }
+  // More than 1 item to warn, create notes letting the user know which ones
+  // are bad.
+  for (unsigned WarnIndex : WarnIndexes) {
+    const clang::CXXCtorInitializer *PrevInit = Inits[WarnIndex - 1];
+    auto D = SemaRef.Diag(PrevInit->getSourceLocation(),
+                          diag::note_initializer_out_of_order);
+    AddInitializerToDiag(D, PrevInit, Inits[WarnIndex]);
+    D << PrevInit->getSourceRange();
+  }
+}
+
+namespace {
+bool CheckRedundantInit(Sema &S,
+                        CXXCtorInitializer *Init,
+                        CXXCtorInitializer *&PrevInit) {
+  if (!PrevInit) {
+    PrevInit = Init;
+    return false;
+  }
+
+  if (FieldDecl *Field = Init->getAnyMember())
+    S.Diag(Init->getSourceLocation(),
+           diag::err_multiple_mem_initialization)
+      << Field->getDeclName()
+      << Init->getSourceRange();
+  else {
+    const Type *BaseClass = Init->getBaseClass();
+    assert(BaseClass && "neither field nor base");
+    S.Diag(Init->getSourceLocation(),
+           diag::err_multiple_base_initialization)
+      << QualType(BaseClass, 0)
+      << Init->getSourceRange();
+  }
+  S.Diag(PrevInit->getSourceLocation(), diag::note_previous_initializer)
+    << 0 << PrevInit->getSourceRange();
+
+  return true;
+}
+
+typedef std::pair<NamedDecl *, CXXCtorInitializer *> UnionEntry;
+typedef llvm::DenseMap<RecordDecl*, UnionEntry> RedundantUnionMap;
+
+bool CheckRedundantUnionInit(Sema &S,
+                             CXXCtorInitializer *Init,
+                             RedundantUnionMap &Unions) {
+  FieldDecl *Field = Init->getAnyMember();
+  RecordDecl *Parent = Field->getParent();
+  NamedDecl *Child = Field;
+
+  while (Parent->isAnonymousStructOrUnion() || Parent->isUnion()) {
+    if (Parent->isUnion()) {
+      UnionEntry &En = Unions[Parent];
+      if (En.first && En.first != Child) {
+        S.Diag(Init->getSourceLocation(),
+               diag::err_multiple_mem_union_initialization)
+          << Field->getDeclName()
+          << Init->getSourceRange();
+        S.Diag(En.second->getSourceLocation(), diag::note_previous_initializer)
+          << 0 << En.second->getSourceRange();
+        return true;
+      }
+      if (!En.first) {
+        En.first = Child;
+        En.second = Init;
+      }
+      if (!Parent->isAnonymousStructOrUnion())
+        return false;
+    }
+
+    Child = Parent;
+    Parent = cast<RecordDecl>(Parent->getDeclContext());
+  }
+
+  return false;
+}
+} // namespace
+
+/// ActOnMemInitializers - Handle the member initializers for a constructor.
+void Sema::ActOnMemInitializers(Decl *ConstructorDecl,
+                                SourceLocation ColonLoc,
+                                ArrayRef<CXXCtorInitializer*> MemInits,
+                                bool AnyErrors) {
+  if (!ConstructorDecl)
+    return;
+
+  AdjustDeclIfTemplate(ConstructorDecl);
+
+  CXXConstructorDecl *Constructor
+    = dyn_cast<CXXConstructorDecl>(ConstructorDecl);
+
+  if (!Constructor) {
+    Diag(ColonLoc, diag::err_only_constructors_take_base_inits);
+    return;
+  }
+
+  // Mapping for the duplicate initializers check.
+  // For member initializers, this is keyed with a FieldDecl*.
+  // For base initializers, this is keyed with a Type*.
+  llvm::DenseMap<const void *, CXXCtorInitializer *> Members;
+
+  // Mapping for the inconsistent anonymous-union initializers check.
+  RedundantUnionMap MemberUnions;
+
+  bool HadError = false;
+  for (unsigned i = 0; i < MemInits.size(); i++) {
+    CXXCtorInitializer *Init = MemInits[i];
+
+    // Set the source order index.
+    Init->setSourceOrder(i);
+
+    if (Init->isAnyMemberInitializer()) {
+      const void *Key = GetKeyForMember(Context, Init);
+      if (CheckRedundantInit(*this, Init, Members[Key]) ||
+          CheckRedundantUnionInit(*this, Init, MemberUnions))
+        HadError = true;
+    } else if (Init->isBaseInitializer()) {
+      const void *Key = GetKeyForMember(Context, Init);
+      if (CheckRedundantInit(*this, Init, Members[Key]))
+        HadError = true;
+    } else {
+      assert(Init->isDelegatingInitializer());
+      // This must be the only initializer
+      if (MemInits.size() != 1) {
+        Diag(Init->getSourceLocation(),
+             diag::err_delegating_initializer_alone)
+          << Init->getSourceRange() << MemInits[i ? 0 : 1]->getSourceRange();
+        // We will treat this as being the only initializer.
+      }
+      SetDelegatingInitializer(Constructor, MemInits[i]);
+      // Return immediately as the initializer is set.
+      return;
+    }
+  }
+
+  if (HadError)
+    return;
+
+  DiagnoseBaseOrMemInitializerOrder(*this, Constructor, MemInits);
+
+  SetCtorInitializers(Constructor, AnyErrors, MemInits);
+
+  DiagnoseUninitializedFields(*this, Constructor);
+}
+
+void
+Sema::MarkBaseAndMemberDestructorsReferenced(SourceLocation Location,
+                                             CXXRecordDecl *ClassDecl) {
+  // Ignore dependent contexts. Also ignore unions, since their members never
+  // have destructors implicitly called.
+  if (ClassDecl->isDependentContext() || ClassDecl->isUnion())
+    return;
+
+  // FIXME: all the access-control diagnostics are positioned on the
+  // field/base declaration.  That's probably good; that said, the
+  // user might reasonably want to know why the destructor is being
+  // emitted, and we currently don't say.
+
+  // Non-static data members.
+  for (auto *Field : ClassDecl->fields()) {
+    if (Field->isInvalidDecl())
+      continue;
+
+    // Don't destroy incomplete or zero-length arrays.
+    if (isIncompleteOrZeroLengthArrayType(Context, Field->getType()))
+      continue;
+
+    QualType FieldType = Context.getBaseElementType(Field->getType());
+
+    const RecordType* RT = FieldType->getAs<RecordType>();
+    if (!RT)
+      continue;
+
+    CXXRecordDecl *FieldClassDecl = cast<CXXRecordDecl>(RT->getDecl());
+    if (FieldClassDecl->isInvalidDecl())
+      continue;
+    if (FieldClassDecl->hasIrrelevantDestructor())
+      continue;
+    // The destructor for an implicit anonymous union member is never invoked.
+    if (FieldClassDecl->isUnion() && FieldClassDecl->isAnonymousStructOrUnion())
+      continue;
+
+    CXXDestructorDecl *Dtor = LookupDestructor(FieldClassDecl);
+    assert(Dtor && "No dtor found for FieldClassDecl!");
+    CheckDestructorAccess(Field->getLocation(), Dtor,
+                          PDiag(diag::err_access_dtor_field)
+                            << Field->getDeclName()
+                            << FieldType);
+
+    MarkFunctionReferenced(Location, Dtor);
+    DiagnoseUseOfDecl(Dtor, Location);
+  }
+
+  // We only potentially invoke the destructors of potentially constructed
+  // subobjects.
+  bool VisitVirtualBases = !ClassDecl->isAbstract();
+
+  // If the destructor exists and has already been marked used in the MS ABI,
+  // then virtual base destructors have already been checked and marked used.
+  // Skip checking them again to avoid duplicate diagnostics.
+  if (Context.getTargetInfo().getCXXABI().isMicrosoft()) {
+    CXXDestructorDecl *Dtor = ClassDecl->getDestructor();
+    if (Dtor && Dtor->isUsed())
+      VisitVirtualBases = false;
+  }
+
+  llvm::SmallPtrSet<const RecordType *, 8> DirectVirtualBases;
+
+  // Bases.
+  for (const auto &Base : ClassDecl->bases()) {
+    const RecordType *RT = Base.getType()->getAs<RecordType>();
+    if (!RT)
+      continue;
+
+    // Remember direct virtual bases.
+    if (Base.isVirtual()) {
+      if (!VisitVirtualBases)
+        continue;
+      DirectVirtualBases.insert(RT);
+    }
+
+    CXXRecordDecl *BaseClassDecl = cast<CXXRecordDecl>(RT->getDecl());
+    // If our base class is invalid, we probably can't get its dtor anyway.
+    if (BaseClassDecl->isInvalidDecl())
+      continue;
+    if (BaseClassDecl->hasIrrelevantDestructor())
+      continue;
+
+    CXXDestructorDecl *Dtor = LookupDestructor(BaseClassDecl);
+    assert(Dtor && "No dtor found for BaseClassDecl!");
+
+    // FIXME: caret should be on the start of the class name
+    CheckDestructorAccess(Base.getBeginLoc(), Dtor,
+                          PDiag(diag::err_access_dtor_base)
+                              << Base.getType() << Base.getSourceRange(),
+                          Context.getTypeDeclType(ClassDecl));
+
+    MarkFunctionReferenced(Location, Dtor);
+    DiagnoseUseOfDecl(Dtor, Location);
+  }
+
+  if (VisitVirtualBases)
+    MarkVirtualBaseDestructorsReferenced(Location, ClassDecl,
+                                         &DirectVirtualBases);
+}
+
+void Sema::MarkVirtualBaseDestructorsReferenced(
+    SourceLocation Location, CXXRecordDecl *ClassDecl,
+    llvm::SmallPtrSetImpl<const RecordType *> *DirectVirtualBases) {
+  // Virtual bases.
+  for (const auto &VBase : ClassDecl->vbases()) {
+    // Bases are always records in a well-formed non-dependent class.
+    const RecordType *RT = VBase.getType()->castAs<RecordType>();
+
+    // Ignore already visited direct virtual bases.
+    if (DirectVirtualBases && DirectVirtualBases->count(RT))
+      continue;
+
+    CXXRecordDecl *BaseClassDecl = cast<CXXRecordDecl>(RT->getDecl());
+    // If our base class is invalid, we probably can't get its dtor anyway.
+    if (BaseClassDecl->isInvalidDecl())
+      continue;
+    if (BaseClassDecl->hasIrrelevantDestructor())
+      continue;
+
+    CXXDestructorDecl *Dtor = LookupDestructor(BaseClassDecl);
+    assert(Dtor && "No dtor found for BaseClassDecl!");
+    if (CheckDestructorAccess(
+            ClassDecl->getLocation(), Dtor,
+            PDiag(diag::err_access_dtor_vbase)
+                << Context.getTypeDeclType(ClassDecl) << VBase.getType(),
+            Context.getTypeDeclType(ClassDecl)) ==
+        AR_accessible) {
+      CheckDerivedToBaseConversion(
+          Context.getTypeDeclType(ClassDecl), VBase.getType(),
+          diag::err_access_dtor_vbase, 0, ClassDecl->getLocation(),
+          SourceRange(), DeclarationName(), nullptr);
+    }
+
+    MarkFunctionReferenced(Location, Dtor);
+    DiagnoseUseOfDecl(Dtor, Location);
+  }
+}
+
+void Sema::ActOnDefaultCtorInitializers(Decl *CDtorDecl) {
+  if (!CDtorDecl)
+    return;
+
+  if (CXXConstructorDecl *Constructor
+      = dyn_cast<CXXConstructorDecl>(CDtorDecl)) {
+    SetCtorInitializers(Constructor, /*AnyErrors=*/false);
+    DiagnoseUninitializedFields(*this, Constructor);
+  }
+}
+
+bool Sema::isAbstractType(SourceLocation Loc, QualType T) {
+  if (!getLangOpts().CPlusPlus)
+    return false;
+
+  const auto *RD = Context.getBaseElementType(T)->getAsCXXRecordDecl();
+  if (!RD)
+    return false;
+
+  // FIXME: Per [temp.inst]p1, we are supposed to trigger instantiation of a
+  // class template specialization here, but doing so breaks a lot of code.
+
+  // We can't answer whether something is abstract until it has a
+  // definition. If it's currently being defined, we'll walk back
+  // over all the declarations when we have a full definition.
+  const CXXRecordDecl *Def = RD->getDefinition();
+  if (!Def || Def->isBeingDefined())
+    return false;
+
+  return RD->isAbstract();
+}
+
+bool Sema::RequireNonAbstractType(SourceLocation Loc, QualType T,
+                                  TypeDiagnoser &Diagnoser) {
+  if (!isAbstractType(Loc, T))
+    return false;
+
+  T = Context.getBaseElementType(T);
+  Diagnoser.diagnose(*this, Loc, T);
+  DiagnoseAbstractType(T->getAsCXXRecordDecl());
+  return true;
+}
+
+void Sema::DiagnoseAbstractType(const CXXRecordDecl *RD) {
+  // Check if we've already emitted the list of pure virtual functions
+  // for this class.
+  if (PureVirtualClassDiagSet && PureVirtualClassDiagSet->count(RD))
+    return;
+
+  // If the diagnostic is suppressed, don't emit the notes. We're only
+  // going to emit them once, so try to attach them to a diagnostic we're
+  // actually going to show.
+  if (Diags.isLastDiagnosticIgnored())
+    return;
+
+  CXXFinalOverriderMap FinalOverriders;
+  RD->getFinalOverriders(FinalOverriders);
+
+  // Keep a set of seen pure methods so we won't diagnose the same method
+  // more than once.
+  llvm::SmallPtrSet<const CXXMethodDecl *, 8> SeenPureMethods;
+
+  for (CXXFinalOverriderMap::iterator M = FinalOverriders.begin(),
+                                   MEnd = FinalOverriders.end();
+       M != MEnd;
+       ++M) {
+    for (OverridingMethods::iterator SO = M->second.begin(),
+                                  SOEnd = M->second.end();
+         SO != SOEnd; ++SO) {
+      // C++ [class.abstract]p4:
+      //   A class is abstract if it contains or inherits at least one
+      //   pure virtual function for which the final overrider is pure
+      //   virtual.
+
+      //
+      if (SO->second.size() != 1)
+        continue;
+
+      if (!SO->second.front().Method->isPure())
+        continue;
+
+      if (!SeenPureMethods.insert(SO->second.front().Method).second)
+        continue;
+
+      Diag(SO->second.front().Method->getLocation(),
+           diag::note_pure_virtual_function)
+        << SO->second.front().Method->getDeclName() << RD->getDeclName();
+    }
+  }
+
+  if (!PureVirtualClassDiagSet)
+    PureVirtualClassDiagSet.reset(new RecordDeclSetTy);
+  PureVirtualClassDiagSet->insert(RD);
+}
+
+namespace {
+struct AbstractUsageInfo {
+  Sema &S;
+  CXXRecordDecl *Record;
+  CanQualType AbstractType;
+  bool Invalid;
+
+  AbstractUsageInfo(Sema &S, CXXRecordDecl *Record)
+    : S(S), Record(Record),
+      AbstractType(S.Context.getCanonicalType(
+                   S.Context.getTypeDeclType(Record))),
+      Invalid(false) {}
+
+  void DiagnoseAbstractType() {
+    if (Invalid) return;
+    S.DiagnoseAbstractType(Record);
+    Invalid = true;
+  }
+
+  void CheckType(const NamedDecl *D, TypeLoc TL, Sema::AbstractDiagSelID Sel);
+};
+
+struct CheckAbstractUsage {
+  AbstractUsageInfo &Info;
+  const NamedDecl *Ctx;
+
+  CheckAbstractUsage(AbstractUsageInfo &Info, const NamedDecl *Ctx)
+    : Info(Info), Ctx(Ctx) {}
+
+  void Visit(TypeLoc TL, Sema::AbstractDiagSelID Sel) {
+    switch (TL.getTypeLocClass()) {
+#define ABSTRACT_TYPELOC(CLASS, PARENT)
+#define TYPELOC(CLASS, PARENT) \
+    case TypeLoc::CLASS: Check(TL.castAs<CLASS##TypeLoc>(), Sel); break;
+#include "clang/AST/TypeLocNodes.def"
+    }
+  }
+
+  void Check(FunctionProtoTypeLoc TL, Sema::AbstractDiagSelID Sel) {
+    Visit(TL.getReturnLoc(), Sema::AbstractReturnType);
+    for (unsigned I = 0, E = TL.getNumParams(); I != E; ++I) {
+      if (!TL.getParam(I))
+        continue;
+
+      TypeSourceInfo *TSI = TL.getParam(I)->getTypeSourceInfo();
+      if (TSI) Visit(TSI->getTypeLoc(), Sema::AbstractParamType);
+    }
+  }
+
+  void Check(ArrayTypeLoc TL, Sema::AbstractDiagSelID Sel) {
+    Visit(TL.getElementLoc(), Sema::AbstractArrayType);
+  }
+
+  void Check(TemplateSpecializationTypeLoc TL, Sema::AbstractDiagSelID Sel) {
+    // Visit the type parameters from a permissive context.
+    for (unsigned I = 0, E = TL.getNumArgs(); I != E; ++I) {
+      TemplateArgumentLoc TAL = TL.getArgLoc(I);
+      if (TAL.getArgument().getKind() == TemplateArgument::Type)
+        if (TypeSourceInfo *TSI = TAL.getTypeSourceInfo())
+          Visit(TSI->getTypeLoc(), Sema::AbstractNone);
+      // TODO: other template argument types?
+    }
+  }
+
+  // Visit pointee types from a permissive context.
+#define CheckPolymorphic(Type) \
+  void Check(Type TL, Sema::AbstractDiagSelID Sel) { \
+    Visit(TL.getNextTypeLoc(), Sema::AbstractNone); \
+  }
+  CheckPolymorphic(PointerTypeLoc)
+  CheckPolymorphic(ReferenceTypeLoc)
+  CheckPolymorphic(MemberPointerTypeLoc)
+  CheckPolymorphic(BlockPointerTypeLoc)
+  CheckPolymorphic(AtomicTypeLoc)
+
+  /// Handle all the types we haven't given a more specific
+  /// implementation for above.
+  void Check(TypeLoc TL, Sema::AbstractDiagSelID Sel) {
+    // Every other kind of type that we haven't called out already
+    // that has an inner type is either (1) sugar or (2) contains that
+    // inner type in some way as a subobject.
+    if (TypeLoc Next = TL.getNextTypeLoc())
+      return Visit(Next, Sel);
+
+    // If there's no inner type and we're in a permissive context,
+    // don't diagnose.
+    if (Sel == Sema::AbstractNone) return;
+
+    // Check whether the type matches the abstract type.
+    QualType T = TL.getType();
+    if (T->isArrayType()) {
+      Sel = Sema::AbstractArrayType;
+      T = Info.S.Context.getBaseElementType(T);
+    }
+    CanQualType CT = T->getCanonicalTypeUnqualified().getUnqualifiedType();
+    if (CT != Info.AbstractType) return;
+
+    // It matched; do some magic.
+    // FIXME: These should be at most warnings. See P0929R2, CWG1640, CWG1646.
+    if (Sel == Sema::AbstractArrayType) {
+      Info.S.Diag(Ctx->getLocation(), diag::err_array_of_abstract_type)
+        << T << TL.getSourceRange();
+    } else {
+      Info.S.Diag(Ctx->getLocation(), diag::err_abstract_type_in_decl)
+        << Sel << T << TL.getSourceRange();
+    }
+    Info.DiagnoseAbstractType();
+  }
+};
+
+void AbstractUsageInfo::CheckType(const NamedDecl *D, TypeLoc TL,
+                                  Sema::AbstractDiagSelID Sel) {
+  CheckAbstractUsage(*this, D).Visit(TL, Sel);
+}
+
+}
+
+/// Check for invalid uses of an abstract type in a function declaration.
+static void CheckAbstractClassUsage(AbstractUsageInfo &Info,
+                                    FunctionDecl *FD) {
+  // No need to do the check on definitions, which require that
+  // the return/param types be complete.
+  if (FD->doesThisDeclarationHaveABody())
+    return;
+
+  // For safety's sake, just ignore it if we don't have type source
+  // information.  This should never happen for non-implicit methods,
+  // but...
+  if (TypeSourceInfo *TSI = FD->getTypeSourceInfo())
+    Info.CheckType(FD, TSI->getTypeLoc(), Sema::AbstractNone);
+}
+
+/// Check for invalid uses of an abstract type in a variable0 declaration.
+static void CheckAbstractClassUsage(AbstractUsageInfo &Info,
+                                    VarDecl *VD) {
+  // No need to do the check on definitions, which require that
+  // the type is complete.
+  if (VD->isThisDeclarationADefinition())
+    return;
+
+  Info.CheckType(VD, VD->getTypeSourceInfo()->getTypeLoc(),
+                 Sema::AbstractVariableType);
+}
+
+/// Check for invalid uses of an abstract type within a class definition.
+static void CheckAbstractClassUsage(AbstractUsageInfo &Info,
+                                    CXXRecordDecl *RD) {
+  for (auto *D : RD->decls()) {
+    if (D->isImplicit()) continue;
+
+    // Step through friends to the befriended declaration.
+    if (auto *FD = dyn_cast<FriendDecl>(D)) {
+      D = FD->getFriendDecl();
+      if (!D) continue;
+    }
+
+    // Functions and function templates.
+    if (auto *FD = dyn_cast<FunctionDecl>(D)) {
+      CheckAbstractClassUsage(Info, FD);
+    } else if (auto *FTD = dyn_cast<FunctionTemplateDecl>(D)) {
+      CheckAbstractClassUsage(Info, FTD->getTemplatedDecl());
+
+    // Fields and static variables.
+    } else if (auto *FD = dyn_cast<FieldDecl>(D)) {
+      if (TypeSourceInfo *TSI = FD->getTypeSourceInfo())
+        Info.CheckType(FD, TSI->getTypeLoc(), Sema::AbstractFieldType);
+    } else if (auto *VD = dyn_cast<VarDecl>(D)) {
+      CheckAbstractClassUsage(Info, VD);
+    } else if (auto *VTD = dyn_cast<VarTemplateDecl>(D)) {
+      CheckAbstractClassUsage(Info, VTD->getTemplatedDecl());
+
+    // Nested classes and class templates.
+    } else if (auto *RD = dyn_cast<CXXRecordDecl>(D)) {
+      CheckAbstractClassUsage(Info, RD);
+    } else if (auto *CTD = dyn_cast<ClassTemplateDecl>(D)) {
+      CheckAbstractClassUsage(Info, CTD->getTemplatedDecl());
+    }
+  }
+}
+
+static void ReferenceDllExportedMembers(Sema &S, CXXRecordDecl *Class) {
+  Attr *ClassAttr = getDLLAttr(Class);
+  if (!ClassAttr)
+    return;
+
+  assert(ClassAttr->getKind() == attr::DLLExport);
+
+  TemplateSpecializationKind TSK = Class->getTemplateSpecializationKind();
+
+  if (TSK == TSK_ExplicitInstantiationDeclaration)
+    // Don't go any further if this is just an explicit instantiation
+    // declaration.
+    return;
+
+  // Add a context note to explain how we got to any diagnostics produced below.
+  struct MarkingClassDllexported {
+    Sema &S;
+    MarkingClassDllexported(Sema &S, CXXRecordDecl *Class,
+                            SourceLocation AttrLoc)
+        : S(S) {
+      Sema::CodeSynthesisContext Ctx;
+      Ctx.Kind = Sema::CodeSynthesisContext::MarkingClassDllexported;
+      Ctx.PointOfInstantiation = AttrLoc;
+      Ctx.Entity = Class;
+      S.pushCodeSynthesisContext(Ctx);
+    }
+    ~MarkingClassDllexported() {
+      S.popCodeSynthesisContext();
+    }
+  } MarkingDllexportedContext(S, Class, ClassAttr->getLocation());
+
+  if (S.Context.getTargetInfo().getTriple().isWindowsGNUEnvironment())
+    S.MarkVTableUsed(Class->getLocation(), Class, true);
+
+  for (Decl *Member : Class->decls()) {
+    // Skip members that were not marked exported.
+    if (!Member->hasAttr<DLLExportAttr>())
+      continue;
+
+    // Defined static variables that are members of an exported base
+    // class must be marked export too.
+    auto *VD = dyn_cast<VarDecl>(Member);
+    if (VD && VD->getStorageClass() == SC_Static &&
+        TSK == TSK_ImplicitInstantiation)
+      S.MarkVariableReferenced(VD->getLocation(), VD);
+
+    auto *MD = dyn_cast<CXXMethodDecl>(Member);
+    if (!MD)
+      continue;
+
+    if (MD->isUserProvided()) {
+      // Instantiate non-default class member functions ...
+
+      // .. except for certain kinds of template specializations.
+      if (TSK == TSK_ImplicitInstantiation && !ClassAttr->isInherited())
+        continue;
+
+      // If this is an MS ABI dllexport default constructor, instantiate any
+      // default arguments.
+      if (S.Context.getTargetInfo().getCXXABI().isMicrosoft()) {
+        auto *CD = dyn_cast<CXXConstructorDecl>(MD);
+        if (CD && CD->isDefaultConstructor() && TSK == TSK_Undeclared) {
+          S.InstantiateDefaultCtorDefaultArgs(CD);
+        }
+      }
+
+      S.MarkFunctionReferenced(Class->getLocation(), MD);
+
+      // The function will be passed to the consumer when its definition is
+      // encountered.
+    } else if (MD->isExplicitlyDefaulted()) {
+      // Synthesize and instantiate explicitly defaulted methods.
+      S.MarkFunctionReferenced(Class->getLocation(), MD);
+
+      if (TSK != TSK_ExplicitInstantiationDefinition) {
+        // Except for explicit instantiation defs, we will not see the
+        // definition again later, so pass it to the consumer now.
+        S.Consumer.HandleTopLevelDecl(DeclGroupRef(MD));
+      }
+    } else if (!MD->isTrivial() ||
+               MD->isCopyAssignmentOperator() ||
+               MD->isMoveAssignmentOperator()) {
+      // Synthesize and instantiate non-trivial implicit methods, and the copy
+      // and move assignment operators. The latter are exported even if they
+      // are trivial, because the address of an operator can be taken and
+      // should compare equal across libraries.
+      S.MarkFunctionReferenced(Class->getLocation(), MD);
+
+      // There is no later point when we will see the definition of this
+      // function, so pass it to the consumer now.
+      S.Consumer.HandleTopLevelDecl(DeclGroupRef(MD));
+    }
+  }
+}
+
+static void checkForMultipleExportedDefaultConstructors(Sema &S,
+                                                        CXXRecordDecl *Class) {
+  // Only the MS ABI has default constructor closures, so we don't need to do
+  // this semantic checking anywhere else.
+  if (!S.Context.getTargetInfo().getCXXABI().isMicrosoft())
+    return;
+
+  CXXConstructorDecl *LastExportedDefaultCtor = nullptr;
+  for (Decl *Member : Class->decls()) {
+    // Look for exported default constructors.
+    auto *CD = dyn_cast<CXXConstructorDecl>(Member);
+    if (!CD || !CD->isDefaultConstructor())
+      continue;
+    auto *Attr = CD->getAttr<DLLExportAttr>();
+    if (!Attr)
+      continue;
+
+    // If the class is non-dependent, mark the default arguments as ODR-used so
+    // that we can properly codegen the constructor closure.
+    if (!Class->isDependentContext()) {
+      for (ParmVarDecl *PD : CD->parameters()) {
+        (void)S.CheckCXXDefaultArgExpr(Attr->getLocation(), CD, PD);
+        S.DiscardCleanupsInEvaluationContext();
+      }
+    }
+
+    if (LastExportedDefaultCtor) {
+      S.Diag(LastExportedDefaultCtor->getLocation(),
+             diag::err_attribute_dll_ambiguous_default_ctor)
+          << Class;
+      S.Diag(CD->getLocation(), diag::note_entity_declared_at)
+          << CD->getDeclName();
+      return;
+    }
+    LastExportedDefaultCtor = CD;
+  }
+}
+
+static void checkCUDADeviceBuiltinSurfaceClassTemplate(Sema &S,
+                                                       CXXRecordDecl *Class) {
+  bool ErrorReported = false;
+  auto reportIllegalClassTemplate = [&ErrorReported](Sema &S,
+                                                     ClassTemplateDecl *TD) {
+    if (ErrorReported)
+      return;
+    S.Diag(TD->getLocation(),
+           diag::err_cuda_device_builtin_surftex_cls_template)
+        << /*surface*/ 0 << TD;
+    ErrorReported = true;
+  };
+
+  ClassTemplateDecl *TD = Class->getDescribedClassTemplate();
+  if (!TD) {
+    auto *SD = dyn_cast<ClassTemplateSpecializationDecl>(Class);
+    if (!SD) {
+      S.Diag(Class->getLocation(),
+             diag::err_cuda_device_builtin_surftex_ref_decl)
+          << /*surface*/ 0 << Class;
+      S.Diag(Class->getLocation(),
+             diag::note_cuda_device_builtin_surftex_should_be_template_class)
+          << Class;
+      return;
+    }
+    TD = SD->getSpecializedTemplate();
+  }
+
+  TemplateParameterList *Params = TD->getTemplateParameters();
+  unsigned N = Params->size();
+
+  if (N != 2) {
+    reportIllegalClassTemplate(S, TD);
+    S.Diag(TD->getLocation(),
+           diag::note_cuda_device_builtin_surftex_cls_should_have_n_args)
+        << TD << 2;
+  }
+  if (N > 0 && !isa<TemplateTypeParmDecl>(Params->getParam(0))) {
+    reportIllegalClassTemplate(S, TD);
+    S.Diag(TD->getLocation(),
+           diag::note_cuda_device_builtin_surftex_cls_should_have_match_arg)
+        << TD << /*1st*/ 0 << /*type*/ 0;
+  }
+  if (N > 1) {
+    auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(Params->getParam(1));
+    if (!NTTP || !NTTP->getType()->isIntegralOrEnumerationType()) {
+      reportIllegalClassTemplate(S, TD);
+      S.Diag(TD->getLocation(),
+             diag::note_cuda_device_builtin_surftex_cls_should_have_match_arg)
+          << TD << /*2nd*/ 1 << /*integer*/ 1;
+    }
+  }
+}
+
+static void checkCUDADeviceBuiltinTextureClassTemplate(Sema &S,
+                                                       CXXRecordDecl *Class) {
+  bool ErrorReported = false;
+  auto reportIllegalClassTemplate = [&ErrorReported](Sema &S,
+                                                     ClassTemplateDecl *TD) {
+    if (ErrorReported)
+      return;
+    S.Diag(TD->getLocation(),
+           diag::err_cuda_device_builtin_surftex_cls_template)
+        << /*texture*/ 1 << TD;
+    ErrorReported = true;
+  };
+
+  ClassTemplateDecl *TD = Class->getDescribedClassTemplate();
+  if (!TD) {
+    auto *SD = dyn_cast<ClassTemplateSpecializationDecl>(Class);
+    if (!SD) {
+      S.Diag(Class->getLocation(),
+             diag::err_cuda_device_builtin_surftex_ref_decl)
+          << /*texture*/ 1 << Class;
+      S.Diag(Class->getLocation(),
+             diag::note_cuda_device_builtin_surftex_should_be_template_class)
+          << Class;
+      return;
+    }
+    TD = SD->getSpecializedTemplate();
+  }
+
+  TemplateParameterList *Params = TD->getTemplateParameters();
+  unsigned N = Params->size();
+
+  if (N != 3) {
+    reportIllegalClassTemplate(S, TD);
+    S.Diag(TD->getLocation(),
+           diag::note_cuda_device_builtin_surftex_cls_should_have_n_args)
+        << TD << 3;
+  }
+  if (N > 0 && !isa<TemplateTypeParmDecl>(Params->getParam(0))) {
+    reportIllegalClassTemplate(S, TD);
+    S.Diag(TD->getLocation(),
+           diag::note_cuda_device_builtin_surftex_cls_should_have_match_arg)
+        << TD << /*1st*/ 0 << /*type*/ 0;
+  }
+  if (N > 1) {
+    auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(Params->getParam(1));
+    if (!NTTP || !NTTP->getType()->isIntegralOrEnumerationType()) {
+      reportIllegalClassTemplate(S, TD);
+      S.Diag(TD->getLocation(),
+             diag::note_cuda_device_builtin_surftex_cls_should_have_match_arg)
+          << TD << /*2nd*/ 1 << /*integer*/ 1;
+    }
+  }
+  if (N > 2) {
+    auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(Params->getParam(2));
+    if (!NTTP || !NTTP->getType()->isIntegralOrEnumerationType()) {
+      reportIllegalClassTemplate(S, TD);
+      S.Diag(TD->getLocation(),
+             diag::note_cuda_device_builtin_surftex_cls_should_have_match_arg)
+          << TD << /*3rd*/ 2 << /*integer*/ 1;
+    }
+  }
+}
+
+void Sema::checkClassLevelCodeSegAttribute(CXXRecordDecl *Class) {
+  // Mark any compiler-generated routines with the implicit code_seg attribute.
+  for (auto *Method : Class->methods()) {
+    if (Method->isUserProvided())
+      continue;
+    if (Attr *A = getImplicitCodeSegOrSectionAttrForFunction(Method, /*IsDefinition=*/true))
+      Method->addAttr(A);
+  }
+}
+
+/// Check class-level dllimport/dllexport attribute.
+void Sema::checkClassLevelDLLAttribute(CXXRecordDecl *Class) {
+  Attr *ClassAttr = getDLLAttr(Class);
+
+  // MSVC inherits DLL attributes to partial class template specializations.
+  if (Context.getTargetInfo().shouldDLLImportComdatSymbols() && !ClassAttr) {
+    if (auto *Spec = dyn_cast<ClassTemplatePartialSpecializationDecl>(Class)) {
+      if (Attr *TemplateAttr =
+              getDLLAttr(Spec->getSpecializedTemplate()->getTemplatedDecl())) {
+        auto *A = cast<InheritableAttr>(TemplateAttr->clone(getASTContext()));
+        A->setInherited(true);
+        ClassAttr = A;
+      }
+    }
+  }
+
+  if (!ClassAttr)
+    return;
+
+  if (!Class->isExternallyVisible()) {
+    Diag(Class->getLocation(), diag::err_attribute_dll_not_extern)
+        << Class << ClassAttr;
+    return;
+  }
+
+  if (Context.getTargetInfo().shouldDLLImportComdatSymbols() &&
+      !ClassAttr->isInherited()) {
+    // Diagnose dll attributes on members of class with dll attribute.
+    for (Decl *Member : Class->decls()) {
+      if (!isa<VarDecl>(Member) && !isa<CXXMethodDecl>(Member))
+        continue;
+      InheritableAttr *MemberAttr = getDLLAttr(Member);
+      if (!MemberAttr || MemberAttr->isInherited() || Member->isInvalidDecl())
+        continue;
+
+      Diag(MemberAttr->getLocation(),
+             diag::err_attribute_dll_member_of_dll_class)
+          << MemberAttr << ClassAttr;
+      Diag(ClassAttr->getLocation(), diag::note_previous_attribute);
+      Member->setInvalidDecl();
+    }
+  }
+
+  if (Class->getDescribedClassTemplate())
+    // Don't inherit dll attribute until the template is instantiated.
+    return;
+
+  // The class is either imported or exported.
+  const bool ClassExported = ClassAttr->getKind() == attr::DLLExport;
+
+  // Check if this was a dllimport attribute propagated from a derived class to
+  // a base class template specialization. We don't apply these attributes to
+  // static data members.
+  const bool PropagatedImport =
+      !ClassExported &&
+      cast<DLLImportAttr>(ClassAttr)->wasPropagatedToBaseTemplate();
+
+  TemplateSpecializationKind TSK = Class->getTemplateSpecializationKind();
+
+  // Ignore explicit dllexport on explicit class template instantiation
+  // declarations, except in MinGW mode.
+  if (ClassExported && !ClassAttr->isInherited() &&
+      TSK == TSK_ExplicitInstantiationDeclaration &&
+      !Context.getTargetInfo().getTriple().isWindowsGNUEnvironment()) {
+    Class->dropAttr<DLLExportAttr>();
+    return;
+  }
+
+  // Force declaration of implicit members so they can inherit the attribute.
+  ForceDeclarationOfImplicitMembers(Class);
+
+  // FIXME: MSVC's docs say all bases must be exportable, but this doesn't
+  // seem to be true in practice?
+
+  for (Decl *Member : Class->decls()) {
+    VarDecl *VD = dyn_cast<VarDecl>(Member);
+    CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Member);
+
+    // Only methods and static fields inherit the attributes.
+    if (!VD && !MD)
+      continue;
+
+    if (MD) {
+      // Don't process deleted methods.
+      if (MD->isDeleted())
+        continue;
+
+      if (MD->isInlined()) {
+        // MinGW does not import or export inline methods. But do it for
+        // template instantiations.
+        if (!Context.getTargetInfo().shouldDLLImportComdatSymbols() &&
+            TSK != TSK_ExplicitInstantiationDeclaration &&
+            TSK != TSK_ExplicitInstantiationDefinition)
+          continue;
+
+        // MSVC versions before 2015 don't export the move assignment operators
+        // and move constructor, so don't attempt to import/export them if
+        // we have a definition.
+        auto *Ctor = dyn_cast<CXXConstructorDecl>(MD);
+        if ((MD->isMoveAssignmentOperator() ||
+             (Ctor && Ctor->isMoveConstructor())) &&
+            !getLangOpts().isCompatibleWithMSVC(LangOptions::MSVC2015))
+          continue;
+
+        // MSVC2015 doesn't export trivial defaulted x-tor but copy assign
+        // operator is exported anyway.
+        if (getLangOpts().isCompatibleWithMSVC(LangOptions::MSVC2015) &&
+            (Ctor || isa<CXXDestructorDecl>(MD)) && MD->isTrivial())
+          continue;
+      }
+    }
+
+    // Don't apply dllimport attributes to static data members of class template
+    // instantiations when the attribute is propagated from a derived class.
+    if (VD && PropagatedImport)
+      continue;
+
+    if (!cast<NamedDecl>(Member)->isExternallyVisible())
+      continue;
+
+    if (!getDLLAttr(Member)) {
+      InheritableAttr *NewAttr = nullptr;
+
+      // Do not export/import inline function when -fno-dllexport-inlines is
+      // passed. But add attribute for later local static var check.
+      if (!getLangOpts().DllExportInlines && MD && MD->isInlined() &&
+          TSK != TSK_ExplicitInstantiationDeclaration &&
+          TSK != TSK_ExplicitInstantiationDefinition) {
+        if (ClassExported) {
+          NewAttr = ::new (getASTContext())
+              DLLExportStaticLocalAttr(getASTContext(), *ClassAttr);
+        } else {
+          NewAttr = ::new (getASTContext())
+              DLLImportStaticLocalAttr(getASTContext(), *ClassAttr);
+        }
+      } else {
+        NewAttr = cast<InheritableAttr>(ClassAttr->clone(getASTContext()));
+      }
+
+      NewAttr->setInherited(true);
+      Member->addAttr(NewAttr);
+
+      if (MD) {
+        // Propagate DLLAttr to friend re-declarations of MD that have already
+        // been constructed.
+        for (FunctionDecl *FD = MD->getMostRecentDecl(); FD;
+             FD = FD->getPreviousDecl()) {
+          if (FD->getFriendObjectKind() == Decl::FOK_None)
+            continue;
+          assert(!getDLLAttr(FD) &&
+                 "friend re-decl should not already have a DLLAttr");
+          NewAttr = cast<InheritableAttr>(ClassAttr->clone(getASTContext()));
+          NewAttr->setInherited(true);
+          FD->addAttr(NewAttr);
+        }
+      }
+    }
+  }
+
+  if (ClassExported)
+    DelayedDllExportClasses.push_back(Class);
+}
+
+/// Perform propagation of DLL attributes from a derived class to a
+/// templated base class for MS compatibility.
+void Sema::propagateDLLAttrToBaseClassTemplate(
+    CXXRecordDecl *Class, Attr *ClassAttr,
+    ClassTemplateSpecializationDecl *BaseTemplateSpec, SourceLocation BaseLoc) {
+  if (getDLLAttr(
+          BaseTemplateSpec->getSpecializedTemplate()->getTemplatedDecl())) {
+    // If the base class template has a DLL attribute, don't try to change it.
+    return;
+  }
+
+  auto TSK = BaseTemplateSpec->getSpecializationKind();
+  if (!getDLLAttr(BaseTemplateSpec) &&
+      (TSK == TSK_Undeclared || TSK == TSK_ExplicitInstantiationDeclaration ||
+       TSK == TSK_ImplicitInstantiation)) {
+    // The template hasn't been instantiated yet (or it has, but only as an
+    // explicit instantiation declaration or implicit instantiation, which means
+    // we haven't codegenned any members yet), so propagate the attribute.
+    auto *NewAttr = cast<InheritableAttr>(ClassAttr->clone(getASTContext()));
+    NewAttr->setInherited(true);
+    BaseTemplateSpec->addAttr(NewAttr);
+
+    // If this was an import, mark that we propagated it from a derived class to
+    // a base class template specialization.
+    if (auto *ImportAttr = dyn_cast<DLLImportAttr>(NewAttr))
+      ImportAttr->setPropagatedToBaseTemplate();
+
+    // If the template is already instantiated, checkDLLAttributeRedeclaration()
+    // needs to be run again to work see the new attribute. Otherwise this will
+    // get run whenever the template is instantiated.
+    if (TSK != TSK_Undeclared)
+      checkClassLevelDLLAttribute(BaseTemplateSpec);
+
+    return;
+  }
+
+  if (getDLLAttr(BaseTemplateSpec)) {
+    // The template has already been specialized or instantiated with an
+    // attribute, explicitly or through propagation. We should not try to change
+    // it.
+    return;
+  }
+
+  // The template was previously instantiated or explicitly specialized without
+  // a dll attribute, It's too late for us to add an attribute, so warn that
+  // this is unsupported.
+  Diag(BaseLoc, diag::warn_attribute_dll_instantiated_base_class)
+      << BaseTemplateSpec->isExplicitSpecialization();
+  Diag(ClassAttr->getLocation(), diag::note_attribute);
+  if (BaseTemplateSpec->isExplicitSpecialization()) {
+    Diag(BaseTemplateSpec->getLocation(),
+           diag::note_template_class_explicit_specialization_was_here)
+        << BaseTemplateSpec;
+  } else {
+    Diag(BaseTemplateSpec->getPointOfInstantiation(),
+           diag::note_template_class_instantiation_was_here)
+        << BaseTemplateSpec;
+  }
+}
+
+/// Determine the kind of defaulting that would be done for a given function.
+///
+/// If the function is both a default constructor and a copy / move constructor
+/// (due to having a default argument for the first parameter), this picks
+/// CXXDefaultConstructor.
+///
+/// FIXME: Check that case is properly handled by all callers.
+Sema::DefaultedFunctionKind
+Sema::getDefaultedFunctionKind(const FunctionDecl *FD) {
+  if (auto *MD = dyn_cast<CXXMethodDecl>(FD)) {
+    if (const CXXConstructorDecl *Ctor = dyn_cast<CXXConstructorDecl>(FD)) {
+      if (Ctor->isDefaultConstructor())
+        return Sema::CXXDefaultConstructor;
+
+      if (Ctor->isCopyConstructor())
+        return Sema::CXXCopyConstructor;
+
+      if (Ctor->isMoveConstructor())
+        return Sema::CXXMoveConstructor;
+    }
+
+    if (MD->isCopyAssignmentOperator())
+      return Sema::CXXCopyAssignment;
+
+    if (MD->isMoveAssignmentOperator())
+      return Sema::CXXMoveAssignment;
+
+    if (isa<CXXDestructorDecl>(FD))
+      return Sema::CXXDestructor;
+  }
+
+  switch (FD->getDeclName().getCXXOverloadedOperator()) {
+  case OO_EqualEqual:
+    return DefaultedComparisonKind::Equal;
+
+  case OO_ExclaimEqual:
+    return DefaultedComparisonKind::NotEqual;
+
+  case OO_Spaceship:
+    // No point allowing this if <=> doesn't exist in the current language mode.
+    if (!getLangOpts().CPlusPlus20)
+      break;
+    return DefaultedComparisonKind::ThreeWay;
+
+  case OO_Less:
+  case OO_LessEqual:
+  case OO_Greater:
+  case OO_GreaterEqual:
+    // No point allowing this if <=> doesn't exist in the current language mode.
+    if (!getLangOpts().CPlusPlus20)
+      break;
+    return DefaultedComparisonKind::Relational;
+
+  default:
+    break;
+  }
+
+  // Not defaultable.
+  return DefaultedFunctionKind();
+}
+
+static void DefineDefaultedFunction(Sema &S, FunctionDecl *FD,
+                                    SourceLocation DefaultLoc) {
+  Sema::DefaultedFunctionKind DFK = S.getDefaultedFunctionKind(FD);
+  if (DFK.isComparison())
+    return S.DefineDefaultedComparison(DefaultLoc, FD, DFK.asComparison());
+
+  switch (DFK.asSpecialMember()) {
+  case Sema::CXXDefaultConstructor:
+    S.DefineImplicitDefaultConstructor(DefaultLoc,
+                                       cast<CXXConstructorDecl>(FD));
+    break;
+  case Sema::CXXCopyConstructor:
+    S.DefineImplicitCopyConstructor(DefaultLoc, cast<CXXConstructorDecl>(FD));
+    break;
+  case Sema::CXXCopyAssignment:
+    S.DefineImplicitCopyAssignment(DefaultLoc, cast<CXXMethodDecl>(FD));
+    break;
+  case Sema::CXXDestructor:
+    S.DefineImplicitDestructor(DefaultLoc, cast<CXXDestructorDecl>(FD));
+    break;
+  case Sema::CXXMoveConstructor:
+    S.DefineImplicitMoveConstructor(DefaultLoc, cast<CXXConstructorDecl>(FD));
+    break;
+  case Sema::CXXMoveAssignment:
+    S.DefineImplicitMoveAssignment(DefaultLoc, cast<CXXMethodDecl>(FD));
+    break;
+  case Sema::CXXInvalid:
+    llvm_unreachable("Invalid special member.");
+  }
+}
+
+/// Determine whether a type is permitted to be passed or returned in
+/// registers, per C++ [class.temporary]p3.
+static bool canPassInRegisters(Sema &S, CXXRecordDecl *D,
+                               TargetInfo::CallingConvKind CCK) {
+  if (D->isDependentType() || D->isInvalidDecl())
+    return false;
+
+  // Clang <= 4 used the pre-C++11 rule, which ignores move operations.
+  // The PS4 platform ABI follows the behavior of Clang 3.2.
+  if (CCK == TargetInfo::CCK_ClangABI4OrPS4)
+    return !D->hasNonTrivialDestructorForCall() &&
+           !D->hasNonTrivialCopyConstructorForCall();
+
+  if (CCK == TargetInfo::CCK_MicrosoftWin64) {
+    bool CopyCtorIsTrivial = false, CopyCtorIsTrivialForCall = false;
+    bool DtorIsTrivialForCall = false;
+
+    // If a class has at least one non-deleted, trivial copy constructor, it
+    // is passed according to the C ABI. Otherwise, it is passed indirectly.
+    //
+    // Note: This permits classes with non-trivial copy or move ctors to be
+    // passed in registers, so long as they *also* have a trivial copy ctor,
+    // which is non-conforming.
+    if (D->needsImplicitCopyConstructor()) {
+      if (!D->defaultedCopyConstructorIsDeleted()) {
+        if (D->hasTrivialCopyConstructor())
+          CopyCtorIsTrivial = true;
+        if (D->hasTrivialCopyConstructorForCall())
+          CopyCtorIsTrivialForCall = true;
+      }
+    } else {
+      for (const CXXConstructorDecl *CD : D->ctors()) {
+        if (CD->isCopyConstructor() && !CD->isDeleted()) {
+          if (CD->isTrivial())
+            CopyCtorIsTrivial = true;
+          if (CD->isTrivialForCall())
+            CopyCtorIsTrivialForCall = true;
+        }
+      }
+    }
+
+    if (D->needsImplicitDestructor()) {
+      if (!D->defaultedDestructorIsDeleted() &&
+          D->hasTrivialDestructorForCall())
+        DtorIsTrivialForCall = true;
+    } else if (const auto *DD = D->getDestructor()) {
+      if (!DD->isDeleted() && DD->isTrivialForCall())
+        DtorIsTrivialForCall = true;
+    }
+
+    // If the copy ctor and dtor are both trivial-for-calls, pass direct.
+    if (CopyCtorIsTrivialForCall && DtorIsTrivialForCall)
+      return true;
+
+    // If a class has a destructor, we'd really like to pass it indirectly
+    // because it allows us to elide copies.  Unfortunately, MSVC makes that
+    // impossible for small types, which it will pass in a single register or
+    // stack slot. Most objects with dtors are large-ish, so handle that early.
+    // We can't call out all large objects as being indirect because there are
+    // multiple x64 calling conventions and the C++ ABI code shouldn't dictate
+    // how we pass large POD types.
+
+    // Note: This permits small classes with nontrivial destructors to be
+    // passed in registers, which is non-conforming.
+    bool isAArch64 = S.Context.getTargetInfo().getTriple().isAArch64();
+    uint64_t TypeSize = isAArch64 ? 128 : 64;
+
+    if (CopyCtorIsTrivial &&
+        S.getASTContext().getTypeSize(D->getTypeForDecl()) <= TypeSize)
+      return true;
+    return false;
+  }
+
+  // Per C++ [class.temporary]p3, the relevant condition is:
+  //   each copy constructor, move constructor, and destructor of X is
+  //   either trivial or deleted, and X has at least one non-deleted copy
+  //   or move constructor
+  bool HasNonDeletedCopyOrMove = false;
+
+  if (D->needsImplicitCopyConstructor() &&
+      !D->defaultedCopyConstructorIsDeleted()) {
+    if (!D->hasTrivialCopyConstructorForCall())
+      return false;
+    HasNonDeletedCopyOrMove = true;
+  }
+
+  if (S.getLangOpts().CPlusPlus11 && D->needsImplicitMoveConstructor() &&
+      !D->defaultedMoveConstructorIsDeleted()) {
+    if (!D->hasTrivialMoveConstructorForCall())
+      return false;
+    HasNonDeletedCopyOrMove = true;
+  }
+
+  if (D->needsImplicitDestructor() && !D->defaultedDestructorIsDeleted() &&
+      !D->hasTrivialDestructorForCall())
+    return false;
+
+  for (const CXXMethodDecl *MD : D->methods()) {
+    if (MD->isDeleted())
+      continue;
+
+    auto *CD = dyn_cast<CXXConstructorDecl>(MD);
+    if (CD && CD->isCopyOrMoveConstructor())
+      HasNonDeletedCopyOrMove = true;
+    else if (!isa<CXXDestructorDecl>(MD))
+      continue;
+
+    if (!MD->isTrivialForCall())
+      return false;
+  }
+
+  return HasNonDeletedCopyOrMove;
+}
+
+/// Report an error regarding overriding, along with any relevant
+/// overridden methods.
+///
+/// \param DiagID the primary error to report.
+/// \param MD the overriding method.
+static bool
+ReportOverrides(Sema &S, unsigned DiagID, const CXXMethodDecl *MD,
+                llvm::function_ref<bool(const CXXMethodDecl *)> Report) {
+  bool IssuedDiagnostic = false;
+  for (const CXXMethodDecl *O : MD->overridden_methods()) {
+    if (Report(O)) {
+      if (!IssuedDiagnostic) {
+        S.Diag(MD->getLocation(), DiagID) << MD->getDeclName();
+        IssuedDiagnostic = true;
+      }
+      S.Diag(O->getLocation(), diag::note_overridden_virtual_function);
+    }
+  }
+  return IssuedDiagnostic;
+}
+
+/// Perform semantic checks on a class definition that has been
+/// completing, introducing implicitly-declared members, checking for
+/// abstract types, etc.
+///
+/// \param S The scope in which the class was parsed. Null if we didn't just
+///        parse a class definition.
+/// \param Record The completed class.
+void Sema::CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record) {
+  if (!Record)
+    return;
+
+  if (Record->isAbstract() && !Record->isInvalidDecl()) {
+    AbstractUsageInfo Info(*this, Record);
+    CheckAbstractClassUsage(Info, Record);
+  }
+
+  // If this is not an aggregate type and has no user-declared constructor,
+  // complain about any non-static data members of reference or const scalar
+  // type, since they will never get initializers.
+  if (!Record->isInvalidDecl() && !Record->isDependentType() &&
+      !Record->isAggregate() && !Record->hasUserDeclaredConstructor() &&
+      !Record->isLambda()) {
+    bool Complained = false;
+    for (const auto *F : Record->fields()) {
+      if (F->hasInClassInitializer() || F->isUnnamedBitfield())
+        continue;
+
+      if (F->getType()->isReferenceType() ||
+          (F->getType().isConstQualified() && F->getType()->isScalarType())) {
+        if (!Complained) {
+          Diag(Record->getLocation(), diag::warn_no_constructor_for_refconst)
+            << Record->getTagKind() << Record;
+          Complained = true;
+        }
+
+        Diag(F->getLocation(), diag::note_refconst_member_not_initialized)
+          << F->getType()->isReferenceType()
+          << F->getDeclName();
+      }
+    }
+  }
+
+  if (Record->getIdentifier()) {
+    // C++ [class.mem]p13:
+    //   If T is the name of a class, then each of the following shall have a
+    //   name different from T:
+    //     - every member of every anonymous union that is a member of class T.
+    //
+    // C++ [class.mem]p14:
+    //   In addition, if class T has a user-declared constructor (12.1), every
+    //   non-static data member of class T shall have a name different from T.
+    DeclContext::lookup_result R = Record->lookup(Record->getDeclName());
+    for (DeclContext::lookup_iterator I = R.begin(), E = R.end(); I != E;
+         ++I) {
+      NamedDecl *D = (*I)->getUnderlyingDecl();
+      if (((isa<FieldDecl>(D) || isa<UnresolvedUsingValueDecl>(D)) &&
+           Record->hasUserDeclaredConstructor()) ||
+          isa<IndirectFieldDecl>(D)) {
+        Diag((*I)->getLocation(), diag::err_member_name_of_class)
+          << D->getDeclName();
+        break;
+      }
+    }
+  }
+
+  // Warn if the class has virtual methods but non-virtual public destructor.
+  if (Record->isPolymorphic() && !Record->isDependentType()) {
+    CXXDestructorDecl *dtor = Record->getDestructor();
+    if ((!dtor || (!dtor->isVirtual() && dtor->getAccess() == AS_public)) &&
+        !Record->hasAttr<FinalAttr>())
+      Diag(dtor ? dtor->getLocation() : Record->getLocation(),
+           diag::warn_non_virtual_dtor) << Context.getRecordType(Record);
+  }
+
+  if (Record->isAbstract()) {
+    if (FinalAttr *FA = Record->getAttr<FinalAttr>()) {
+      Diag(Record->getLocation(), diag::warn_abstract_final_class)
+        << FA->isSpelledAsSealed();
+      DiagnoseAbstractType(Record);
+    }
+  }
+
+  // Warn if the class has a final destructor but is not itself marked final.
+  if (!Record->hasAttr<FinalAttr>()) {
+    if (const CXXDestructorDecl *dtor = Record->getDestructor()) {
+      if (const FinalAttr *FA = dtor->getAttr<FinalAttr>()) {
+        Diag(FA->getLocation(), diag::warn_final_dtor_non_final_class)
+            << FA->isSpelledAsSealed()
+            << FixItHint::CreateInsertion(
+                   getLocForEndOfToken(Record->getLocation()),
+                   (FA->isSpelledAsSealed() ? " sealed" : " final"));
+        Diag(Record->getLocation(),
+             diag::note_final_dtor_non_final_class_silence)
+            << Context.getRecordType(Record) << FA->isSpelledAsSealed();
+      }
+    }
+  }
+
+  // See if trivial_abi has to be dropped.
+  if (Record->hasAttr<TrivialABIAttr>())
+    checkIllFormedTrivialABIStruct(*Record);
+
+  // Set HasTrivialSpecialMemberForCall if the record has attribute
+  // "trivial_abi".
+  bool HasTrivialABI = Record->hasAttr<TrivialABIAttr>();
+
+  if (HasTrivialABI)
+    Record->setHasTrivialSpecialMemberForCall();
+
+  // Explicitly-defaulted secondary comparison functions (!=, <, <=, >, >=).
+  // We check these last because they can depend on the properties of the
+  // primary comparison functions (==, <=>).
+  llvm::SmallVector<FunctionDecl*, 5> DefaultedSecondaryComparisons;
+
+  // Perform checks that can't be done until we know all the properties of a
+  // member function (whether it's defaulted, deleted, virtual, overriding,
+  // ...).
+  auto CheckCompletedMemberFunction = [&](CXXMethodDecl *MD) {
+    // A static function cannot override anything.
+    if (MD->getStorageClass() == SC_Static) {
+      if (ReportOverrides(*this, diag::err_static_overrides_virtual, MD,
+                          [](const CXXMethodDecl *) { return true; }))
+        return;
+    }
+
+    // A deleted function cannot override a non-deleted function and vice
+    // versa.
+    if (ReportOverrides(*this,
+                        MD->isDeleted() ? diag::err_deleted_override
+                                        : diag::err_non_deleted_override,
+                        MD, [&](const CXXMethodDecl *V) {
+                          return MD->isDeleted() != V->isDeleted();
+                        })) {
+      if (MD->isDefaulted() && MD->isDeleted())
+        // Explain why this defaulted function was deleted.
+        DiagnoseDeletedDefaultedFunction(MD);
+      return;
+    }
+
+    // A consteval function cannot override a non-consteval function and vice
+    // versa.
+    if (ReportOverrides(*this,
+                        MD->isConsteval() ? diag::err_consteval_override
+                                          : diag::err_non_consteval_override,
+                        MD, [&](const CXXMethodDecl *V) {
+                          return MD->isConsteval() != V->isConsteval();
+                        })) {
+      if (MD->isDefaulted() && MD->isDeleted())
+        // Explain why this defaulted function was deleted.
+        DiagnoseDeletedDefaultedFunction(MD);
+      return;
+    }
+  };
+
+  auto CheckForDefaultedFunction = [&](FunctionDecl *FD) -> bool {
+    if (!FD || FD->isInvalidDecl() || !FD->isExplicitlyDefaulted())
+      return false;
+
+    DefaultedFunctionKind DFK = getDefaultedFunctionKind(FD);
+    if (DFK.asComparison() == DefaultedComparisonKind::NotEqual ||
+        DFK.asComparison() == DefaultedComparisonKind::Relational) {
+      DefaultedSecondaryComparisons.push_back(FD);
+      return true;
+    }
+
+    CheckExplicitlyDefaultedFunction(S, FD);
+    return false;
+  };
+
+  auto CompleteMemberFunction = [&](CXXMethodDecl *M) {
+    // Check whether the explicitly-defaulted members are valid.
+    bool Incomplete = CheckForDefaultedFunction(M);
+
+    // Skip the rest of the checks for a member of a dependent class.
+    if (Record->isDependentType())
+      return;
+
+    // For an explicitly defaulted or deleted special member, we defer
+    // determining triviality until the class is complete. That time is now!
+    CXXSpecialMember CSM = getSpecialMember(M);
+    if (!M->isImplicit() && !M->isUserProvided()) {
+      if (CSM != CXXInvalid) {
+        M->setTrivial(SpecialMemberIsTrivial(M, CSM));
+        // Inform the class that we've finished declaring this member.
+        Record->finishedDefaultedOrDeletedMember(M);
+        M->setTrivialForCall(
+            HasTrivialABI ||
+            SpecialMemberIsTrivial(M, CSM, TAH_ConsiderTrivialABI));
+        Record->setTrivialForCallFlags(M);
+      }
+    }
+
+    // Set triviality for the purpose of calls if this is a user-provided
+    // copy/move constructor or destructor.
+    if ((CSM == CXXCopyConstructor || CSM == CXXMoveConstructor ||
+         CSM == CXXDestructor) && M->isUserProvided()) {
+      M->setTrivialForCall(HasTrivialABI);
+      Record->setTrivialForCallFlags(M);
+    }
+
+    if (!M->isInvalidDecl() && M->isExplicitlyDefaulted() &&
+        M->hasAttr<DLLExportAttr>()) {
+      if (getLangOpts().isCompatibleWithMSVC(LangOptions::MSVC2015) &&
+          M->isTrivial() &&
+          (CSM == CXXDefaultConstructor || CSM == CXXCopyConstructor ||
+           CSM == CXXDestructor))
+        M->dropAttr<DLLExportAttr>();
+
+      if (M->hasAttr<DLLExportAttr>()) {
+        // Define after any fields with in-class initializers have been parsed.
+        DelayedDllExportMemberFunctions.push_back(M);
+      }
+    }
+
+    // Define defaulted constexpr virtual functions that override a base class
+    // function right away.
+    // FIXME: We can defer doing this until the vtable is marked as used.
+    if (M->isDefaulted() && M->isConstexpr() && M->size_overridden_methods())
+      DefineDefaultedFunction(*this, M, M->getLocation());
+
+    if (!Incomplete)
+      CheckCompletedMemberFunction(M);
+  };
+
+  // Check the destructor before any other member function. We need to
+  // determine whether it's trivial in order to determine whether the claas
+  // type is a literal type, which is a prerequisite for determining whether
+  // other special member functions are valid and whether they're implicitly
+  // 'constexpr'.
+  if (CXXDestructorDecl *Dtor = Record->getDestructor())
+    CompleteMemberFunction(Dtor);
+
+  bool HasMethodWithOverrideControl = false,
+       HasOverridingMethodWithoutOverrideControl = false;
+  for (auto *D : Record->decls()) {
+    if (auto *M = dyn_cast<CXXMethodDecl>(D)) {
+      // FIXME: We could do this check for dependent types with non-dependent
+      // bases.
+      if (!Record->isDependentType()) {
+        // See if a method overloads virtual methods in a base
+        // class without overriding any.
+        if (!M->isStatic())
+          DiagnoseHiddenVirtualMethods(M);
+        if (M->hasAttr<OverrideAttr>())
+          HasMethodWithOverrideControl = true;
+        else if (M->size_overridden_methods() > 0)
+          HasOverridingMethodWithoutOverrideControl = true;
+      }
+
+      if (!isa<CXXDestructorDecl>(M))
+        CompleteMemberFunction(M);
+    } else if (auto *F = dyn_cast<FriendDecl>(D)) {
+      CheckForDefaultedFunction(
+          dyn_cast_or_null<FunctionDecl>(F->getFriendDecl()));
+    }
+  }
+
+  if (HasOverridingMethodWithoutOverrideControl) {
+    bool HasInconsistentOverrideControl = HasMethodWithOverrideControl;
+    for (auto *M : Record->methods())
+      DiagnoseAbsenceOfOverrideControl(M, HasInconsistentOverrideControl);
+  }
+
+  // Check the defaulted secondary comparisons after any other member functions.
+  for (FunctionDecl *FD : DefaultedSecondaryComparisons) {
+    CheckExplicitlyDefaultedFunction(S, FD);
+
+    // If this is a member function, we deferred checking it until now.
+    if (auto *MD = dyn_cast<CXXMethodDecl>(FD))
+      CheckCompletedMemberFunction(MD);
+  }
+
+  // ms_struct is a request to use the same ABI rules as MSVC.  Check
+  // whether this class uses any C++ features that are implemented
+  // completely differently in MSVC, and if so, emit a diagnostic.
+  // That diagnostic defaults to an error, but we allow projects to
+  // map it down to a warning (or ignore it).  It's a fairly common
+  // practice among users of the ms_struct pragma to mass-annotate
+  // headers, sweeping up a bunch of types that the project doesn't
+  // really rely on MSVC-compatible layout for.  We must therefore
+  // support "ms_struct except for C++ stuff" as a secondary ABI.
+  // Don't emit this diagnostic if the feature was enabled as a
+  // language option (as opposed to via a pragma or attribute), as
+  // the option -mms-bitfields otherwise essentially makes it impossible
+  // to build C++ code, unless this diagnostic is turned off.
+  if (Record->isMsStruct(Context) && !Context.getLangOpts().MSBitfields &&
+      (Record->isPolymorphic() || Record->getNumBases())) {
+    Diag(Record->getLocation(), diag::warn_cxx_ms_struct);
+  }
+
+  checkClassLevelDLLAttribute(Record);
+  checkClassLevelCodeSegAttribute(Record);
+
+  bool ClangABICompat4 =
+      Context.getLangOpts().getClangABICompat() <= LangOptions::ClangABI::Ver4;
+  TargetInfo::CallingConvKind CCK =
+      Context.getTargetInfo().getCallingConvKind(ClangABICompat4);
+  bool CanPass = canPassInRegisters(*this, Record, CCK);
+
+  // Do not change ArgPassingRestrictions if it has already been set to
+  // APK_CanNeverPassInRegs.
+  if (Record->getArgPassingRestrictions() != RecordDecl::APK_CanNeverPassInRegs)
+    Record->setArgPassingRestrictions(CanPass
+                                          ? RecordDecl::APK_CanPassInRegs
+                                          : RecordDecl::APK_CannotPassInRegs);
+
+  // If canPassInRegisters returns true despite the record having a non-trivial
+  // destructor, the record is destructed in the callee. This happens only when
+  // the record or one of its subobjects has a field annotated with trivial_abi
+  // or a field qualified with ObjC __strong/__weak.
+  if (Context.getTargetInfo().getCXXABI().areArgsDestroyedLeftToRightInCallee())
+    Record->setParamDestroyedInCallee(true);
+  else if (Record->hasNonTrivialDestructor())
+    Record->setParamDestroyedInCallee(CanPass);
+
+  if (getLangOpts().ForceEmitVTables) {
+    // If we want to emit all the vtables, we need to mark it as used.  This
+    // is especially required for cases like vtable assumption loads.
+    MarkVTableUsed(Record->getInnerLocStart(), Record);
+  }
+
+  if (getLangOpts().CUDA) {
+    if (Record->hasAttr<CUDADeviceBuiltinSurfaceTypeAttr>())
+      checkCUDADeviceBuiltinSurfaceClassTemplate(*this, Record);
+    else if (Record->hasAttr<CUDADeviceBuiltinTextureTypeAttr>())
+      checkCUDADeviceBuiltinTextureClassTemplate(*this, Record);
+  }
+}
+
+/// Look up the special member function that would be called by a special
+/// member function for a subobject of class type.
+///
+/// \param Class The class type of the subobject.
+/// \param CSM The kind of special member function.
+/// \param FieldQuals If the subobject is a field, its cv-qualifiers.
+/// \param ConstRHS True if this is a copy operation with a const object
+///        on its RHS, that is, if the argument to the outer special member
+///        function is 'const' and this is not a field marked 'mutable'.
+static Sema::SpecialMemberOverloadResult lookupCallFromSpecialMember(
+    Sema &S, CXXRecordDecl *Class, Sema::CXXSpecialMember CSM,
+    unsigned FieldQuals, bool ConstRHS) {
+  unsigned LHSQuals = 0;
+  if (CSM == Sema::CXXCopyAssignment || CSM == Sema::CXXMoveAssignment)
+    LHSQuals = FieldQuals;
+
+  unsigned RHSQuals = FieldQuals;
+  if (CSM == Sema::CXXDefaultConstructor || CSM == Sema::CXXDestructor)
+    RHSQuals = 0;
+  else if (ConstRHS)
+    RHSQuals |= Qualifiers::Const;
+
+  return S.LookupSpecialMember(Class, CSM,
+                               RHSQuals & Qualifiers::Const,
+                               RHSQuals & Qualifiers::Volatile,
+                               false,
+                               LHSQuals & Qualifiers::Const,
+                               LHSQuals & Qualifiers::Volatile);
+}
+
+class Sema::InheritedConstructorInfo {
+  Sema &S;
+  SourceLocation UseLoc;
+
+  /// A mapping from the base classes through which the constructor was
+  /// inherited to the using shadow declaration in that base class (or a null
+  /// pointer if the constructor was declared in that base class).
+  llvm::DenseMap<CXXRecordDecl *, ConstructorUsingShadowDecl *>
+      InheritedFromBases;
+
+public:
+  InheritedConstructorInfo(Sema &S, SourceLocation UseLoc,
+                           ConstructorUsingShadowDecl *Shadow)
+      : S(S), UseLoc(UseLoc) {
+    bool DiagnosedMultipleConstructedBases = false;
+    CXXRecordDecl *ConstructedBase = nullptr;
+    BaseUsingDecl *ConstructedBaseIntroducer = nullptr;
+
+    // Find the set of such base class subobjects and check that there's a
+    // unique constructed subobject.
+    for (auto *D : Shadow->redecls()) {
+      auto *DShadow = cast<ConstructorUsingShadowDecl>(D);
+      auto *DNominatedBase = DShadow->getNominatedBaseClass();
+      auto *DConstructedBase = DShadow->getConstructedBaseClass();
+
+      InheritedFromBases.insert(
+          std::make_pair(DNominatedBase->getCanonicalDecl(),
+                         DShadow->getNominatedBaseClassShadowDecl()));
+      if (DShadow->constructsVirtualBase())
+        InheritedFromBases.insert(
+            std::make_pair(DConstructedBase->getCanonicalDecl(),
+                           DShadow->getConstructedBaseClassShadowDecl()));
+      else
+        assert(DNominatedBase == DConstructedBase);
+
+      // [class.inhctor.init]p2:
+      //   If the constructor was inherited from multiple base class subobjects
+      //   of type B, the program is ill-formed.
+      if (!ConstructedBase) {
+        ConstructedBase = DConstructedBase;
+        ConstructedBaseIntroducer = D->getIntroducer();
+      } else if (ConstructedBase != DConstructedBase &&
+                 !Shadow->isInvalidDecl()) {
+        if (!DiagnosedMultipleConstructedBases) {
+          S.Diag(UseLoc, diag::err_ambiguous_inherited_constructor)
+              << Shadow->getTargetDecl();
+          S.Diag(ConstructedBaseIntroducer->getLocation(),
+                 diag::note_ambiguous_inherited_constructor_using)
+              << ConstructedBase;
+          DiagnosedMultipleConstructedBases = true;
+        }
+        S.Diag(D->getIntroducer()->getLocation(),
+               diag::note_ambiguous_inherited_constructor_using)
+            << DConstructedBase;
+      }
+    }
+
+    if (DiagnosedMultipleConstructedBases)
+      Shadow->setInvalidDecl();
+  }
+
+  /// Find the constructor to use for inherited construction of a base class,
+  /// and whether that base class constructor inherits the constructor from a
+  /// virtual base class (in which case it won't actually invoke it).
+  std::pair<CXXConstructorDecl *, bool>
+  findConstructorForBase(CXXRecordDecl *Base, CXXConstructorDecl *Ctor) const {
+    auto It = InheritedFromBases.find(Base->getCanonicalDecl());
+    if (It == InheritedFromBases.end())
+      return std::make_pair(nullptr, false);
+
+    // This is an intermediary class.
+    if (It->second)
+      return std::make_pair(
+          S.findInheritingConstructor(UseLoc, Ctor, It->second),
+          It->second->constructsVirtualBase());
+
+    // This is the base class from which the constructor was inherited.
+    return std::make_pair(Ctor, false);
+  }
+};
+
+/// Is the special member function which would be selected to perform the
+/// specified operation on the specified class type a constexpr constructor?
+static bool
+specialMemberIsConstexpr(Sema &S, CXXRecordDecl *ClassDecl,
+                         Sema::CXXSpecialMember CSM, unsigned Quals,
+                         bool ConstRHS,
+                         CXXConstructorDecl *InheritedCtor = nullptr,
+                         Sema::InheritedConstructorInfo *Inherited = nullptr) {
+  // If we're inheriting a constructor, see if we need to call it for this base
+  // class.
+  if (InheritedCtor) {
+    assert(CSM == Sema::CXXDefaultConstructor);
+    auto BaseCtor =
+        Inherited->findConstructorForBase(ClassDecl, InheritedCtor).first;
+    if (BaseCtor)
+      return BaseCtor->isConstexpr();
+  }
+
+  if (CSM == Sema::CXXDefaultConstructor)
+    return ClassDecl->hasConstexprDefaultConstructor();
+  if (CSM == Sema::CXXDestructor)
+    return ClassDecl->hasConstexprDestructor();
+
+  Sema::SpecialMemberOverloadResult SMOR =
+      lookupCallFromSpecialMember(S, ClassDecl, CSM, Quals, ConstRHS);
+  if (!SMOR.getMethod())
+    // A constructor we wouldn't select can't be "involved in initializing"
+    // anything.
+    return true;
+  return SMOR.getMethod()->isConstexpr();
+}
+
+/// Determine whether the specified special member function would be constexpr
+/// if it were implicitly defined.
+static bool defaultedSpecialMemberIsConstexpr(
+    Sema &S, CXXRecordDecl *ClassDecl, Sema::CXXSpecialMember CSM,
+    bool ConstArg, CXXConstructorDecl *InheritedCtor = nullptr,
+    Sema::InheritedConstructorInfo *Inherited = nullptr) {
+  if (!S.getLangOpts().CPlusPlus11)
+    return false;
+
+  // C++11 [dcl.constexpr]p4:
+  // In the definition of a constexpr constructor [...]
+  bool Ctor = true;
+  switch (CSM) {
+  case Sema::CXXDefaultConstructor:
+    if (Inherited)
+      break;
+    // Since default constructor lookup is essentially trivial (and cannot
+    // involve, for instance, template instantiation), we compute whether a
+    // defaulted default constructor is constexpr directly within CXXRecordDecl.
+    //
+    // This is important for performance; we need to know whether the default
+    // constructor is constexpr to determine whether the type is a literal type.
+    return ClassDecl->defaultedDefaultConstructorIsConstexpr();
+
+  case Sema::CXXCopyConstructor:
+  case Sema::CXXMoveConstructor:
+    // For copy or move constructors, we need to perform overload resolution.
+    break;
+
+  case Sema::CXXCopyAssignment:
+  case Sema::CXXMoveAssignment:
+    if (!S.getLangOpts().CPlusPlus14)
+      return false;
+    // In C++1y, we need to perform overload resolution.
+    Ctor = false;
+    break;
+
+  case Sema::CXXDestructor:
+    return ClassDecl->defaultedDestructorIsConstexpr();
+
+  case Sema::CXXInvalid:
+    return false;
+  }
+
+  //   -- if the class is a non-empty union, or for each non-empty anonymous
+  //      union member of a non-union class, exactly one non-static data member
+  //      shall be initialized; [DR1359]
+  //
+  // If we squint, this is guaranteed, since exactly one non-static data member
+  // will be initialized (if the constructor isn't deleted), we just don't know
+  // which one.
+  if (Ctor && ClassDecl->isUnion())
+    return CSM == Sema::CXXDefaultConstructor
+               ? ClassDecl->hasInClassInitializer() ||
+                     !ClassDecl->hasVariantMembers()
+               : true;
+
+  //   -- the class shall not have any virtual base classes;
+  if (Ctor && ClassDecl->getNumVBases())
+    return false;
+
+  // C++1y [class.copy]p26:
+  //   -- [the class] is a literal type, and
+  if (!Ctor && !ClassDecl->isLiteral())
+    return false;
+
+  //   -- every constructor involved in initializing [...] base class
+  //      sub-objects shall be a constexpr constructor;
+  //   -- the assignment operator selected to copy/move each direct base
+  //      class is a constexpr function, and
+  for (const auto &B : ClassDecl->bases()) {
+    const RecordType *BaseType = B.getType()->getAs<RecordType>();
+    if (!BaseType) continue;
+
+    CXXRecordDecl *BaseClassDecl = cast<CXXRecordDecl>(BaseType->getDecl());
+    if (!specialMemberIsConstexpr(S, BaseClassDecl, CSM, 0, ConstArg,
+                                  InheritedCtor, Inherited))
+      return false;
+  }
+
+  //   -- every constructor involved in initializing non-static data members
+  //      [...] shall be a constexpr constructor;
+  //   -- every non-static data member and base class sub-object shall be
+  //      initialized
+  //   -- for each non-static data member of X that is of class type (or array
+  //      thereof), the assignment operator selected to copy/move that member is
+  //      a constexpr function
+  for (const auto *F : ClassDecl->fields()) {
+    if (F->isInvalidDecl())
+      continue;
+    if (CSM == Sema::CXXDefaultConstructor && F->hasInClassInitializer())
+      continue;
+    QualType BaseType = S.Context.getBaseElementType(F->getType());
+    if (const RecordType *RecordTy = BaseType->getAs<RecordType>()) {
+      CXXRecordDecl *FieldRecDecl = cast<CXXRecordDecl>(RecordTy->getDecl());
+      if (!specialMemberIsConstexpr(S, FieldRecDecl, CSM,
+                                    BaseType.getCVRQualifiers(),
+                                    ConstArg && !F->isMutable()))
+        return false;
+    } else if (CSM == Sema::CXXDefaultConstructor) {
+      return false;
+    }
+  }
+
+  // All OK, it's constexpr!
+  return true;
+}
+
+namespace {
+/// RAII object to register a defaulted function as having its exception
+/// specification computed.
+struct ComputingExceptionSpec {
+  Sema &S;
+
+  ComputingExceptionSpec(Sema &S, FunctionDecl *FD, SourceLocation Loc)
+      : S(S) {
+    Sema::CodeSynthesisContext Ctx;
+    Ctx.Kind = Sema::CodeSynthesisContext::ExceptionSpecEvaluation;
+    Ctx.PointOfInstantiation = Loc;
+    Ctx.Entity = FD;
+    S.pushCodeSynthesisContext(Ctx);
+  }
+  ~ComputingExceptionSpec() {
+    S.popCodeSynthesisContext();
+  }
+};
+}
+
+static Sema::ImplicitExceptionSpecification
+ComputeDefaultedSpecialMemberExceptionSpec(
+    Sema &S, SourceLocation Loc, CXXMethodDecl *MD, Sema::CXXSpecialMember CSM,
+    Sema::InheritedConstructorInfo *ICI);
+
+static Sema::ImplicitExceptionSpecification
+ComputeDefaultedComparisonExceptionSpec(Sema &S, SourceLocation Loc,
+                                        FunctionDecl *FD,
+                                        Sema::DefaultedComparisonKind DCK);
+
+static Sema::ImplicitExceptionSpecification
+computeImplicitExceptionSpec(Sema &S, SourceLocation Loc, FunctionDecl *FD) {
+  auto DFK = S.getDefaultedFunctionKind(FD);
+  if (DFK.isSpecialMember())
+    return ComputeDefaultedSpecialMemberExceptionSpec(
+        S, Loc, cast<CXXMethodDecl>(FD), DFK.asSpecialMember(), nullptr);
+  if (DFK.isComparison())
+    return ComputeDefaultedComparisonExceptionSpec(S, Loc, FD,
+                                                   DFK.asComparison());
+
+  auto *CD = cast<CXXConstructorDecl>(FD);
+  assert(CD->getInheritedConstructor() &&
+         "only defaulted functions and inherited constructors have implicit "
+         "exception specs");
+  Sema::InheritedConstructorInfo ICI(
+      S, Loc, CD->getInheritedConstructor().getShadowDecl());
+  return ComputeDefaultedSpecialMemberExceptionSpec(
+      S, Loc, CD, Sema::CXXDefaultConstructor, &ICI);
+}
+
+static FunctionProtoType::ExtProtoInfo getImplicitMethodEPI(Sema &S,
+                                                            CXXMethodDecl *MD) {
+  FunctionProtoType::ExtProtoInfo EPI;
+
+  // Build an exception specification pointing back at this member.
+  EPI.ExceptionSpec.Type = EST_Unevaluated;
+  EPI.ExceptionSpec.SourceDecl = MD;
+
+  // Set the calling convention to the default for C++ instance methods.
+  EPI.ExtInfo = EPI.ExtInfo.withCallingConv(
+      S.Context.getDefaultCallingConvention(/*IsVariadic=*/false,
+                                            /*IsCXXMethod=*/true));
+  return EPI;
+}
+
+void Sema::EvaluateImplicitExceptionSpec(SourceLocation Loc, FunctionDecl *FD) {
+  const FunctionProtoType *FPT = FD->getType()->castAs<FunctionProtoType>();
+  if (FPT->getExceptionSpecType() != EST_Unevaluated)
+    return;
+
+  // Evaluate the exception specification.
+  auto IES = computeImplicitExceptionSpec(*this, Loc, FD);
+  auto ESI = IES.getExceptionSpec();
+
+  // Update the type of the special member to use it.
+  UpdateExceptionSpec(FD, ESI);
+}
+
+void Sema::CheckExplicitlyDefaultedFunction(Scope *S, FunctionDecl *FD) {
+  assert(FD->isExplicitlyDefaulted() && "not explicitly-defaulted");
+
+  DefaultedFunctionKind DefKind = getDefaultedFunctionKind(FD);
+  if (!DefKind) {
+    assert(FD->getDeclContext()->isDependentContext());
+    return;
+  }
+
+  if (DefKind.isComparison())
+    UnusedPrivateFields.clear();
+
+  if (DefKind.isSpecialMember()
+          ? CheckExplicitlyDefaultedSpecialMember(cast<CXXMethodDecl>(FD),
+                                                  DefKind.asSpecialMember())
+          : CheckExplicitlyDefaultedComparison(S, FD, DefKind.asComparison()))
+    FD->setInvalidDecl();
+}
+
+bool Sema::CheckExplicitlyDefaultedSpecialMember(CXXMethodDecl *MD,
+                                                 CXXSpecialMember CSM) {
+  CXXRecordDecl *RD = MD->getParent();
+
+  assert(MD->isExplicitlyDefaulted() && CSM != CXXInvalid &&
+         "not an explicitly-defaulted special member");
+
+  // Defer all checking for special members of a dependent type.
+  if (RD->isDependentType())
+    return false;
+
+  // Whether this was the first-declared instance of the constructor.
+  // This affects whether we implicitly add an exception spec and constexpr.
+  bool First = MD == MD->getCanonicalDecl();
+
+  bool HadError = false;
+
+  // C++11 [dcl.fct.def.default]p1:
+  //   A function that is explicitly defaulted shall
+  //     -- be a special member function [...] (checked elsewhere),
+  //     -- have the same type (except for ref-qualifiers, and except that a
+  //        copy operation can take a non-const reference) as an implicit
+  //        declaration, and
+  //     -- not have default arguments.
+  // C++2a changes the second bullet to instead delete the function if it's
+  // defaulted on its first declaration, unless it's "an assignment operator,
+  // and its return type differs or its parameter type is not a reference".
+  bool DeleteOnTypeMismatch = getLangOpts().CPlusPlus20 && First;
+  bool ShouldDeleteForTypeMismatch = false;
+  unsigned ExpectedParams = 1;
+  if (CSM == CXXDefaultConstructor || CSM == CXXDestructor)
+    ExpectedParams = 0;
+  if (MD->getNumParams() != ExpectedParams) {
+    // This checks for default arguments: a copy or move constructor with a
+    // default argument is classified as a default constructor, and assignment
+    // operations and destructors can't have default arguments.
+    Diag(MD->getLocation(), diag::err_defaulted_special_member_params)
+      << CSM << MD->getSourceRange();
+    HadError = true;
+  } else if (MD->isVariadic()) {
+    if (DeleteOnTypeMismatch)
+      ShouldDeleteForTypeMismatch = true;
+    else {
+      Diag(MD->getLocation(), diag::err_defaulted_special_member_variadic)
+        << CSM << MD->getSourceRange();
+      HadError = true;
+    }
+  }
+
+  const FunctionProtoType *Type = MD->getType()->getAs<FunctionProtoType>();
+
+  bool CanHaveConstParam = false;
+  if (CSM == CXXCopyConstructor)
+    CanHaveConstParam = RD->implicitCopyConstructorHasConstParam();
+  else if (CSM == CXXCopyAssignment)
+    CanHaveConstParam = RD->implicitCopyAssignmentHasConstParam();
+
+  QualType ReturnType = Context.VoidTy;
+  if (CSM == CXXCopyAssignment || CSM == CXXMoveAssignment) {
+    // Check for return type matching.
+    ReturnType = Type->getReturnType();
+
+    QualType DeclType = Context.getTypeDeclType(RD);
+    DeclType = Context.getAddrSpaceQualType(DeclType, MD->getMethodQualifiers().getAddressSpace());
+    QualType ExpectedReturnType = Context.getLValueReferenceType(DeclType);
+
+    if (!Context.hasSameType(ReturnType, ExpectedReturnType)) {
+      Diag(MD->getLocation(), diag::err_defaulted_special_member_return_type)
+        << (CSM == CXXMoveAssignment) << ExpectedReturnType;
+      HadError = true;
+    }
+
+    // A defaulted special member cannot have cv-qualifiers.
+    if (Type->getMethodQuals().hasConst() || Type->getMethodQuals().hasVolatile()) {
+      if (DeleteOnTypeMismatch)
+        ShouldDeleteForTypeMismatch = true;
+      else {
+        Diag(MD->getLocation(), diag::err_defaulted_special_member_quals)
+          << (CSM == CXXMoveAssignment) << getLangOpts().CPlusPlus14;
+        HadError = true;
+      }
+    }
+  }
+
+  // Check for parameter type matching.
+  QualType ArgType = ExpectedParams ? Type->getParamType(0) : QualType();
+  bool HasConstParam = false;
+  if (ExpectedParams && ArgType->isReferenceType()) {
+    // Argument must be reference to possibly-const T.
+    QualType ReferentType = ArgType->getPointeeType();
+    HasConstParam = ReferentType.isConstQualified();
+
+    if (ReferentType.isVolatileQualified()) {
+      if (DeleteOnTypeMismatch)
+        ShouldDeleteForTypeMismatch = true;
+      else {
+        Diag(MD->getLocation(),
+             diag::err_defaulted_special_member_volatile_param) << CSM;
+        HadError = true;
+      }
+    }
+
+    if (HasConstParam && !CanHaveConstParam) {
+      if (DeleteOnTypeMismatch)
+        ShouldDeleteForTypeMismatch = true;
+      else if (CSM == CXXCopyConstructor || CSM == CXXCopyAssignment) {
+        Diag(MD->getLocation(),
+             diag::err_defaulted_special_member_copy_const_param)
+          << (CSM == CXXCopyAssignment);
+        // FIXME: Explain why this special member can't be const.
+        HadError = true;
+      } else {
+        Diag(MD->getLocation(),
+             diag::err_defaulted_special_member_move_const_param)
+          << (CSM == CXXMoveAssignment);
+        HadError = true;
+      }
+    }
+  } else if (ExpectedParams) {
+    // A copy assignment operator can take its argument by value, but a
+    // defaulted one cannot.
+    assert(CSM == CXXCopyAssignment && "unexpected non-ref argument");
+    Diag(MD->getLocation(), diag::err_defaulted_copy_assign_not_ref);
+    HadError = true;
+  }
+
+  // C++11 [dcl.fct.def.default]p2:
+  //   An explicitly-defaulted function may be declared constexpr only if it
+  //   would have been implicitly declared as constexpr,
+  // Do not apply this rule to members of class templates, since core issue 1358
+  // makes such functions always instantiate to constexpr functions. For
+  // functions which cannot be constexpr (for non-constructors in C++11 and for
+  // destructors in C++14 and C++17), this is checked elsewhere.
+  //
+  // FIXME: This should not apply if the member is deleted.
+  bool Constexpr = defaultedSpecialMemberIsConstexpr(*this, RD, CSM,
+                                                     HasConstParam);
+  if ((getLangOpts().CPlusPlus20 ||
+       (getLangOpts().CPlusPlus14 ? !isa<CXXDestructorDecl>(MD)
+                                  : isa<CXXConstructorDecl>(MD))) &&
+      MD->isConstexpr() && !Constexpr &&
+      MD->getTemplatedKind() == FunctionDecl::TK_NonTemplate) {
+    Diag(MD->getBeginLoc(), MD->isConsteval()
+                                ? diag::err_incorrect_defaulted_consteval
+                                : diag::err_incorrect_defaulted_constexpr)
+        << CSM;
+    // FIXME: Explain why the special member can't be constexpr.
+    HadError = true;
+  }
+
+  if (First) {
+    // C++2a [dcl.fct.def.default]p3:
+    //   If a function is explicitly defaulted on its first declaration, it is
+    //   implicitly considered to be constexpr if the implicit declaration
+    //   would be.
+    MD->setConstexprKind(Constexpr ? (MD->isConsteval()
+                                          ? ConstexprSpecKind::Consteval
+                                          : ConstexprSpecKind::Constexpr)
+                                   : ConstexprSpecKind::Unspecified);
+
+    if (!Type->hasExceptionSpec()) {
+      // C++2a [except.spec]p3:
+      //   If a declaration of a function does not have a noexcept-specifier
+      //   [and] is defaulted on its first declaration, [...] the exception
+      //   specification is as specified below
+      FunctionProtoType::ExtProtoInfo EPI = Type->getExtProtoInfo();
+      EPI.ExceptionSpec.Type = EST_Unevaluated;
+      EPI.ExceptionSpec.SourceDecl = MD;
+      MD->setType(Context.getFunctionType(ReturnType,
+                                          llvm::makeArrayRef(&ArgType,
+                                                             ExpectedParams),
+                                          EPI));
+    }
+  }
+
+  if (ShouldDeleteForTypeMismatch || ShouldDeleteSpecialMember(MD, CSM)) {
+    if (First) {
+      SetDeclDeleted(MD, MD->getLocation());
+      if (!inTemplateInstantiation() && !HadError) {
+        Diag(MD->getLocation(), diag::warn_defaulted_method_deleted) << CSM;
+        if (ShouldDeleteForTypeMismatch) {
+          Diag(MD->getLocation(), diag::note_deleted_type_mismatch) << CSM;
+        } else {
+          ShouldDeleteSpecialMember(MD, CSM, nullptr, /*Diagnose*/true);
+        }
+      }
+      if (ShouldDeleteForTypeMismatch && !HadError) {
+        Diag(MD->getLocation(),
+             diag::warn_cxx17_compat_defaulted_method_type_mismatch) << CSM;
+      }
+    } else {
+      // C++11 [dcl.fct.def.default]p4:
+      //   [For a] user-provided explicitly-defaulted function [...] if such a
+      //   function is implicitly defined as deleted, the program is ill-formed.
+      Diag(MD->getLocation(), diag::err_out_of_line_default_deletes) << CSM;
+      assert(!ShouldDeleteForTypeMismatch && "deleted non-first decl");
+      ShouldDeleteSpecialMember(MD, CSM, nullptr, /*Diagnose*/true);
+      HadError = true;
+    }
+  }
+
+  return HadError;
+}
+
+namespace {
+/// Helper class for building and checking a defaulted comparison.
+///
+/// Defaulted functions are built in two phases:
+///
+///  * First, the set of operations that the function will perform are
+///    identified, and some of them are checked. If any of the checked
+///    operations is invalid in certain ways, the comparison function is
+///    defined as deleted and no body is built.
+///  * Then, if the function is not defined as deleted, the body is built.
+///
+/// This is accomplished by performing two visitation steps over the eventual
+/// body of the function.
+template<typename Derived, typename ResultList, typename Result,
+         typename Subobject>
+class DefaultedComparisonVisitor {
+public:
+  using DefaultedComparisonKind = Sema::DefaultedComparisonKind;
+
+  DefaultedComparisonVisitor(Sema &S, CXXRecordDecl *RD, FunctionDecl *FD,
+                             DefaultedComparisonKind DCK)
+      : S(S), RD(RD), FD(FD), DCK(DCK) {
+    if (auto *Info = FD->getDefaultedFunctionInfo()) {
+      // FIXME: Change CreateOverloadedBinOp to take an ArrayRef instead of an
+      // UnresolvedSet to avoid this copy.
+      Fns.assign(Info->getUnqualifiedLookups().begin(),
+                 Info->getUnqualifiedLookups().end());
+    }
+  }
+
+  ResultList visit() {
+    // The type of an lvalue naming a parameter of this function.
+    QualType ParamLvalType =
+        FD->getParamDecl(0)->getType().getNonReferenceType();
+
+    ResultList Results;
+
+    switch (DCK) {
+    case DefaultedComparisonKind::None:
+      llvm_unreachable("not a defaulted comparison");
+
+    case DefaultedComparisonKind::Equal:
+    case DefaultedComparisonKind::ThreeWay:
+      getDerived().visitSubobjects(Results, RD, ParamLvalType.getQualifiers());
+      return Results;
+
+    case DefaultedComparisonKind::NotEqual:
+    case DefaultedComparisonKind::Relational:
+      Results.add(getDerived().visitExpandedSubobject(
+          ParamLvalType, getDerived().getCompleteObject()));
+      return Results;
+    }
+    llvm_unreachable("");
+  }
+
+protected:
+  Derived &getDerived() { return static_cast<Derived&>(*this); }
+
+  /// Visit the expanded list of subobjects of the given type, as specified in
+  /// C++2a [class.compare.default].
+  ///
+  /// \return \c true if the ResultList object said we're done, \c false if not.
+  bool visitSubobjects(ResultList &Results, CXXRecordDecl *Record,
+                       Qualifiers Quals) {
+    // C++2a [class.compare.default]p4:
+    //   The direct base class subobjects of C
+    for (CXXBaseSpecifier &Base : Record->bases())
+      if (Results.add(getDerived().visitSubobject(
+              S.Context.getQualifiedType(Base.getType(), Quals),
+              getDerived().getBase(&Base))))
+        return true;
+
+    //   followed by the non-static data members of C
+    for (FieldDecl *Field : Record->fields()) {
+      // Recursively expand anonymous structs.
+      if (Field->isAnonymousStructOrUnion()) {
+        if (visitSubobjects(Results, Field->getType()->getAsCXXRecordDecl(),
+                            Quals))
+          return true;
+        continue;
+      }
+
+      // Figure out the type of an lvalue denoting this field.
+      Qualifiers FieldQuals = Quals;
+      if (Field->isMutable())
+        FieldQuals.removeConst();
+      QualType FieldType =
+          S.Context.getQualifiedType(Field->getType(), FieldQuals);
+
+      if (Results.add(getDerived().visitSubobject(
+              FieldType, getDerived().getField(Field))))
+        return true;
+    }
+
+    //   form a list of subobjects.
+    return false;
+  }
+
+  Result visitSubobject(QualType Type, Subobject Subobj) {
+    //   In that list, any subobject of array type is recursively expanded
+    const ArrayType *AT = S.Context.getAsArrayType(Type);
+    if (auto *CAT = dyn_cast_or_null<ConstantArrayType>(AT))
+      return getDerived().visitSubobjectArray(CAT->getElementType(),
+                                              CAT->getSize(), Subobj);
+    return getDerived().visitExpandedSubobject(Type, Subobj);
+  }
+
+  Result visitSubobjectArray(QualType Type, const llvm::APInt &Size,
+                             Subobject Subobj) {
+    return getDerived().visitSubobject(Type, Subobj);
+  }
+
+protected:
+  Sema &S;
+  CXXRecordDecl *RD;
+  FunctionDecl *FD;
+  DefaultedComparisonKind DCK;
+  UnresolvedSet<16> Fns;
+};
+
+/// Information about a defaulted comparison, as determined by
+/// DefaultedComparisonAnalyzer.
+struct DefaultedComparisonInfo {
+  bool Deleted = false;
+  bool Constexpr = true;
+  ComparisonCategoryType Category = ComparisonCategoryType::StrongOrdering;
+
+  static DefaultedComparisonInfo deleted() {
+    DefaultedComparisonInfo Deleted;
+    Deleted.Deleted = true;
+    return Deleted;
+  }
+
+  bool add(const DefaultedComparisonInfo &R) {
+    Deleted |= R.Deleted;
+    Constexpr &= R.Constexpr;
+    Category = commonComparisonType(Category, R.Category);
+    return Deleted;
+  }
+};
+
+/// An element in the expanded list of subobjects of a defaulted comparison, as
+/// specified in C++2a [class.compare.default]p4.
+struct DefaultedComparisonSubobject {
+  enum { CompleteObject, Member, Base } Kind;
+  NamedDecl *Decl;
+  SourceLocation Loc;
+};
+
+/// A visitor over the notional body of a defaulted comparison that determines
+/// whether that body would be deleted or constexpr.
+class DefaultedComparisonAnalyzer
+    : public DefaultedComparisonVisitor<DefaultedComparisonAnalyzer,
+                                        DefaultedComparisonInfo,
+                                        DefaultedComparisonInfo,
+                                        DefaultedComparisonSubobject> {
+public:
+  enum DiagnosticKind { NoDiagnostics, ExplainDeleted, ExplainConstexpr };
+
+private:
+  DiagnosticKind Diagnose;
+
+public:
+  using Base = DefaultedComparisonVisitor;
+  using Result = DefaultedComparisonInfo;
+  using Subobject = DefaultedComparisonSubobject;
+
+  friend Base;
+
+  DefaultedComparisonAnalyzer(Sema &S, CXXRecordDecl *RD, FunctionDecl *FD,
+                              DefaultedComparisonKind DCK,
+                              DiagnosticKind Diagnose = NoDiagnostics)
+      : Base(S, RD, FD, DCK), Diagnose(Diagnose) {}
+
+  Result visit() {
+    if ((DCK == DefaultedComparisonKind::Equal ||
+         DCK == DefaultedComparisonKind::ThreeWay) &&
+        RD->hasVariantMembers()) {
+      // C++2a [class.compare.default]p2 [P2002R0]:
+      //   A defaulted comparison operator function for class C is defined as
+      //   deleted if [...] C has variant members.
+      if (Diagnose == ExplainDeleted) {
+        S.Diag(FD->getLocation(), diag::note_defaulted_comparison_union)
+          << FD << RD->isUnion() << RD;
+      }
+      return Result::deleted();
+    }
+
+    return Base::visit();
+  }
+
+private:
+  Subobject getCompleteObject() {
+    return Subobject{Subobject::CompleteObject, RD, FD->getLocation()};
+  }
+
+  Subobject getBase(CXXBaseSpecifier *Base) {
+    return Subobject{Subobject::Base, Base->getType()->getAsCXXRecordDecl(),
+                     Base->getBaseTypeLoc()};
+  }
+
+  Subobject getField(FieldDecl *Field) {
+    return Subobject{Subobject::Member, Field, Field->getLocation()};
+  }
+
+  Result visitExpandedSubobject(QualType Type, Subobject Subobj) {
+    // C++2a [class.compare.default]p2 [P2002R0]:
+    //   A defaulted <=> or == operator function for class C is defined as
+    //   deleted if any non-static data member of C is of reference type
+    if (Type->isReferenceType()) {
+      if (Diagnose == ExplainDeleted) {
+        S.Diag(Subobj.Loc, diag::note_defaulted_comparison_reference_member)
+            << FD << RD;
+      }
+      return Result::deleted();
+    }
+
+    // [...] Let xi be an lvalue denoting the ith element [...]
+    OpaqueValueExpr Xi(FD->getLocation(), Type, VK_LValue);
+    Expr *Args[] = {&Xi, &Xi};
+
+    // All operators start by trying to apply that same operator recursively.
+    OverloadedOperatorKind OO = FD->getOverloadedOperator();
+    assert(OO != OO_None && "not an overloaded operator!");
+    return visitBinaryOperator(OO, Args, Subobj);
+  }
+
+  Result
+  visitBinaryOperator(OverloadedOperatorKind OO, ArrayRef<Expr *> Args,
+                      Subobject Subobj,
+                      OverloadCandidateSet *SpaceshipCandidates = nullptr) {
+    // Note that there is no need to consider rewritten candidates here if
+    // we've already found there is no viable 'operator<=>' candidate (and are
+    // considering synthesizing a '<=>' from '==' and '<').
+    OverloadCandidateSet CandidateSet(
+        FD->getLocation(), OverloadCandidateSet::CSK_Operator,
+        OverloadCandidateSet::OperatorRewriteInfo(
+            OO, /*AllowRewrittenCandidates=*/!SpaceshipCandidates));
+
+    /// C++2a [class.compare.default]p1 [P2002R0]:
+    ///   [...] the defaulted function itself is never a candidate for overload
+    ///   resolution [...]
+    CandidateSet.exclude(FD);
+
+    if (Args[0]->getType()->isOverloadableType())
+      S.LookupOverloadedBinOp(CandidateSet, OO, Fns, Args);
+    else
+      // FIXME: We determine whether this is a valid expression by checking to
+      // see if there's a viable builtin operator candidate for it. That isn't
+      // really what the rules ask us to do, but should give the right results.
+      S.AddBuiltinOperatorCandidates(OO, FD->getLocation(), Args, CandidateSet);
+
+    Result R;
+
+    OverloadCandidateSet::iterator Best;
+    switch (CandidateSet.BestViableFunction(S, FD->getLocation(), Best)) {
+    case OR_Success: {
+      // C++2a [class.compare.secondary]p2 [P2002R0]:
+      //   The operator function [...] is defined as deleted if [...] the
+      //   candidate selected by overload resolution is not a rewritten
+      //   candidate.
+      if ((DCK == DefaultedComparisonKind::NotEqual ||
+           DCK == DefaultedComparisonKind::Relational) &&
+          !Best->RewriteKind) {
+        if (Diagnose == ExplainDeleted) {
+          if (Best->Function) {
+            S.Diag(Best->Function->getLocation(),
+                   diag::note_defaulted_comparison_not_rewritten_callee)
+                << FD;
+          } else {
+            assert(Best->Conversions.size() == 2 &&
+                   Best->Conversions[0].isUserDefined() &&
+                   "non-user-defined conversion from class to built-in "
+                   "comparison");
+            S.Diag(Best->Conversions[0]
+                       .UserDefined.FoundConversionFunction.getDecl()
+                       ->getLocation(),
+                   diag::note_defaulted_comparison_not_rewritten_conversion)
+                << FD;
+          }
+        }
+        return Result::deleted();
+      }
+
+      // Throughout C++2a [class.compare]: if overload resolution does not
+      // result in a usable function, the candidate function is defined as
+      // deleted. This requires that we selected an accessible function.
+      //
+      // Note that this only considers the access of the function when named
+      // within the type of the subobject, and not the access path for any
+      // derived-to-base conversion.
+      CXXRecordDecl *ArgClass = Args[0]->getType()->getAsCXXRecordDecl();
+      if (ArgClass && Best->FoundDecl.getDecl() &&
+          Best->FoundDecl.getDecl()->isCXXClassMember()) {
+        QualType ObjectType = Subobj.Kind == Subobject::Member
+                                  ? Args[0]->getType()
+                                  : S.Context.getRecordType(RD);
+        if (!S.isMemberAccessibleForDeletion(
+                ArgClass, Best->FoundDecl, ObjectType, Subobj.Loc,
+                Diagnose == ExplainDeleted
+                    ? S.PDiag(diag::note_defaulted_comparison_inaccessible)
+                          << FD << Subobj.Kind << Subobj.Decl
+                    : S.PDiag()))
+          return Result::deleted();
+      }
+
+      bool NeedsDeducing =
+          OO == OO_Spaceship && FD->getReturnType()->isUndeducedAutoType();
+
+      if (FunctionDecl *BestFD = Best->Function) {
+        // C++2a [class.compare.default]p3 [P2002R0]:
+        //   A defaulted comparison function is constexpr-compatible if
+        //   [...] no overlod resolution performed [...] results in a
+        //   non-constexpr function.
+        assert(!BestFD->isDeleted() && "wrong overload resolution result");
+        // If it's not constexpr, explain why not.
+        if (Diagnose == ExplainConstexpr && !BestFD->isConstexpr()) {
+          if (Subobj.Kind != Subobject::CompleteObject)
+            S.Diag(Subobj.Loc, diag::note_defaulted_comparison_not_constexpr)
+              << Subobj.Kind << Subobj.Decl;
+          S.Diag(BestFD->getLocation(),
+                 diag::note_defaulted_comparison_not_constexpr_here);
+          // Bail out after explaining; we don't want any more notes.
+          return Result::deleted();
+        }
+        R.Constexpr &= BestFD->isConstexpr();
+
+        if (NeedsDeducing) {
+          // If any callee has an undeduced return type, deduce it now.
+          // FIXME: It's not clear how a failure here should be handled. For
+          // now, we produce an eager diagnostic, because that is forward
+          // compatible with most (all?) other reasonable options.
+          if (BestFD->getReturnType()->isUndeducedType() &&
+              S.DeduceReturnType(BestFD, FD->getLocation(),
+                                 /*Diagnose=*/false)) {
+            // Don't produce a duplicate error when asked to explain why the
+            // comparison is deleted: we diagnosed that when initially checking
+            // the defaulted operator.
+            if (Diagnose == NoDiagnostics) {
+              S.Diag(
+                  FD->getLocation(),
+                  diag::err_defaulted_comparison_cannot_deduce_undeduced_auto)
+                  << Subobj.Kind << Subobj.Decl;
+              S.Diag(
+                  Subobj.Loc,
+                  diag::note_defaulted_comparison_cannot_deduce_undeduced_auto)
+                  << Subobj.Kind << Subobj.Decl;
+              S.Diag(BestFD->getLocation(),
+                     diag::note_defaulted_comparison_cannot_deduce_callee)
+                  << Subobj.Kind << Subobj.Decl;
+            }
+            return Result::deleted();
+          }
+          auto *Info = S.Context.CompCategories.lookupInfoForType(
+              BestFD->getCallResultType());
+          if (!Info) {
+            if (Diagnose == ExplainDeleted) {
+              S.Diag(Subobj.Loc, diag::note_defaulted_comparison_cannot_deduce)
+                  << Subobj.Kind << Subobj.Decl
+                  << BestFD->getCallResultType().withoutLocalFastQualifiers();
+              S.Diag(BestFD->getLocation(),
+                     diag::note_defaulted_comparison_cannot_deduce_callee)
+                  << Subobj.Kind << Subobj.Decl;
+            }
+            return Result::deleted();
+          }
+          R.Category = Info->Kind;
+        }
+      } else {
+        QualType T = Best->BuiltinParamTypes[0];
+        assert(T == Best->BuiltinParamTypes[1] &&
+               "builtin comparison for different types?");
+        assert(Best->BuiltinParamTypes[2].isNull() &&
+               "invalid builtin comparison");
+
+        if (NeedsDeducing) {
+          Optional<ComparisonCategoryType> Cat =
+              getComparisonCategoryForBuiltinCmp(T);
+          assert(Cat && "no category for builtin comparison?");
+          R.Category = *Cat;
+        }
+      }
+
+      // Note that we might be rewriting to a different operator. That call is
+      // not considered until we come to actually build the comparison function.
+      break;
+    }
+
+    case OR_Ambiguous:
+      if (Diagnose == ExplainDeleted) {
+        unsigned Kind = 0;
+        if (FD->getOverloadedOperator() == OO_Spaceship && OO != OO_Spaceship)
+          Kind = OO == OO_EqualEqual ? 1 : 2;
+        CandidateSet.NoteCandidates(
+            PartialDiagnosticAt(
+                Subobj.Loc, S.PDiag(diag::note_defaulted_comparison_ambiguous)
+                                << FD << Kind << Subobj.Kind << Subobj.Decl),
+            S, OCD_AmbiguousCandidates, Args);
+      }
+      R = Result::deleted();
+      break;
+
+    case OR_Deleted:
+      if (Diagnose == ExplainDeleted) {
+        if ((DCK == DefaultedComparisonKind::NotEqual ||
+             DCK == DefaultedComparisonKind::Relational) &&
+            !Best->RewriteKind) {
+          S.Diag(Best->Function->getLocation(),
+                 diag::note_defaulted_comparison_not_rewritten_callee)
+              << FD;
+        } else {
+          S.Diag(Subobj.Loc,
+                 diag::note_defaulted_comparison_calls_deleted)
+              << FD << Subobj.Kind << Subobj.Decl;
+          S.NoteDeletedFunction(Best->Function);
+        }
+      }
+      R = Result::deleted();
+      break;
+
+    case OR_No_Viable_Function:
+      // If there's no usable candidate, we're done unless we can rewrite a
+      // '<=>' in terms of '==' and '<'.
+      if (OO == OO_Spaceship &&
+          S.Context.CompCategories.lookupInfoForType(FD->getReturnType())) {
+        // For any kind of comparison category return type, we need a usable
+        // '==' and a usable '<'.
+        if (!R.add(visitBinaryOperator(OO_EqualEqual, Args, Subobj,
+                                       &CandidateSet)))
+          R.add(visitBinaryOperator(OO_Less, Args, Subobj, &CandidateSet));
+        break;
+      }
+
+      if (Diagnose == ExplainDeleted) {
+        S.Diag(Subobj.Loc, diag::note_defaulted_comparison_no_viable_function)
+            << FD << (OO == OO_ExclaimEqual) << Subobj.Kind << Subobj.Decl;
+
+        // For a three-way comparison, list both the candidates for the
+        // original operator and the candidates for the synthesized operator.
+        if (SpaceshipCandidates) {
+          SpaceshipCandidates->NoteCandidates(
+              S, Args,
+              SpaceshipCandidates->CompleteCandidates(S, OCD_AllCandidates,
+                                                      Args, FD->getLocation()));
+          S.Diag(Subobj.Loc,
+                 diag::note_defaulted_comparison_no_viable_function_synthesized)
+              << (OO == OO_EqualEqual ? 0 : 1);
+        }
+
+        CandidateSet.NoteCandidates(
+            S, Args,
+            CandidateSet.CompleteCandidates(S, OCD_AllCandidates, Args,
+                                            FD->getLocation()));
+      }
+      R = Result::deleted();
+      break;
+    }
+
+    return R;
+  }
+};
+
+/// A list of statements.
+struct StmtListResult {
+  bool IsInvalid = false;
+  llvm::SmallVector<Stmt*, 16> Stmts;
+
+  bool add(const StmtResult &S) {
+    IsInvalid |= S.isInvalid();
+    if (IsInvalid)
+      return true;
+    Stmts.push_back(S.get());
+    return false;
+  }
+};
+
+/// A visitor over the notional body of a defaulted comparison that synthesizes
+/// the actual body.
+class DefaultedComparisonSynthesizer
+    : public DefaultedComparisonVisitor<DefaultedComparisonSynthesizer,
+                                        StmtListResult, StmtResult,
+                                        std::pair<ExprResult, ExprResult>> {
+  SourceLocation Loc;
+  unsigned ArrayDepth = 0;
+
+public:
+  using Base = DefaultedComparisonVisitor;
+  using ExprPair = std::pair<ExprResult, ExprResult>;
+
+  friend Base;
+
+  DefaultedComparisonSynthesizer(Sema &S, CXXRecordDecl *RD, FunctionDecl *FD,
+                                 DefaultedComparisonKind DCK,
+                                 SourceLocation BodyLoc)
+      : Base(S, RD, FD, DCK), Loc(BodyLoc) {}
+
+  /// Build a suitable function body for this defaulted comparison operator.
+  StmtResult build() {
+    Sema::CompoundScopeRAII CompoundScope(S);
+
+    StmtListResult Stmts = visit();
+    if (Stmts.IsInvalid)
+      return StmtError();
+
+    ExprResult RetVal;
+    switch (DCK) {
+    case DefaultedComparisonKind::None:
+      llvm_unreachable("not a defaulted comparison");
+
+    case DefaultedComparisonKind::Equal: {
+      // C++2a [class.eq]p3:
+      //   [...] compar[e] the corresponding elements [...] until the first
+      //   index i where xi == yi yields [...] false. If no such index exists,
+      //   V is true. Otherwise, V is false.
+      //
+      // Join the comparisons with '&&'s and return the result. Use a right
+      // fold (traversing the conditions right-to-left), because that
+      // short-circuits more naturally.
+      auto OldStmts = std::move(Stmts.Stmts);
+      Stmts.Stmts.clear();
+      ExprResult CmpSoFar;
+      // Finish a particular comparison chain.
+      auto FinishCmp = [&] {
+        if (Expr *Prior = CmpSoFar.get()) {
+          // Convert the last expression to 'return ...;'
+          if (RetVal.isUnset() && Stmts.Stmts.empty())
+            RetVal = CmpSoFar;
+          // Convert any prior comparison to 'if (!(...)) return false;'
+          else if (Stmts.add(buildIfNotCondReturnFalse(Prior)))
+            return true;
+          CmpSoFar = ExprResult();
+        }
+        return false;
+      };
+      for (Stmt *EAsStmt : llvm::reverse(OldStmts)) {
+        Expr *E = dyn_cast<Expr>(EAsStmt);
+        if (!E) {
+          // Found an array comparison.
+          if (FinishCmp() || Stmts.add(EAsStmt))
+            return StmtError();
+          continue;
+        }
+
+        if (CmpSoFar.isUnset()) {
+          CmpSoFar = E;
+          continue;
+        }
+        CmpSoFar = S.CreateBuiltinBinOp(Loc, BO_LAnd, E, CmpSoFar.get());
+        if (CmpSoFar.isInvalid())
+          return StmtError();
+      }
+      if (FinishCmp())
+        return StmtError();
+      std::reverse(Stmts.Stmts.begin(), Stmts.Stmts.end());
+      //   If no such index exists, V is true.
+      if (RetVal.isUnset())
+        RetVal = S.ActOnCXXBoolLiteral(Loc, tok::kw_true);
+      break;
+    }
+
+    case DefaultedComparisonKind::ThreeWay: {
+      // Per C++2a [class.spaceship]p3, as a fallback add:
+      // return static_cast<R>(std::strong_ordering::equal);
+      QualType StrongOrdering = S.CheckComparisonCategoryType(
+          ComparisonCategoryType::StrongOrdering, Loc,
+          Sema::ComparisonCategoryUsage::DefaultedOperator);
+      if (StrongOrdering.isNull())
+        return StmtError();
+      VarDecl *EqualVD = S.Context.CompCategories.getInfoForType(StrongOrdering)
+                             .getValueInfo(ComparisonCategoryResult::Equal)
+                             ->VD;
+      RetVal = getDecl(EqualVD);
+      if (RetVal.isInvalid())
+        return StmtError();
+      RetVal = buildStaticCastToR(RetVal.get());
+      break;
+    }
+
+    case DefaultedComparisonKind::NotEqual:
+    case DefaultedComparisonKind::Relational:
+      RetVal = cast<Expr>(Stmts.Stmts.pop_back_val());
+      break;
+    }
+
+    // Build the final return statement.
+    if (RetVal.isInvalid())
+      return StmtError();
+    StmtResult ReturnStmt = S.BuildReturnStmt(Loc, RetVal.get());
+    if (ReturnStmt.isInvalid())
+      return StmtError();
+    Stmts.Stmts.push_back(ReturnStmt.get());
+
+    return S.ActOnCompoundStmt(Loc, Loc, Stmts.Stmts, /*IsStmtExpr=*/false);
+  }
+
+private:
+  ExprResult getDecl(ValueDecl *VD) {
+    return S.BuildDeclarationNameExpr(
+        CXXScopeSpec(), DeclarationNameInfo(VD->getDeclName(), Loc), VD);
+  }
+
+  ExprResult getParam(unsigned I) {
+    ParmVarDecl *PD = FD->getParamDecl(I);
+    return getDecl(PD);
+  }
+
+  ExprPair getCompleteObject() {
+    unsigned Param = 0;
+    ExprResult LHS;
+    if (isa<CXXMethodDecl>(FD)) {
+      // LHS is '*this'.
+      LHS = S.ActOnCXXThis(Loc);
+      if (!LHS.isInvalid())
+        LHS = S.CreateBuiltinUnaryOp(Loc, UO_Deref, LHS.get());
+    } else {
+      LHS = getParam(Param++);
+    }
+    ExprResult RHS = getParam(Param++);
+    assert(Param == FD->getNumParams());
+    return {LHS, RHS};
+  }
+
+  ExprPair getBase(CXXBaseSpecifier *Base) {
+    ExprPair Obj = getCompleteObject();
+    if (Obj.first.isInvalid() || Obj.second.isInvalid())
+      return {ExprError(), ExprError()};
+    CXXCastPath Path = {Base};
+    return {S.ImpCastExprToType(Obj.first.get(), Base->getType(),
+                                CK_DerivedToBase, VK_LValue, &Path),
+            S.ImpCastExprToType(Obj.second.get(), Base->getType(),
+                                CK_DerivedToBase, VK_LValue, &Path)};
+  }
+
+  ExprPair getField(FieldDecl *Field) {
+    ExprPair Obj = getCompleteObject();
+    if (Obj.first.isInvalid() || Obj.second.isInvalid())
+      return {ExprError(), ExprError()};
+
+    DeclAccessPair Found = DeclAccessPair::make(Field, Field->getAccess());
+    DeclarationNameInfo NameInfo(Field->getDeclName(), Loc);
+    return {S.BuildFieldReferenceExpr(Obj.first.get(), /*IsArrow=*/false, Loc,
+                                      CXXScopeSpec(), Field, Found, NameInfo),
+            S.BuildFieldReferenceExpr(Obj.second.get(), /*IsArrow=*/false, Loc,
+                                      CXXScopeSpec(), Field, Found, NameInfo)};
+  }
+
+  // FIXME: When expanding a subobject, register a note in the code synthesis
+  // stack to say which subobject we're comparing.
+
+  StmtResult buildIfNotCondReturnFalse(ExprResult Cond) {
+    if (Cond.isInvalid())
+      return StmtError();
+
+    ExprResult NotCond = S.CreateBuiltinUnaryOp(Loc, UO_LNot, Cond.get());
+    if (NotCond.isInvalid())
+      return StmtError();
+
+    ExprResult False = S.ActOnCXXBoolLiteral(Loc, tok::kw_false);
+    assert(!False.isInvalid() && "should never fail");
+    StmtResult ReturnFalse = S.BuildReturnStmt(Loc, False.get());
+    if (ReturnFalse.isInvalid())
+      return StmtError();
+
+    return S.ActOnIfStmt(Loc, IfStatementKind::Ordinary, Loc, nullptr,
+                         S.ActOnCondition(nullptr, Loc, NotCond.get(),
+                                          Sema::ConditionKind::Boolean),
+                         Loc, ReturnFalse.get(), SourceLocation(), nullptr);
+  }
+
+  StmtResult visitSubobjectArray(QualType Type, llvm::APInt Size,
+                                 ExprPair Subobj) {
+    QualType SizeType = S.Context.getSizeType();
+    Size = Size.zextOrTrunc(S.Context.getTypeSize(SizeType));
+
+    // Build 'size_t i$n = 0'.
+    IdentifierInfo *IterationVarName = nullptr;
+    {
+      SmallString<8> Str;
+      llvm::raw_svector_ostream OS(Str);
+      OS << "i" << ArrayDepth;
+      IterationVarName = &S.Context.Idents.get(OS.str());
+    }
+    VarDecl *IterationVar = VarDecl::Create(
+        S.Context, S.CurContext, Loc, Loc, IterationVarName, SizeType,
+        S.Context.getTrivialTypeSourceInfo(SizeType, Loc), SC_None);
+    llvm::APInt Zero(S.Context.getTypeSize(SizeType), 0);
+    IterationVar->setInit(
+        IntegerLiteral::Create(S.Context, Zero, SizeType, Loc));
+    Stmt *Init = new (S.Context) DeclStmt(DeclGroupRef(IterationVar), Loc, Loc);
+
+    auto IterRef = [&] {
+      ExprResult Ref = S.BuildDeclarationNameExpr(
+          CXXScopeSpec(), DeclarationNameInfo(IterationVarName, Loc),
+          IterationVar);
+      assert(!Ref.isInvalid() && "can't reference our own variable?");
+      return Ref.get();
+    };
+
+    // Build 'i$n != Size'.
+    ExprResult Cond = S.CreateBuiltinBinOp(
+        Loc, BO_NE, IterRef(),
+        IntegerLiteral::Create(S.Context, Size, SizeType, Loc));
+    assert(!Cond.isInvalid() && "should never fail");
+
+    // Build '++i$n'.
+    ExprResult Inc = S.CreateBuiltinUnaryOp(Loc, UO_PreInc, IterRef());
+    assert(!Inc.isInvalid() && "should never fail");
+
+    // Build 'a[i$n]' and 'b[i$n]'.
+    auto Index = [&](ExprResult E) {
+      if (E.isInvalid())
+        return ExprError();
+      return S.CreateBuiltinArraySubscriptExpr(E.get(), Loc, IterRef(), Loc);
+    };
+    Subobj.first = Index(Subobj.first);
+    Subobj.second = Index(Subobj.second);
+
+    // Compare the array elements.
+    ++ArrayDepth;
+    StmtResult Substmt = visitSubobject(Type, Subobj);
+    --ArrayDepth;
+
+    if (Substmt.isInvalid())
+      return StmtError();
+
+    // For the inner level of an 'operator==', build 'if (!cmp) return false;'.
+    // For outer levels or for an 'operator<=>' we already have a suitable
+    // statement that returns as necessary.
+    if (Expr *ElemCmp = dyn_cast<Expr>(Substmt.get())) {
+      assert(DCK == DefaultedComparisonKind::Equal &&
+             "should have non-expression statement");
+      Substmt = buildIfNotCondReturnFalse(ElemCmp);
+      if (Substmt.isInvalid())
+        return StmtError();
+    }
+
+    // Build 'for (...) ...'
+    return S.ActOnForStmt(Loc, Loc, Init,
+                          S.ActOnCondition(nullptr, Loc, Cond.get(),
+                                           Sema::ConditionKind::Boolean),
+                          S.MakeFullDiscardedValueExpr(Inc.get()), Loc,
+                          Substmt.get());
+  }
+
+  StmtResult visitExpandedSubobject(QualType Type, ExprPair Obj) {
+    if (Obj.first.isInvalid() || Obj.second.isInvalid())
+      return StmtError();
+
+    OverloadedOperatorKind OO = FD->getOverloadedOperator();
+    BinaryOperatorKind Opc = BinaryOperator::getOverloadedOpcode(OO);
+    ExprResult Op;
+    if (Type->isOverloadableType())
+      Op = S.CreateOverloadedBinOp(Loc, Opc, Fns, Obj.first.get(),
+                                   Obj.second.get(), /*PerformADL=*/true,
+                                   /*AllowRewrittenCandidates=*/true, FD);
+    else
+      Op = S.CreateBuiltinBinOp(Loc, Opc, Obj.first.get(), Obj.second.get());
+    if (Op.isInvalid())
+      return StmtError();
+
+    switch (DCK) {
+    case DefaultedComparisonKind::None:
+      llvm_unreachable("not a defaulted comparison");
+
+    case DefaultedComparisonKind::Equal:
+      // Per C++2a [class.eq]p2, each comparison is individually contextually
+      // converted to bool.
+      Op = S.PerformContextuallyConvertToBool(Op.get());
+      if (Op.isInvalid())
+        return StmtError();
+      return Op.get();
+
+    case DefaultedComparisonKind::ThreeWay: {
+      // Per C++2a [class.spaceship]p3, form:
+      //   if (R cmp = static_cast<R>(op); cmp != 0)
+      //     return cmp;
+      QualType R = FD->getReturnType();
+      Op = buildStaticCastToR(Op.get());
+      if (Op.isInvalid())
+        return StmtError();
+
+      // R cmp = ...;
+      IdentifierInfo *Name = &S.Context.Idents.get("cmp");
+      VarDecl *VD =
+          VarDecl::Create(S.Context, S.CurContext, Loc, Loc, Name, R,
+                          S.Context.getTrivialTypeSourceInfo(R, Loc), SC_None);
+      S.AddInitializerToDecl(VD, Op.get(), /*DirectInit=*/false);
+      Stmt *InitStmt = new (S.Context) DeclStmt(DeclGroupRef(VD), Loc, Loc);
+
+      // cmp != 0
+      ExprResult VDRef = getDecl(VD);
+      if (VDRef.isInvalid())
+        return StmtError();
+      llvm::APInt ZeroVal(S.Context.getIntWidth(S.Context.IntTy), 0);
+      Expr *Zero =
+          IntegerLiteral::Create(S.Context, ZeroVal, S.Context.IntTy, Loc);
+      ExprResult Comp;
+      if (VDRef.get()->getType()->isOverloadableType())
+        Comp = S.CreateOverloadedBinOp(Loc, BO_NE, Fns, VDRef.get(), Zero, true,
+                                       true, FD);
+      else
+        Comp = S.CreateBuiltinBinOp(Loc, BO_NE, VDRef.get(), Zero);
+      if (Comp.isInvalid())
+        return StmtError();
+      Sema::ConditionResult Cond = S.ActOnCondition(
+          nullptr, Loc, Comp.get(), Sema::ConditionKind::Boolean);
+      if (Cond.isInvalid())
+        return StmtError();
+
+      // return cmp;
+      VDRef = getDecl(VD);
+      if (VDRef.isInvalid())
+        return StmtError();
+      StmtResult ReturnStmt = S.BuildReturnStmt(Loc, VDRef.get());
+      if (ReturnStmt.isInvalid())
+        return StmtError();
+
+      // if (...)
+      return S.ActOnIfStmt(Loc, IfStatementKind::Ordinary, Loc, InitStmt, Cond,
+                           Loc, ReturnStmt.get(),
+                           /*ElseLoc=*/SourceLocation(), /*Else=*/nullptr);
+    }
+
+    case DefaultedComparisonKind::NotEqual:
+    case DefaultedComparisonKind::Relational:
+      // C++2a [class.compare.secondary]p2:
+      //   Otherwise, the operator function yields x @ y.
+      return Op.get();
+    }
+    llvm_unreachable("");
+  }
+
+  /// Build "static_cast<R>(E)".
+  ExprResult buildStaticCastToR(Expr *E) {
+    QualType R = FD->getReturnType();
+    assert(!R->isUndeducedType() && "type should have been deduced already");
+
+    // Don't bother forming a no-op cast in the common case.
+    if (E->isPRValue() && S.Context.hasSameType(E->getType(), R))
+      return E;
+    return S.BuildCXXNamedCast(Loc, tok::kw_static_cast,
+                               S.Context.getTrivialTypeSourceInfo(R, Loc), E,
+                               SourceRange(Loc, Loc), SourceRange(Loc, Loc));
+  }
+};
+}
+
+/// Perform the unqualified lookups that might be needed to form a defaulted
+/// comparison function for the given operator.
+static void lookupOperatorsForDefaultedComparison(Sema &Self, Scope *S,
+                                                  UnresolvedSetImpl &Operators,
+                                                  OverloadedOperatorKind Op) {
+  auto Lookup = [&](OverloadedOperatorKind OO) {
+    Self.LookupOverloadedOperatorName(OO, S, Operators);
+  };
+
+  // Every defaulted operator looks up itself.
+  Lookup(Op);
+  // ... and the rewritten form of itself, if any.
+  if (OverloadedOperatorKind ExtraOp = getRewrittenOverloadedOperator(Op))
+    Lookup(ExtraOp);
+
+  // For 'operator<=>', we also form a 'cmp != 0' expression, and might
+  // synthesize a three-way comparison from '<' and '=='. In a dependent
+  // context, we also need to look up '==' in case we implicitly declare a
+  // defaulted 'operator=='.
+  if (Op == OO_Spaceship) {
+    Lookup(OO_ExclaimEqual);
+    Lookup(OO_Less);
+    Lookup(OO_EqualEqual);
+  }
+}
+
+bool Sema::CheckExplicitlyDefaultedComparison(Scope *S, FunctionDecl *FD,
+                                              DefaultedComparisonKind DCK) {
+  assert(DCK != DefaultedComparisonKind::None && "not a defaulted comparison");
+
+  // Perform any unqualified lookups we're going to need to default this
+  // function.
+  if (S) {
+    UnresolvedSet<32> Operators;
+    lookupOperatorsForDefaultedComparison(*this, S, Operators,
+                                          FD->getOverloadedOperator());
+    FD->setDefaultedFunctionInfo(FunctionDecl::DefaultedFunctionInfo::Create(
+        Context, Operators.pairs()));
+  }
+
+  // C++2a [class.compare.default]p1:
+  //   A defaulted comparison operator function for some class C shall be a
+  //   non-template function declared in the member-specification of C that is
+  //    -- a non-static const member of C having one parameter of type
+  //       const C&, or
+  //    -- a friend of C having two parameters of type const C& or two
+  //       parameters of type C.
+
+  CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(FD->getLexicalDeclContext());
+  bool IsMethod = isa<CXXMethodDecl>(FD);
+  if (IsMethod) {
+    auto *MD = cast<CXXMethodDecl>(FD);
+    assert(!MD->isStatic() && "comparison function cannot be a static member");
+
+    // If we're out-of-class, this is the class we're comparing.
+    if (!RD)
+      RD = MD->getParent();
+
+    if (!MD->isConst()) {
+      SourceLocation InsertLoc;
+      if (FunctionTypeLoc Loc = MD->getFunctionTypeLoc())
+        InsertLoc = getLocForEndOfToken(Loc.getRParenLoc());
+      // Don't diagnose an implicit 'operator=='; we will have diagnosed the
+      // corresponding defaulted 'operator<=>' already.
+      if (!MD->isImplicit()) {
+        Diag(MD->getLocation(), diag::err_defaulted_comparison_non_const)
+            << (int)DCK << FixItHint::CreateInsertion(InsertLoc, " const");
+      }
+
+      // Add the 'const' to the type to recover.
+      const auto *FPT = MD->getType()->castAs<FunctionProtoType>();
+      FunctionProtoType::ExtProtoInfo EPI = FPT->getExtProtoInfo();
+      EPI.TypeQuals.addConst();
+      MD->setType(Context.getFunctionType(FPT->getReturnType(),
+                                          FPT->getParamTypes(), EPI));
+    }
+  }
+
+  if (FD->getNumParams() != (IsMethod ? 1 : 2)) {
+    // Let's not worry about using a variadic template pack here -- who would do
+    // such a thing?
+    Diag(FD->getLocation(), diag::err_defaulted_comparison_num_args)
+        << int(IsMethod) << int(DCK);
+    return true;
+  }
+
+  const ParmVarDecl *KnownParm = nullptr;
+  for (const ParmVarDecl *Param : FD->parameters()) {
+    QualType ParmTy = Param->getType();
+    if (ParmTy->isDependentType())
+      continue;
+    if (!KnownParm) {
+      auto CTy = ParmTy;
+      // Is it `T const &`?
+      bool Ok = !IsMethod;
+      QualType ExpectedTy;
+      if (RD)
+        ExpectedTy = Context.getRecordType(RD);
+      if (auto *Ref = CTy->getAs<ReferenceType>()) {
+        CTy = Ref->getPointeeType();
+        if (RD)
+          ExpectedTy.addConst();
+        Ok = true;
+      }
+
+      // Is T a class?
+      if (!Ok) {
+      } else if (RD) {
+        if (!RD->isDependentType() && !Context.hasSameType(CTy, ExpectedTy))
+          Ok = false;
+      } else if (auto *CRD = CTy->getAsRecordDecl()) {
+        RD = cast<CXXRecordDecl>(CRD);
+      } else {
+        Ok = false;
+      }
+
+      if (Ok) {
+        KnownParm = Param;
+      } else {
+        // Don't diagnose an implicit 'operator=='; we will have diagnosed the
+        // corresponding defaulted 'operator<=>' already.
+        if (!FD->isImplicit()) {
+          if (RD) {
+            QualType PlainTy = Context.getRecordType(RD);
+            QualType RefTy =
+                Context.getLValueReferenceType(PlainTy.withConst());
+            Diag(FD->getLocation(), diag::err_defaulted_comparison_param)
+                << int(DCK) << ParmTy << RefTy << int(!IsMethod) << PlainTy
+                << Param->getSourceRange();
+          } else {
+            assert(!IsMethod && "should know expected type for method");
+            Diag(FD->getLocation(),
+                 diag::err_defaulted_comparison_param_unknown)
+                << int(DCK) << ParmTy << Param->getSourceRange();
+          }
+        }
+        return true;
+      }
+    } else if (!Context.hasSameType(KnownParm->getType(), ParmTy)) {
+      Diag(FD->getLocation(), diag::err_defaulted_comparison_param_mismatch)
+          << int(DCK) << KnownParm->getType() << KnownParm->getSourceRange()
+          << ParmTy << Param->getSourceRange();
+      return true;
+    }
+  }
+
+  assert(RD && "must have determined class");
+  if (IsMethod) {
+  } else if (isa<CXXRecordDecl>(FD->getLexicalDeclContext())) {
+    // In-class, must be a friend decl.
+    assert(FD->getFriendObjectKind() && "expected a friend declaration");
+  } else {
+    // Out of class, require the defaulted comparison to be a friend (of a
+    // complete type).
+    if (RequireCompleteType(FD->getLocation(), Context.getRecordType(RD),
+                            diag::err_defaulted_comparison_not_friend, int(DCK),
+                            int(1)))
+      return true;
+
+    if (llvm::find_if(RD->friends(), [&](const FriendDecl *F) {
+          return FD->getCanonicalDecl() ==
+                 F->getFriendDecl()->getCanonicalDecl();
+        }) == RD->friends().end()) {
+      Diag(FD->getLocation(), diag::err_defaulted_comparison_not_friend)
+          << int(DCK) << int(0) << RD;
+      Diag(RD->getCanonicalDecl()->getLocation(), diag::note_declared_at);
+      return true;
+    }
+  }
+
+  // C++2a [class.eq]p1, [class.rel]p1:
+  //   A [defaulted comparison other than <=>] shall have a declared return
+  //   type bool.
+  if (DCK != DefaultedComparisonKind::ThreeWay &&
+      !FD->getDeclaredReturnType()->isDependentType() &&
+      !Context.hasSameType(FD->getDeclaredReturnType(), Context.BoolTy)) {
+    Diag(FD->getLocation(), diag::err_defaulted_comparison_return_type_not_bool)
+        << (int)DCK << FD->getDeclaredReturnType() << Context.BoolTy
+        << FD->getReturnTypeSourceRange();
+    return true;
+  }
+  // C++2a [class.spaceship]p2 [P2002R0]:
+  //   Let R be the declared return type [...]. If R is auto, [...]. Otherwise,
+  //   R shall not contain a placeholder type.
+  if (DCK == DefaultedComparisonKind::ThreeWay &&
+      FD->getDeclaredReturnType()->getContainedDeducedType() &&
+      !Context.hasSameType(FD->getDeclaredReturnType(),
+                           Context.getAutoDeductType())) {
+    Diag(FD->getLocation(),
+         diag::err_defaulted_comparison_deduced_return_type_not_auto)
+        << (int)DCK << FD->getDeclaredReturnType() << Context.AutoDeductTy
+        << FD->getReturnTypeSourceRange();
+    return true;
+  }
+
+  // For a defaulted function in a dependent class, defer all remaining checks
+  // until instantiation.
+  if (RD->isDependentType())
+    return false;
+
+  // Determine whether the function should be defined as deleted.
+  DefaultedComparisonInfo Info =
+      DefaultedComparisonAnalyzer(*this, RD, FD, DCK).visit();
+
+  bool First = FD == FD->getCanonicalDecl();
+
+  // If we want to delete the function, then do so; there's nothing else to
+  // check in that case.
+  if (Info.Deleted) {
+    if (!First) {
+      // C++11 [dcl.fct.def.default]p4:
+      //   [For a] user-provided explicitly-defaulted function [...] if such a
+      //   function is implicitly defined as deleted, the program is ill-formed.
+      //
+      // This is really just a consequence of the general rule that you can
+      // only delete a function on its first declaration.
+      Diag(FD->getLocation(), diag::err_non_first_default_compare_deletes)
+          << FD->isImplicit() << (int)DCK;
+      DefaultedComparisonAnalyzer(*this, RD, FD, DCK,
+                                  DefaultedComparisonAnalyzer::ExplainDeleted)
+          .visit();
+      return true;
+    }
+
+    SetDeclDeleted(FD, FD->getLocation());
+    if (!inTemplateInstantiation() && !FD->isImplicit()) {
+      Diag(FD->getLocation(), diag::warn_defaulted_comparison_deleted)
+          << (int)DCK;
+      DefaultedComparisonAnalyzer(*this, RD, FD, DCK,
+                                  DefaultedComparisonAnalyzer::ExplainDeleted)
+          .visit();
+    }
+    return false;
+  }
+
+  // C++2a [class.spaceship]p2:
+  //   The return type is deduced as the common comparison type of R0, R1, ...
+  if (DCK == DefaultedComparisonKind::ThreeWay &&
+      FD->getDeclaredReturnType()->isUndeducedAutoType()) {
+    SourceLocation RetLoc = FD->getReturnTypeSourceRange().getBegin();
+    if (RetLoc.isInvalid())
+      RetLoc = FD->getBeginLoc();
+    // FIXME: Should we really care whether we have the complete type and the
+    // 'enumerator' constants here? A forward declaration seems sufficient.
+    QualType Cat = CheckComparisonCategoryType(
+        Info.Category, RetLoc, ComparisonCategoryUsage::DefaultedOperator);
+    if (Cat.isNull())
+      return true;
+    Context.adjustDeducedFunctionResultType(
+        FD, SubstAutoType(FD->getDeclaredReturnType(), Cat));
+  }
+
+  // C++2a [dcl.fct.def.default]p3 [P2002R0]:
+  //   An explicitly-defaulted function that is not defined as deleted may be
+  //   declared constexpr or consteval only if it is constexpr-compatible.
+  // C++2a [class.compare.default]p3 [P2002R0]:
+  //   A defaulted comparison function is constexpr-compatible if it satisfies
+  //   the requirements for a constexpr function [...]
+  // The only relevant requirements are that the parameter and return types are
+  // literal types. The remaining conditions are checked by the analyzer.
+  if (FD->isConstexpr()) {
+    if (CheckConstexprReturnType(*this, FD, CheckConstexprKind::Diagnose) &&
+        CheckConstexprParameterTypes(*this, FD, CheckConstexprKind::Diagnose) &&
+        !Info.Constexpr) {
+      Diag(FD->getBeginLoc(),
+           diag::err_incorrect_defaulted_comparison_constexpr)
+          << FD->isImplicit() << (int)DCK << FD->isConsteval();
+      DefaultedComparisonAnalyzer(*this, RD, FD, DCK,
+                                  DefaultedComparisonAnalyzer::ExplainConstexpr)
+          .visit();
+    }
+  }
+
+  // C++2a [dcl.fct.def.default]p3 [P2002R0]:
+  //   If a constexpr-compatible function is explicitly defaulted on its first
+  //   declaration, it is implicitly considered to be constexpr.
+  // FIXME: Only applying this to the first declaration seems problematic, as
+  // simple reorderings can affect the meaning of the program.
+  if (First && !FD->isConstexpr() && Info.Constexpr)
+    FD->setConstexprKind(ConstexprSpecKind::Constexpr);
+
+  // C++2a [except.spec]p3:
+  //   If a declaration of a function does not have a noexcept-specifier
+  //   [and] is defaulted on its first declaration, [...] the exception
+  //   specification is as specified below
+  if (FD->getExceptionSpecType() == EST_None) {
+    auto *FPT = FD->getType()->castAs<FunctionProtoType>();
+    FunctionProtoType::ExtProtoInfo EPI = FPT->getExtProtoInfo();
+    EPI.ExceptionSpec.Type = EST_Unevaluated;
+    EPI.ExceptionSpec.SourceDecl = FD;
+    FD->setType(Context.getFunctionType(FPT->getReturnType(),
+                                        FPT->getParamTypes(), EPI));
+  }
+
+  return false;
+}
+
+void Sema::DeclareImplicitEqualityComparison(CXXRecordDecl *RD,
+                                             FunctionDecl *Spaceship) {
+  Sema::CodeSynthesisContext Ctx;
+  Ctx.Kind = Sema::CodeSynthesisContext::DeclaringImplicitEqualityComparison;
+  Ctx.PointOfInstantiation = Spaceship->getEndLoc();
+  Ctx.Entity = Spaceship;
+  pushCodeSynthesisContext(Ctx);
+
+  if (FunctionDecl *EqualEqual = SubstSpaceshipAsEqualEqual(RD, Spaceship))
+    EqualEqual->setImplicit();
+
+  popCodeSynthesisContext();
+}
+
+void Sema::DefineDefaultedComparison(SourceLocation UseLoc, FunctionDecl *FD,
+                                     DefaultedComparisonKind DCK) {
+  assert(FD->isDefaulted() && !FD->isDeleted() &&
+         !FD->doesThisDeclarationHaveABody());
+  if (FD->willHaveBody() || FD->isInvalidDecl())
+    return;
+
+  SynthesizedFunctionScope Scope(*this, FD);
+
+  // Add a context note for diagnostics produced after this point.
+  Scope.addContextNote(UseLoc);
+
+  {
+    // Build and set up the function body.
+    // The first parameter has type maybe-ref-to maybe-const T, use that to get
+    // the type of the class being compared.
+    auto PT = FD->getParamDecl(0)->getType();
+    CXXRecordDecl *RD = PT.getNonReferenceType()->getAsCXXRecordDecl();
+    SourceLocation BodyLoc =
+        FD->getEndLoc().isValid() ? FD->getEndLoc() : FD->getLocation();
+    StmtResult Body =
+        DefaultedComparisonSynthesizer(*this, RD, FD, DCK, BodyLoc).build();
+    if (Body.isInvalid()) {
+      FD->setInvalidDecl();
+      return;
+    }
+    FD->setBody(Body.get());
+    FD->markUsed(Context);
+  }
+
+  // The exception specification is needed because we are defining the
+  // function. Note that this will reuse the body we just built.
+  ResolveExceptionSpec(UseLoc, FD->getType()->castAs<FunctionProtoType>());
+
+  if (ASTMutationListener *L = getASTMutationListener())
+    L->CompletedImplicitDefinition(FD);
+}
+
+static Sema::ImplicitExceptionSpecification
+ComputeDefaultedComparisonExceptionSpec(Sema &S, SourceLocation Loc,
+                                        FunctionDecl *FD,
+                                        Sema::DefaultedComparisonKind DCK) {
+  ComputingExceptionSpec CES(S, FD, Loc);
+  Sema::ImplicitExceptionSpecification ExceptSpec(S);
+
+  if (FD->isInvalidDecl())
+    return ExceptSpec;
+
+  // The common case is that we just defined the comparison function. In that
+  // case, just look at whether the body can throw.
+  if (FD->hasBody()) {
+    ExceptSpec.CalledStmt(FD->getBody());
+  } else {
+    // Otherwise, build a body so we can check it. This should ideally only
+    // happen when we're not actually marking the function referenced. (This is
+    // only really important for efficiency: we don't want to build and throw
+    // away bodies for comparison functions more than we strictly need to.)
+
+    // Pretend to synthesize the function body in an unevaluated context.
+    // Note that we can't actually just go ahead and define the function here:
+    // we are not permitted to mark its callees as referenced.
+    Sema::SynthesizedFunctionScope Scope(S, FD);
+    EnterExpressionEvaluationContext Context(
+        S, Sema::ExpressionEvaluationContext::Unevaluated);
+
+    CXXRecordDecl *RD = cast<CXXRecordDecl>(FD->getLexicalParent());
+    SourceLocation BodyLoc =
+        FD->getEndLoc().isValid() ? FD->getEndLoc() : FD->getLocation();
+    StmtResult Body =
+        DefaultedComparisonSynthesizer(S, RD, FD, DCK, BodyLoc).build();
+    if (!Body.isInvalid())
+      ExceptSpec.CalledStmt(Body.get());
+
+    // FIXME: Can we hold onto this body and just transform it to potentially
+    // evaluated when we're asked to define the function rather than rebuilding
+    // it? Either that, or we should only build the bits of the body that we
+    // need (the expressions, not the statements).
+  }
+
+  return ExceptSpec;
+}
+
+void Sema::CheckDelayedMemberExceptionSpecs() {
+  decltype(DelayedOverridingExceptionSpecChecks) Overriding;
+  decltype(DelayedEquivalentExceptionSpecChecks) Equivalent;
+
+  std::swap(Overriding, DelayedOverridingExceptionSpecChecks);
+  std::swap(Equivalent, DelayedEquivalentExceptionSpecChecks);
+
+  // Perform any deferred checking of exception specifications for virtual
+  // destructors.
+  for (auto &Check : Overriding)
+    CheckOverridingFunctionExceptionSpec(Check.first, Check.second);
+
+  // Perform any deferred checking of exception specifications for befriended
+  // special members.
+  for (auto &Check : Equivalent)
+    CheckEquivalentExceptionSpec(Check.second, Check.first);
+}
+
+namespace {
+/// CRTP base class for visiting operations performed by a special member
+/// function (or inherited constructor).
+template<typename Derived>
+struct SpecialMemberVisitor {
+  Sema &S;
+  CXXMethodDecl *MD;
+  Sema::CXXSpecialMember CSM;
+  Sema::InheritedConstructorInfo *ICI;
+
+  // Properties of the special member, computed for convenience.
+  bool IsConstructor = false, IsAssignment = false, ConstArg = false;
+
+  SpecialMemberVisitor(Sema &S, CXXMethodDecl *MD, Sema::CXXSpecialMember CSM,
+                       Sema::InheritedConstructorInfo *ICI)
+      : S(S), MD(MD), CSM(CSM), ICI(ICI) {
+    switch (CSM) {
+    case Sema::CXXDefaultConstructor:
+    case Sema::CXXCopyConstructor:
+    case Sema::CXXMoveConstructor:
+      IsConstructor = true;
+      break;
+    case Sema::CXXCopyAssignment:
+    case Sema::CXXMoveAssignment:
+      IsAssignment = true;
+      break;
+    case Sema::CXXDestructor:
+      break;
+    case Sema::CXXInvalid:
+      llvm_unreachable("invalid special member kind");
+    }
+
+    if (MD->getNumParams()) {
+      if (const ReferenceType *RT =
+              MD->getParamDecl(0)->getType()->getAs<ReferenceType>())
+        ConstArg = RT->getPointeeType().isConstQualified();
+    }
+  }
+
+  Derived &getDerived() { return static_cast<Derived&>(*this); }
+
+  /// Is this a "move" special member?
+  bool isMove() const {
+    return CSM == Sema::CXXMoveConstructor || CSM == Sema::CXXMoveAssignment;
+  }
+
+  /// Look up the corresponding special member in the given class.
+  Sema::SpecialMemberOverloadResult lookupIn(CXXRecordDecl *Class,
+                                             unsigned Quals, bool IsMutable) {
+    return lookupCallFromSpecialMember(S, Class, CSM, Quals,
+                                       ConstArg && !IsMutable);
+  }
+
+  /// Look up the constructor for the specified base class to see if it's
+  /// overridden due to this being an inherited constructor.
+  Sema::SpecialMemberOverloadResult lookupInheritedCtor(CXXRecordDecl *Class) {
+    if (!ICI)
+      return {};
+    assert(CSM == Sema::CXXDefaultConstructor);
+    auto *BaseCtor =
+      cast<CXXConstructorDecl>(MD)->getInheritedConstructor().getConstructor();
+    if (auto *MD = ICI->findConstructorForBase(Class, BaseCtor).first)
+      return MD;
+    return {};
+  }
+
+  /// A base or member subobject.
+  typedef llvm::PointerUnion<CXXBaseSpecifier*, FieldDecl*> Subobject;
+
+  /// Get the location to use for a subobject in diagnostics.
+  static SourceLocation getSubobjectLoc(Subobject Subobj) {
+    // FIXME: For an indirect virtual base, the direct base leading to
+    // the indirect virtual base would be a more useful choice.
+    if (auto *B = Subobj.dyn_cast<CXXBaseSpecifier*>())
+      return B->getBaseTypeLoc();
+    else
+      return Subobj.get<FieldDecl*>()->getLocation();
+  }
+
+  enum BasesToVisit {
+    /// Visit all non-virtual (direct) bases.
+    VisitNonVirtualBases,
+    /// Visit all direct bases, virtual or not.
+    VisitDirectBases,
+    /// Visit all non-virtual bases, and all virtual bases if the class
+    /// is not abstract.
+    VisitPotentiallyConstructedBases,
+    /// Visit all direct or virtual bases.
+    VisitAllBases
+  };
+
+  // Visit the bases and members of the class.
+  bool visit(BasesToVisit Bases) {
+    CXXRecordDecl *RD = MD->getParent();
+
+    if (Bases == VisitPotentiallyConstructedBases)
+      Bases = RD->isAbstract() ? VisitNonVirtualBases : VisitAllBases;
+
+    for (auto &B : RD->bases())
+      if ((Bases == VisitDirectBases || !B.isVirtual()) &&
+          getDerived().visitBase(&B))
+        return true;
+
+    if (Bases == VisitAllBases)
+      for (auto &B : RD->vbases())
+        if (getDerived().visitBase(&B))
+          return true;
+
+    for (auto *F : RD->fields())
+      if (!F->isInvalidDecl() && !F->isUnnamedBitfield() &&
+          getDerived().visitField(F))
+        return true;
+
+    return false;
+  }
+};
+}
+
+namespace {
+struct SpecialMemberDeletionInfo
+    : SpecialMemberVisitor<SpecialMemberDeletionInfo> {
+  bool Diagnose;
+
+  SourceLocation Loc;
+
+  bool AllFieldsAreConst;
+
+  SpecialMemberDeletionInfo(Sema &S, CXXMethodDecl *MD,
+                            Sema::CXXSpecialMember CSM,
+                            Sema::InheritedConstructorInfo *ICI, bool Diagnose)
+      : SpecialMemberVisitor(S, MD, CSM, ICI), Diagnose(Diagnose),
+        Loc(MD->getLocation()), AllFieldsAreConst(true) {}
+
+  bool inUnion() const { return MD->getParent()->isUnion(); }
+
+  Sema::CXXSpecialMember getEffectiveCSM() {
+    return ICI ? Sema::CXXInvalid : CSM;
+  }
+
+  bool shouldDeleteForVariantObjCPtrMember(FieldDecl *FD, QualType FieldType);
+
+  bool visitBase(CXXBaseSpecifier *Base) { return shouldDeleteForBase(Base); }
+  bool visitField(FieldDecl *Field) { return shouldDeleteForField(Field); }
+
+  bool shouldDeleteForBase(CXXBaseSpecifier *Base);
+  bool shouldDeleteForField(FieldDecl *FD);
+  bool shouldDeleteForAllConstMembers();
+
+  bool shouldDeleteForClassSubobject(CXXRecordDecl *Class, Subobject Subobj,
+                                     unsigned Quals);
+  bool shouldDeleteForSubobjectCall(Subobject Subobj,
+                                    Sema::SpecialMemberOverloadResult SMOR,
+                                    bool IsDtorCallInCtor);
+
+  bool isAccessible(Subobject Subobj, CXXMethodDecl *D);
+};
+}
+
+/// Is the given special member inaccessible when used on the given
+/// sub-object.
+bool SpecialMemberDeletionInfo::isAccessible(Subobject Subobj,
+                                             CXXMethodDecl *target) {
+  /// If we're operating on a base class, the object type is the
+  /// type of this special member.
+  QualType objectTy;
+  AccessSpecifier access = target->getAccess();
+  if (CXXBaseSpecifier *base = Subobj.dyn_cast<CXXBaseSpecifier*>()) {
+    objectTy = S.Context.getTypeDeclType(MD->getParent());
+    access = CXXRecordDecl::MergeAccess(base->getAccessSpecifier(), access);
+
+  // If we're operating on a field, the object type is the type of the field.
+  } else {
+    objectTy = S.Context.getTypeDeclType(target->getParent());
+  }
+
+  return S.isMemberAccessibleForDeletion(
+      target->getParent(), DeclAccessPair::make(target, access), objectTy);
+}
+
+/// Check whether we should delete a special member due to the implicit
+/// definition containing a call to a special member of a subobject.
+bool SpecialMemberDeletionInfo::shouldDeleteForSubobjectCall(
+    Subobject Subobj, Sema::SpecialMemberOverloadResult SMOR,
+    bool IsDtorCallInCtor) {
+  CXXMethodDecl *Decl = SMOR.getMethod();
+  FieldDecl *Field = Subobj.dyn_cast<FieldDecl*>();
+
+  int DiagKind = -1;
+
+  if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::NoMemberOrDeleted)
+    DiagKind = !Decl ? 0 : 1;
+  else if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::Ambiguous)
+    DiagKind = 2;
+  else if (!isAccessible(Subobj, Decl))
+    DiagKind = 3;
+  else if (!IsDtorCallInCtor && Field && Field->getParent()->isUnion() &&
+           !Decl->isTrivial()) {
+    // A member of a union must have a trivial corresponding special member.
+    // As a weird special case, a destructor call from a union's constructor
+    // must be accessible and non-deleted, but need not be trivial. Such a
+    // destructor is never actually called, but is semantically checked as
+    // if it were.
+    DiagKind = 4;
+  }
+
+  if (DiagKind == -1)
+    return false;
+
+  if (Diagnose) {
+    if (Field) {
+      S.Diag(Field->getLocation(),
+             diag::note_deleted_special_member_class_subobject)
+        << getEffectiveCSM() << MD->getParent() << /*IsField*/true
+        << Field << DiagKind << IsDtorCallInCtor << /*IsObjCPtr*/false;
+    } else {
+      CXXBaseSpecifier *Base = Subobj.get<CXXBaseSpecifier*>();
+      S.Diag(Base->getBeginLoc(),
+             diag::note_deleted_special_member_class_subobject)
+          << getEffectiveCSM() << MD->getParent() << /*IsField*/ false
+          << Base->getType() << DiagKind << IsDtorCallInCtor
+          << /*IsObjCPtr*/false;
+    }
+
+    if (DiagKind == 1)
+      S.NoteDeletedFunction(Decl);
+    // FIXME: Explain inaccessibility if DiagKind == 3.
+  }
+
+  return true;
+}
+
+/// Check whether we should delete a special member function due to having a
+/// direct or virtual base class or non-static data member of class type M.
+bool SpecialMemberDeletionInfo::shouldDeleteForClassSubobject(
+    CXXRecordDecl *Class, Subobject Subobj, unsigned Quals) {
+  FieldDecl *Field = Subobj.dyn_cast<FieldDecl*>();
+  bool IsMutable = Field && Field->isMutable();
+
+  // C++11 [class.ctor]p5:
+  // -- any direct or virtual base class, or non-static data member with no
+  //    brace-or-equal-initializer, has class type M (or array thereof) and
+  //    either M has no default constructor or overload resolution as applied
+  //    to M's default constructor results in an ambiguity or in a function
+  //    that is deleted or inaccessible
+  // C++11 [class.copy]p11, C++11 [class.copy]p23:
+  // -- a direct or virtual base class B that cannot be copied/moved because
+  //    overload resolution, as applied to B's corresponding special member,
+  //    results in an ambiguity or a function that is deleted or inaccessible
+  //    from the defaulted special member
+  // C++11 [class.dtor]p5:
+  // -- any direct or virtual base class [...] has a type with a destructor
+  //    that is deleted or inaccessible
+  if (!(CSM == Sema::CXXDefaultConstructor &&
+        Field && Field->hasInClassInitializer()) &&
+      shouldDeleteForSubobjectCall(Subobj, lookupIn(Class, Quals, IsMutable),
+                                   false))
+    return true;
+
+  // C++11 [class.ctor]p5, C++11 [class.copy]p11:
+  // -- any direct or virtual base class or non-static data member has a
+  //    type with a destructor that is deleted or inaccessible
+  if (IsConstructor) {
+    Sema::SpecialMemberOverloadResult SMOR =
+        S.LookupSpecialMember(Class, Sema::CXXDestructor,
+                              false, false, false, false, false);
+    if (shouldDeleteForSubobjectCall(Subobj, SMOR, true))
+      return true;
+  }
+
+  return false;
+}
+
+bool SpecialMemberDeletionInfo::shouldDeleteForVariantObjCPtrMember(
+    FieldDecl *FD, QualType FieldType) {
+  // The defaulted special functions are defined as deleted if this is a variant
+  // member with a non-trivial ownership type, e.g., ObjC __strong or __weak
+  // type under ARC.
+  if (!FieldType.hasNonTrivialObjCLifetime())
+    return false;
+
+  // Don't make the defaulted default constructor defined as deleted if the
+  // member has an in-class initializer.
+  if (CSM == Sema::CXXDefaultConstructor && FD->hasInClassInitializer())
+    return false;
+
+  if (Diagnose) {
+    auto *ParentClass = cast<CXXRecordDecl>(FD->getParent());
+    S.Diag(FD->getLocation(),
+           diag::note_deleted_special_member_class_subobject)
+        << getEffectiveCSM() << ParentClass << /*IsField*/true
+        << FD << 4 << /*IsDtorCallInCtor*/false << /*IsObjCPtr*/true;
+  }
+
+  return true;
+}
+
+/// Check whether we should delete a special member function due to the class
+/// having a particular direct or virtual base class.
+bool SpecialMemberDeletionInfo::shouldDeleteForBase(CXXBaseSpecifier *Base) {
+  CXXRecordDecl *BaseClass = Base->getType()->getAsCXXRecordDecl();
+  // If program is correct, BaseClass cannot be null, but if it is, the error
+  // must be reported elsewhere.
+  if (!BaseClass)
+    return false;
+  // If we have an inheriting constructor, check whether we're calling an
+  // inherited constructor instead of a default constructor.
+  Sema::SpecialMemberOverloadResult SMOR = lookupInheritedCtor(BaseClass);
+  if (auto *BaseCtor = SMOR.getMethod()) {
+    // Note that we do not check access along this path; other than that,
+    // this is the same as shouldDeleteForSubobjectCall(Base, BaseCtor, false);
+    // FIXME: Check that the base has a usable destructor! Sink this into
+    // shouldDeleteForClassSubobject.
+    if (BaseCtor->isDeleted() && Diagnose) {
+      S.Diag(Base->getBeginLoc(),
+             diag::note_deleted_special_member_class_subobject)
+          << getEffectiveCSM() << MD->getParent() << /*IsField*/ false
+          << Base->getType() << /*Deleted*/ 1 << /*IsDtorCallInCtor*/ false
+          << /*IsObjCPtr*/false;
+      S.NoteDeletedFunction(BaseCtor);
+    }
+    return BaseCtor->isDeleted();
+  }
+  return shouldDeleteForClassSubobject(BaseClass, Base, 0);
+}
+
+/// Check whether we should delete a special member function due to the class
+/// having a particular non-static data member.
+bool SpecialMemberDeletionInfo::shouldDeleteForField(FieldDecl *FD) {
+  QualType FieldType = S.Context.getBaseElementType(FD->getType());
+  CXXRecordDecl *FieldRecord = FieldType->getAsCXXRecordDecl();
+
+  if (inUnion() && shouldDeleteForVariantObjCPtrMember(FD, FieldType))
+    return true;
+
+  if (CSM == Sema::CXXDefaultConstructor) {
+    // For a default constructor, all references must be initialized in-class
+    // and, if a union, it must have a non-const member.
+    if (FieldType->isReferenceType() && !FD->hasInClassInitializer()) {
+      if (Diagnose)
+        S.Diag(FD->getLocation(), diag::note_deleted_default_ctor_uninit_field)
+          << !!ICI << MD->getParent() << FD << FieldType << /*Reference*/0;
+      return true;
+    }
+    // C++11 [class.ctor]p5: any non-variant non-static data member of
+    // const-qualified type (or array thereof) with no
+    // brace-or-equal-initializer does not have a user-provided default
+    // constructor.
+    if (!inUnion() && FieldType.isConstQualified() &&
+        !FD->hasInClassInitializer() &&
+        (!FieldRecord || !FieldRecord->hasUserProvidedDefaultConstructor())) {
+      if (Diagnose)
+        S.Diag(FD->getLocation(), diag::note_deleted_default_ctor_uninit_field)
+          << !!ICI << MD->getParent() << FD << FD->getType() << /*Const*/1;
+      return true;
+    }
+
+    if (inUnion() && !FieldType.isConstQualified())
+      AllFieldsAreConst = false;
+  } else if (CSM == Sema::CXXCopyConstructor) {
+    // For a copy constructor, data members must not be of rvalue reference
+    // type.
+    if (FieldType->isRValueReferenceType()) {
+      if (Diagnose)
+        S.Diag(FD->getLocation(), diag::note_deleted_copy_ctor_rvalue_reference)
+          << MD->getParent() << FD << FieldType;
+      return true;
+    }
+  } else if (IsAssignment) {
+    // For an assignment operator, data members must not be of reference type.
+    if (FieldType->isReferenceType()) {
+      if (Diagnose)
+        S.Diag(FD->getLocation(), diag::note_deleted_assign_field)
+          << isMove() << MD->getParent() << FD << FieldType << /*Reference*/0;
+      return true;
+    }
+    if (!FieldRecord && FieldType.isConstQualified()) {
+      // C++11 [class.copy]p23:
+      // -- a non-static data member of const non-class type (or array thereof)
+      if (Diagnose)
+        S.Diag(FD->getLocation(), diag::note_deleted_assign_field)
+          << isMove() << MD->getParent() << FD << FD->getType() << /*Const*/1;
+      return true;
+    }
+  }
+
+  if (FieldRecord) {
+    // Some additional restrictions exist on the variant members.
+    if (!inUnion() && FieldRecord->isUnion() &&
+        FieldRecord->isAnonymousStructOrUnion()) {
+      bool AllVariantFieldsAreConst = true;
+
+      // FIXME: Handle anonymous unions declared within anonymous unions.
+      for (auto *UI : FieldRecord->fields()) {
+        QualType UnionFieldType = S.Context.getBaseElementType(UI->getType());
+
+        if (shouldDeleteForVariantObjCPtrMember(&*UI, UnionFieldType))
+          return true;
+
+        if (!UnionFieldType.isConstQualified())
+          AllVariantFieldsAreConst = false;
+
+        CXXRecordDecl *UnionFieldRecord = UnionFieldType->getAsCXXRecordDecl();
+        if (UnionFieldRecord &&
+            shouldDeleteForClassSubobject(UnionFieldRecord, UI,
+                                          UnionFieldType.getCVRQualifiers()))
+          return true;
+      }
+
+      // At least one member in each anonymous union must be non-const
+      if (CSM == Sema::CXXDefaultConstructor && AllVariantFieldsAreConst &&
+          !FieldRecord->field_empty()) {
+        if (Diagnose)
+          S.Diag(FieldRecord->getLocation(),
+                 diag::note_deleted_default_ctor_all_const)
+            << !!ICI << MD->getParent() << /*anonymous union*/1;
+        return true;
+      }
+
+      // Don't check the implicit member of the anonymous union type.
+      // This is technically non-conformant but supported, and we have a
+      // diagnostic for this elsewhere.
+      return false;
+    }
+
+    if (shouldDeleteForClassSubobject(FieldRecord, FD,
+                                      FieldType.getCVRQualifiers()))
+      return true;
+  }
+
+  return false;
+}
+
+/// C++11 [class.ctor] p5:
+///   A defaulted default constructor for a class X is defined as deleted if
+/// X is a union and all of its variant members are of const-qualified type.
+bool SpecialMemberDeletionInfo::shouldDeleteForAllConstMembers() {
+  // This is a silly definition, because it gives an empty union a deleted
+  // default constructor. Don't do that.
+  if (CSM == Sema::CXXDefaultConstructor && inUnion() && AllFieldsAreConst) {
+    bool AnyFields = false;
+    for (auto *F : MD->getParent()->fields())
+      if ((AnyFields = !F->isUnnamedBitfield()))
+        break;
+    if (!AnyFields)
+      return false;
+    if (Diagnose)
+      S.Diag(MD->getParent()->getLocation(),
+             diag::note_deleted_default_ctor_all_const)
+        << !!ICI << MD->getParent() << /*not anonymous union*/0;
+    return true;
+  }
+  return false;
+}
+
+/// Determine whether a defaulted special member function should be defined as
+/// deleted, as specified in C++11 [class.ctor]p5, C++11 [class.copy]p11,
+/// C++11 [class.copy]p23, and C++11 [class.dtor]p5.
+bool Sema::ShouldDeleteSpecialMember(CXXMethodDecl *MD, CXXSpecialMember CSM,
+                                     InheritedConstructorInfo *ICI,
+                                     bool Diagnose) {
+  if (MD->isInvalidDecl())
+    return false;
+  CXXRecordDecl *RD = MD->getParent();
+  assert(!RD->isDependentType() && "do deletion after instantiation");
+  if (!LangOpts.CPlusPlus11 || RD->isInvalidDecl())
+    return false;
+
+  // C++11 [expr.lambda.prim]p19:
+  //   The closure type associated with a lambda-expression has a
+  //   deleted (8.4.3) default constructor and a deleted copy
+  //   assignment operator.
+  // C++2a adds back these operators if the lambda has no lambda-capture.
+  if (RD->isLambda() && !RD->lambdaIsDefaultConstructibleAndAssignable() &&
+      (CSM == CXXDefaultConstructor || CSM == CXXCopyAssignment)) {
+    if (Diagnose)
+      Diag(RD->getLocation(), diag::note_lambda_decl);
+    return true;
+  }
+
+  // For an anonymous struct or union, the copy and assignment special members
+  // will never be used, so skip the check. For an anonymous union declared at
+  // namespace scope, the constructor and destructor are used.
+  if (CSM != CXXDefaultConstructor && CSM != CXXDestructor &&
+      RD->isAnonymousStructOrUnion())
+    return false;
+
+  // C++11 [class.copy]p7, p18:
+  //   If the class definition declares a move constructor or move assignment
+  //   operator, an implicitly declared copy constructor or copy assignment
+  //   operator is defined as deleted.
+  if (MD->isImplicit() &&
+      (CSM == CXXCopyConstructor || CSM == CXXCopyAssignment)) {
+    CXXMethodDecl *UserDeclaredMove = nullptr;
+
+    // In Microsoft mode up to MSVC 2013, a user-declared move only causes the
+    // deletion of the corresponding copy operation, not both copy operations.
+    // MSVC 2015 has adopted the standards conforming behavior.
+    bool DeletesOnlyMatchingCopy =
+        getLangOpts().MSVCCompat &&
+        !getLangOpts().isCompatibleWithMSVC(LangOptions::MSVC2015);
+
+    if (RD->hasUserDeclaredMoveConstructor() &&
+        (!DeletesOnlyMatchingCopy || CSM == CXXCopyConstructor)) {
+      if (!Diagnose) return true;
+
+      // Find any user-declared move constructor.
+      for (auto *I : RD->ctors()) {
+        if (I->isMoveConstructor()) {
+          UserDeclaredMove = I;
+          break;
+        }
+      }
+      assert(UserDeclaredMove);
+    } else if (RD->hasUserDeclaredMoveAssignment() &&
+               (!DeletesOnlyMatchingCopy || CSM == CXXCopyAssignment)) {
+      if (!Diagnose) return true;
+
+      // Find any user-declared move assignment operator.
+      for (auto *I : RD->methods()) {
+        if (I->isMoveAssignmentOperator()) {
+          UserDeclaredMove = I;
+          break;
+        }
+      }
+      assert(UserDeclaredMove);
+    }
+
+    if (UserDeclaredMove) {
+      Diag(UserDeclaredMove->getLocation(),
+           diag::note_deleted_copy_user_declared_move)
+        << (CSM == CXXCopyAssignment) << RD
+        << UserDeclaredMove->isMoveAssignmentOperator();
+      return true;
+    }
+  }
+
+  // Do access control from the special member function
+  ContextRAII MethodContext(*this, MD);
+
+  // C++11 [class.dtor]p5:
+  // -- for a virtual destructor, lookup of the non-array deallocation function
+  //    results in an ambiguity or in a function that is deleted or inaccessible
+  if (CSM == CXXDestructor && MD->isVirtual()) {
+    FunctionDecl *OperatorDelete = nullptr;
+    DeclarationName Name =
+      Context.DeclarationNames.getCXXOperatorName(OO_Delete);
+    if (FindDeallocationFunction(MD->getLocation(), MD->getParent(), Name,
+                                 OperatorDelete, /*Diagnose*/false)) {
+      if (Diagnose)
+        Diag(RD->getLocation(), diag::note_deleted_dtor_no_operator_delete);
+      return true;
+    }
+  }
+
+  SpecialMemberDeletionInfo SMI(*this, MD, CSM, ICI, Diagnose);
+
+  // Per DR1611, do not consider virtual bases of constructors of abstract
+  // classes, since we are not going to construct them.
+  // Per DR1658, do not consider virtual bases of destructors of abstract
+  // classes either.
+  // Per DR2180, for assignment operators we only assign (and thus only
+  // consider) direct bases.
+  if (SMI.visit(SMI.IsAssignment ? SMI.VisitDirectBases
+                                 : SMI.VisitPotentiallyConstructedBases))
+    return true;
+
+  if (SMI.shouldDeleteForAllConstMembers())
+    return true;
+
+  if (getLangOpts().CUDA) {
+    // We should delete the special member in CUDA mode if target inference
+    // failed.
+    // For inherited constructors (non-null ICI), CSM may be passed so that MD
+    // is treated as certain special member, which may not reflect what special
+    // member MD really is. However inferCUDATargetForImplicitSpecialMember
+    // expects CSM to match MD, therefore recalculate CSM.
+    assert(ICI || CSM == getSpecialMember(MD));
+    auto RealCSM = CSM;
+    if (ICI)
+      RealCSM = getSpecialMember(MD);
+
+    return inferCUDATargetForImplicitSpecialMember(RD, RealCSM, MD,
+                                                   SMI.ConstArg, Diagnose);
+  }
+
+  return false;
+}
+
+void Sema::DiagnoseDeletedDefaultedFunction(FunctionDecl *FD) {
+  DefaultedFunctionKind DFK = getDefaultedFunctionKind(FD);
+  assert(DFK && "not a defaultable function");
+  assert(FD->isDefaulted() && FD->isDeleted() && "not defaulted and deleted");
+
+  if (DFK.isSpecialMember()) {
+    ShouldDeleteSpecialMember(cast<CXXMethodDecl>(FD), DFK.asSpecialMember(),
+                              nullptr, /*Diagnose=*/true);
+  } else {
+    DefaultedComparisonAnalyzer(
+        *this, cast<CXXRecordDecl>(FD->getLexicalDeclContext()), FD,
+        DFK.asComparison(), DefaultedComparisonAnalyzer::ExplainDeleted)
+        .visit();
+  }
+}
+
+/// Perform lookup for a special member of the specified kind, and determine
+/// whether it is trivial. If the triviality can be determined without the
+/// lookup, skip it. This is intended for use when determining whether a
+/// special member of a containing object is trivial, and thus does not ever
+/// perform overload resolution for default constructors.
+///
+/// If \p Selected is not \c NULL, \c *Selected will be filled in with the
+/// member that was most likely to be intended to be trivial, if any.
+///
+/// If \p ForCall is true, look at CXXRecord::HasTrivialSpecialMembersForCall to
+/// determine whether the special member is trivial.
+static bool findTrivialSpecialMember(Sema &S, CXXRecordDecl *RD,
+                                     Sema::CXXSpecialMember CSM, unsigned Quals,
+                                     bool ConstRHS,
+                                     Sema::TrivialABIHandling TAH,
+                                     CXXMethodDecl **Selected) {
+  if (Selected)
+    *Selected = nullptr;
+
+  switch (CSM) {
+  case Sema::CXXInvalid:
+    llvm_unreachable("not a special member");
+
+  case Sema::CXXDefaultConstructor:
+    // C++11 [class.ctor]p5:
+    //   A default constructor is trivial if:
+    //    - all the [direct subobjects] have trivial default constructors
+    //
+    // Note, no overload resolution is performed in this case.
+    if (RD->hasTrivialDefaultConstructor())
+      return true;
+
+    if (Selected) {
+      // If there's a default constructor which could have been trivial, dig it
+      // out. Otherwise, if there's any user-provided default constructor, point
+      // to that as an example of why there's not a trivial one.
+      CXXConstructorDecl *DefCtor = nullptr;
+      if (RD->needsImplicitDefaultConstructor())
+        S.DeclareImplicitDefaultConstructor(RD);
+      for (auto *CI : RD->ctors()) {
+        if (!CI->isDefaultConstructor())
+          continue;
+        DefCtor = CI;
+        if (!DefCtor->isUserProvided())
+          break;
+      }
+
+      *Selected = DefCtor;
+    }
+
+    return false;
+
+  case Sema::CXXDestructor:
+    // C++11 [class.dtor]p5:
+    //   A destructor is trivial if:
+    //    - all the direct [subobjects] have trivial destructors
+    if (RD->hasTrivialDestructor() ||
+        (TAH == Sema::TAH_ConsiderTrivialABI &&
+         RD->hasTrivialDestructorForCall()))
+      return true;
+
+    if (Selected) {
+      if (RD->needsImplicitDestructor())
+        S.DeclareImplicitDestructor(RD);
+      *Selected = RD->getDestructor();
+    }
+
+    return false;
+
+  case Sema::CXXCopyConstructor:
+    // C++11 [class.copy]p12:
+    //   A copy constructor is trivial if:
+    //    - the constructor selected to copy each direct [subobject] is trivial
+    if (RD->hasTrivialCopyConstructor() ||
+        (TAH == Sema::TAH_ConsiderTrivialABI &&
+         RD->hasTrivialCopyConstructorForCall())) {
+      if (Quals == Qualifiers::Const)
+        // We must either select the trivial copy constructor or reach an
+        // ambiguity; no need to actually perform overload resolution.
+        return true;
+    } else if (!Selected) {
+      return false;
+    }
+    // In C++98, we are not supposed to perform overload resolution here, but we
+    // treat that as a language defect, as suggested on cxx-abi-dev, to treat
+    // cases like B as having a non-trivial copy constructor:
+    //   struct A { template<typename T> A(T&); };
+    //   struct B { mutable A a; };
+    goto NeedOverloadResolution;
+
+  case Sema::CXXCopyAssignment:
+    // C++11 [class.copy]p25:
+    //   A copy assignment operator is trivial if:
+    //    - the assignment operator selected to copy each direct [subobject] is
+    //      trivial
+    if (RD->hasTrivialCopyAssignment()) {
+      if (Quals == Qualifiers::Const)
+        return true;
+    } else if (!Selected) {
+      return false;
+    }
+    // In C++98, we are not supposed to perform overload resolution here, but we
+    // treat that as a language defect.
+    goto NeedOverloadResolution;
+
+  case Sema::CXXMoveConstructor:
+  case Sema::CXXMoveAssignment:
+  NeedOverloadResolution:
+    Sema::SpecialMemberOverloadResult SMOR =
+        lookupCallFromSpecialMember(S, RD, CSM, Quals, ConstRHS);
+
+    // The standard doesn't describe how to behave if the lookup is ambiguous.
+    // We treat it as not making the member non-trivial, just like the standard
+    // mandates for the default constructor. This should rarely matter, because
+    // the member will also be deleted.
+    if (SMOR.getKind() == Sema::SpecialMemberOverloadResult::Ambiguous)
+      return true;
+
+    if (!SMOR.getMethod()) {
+      assert(SMOR.getKind() ==
+             Sema::SpecialMemberOverloadResult::NoMemberOrDeleted);
+      return false;
+    }
+
+    // We deliberately don't check if we found a deleted special member. We're
+    // not supposed to!
+    if (Selected)
+      *Selected = SMOR.getMethod();
+
+    if (TAH == Sema::TAH_ConsiderTrivialABI &&
+        (CSM == Sema::CXXCopyConstructor || CSM == Sema::CXXMoveConstructor))
+      return SMOR.getMethod()->isTrivialForCall();
+    return SMOR.getMethod()->isTrivial();
+  }
+
+  llvm_unreachable("unknown special method kind");
+}
+
+static CXXConstructorDecl *findUserDeclaredCtor(CXXRecordDecl *RD) {
+  for (auto *CI : RD->ctors())
+    if (!CI->isImplicit())
+      return CI;
+
+  // Look for constructor templates.
+  typedef CXXRecordDecl::specific_decl_iterator<FunctionTemplateDecl> tmpl_iter;
+  for (tmpl_iter TI(RD->decls_begin()), TE(RD->decls_end()); TI != TE; ++TI) {
+    if (CXXConstructorDecl *CD =
+          dyn_cast<CXXConstructorDecl>(TI->getTemplatedDecl()))
+      return CD;
+  }
+
+  return nullptr;
+}
+
+/// The kind of subobject we are checking for triviality. The values of this
+/// enumeration are used in diagnostics.
+enum TrivialSubobjectKind {
+  /// The subobject is a base class.
+  TSK_BaseClass,
+  /// The subobject is a non-static data member.
+  TSK_Field,
+  /// The object is actually the complete object.
+  TSK_CompleteObject
+};
+
+/// Check whether the special member selected for a given type would be trivial.
+static bool checkTrivialSubobjectCall(Sema &S, SourceLocation SubobjLoc,
+                                      QualType SubType, bool ConstRHS,
+                                      Sema::CXXSpecialMember CSM,
+                                      TrivialSubobjectKind Kind,
+                                      Sema::TrivialABIHandling TAH, bool Diagnose) {
+  CXXRecordDecl *SubRD = SubType->getAsCXXRecordDecl();
+  if (!SubRD)
+    return true;
+
+  CXXMethodDecl *Selected;
+  if (findTrivialSpecialMember(S, SubRD, CSM, SubType.getCVRQualifiers(),
+                               ConstRHS, TAH, Diagnose ? &Selected : nullptr))
+    return true;
+
+  if (Diagnose) {
+    if (ConstRHS)
+      SubType.addConst();
+
+    if (!Selected && CSM == Sema::CXXDefaultConstructor) {
+      S.Diag(SubobjLoc, diag::note_nontrivial_no_def_ctor)
+        << Kind << SubType.getUnqualifiedType();
+      if (CXXConstructorDecl *CD = findUserDeclaredCtor(SubRD))
+        S.Diag(CD->getLocation(), diag::note_user_declared_ctor);
+    } else if (!Selected)
+      S.Diag(SubobjLoc, diag::note_nontrivial_no_copy)
+        << Kind << SubType.getUnqualifiedType() << CSM << SubType;
+    else if (Selected->isUserProvided()) {
+      if (Kind == TSK_CompleteObject)
+        S.Diag(Selected->getLocation(), diag::note_nontrivial_user_provided)
+          << Kind << SubType.getUnqualifiedType() << CSM;
+      else {
+        S.Diag(SubobjLoc, diag::note_nontrivial_user_provided)
+          << Kind << SubType.getUnqualifiedType() << CSM;
+        S.Diag(Selected->getLocation(), diag::note_declared_at);
+      }
+    } else {
+      if (Kind != TSK_CompleteObject)
+        S.Diag(SubobjLoc, diag::note_nontrivial_subobject)
+          << Kind << SubType.getUnqualifiedType() << CSM;
+
+      // Explain why the defaulted or deleted special member isn't trivial.
+      S.SpecialMemberIsTrivial(Selected, CSM, Sema::TAH_IgnoreTrivialABI,
+                               Diagnose);
+    }
+  }
+
+  return false;
+}
+
+/// Check whether the members of a class type allow a special member to be
+/// trivial.
+static bool checkTrivialClassMembers(Sema &S, CXXRecordDecl *RD,
+                                     Sema::CXXSpecialMember CSM,
+                                     bool ConstArg,
+                                     Sema::TrivialABIHandling TAH,
+                                     bool Diagnose) {
+  for (const auto *FI : RD->fields()) {
+    if (FI->isInvalidDecl() || FI->isUnnamedBitfield())
+      continue;
+
+    QualType FieldType = S.Context.getBaseElementType(FI->getType());
+
+    // Pretend anonymous struct or union members are members of this class.
+    if (FI->isAnonymousStructOrUnion()) {
+      if (!checkTrivialClassMembers(S, FieldType->getAsCXXRecordDecl(),
+                                    CSM, ConstArg, TAH, Diagnose))
+        return false;
+      continue;
+    }
+
+    // C++11 [class.ctor]p5:
+    //   A default constructor is trivial if [...]
+    //    -- no non-static data member of its class has a
+    //       brace-or-equal-initializer
+    if (CSM == Sema::CXXDefaultConstructor && FI->hasInClassInitializer()) {
+      if (Diagnose)
+        S.Diag(FI->getLocation(), diag::note_nontrivial_default_member_init)
+            << FI;
+      return false;
+    }
+
+    // Objective C ARC 4.3.5:
+    //   [...] nontrivally ownership-qualified types are [...] not trivially
+    //   default constructible, copy constructible, move constructible, copy
+    //   assignable, move assignable, or destructible [...]
+    if (FieldType.hasNonTrivialObjCLifetime()) {
+      if (Diagnose)
+        S.Diag(FI->getLocation(), diag::note_nontrivial_objc_ownership)
+          << RD << FieldType.getObjCLifetime();
+      return false;
+    }
+
+    bool ConstRHS = ConstArg && !FI->isMutable();
+    if (!checkTrivialSubobjectCall(S, FI->getLocation(), FieldType, ConstRHS,
+                                   CSM, TSK_Field, TAH, Diagnose))
+      return false;
+  }
+
+  return true;
+}
+
+/// Diagnose why the specified class does not have a trivial special member of
+/// the given kind.
+void Sema::DiagnoseNontrivial(const CXXRecordDecl *RD, CXXSpecialMember CSM) {
+  QualType Ty = Context.getRecordType(RD);
+
+  bool ConstArg = (CSM == CXXCopyConstructor || CSM == CXXCopyAssignment);
+  checkTrivialSubobjectCall(*this, RD->getLocation(), Ty, ConstArg, CSM,
+                            TSK_CompleteObject, TAH_IgnoreTrivialABI,
+                            /*Diagnose*/true);
+}
+
+/// Determine whether a defaulted or deleted special member function is trivial,
+/// as specified in C++11 [class.ctor]p5, C++11 [class.copy]p12,
+/// C++11 [class.copy]p25, and C++11 [class.dtor]p5.
+bool Sema::SpecialMemberIsTrivial(CXXMethodDecl *MD, CXXSpecialMember CSM,
+                                  TrivialABIHandling TAH, bool Diagnose) {
+  assert(!MD->isUserProvided() && CSM != CXXInvalid && "not special enough");
+
+  CXXRecordDecl *RD = MD->getParent();
+
+  bool ConstArg = false;
+
+  // C++11 [class.copy]p12, p25: [DR1593]
+  //   A [special member] is trivial if [...] its parameter-type-list is
+  //   equivalent to the parameter-type-list of an implicit declaration [...]
+  switch (CSM) {
+  case CXXDefaultConstructor:
+  case CXXDestructor:
+    // Trivial default constructors and destructors cannot have parameters.
+    break;
+
+  case CXXCopyConstructor:
+  case CXXCopyAssignment: {
+    // Trivial copy operations always have const, non-volatile parameter types.
+    ConstArg = true;
+    const ParmVarDecl *Param0 = MD->getParamDecl(0);
+    const ReferenceType *RT = Param0->getType()->getAs<ReferenceType>();
+    if (!RT || RT->getPointeeType().getCVRQualifiers() != Qualifiers::Const) {
+      if (Diagnose)
+        Diag(Param0->getLocation(), diag::note_nontrivial_param_type)
+          << Param0->getSourceRange() << Param0->getType()
+          << Context.getLValueReferenceType(
+               Context.getRecordType(RD).withConst());
+      return false;
+    }
+    break;
+  }
+
+  case CXXMoveConstructor:
+  case CXXMoveAssignment: {
+    // Trivial move operations always have non-cv-qualified parameters.
+    const ParmVarDecl *Param0 = MD->getParamDecl(0);
+    const RValueReferenceType *RT =
+      Param0->getType()->getAs<RValueReferenceType>();
+    if (!RT || RT->getPointeeType().getCVRQualifiers()) {
+      if (Diagnose)
+        Diag(Param0->getLocation(), diag::note_nontrivial_param_type)
+          << Param0->getSourceRange() << Param0->getType()
+          << Context.getRValueReferenceType(Context.getRecordType(RD));
+      return false;
+    }
+    break;
+  }
+
+  case CXXInvalid:
+    llvm_unreachable("not a special member");
+  }
+
+  if (MD->getMinRequiredArguments() < MD->getNumParams()) {
+    if (Diagnose)
+      Diag(MD->getParamDecl(MD->getMinRequiredArguments())->getLocation(),
+           diag::note_nontrivial_default_arg)
+        << MD->getParamDecl(MD->getMinRequiredArguments())->getSourceRange();
+    return false;
+  }
+  if (MD->isVariadic()) {
+    if (Diagnose)
+      Diag(MD->getLocation(), diag::note_nontrivial_variadic);
+    return false;
+  }
+
+  // C++11 [class.ctor]p5, C++11 [class.dtor]p5:
+  //   A copy/move [constructor or assignment operator] is trivial if
+  //    -- the [member] selected to copy/move each direct base class subobject
+  //       is trivial
+  //
+  // C++11 [class.copy]p12, C++11 [class.copy]p25:
+  //   A [default constructor or destructor] is trivial if
+  //    -- all the direct base classes have trivial [default constructors or
+  //       destructors]
+  for (const auto &BI : RD->bases())
+    if (!checkTrivialSubobjectCall(*this, BI.getBeginLoc(), BI.getType(),
+                                   ConstArg, CSM, TSK_BaseClass, TAH, Diagnose))
+      return false;
+
+  // C++11 [class.ctor]p5, C++11 [class.dtor]p5:
+  //   A copy/move [constructor or assignment operator] for a class X is
+  //   trivial if
+  //    -- for each non-static data member of X that is of class type (or array
+  //       thereof), the constructor selected to copy/move that member is
+  //       trivial
+  //
+  // C++11 [class.copy]p12, C++11 [class.copy]p25:
+  //   A [default constructor or destructor] is trivial if
+  //    -- for all of the non-static data members of its class that are of class
+  //       type (or array thereof), each such class has a trivial [default
+  //       constructor or destructor]
+  if (!checkTrivialClassMembers(*this, RD, CSM, ConstArg, TAH, Diagnose))
+    return false;
+
+  // C++11 [class.dtor]p5:
+  //   A destructor is trivial if [...]
+  //    -- the destructor is not virtual
+  if (CSM == CXXDestructor && MD->isVirtual()) {
+    if (Diagnose)
+      Diag(MD->getLocation(), diag::note_nontrivial_virtual_dtor) << RD;
+    return false;
+  }
+
+  // C++11 [class.ctor]p5, C++11 [class.copy]p12, C++11 [class.copy]p25:
+  //   A [special member] for class X is trivial if [...]
+  //    -- class X has no virtual functions and no virtual base classes
+  if (CSM != CXXDestructor && MD->getParent()->isDynamicClass()) {
+    if (!Diagnose)
+      return false;
+
+    if (RD->getNumVBases()) {
+      // Check for virtual bases. We already know that the corresponding
+      // member in all bases is trivial, so vbases must all be direct.
+      CXXBaseSpecifier &BS = *RD->vbases_begin();
+      assert(BS.isVirtual());
+      Diag(BS.getBeginLoc(), diag::note_nontrivial_has_virtual) << RD << 1;
+      return false;
+    }
+
+    // Must have a virtual method.
+    for (const auto *MI : RD->methods()) {
+      if (MI->isVirtual()) {
+        SourceLocation MLoc = MI->getBeginLoc();
+        Diag(MLoc, diag::note_nontrivial_has_virtual) << RD << 0;
+        return false;
+      }
+    }
+
+    llvm_unreachable("dynamic class with no vbases and no virtual functions");
+  }
+
+  // Looks like it's trivial!
+  return true;
+}
+
+namespace {
+struct FindHiddenVirtualMethod {
+  Sema *S;
+  CXXMethodDecl *Method;
+  llvm::SmallPtrSet<const CXXMethodDecl *, 8> OverridenAndUsingBaseMethods;
+  SmallVector<CXXMethodDecl *, 8> OverloadedMethods;
+
+private:
+  /// Check whether any most overridden method from MD in Methods
+  static bool CheckMostOverridenMethods(
+      const CXXMethodDecl *MD,
+      const llvm::SmallPtrSetImpl<const CXXMethodDecl *> &Methods) {
+    if (MD->size_overridden_methods() == 0)
+      return Methods.count(MD->getCanonicalDecl());
+    for (const CXXMethodDecl *O : MD->overridden_methods())
+      if (CheckMostOverridenMethods(O, Methods))
+        return true;
+    return false;
+  }
+
+public:
+  /// Member lookup function that determines whether a given C++
+  /// method overloads virtual methods in a base class without overriding any,
+  /// to be used with CXXRecordDecl::lookupInBases().
+  bool operator()(const CXXBaseSpecifier *Specifier, CXXBasePath &Path) {
+    RecordDecl *BaseRecord =
+        Specifier->getType()->castAs<RecordType>()->getDecl();
+
+    DeclarationName Name = Method->getDeclName();
+    assert(Name.getNameKind() == DeclarationName::Identifier);
+
+    bool foundSameNameMethod = false;
+    SmallVector<CXXMethodDecl *, 8> overloadedMethods;
+    for (Path.Decls = BaseRecord->lookup(Name).begin();
+         Path.Decls != DeclContext::lookup_iterator(); ++Path.Decls) {
+      NamedDecl *D = *Path.Decls;
+      if (CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(D)) {
+        MD = MD->getCanonicalDecl();
+        foundSameNameMethod = true;
+        // Interested only in hidden virtual methods.
+        if (!MD->isVirtual())
+          continue;
+        // If the method we are checking overrides a method from its base
+        // don't warn about the other overloaded methods. Clang deviates from
+        // GCC by only diagnosing overloads of inherited virtual functions that
+        // do not override any other virtual functions in the base. GCC's
+        // -Woverloaded-virtual diagnoses any derived function hiding a virtual
+        // function from a base class. These cases may be better served by a
+        // warning (not specific to virtual functions) on call sites when the
+        // call would select a different function from the base class, were it
+        // visible.
+        // See FIXME in test/SemaCXX/warn-overload-virtual.cpp for an example.
+        if (!S->IsOverload(Method, MD, false))
+          return true;
+        // Collect the overload only if its hidden.
+        if (!CheckMostOverridenMethods(MD, OverridenAndUsingBaseMethods))
+          overloadedMethods.push_back(MD);
+      }
+    }
+
+    if (foundSameNameMethod)
+      OverloadedMethods.append(overloadedMethods.begin(),
+                               overloadedMethods.end());
+    return foundSameNameMethod;
+  }
+};
+} // end anonymous namespace
+
+/// Add the most overridden methods from MD to Methods
+static void AddMostOverridenMethods(const CXXMethodDecl *MD,
+                        llvm::SmallPtrSetImpl<const CXXMethodDecl *>& Methods) {
+  if (MD->size_overridden_methods() == 0)
+    Methods.insert(MD->getCanonicalDecl());
+  else
+    for (const CXXMethodDecl *O : MD->overridden_methods())
+      AddMostOverridenMethods(O, Methods);
+}
+
+/// Check if a method overloads virtual methods in a base class without
+/// overriding any.
+void Sema::FindHiddenVirtualMethods(CXXMethodDecl *MD,
+                          SmallVectorImpl<CXXMethodDecl*> &OverloadedMethods) {
+  if (!MD->getDeclName().isIdentifier())
+    return;
+
+  CXXBasePaths Paths(/*FindAmbiguities=*/true, // true to look in all bases.
+                     /*bool RecordPaths=*/false,
+                     /*bool DetectVirtual=*/false);
+  FindHiddenVirtualMethod FHVM;
+  FHVM.Method = MD;
+  FHVM.S = this;
+
+  // Keep the base methods that were overridden or introduced in the subclass
+  // by 'using' in a set. A base method not in this set is hidden.
+  CXXRecordDecl *DC = MD->getParent();
+  DeclContext::lookup_result R = DC->lookup(MD->getDeclName());
+  for (DeclContext::lookup_iterator I = R.begin(), E = R.end(); I != E; ++I) {
+    NamedDecl *ND = *I;
+    if (UsingShadowDecl *shad = dyn_cast<UsingShadowDecl>(*I))
+      ND = shad->getTargetDecl();
+    if (CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(ND))
+      AddMostOverridenMethods(MD, FHVM.OverridenAndUsingBaseMethods);
+  }
+
+  if (DC->lookupInBases(FHVM, Paths))
+    OverloadedMethods = FHVM.OverloadedMethods;
+}
+
+void Sema::NoteHiddenVirtualMethods(CXXMethodDecl *MD,
+                          SmallVectorImpl<CXXMethodDecl*> &OverloadedMethods) {
+  for (unsigned i = 0, e = OverloadedMethods.size(); i != e; ++i) {
+    CXXMethodDecl *overloadedMD = OverloadedMethods[i];
+    PartialDiagnostic PD = PDiag(
+         diag::note_hidden_overloaded_virtual_declared_here) << overloadedMD;
+    HandleFunctionTypeMismatch(PD, MD->getType(), overloadedMD->getType());
+    Diag(overloadedMD->getLocation(), PD);
+  }
+}
+
+/// Diagnose methods which overload virtual methods in a base class
+/// without overriding any.
+void Sema::DiagnoseHiddenVirtualMethods(CXXMethodDecl *MD) {
+  if (MD->isInvalidDecl())
+    return;
+
+  if (Diags.isIgnored(diag::warn_overloaded_virtual, MD->getLocation()))
+    return;
+
+  SmallVector<CXXMethodDecl *, 8> OverloadedMethods;
+  FindHiddenVirtualMethods(MD, OverloadedMethods);
+  if (!OverloadedMethods.empty()) {
+    Diag(MD->getLocation(), diag::warn_overloaded_virtual)
+      << MD << (OverloadedMethods.size() > 1);
+
+    NoteHiddenVirtualMethods(MD, OverloadedMethods);
+  }
+}
+
+void Sema::checkIllFormedTrivialABIStruct(CXXRecordDecl &RD) {
+  auto PrintDiagAndRemoveAttr = [&](unsigned N) {
+    // No diagnostics if this is a template instantiation.
+    if (!isTemplateInstantiation(RD.getTemplateSpecializationKind())) {
+      Diag(RD.getAttr<TrivialABIAttr>()->getLocation(),
+           diag::ext_cannot_use_trivial_abi) << &RD;
+      Diag(RD.getAttr<TrivialABIAttr>()->getLocation(),
+           diag::note_cannot_use_trivial_abi_reason) << &RD << N;
+    }
+    RD.dropAttr<TrivialABIAttr>();
+  };
+
+  // Ill-formed if the copy and move constructors are deleted.
+  auto HasNonDeletedCopyOrMoveConstructor = [&]() {
+    // If the type is dependent, then assume it might have
+    // implicit copy or move ctor because we won't know yet at this point.
+    if (RD.isDependentType())
+      return true;
+    if (RD.needsImplicitCopyConstructor() &&
+        !RD.defaultedCopyConstructorIsDeleted())
+      return true;
+    if (RD.needsImplicitMoveConstructor() &&
+        !RD.defaultedMoveConstructorIsDeleted())
+      return true;
+    for (const CXXConstructorDecl *CD : RD.ctors())
+      if (CD->isCopyOrMoveConstructor() && !CD->isDeleted())
+        return true;
+    return false;
+  };
+
+  if (!HasNonDeletedCopyOrMoveConstructor()) {
+    PrintDiagAndRemoveAttr(0);
+    return;
+  }
+
+  // Ill-formed if the struct has virtual functions.
+  if (RD.isPolymorphic()) {
+    PrintDiagAndRemoveAttr(1);
+    return;
+  }
+
+  for (const auto &B : RD.bases()) {
+    // Ill-formed if the base class is non-trivial for the purpose of calls or a
+    // virtual base.
+    if (!B.getType()->isDependentType() &&
+        !B.getType()->getAsCXXRecordDecl()->canPassInRegisters()) {
+      PrintDiagAndRemoveAttr(2);
+      return;
+    }
+
+    if (B.isVirtual()) {
+      PrintDiagAndRemoveAttr(3);
+      return;
+    }
+  }
+
+  for (const auto *FD : RD.fields()) {
+    // Ill-formed if the field is an ObjectiveC pointer or of a type that is
+    // non-trivial for the purpose of calls.
+    QualType FT = FD->getType();
+    if (FT.getObjCLifetime() == Qualifiers::OCL_Weak) {
+      PrintDiagAndRemoveAttr(4);
+      return;
+    }
+
+    if (const auto *RT = FT->getBaseElementTypeUnsafe()->getAs<RecordType>())
+      if (!RT->isDependentType() &&
+          !cast<CXXRecordDecl>(RT->getDecl())->canPassInRegisters()) {
+        PrintDiagAndRemoveAttr(5);
+        return;
+      }
+  }
+}
+
+void Sema::ActOnFinishCXXMemberSpecification(
+    Scope *S, SourceLocation RLoc, Decl *TagDecl, SourceLocation LBrac,
+    SourceLocation RBrac, const ParsedAttributesView &AttrList) {
+  if (!TagDecl)
+    return;
+
+  AdjustDeclIfTemplate(TagDecl);
+
+  for (const ParsedAttr &AL : AttrList) {
+    if (AL.getKind() != ParsedAttr::AT_Visibility)
+      continue;
+    AL.setInvalid();
+    Diag(AL.getLoc(), diag::warn_attribute_after_definition_ignored) << AL;
+  }
+
+  ActOnFields(S, RLoc, TagDecl, llvm::makeArrayRef(
+              // strict aliasing violation!
+              reinterpret_cast<Decl**>(FieldCollector->getCurFields()),
+              FieldCollector->getCurNumFields()), LBrac, RBrac, AttrList);
+
+  CheckCompletedCXXClass(S, cast<CXXRecordDecl>(TagDecl));
+}
+
+/// Find the equality comparison functions that should be implicitly declared
+/// in a given class definition, per C++2a [class.compare.default]p3.
+static void findImplicitlyDeclaredEqualityComparisons(
+    ASTContext &Ctx, CXXRecordDecl *RD,
+    llvm::SmallVectorImpl<FunctionDecl *> &Spaceships) {
+  DeclarationName EqEq = Ctx.DeclarationNames.getCXXOperatorName(OO_EqualEqual);
+  if (!RD->lookup(EqEq).empty())
+    // Member operator== explicitly declared: no implicit operator==s.
+    return;
+
+  // Traverse friends looking for an '==' or a '<=>'.
+  for (FriendDecl *Friend : RD->friends()) {
+    FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(Friend->getFriendDecl());
+    if (!FD) continue;
+
+    if (FD->getOverloadedOperator() == OO_EqualEqual) {
+      // Friend operator== explicitly declared: no implicit operator==s.
+      Spaceships.clear();
+      return;
+    }
+
+    if (FD->getOverloadedOperator() == OO_Spaceship &&
+        FD->isExplicitlyDefaulted())
+      Spaceships.push_back(FD);
+  }
+
+  // Look for members named 'operator<=>'.
+  DeclarationName Cmp = Ctx.DeclarationNames.getCXXOperatorName(OO_Spaceship);
+  for (NamedDecl *ND : RD->lookup(Cmp)) {
+    // Note that we could find a non-function here (either a function template
+    // or a using-declaration). Neither case results in an implicit
+    // 'operator=='.
+    if (auto *FD = dyn_cast<FunctionDecl>(ND))
+      if (FD->isExplicitlyDefaulted())
+        Spaceships.push_back(FD);
+  }
+}
+
+/// AddImplicitlyDeclaredMembersToClass - Adds any implicitly-declared
+/// special functions, such as the default constructor, copy
+/// constructor, or destructor, to the given C++ class (C++
+/// [special]p1).  This routine can only be executed just before the
+/// definition of the class is complete.
+void Sema::AddImplicitlyDeclaredMembersToClass(CXXRecordDecl *ClassDecl) {
+  // Don't add implicit special members to templated classes.
+  // FIXME: This means unqualified lookups for 'operator=' within a class
+  // template don't work properly.
+  if (!ClassDecl->isDependentType()) {
+    if (ClassDecl->needsImplicitDefaultConstructor()) {
+      ++getASTContext().NumImplicitDefaultConstructors;
+
+      if (ClassDecl->hasInheritedConstructor())
+        DeclareImplicitDefaultConstructor(ClassDecl);
+    }
+
+    if (ClassDecl->needsImplicitCopyConstructor()) {
+      ++getASTContext().NumImplicitCopyConstructors;
+
+      // If the properties or semantics of the copy constructor couldn't be
+      // determined while the class was being declared, force a declaration
+      // of it now.
+      if (ClassDecl->needsOverloadResolutionForCopyConstructor() ||
+          ClassDecl->hasInheritedConstructor())
+        DeclareImplicitCopyConstructor(ClassDecl);
+      // For the MS ABI we need to know whether the copy ctor is deleted. A
+      // prerequisite for deleting the implicit copy ctor is that the class has
+      // a move ctor or move assignment that is either user-declared or whose
+      // semantics are inherited from a subobject. FIXME: We should provide a
+      // more direct way for CodeGen to ask whether the constructor was deleted.
+      else if (Context.getTargetInfo().getCXXABI().isMicrosoft() &&
+               (ClassDecl->hasUserDeclaredMoveConstructor() ||
+                ClassDecl->needsOverloadResolutionForMoveConstructor() ||
+                ClassDecl->hasUserDeclaredMoveAssignment() ||
+                ClassDecl->needsOverloadResolutionForMoveAssignment()))
+        DeclareImplicitCopyConstructor(ClassDecl);
+    }
+
+    if (getLangOpts().CPlusPlus11 &&
+        ClassDecl->needsImplicitMoveConstructor()) {
+      ++getASTContext().NumImplicitMoveConstructors;
+
+      if (ClassDecl->needsOverloadResolutionForMoveConstructor() ||
+          ClassDecl->hasInheritedConstructor())
+        DeclareImplicitMoveConstructor(ClassDecl);
+    }
+
+    if (ClassDecl->needsImplicitCopyAssignment()) {
+      ++getASTContext().NumImplicitCopyAssignmentOperators;
+
+      // If we have a dynamic class, then the copy assignment operator may be
+      // virtual, so we have to declare it immediately. This ensures that, e.g.,
+      // it shows up in the right place in the vtable and that we diagnose
+      // problems with the implicit exception specification.
+      if (ClassDecl->isDynamicClass() ||
+          ClassDecl->needsOverloadResolutionForCopyAssignment() ||
+          ClassDecl->hasInheritedAssignment())
+        DeclareImplicitCopyAssignment(ClassDecl);
+    }
+
+    if (getLangOpts().CPlusPlus11 && ClassDecl->needsImplicitMoveAssignment()) {
+      ++getASTContext().NumImplicitMoveAssignmentOperators;
+
+      // Likewise for the move assignment operator.
+      if (ClassDecl->isDynamicClass() ||
+          ClassDecl->needsOverloadResolutionForMoveAssignment() ||
+          ClassDecl->hasInheritedAssignment())
+        DeclareImplicitMoveAssignment(ClassDecl);
+    }
+
+    if (ClassDecl->needsImplicitDestructor()) {
+      ++getASTContext().NumImplicitDestructors;
+
+      // If we have a dynamic class, then the destructor may be virtual, so we
+      // have to declare the destructor immediately. This ensures that, e.g., it
+      // shows up in the right place in the vtable and that we diagnose problems
+      // with the implicit exception specification.
+      if (ClassDecl->isDynamicClass() ||
+          ClassDecl->needsOverloadResolutionForDestructor())
+        DeclareImplicitDestructor(ClassDecl);
+    }
+  }
+
+  // C++2a [class.compare.default]p3:
+  //   If the member-specification does not explicitly declare any member or
+  //   friend named operator==, an == operator function is declared implicitly
+  //   for each defaulted three-way comparison operator function defined in
+  //   the member-specification
+  // FIXME: Consider doing this lazily.
+  // We do this during the initial parse for a class template, not during
+  // instantiation, so that we can handle unqualified lookups for 'operator=='
+  // when parsing the template.
+  if (getLangOpts().CPlusPlus20 && !inTemplateInstantiation()) {
+    llvm::SmallVector<FunctionDecl *, 4> DefaultedSpaceships;
+    findImplicitlyDeclaredEqualityComparisons(Context, ClassDecl,
+                                              DefaultedSpaceships);
+    for (auto *FD : DefaultedSpaceships)
+      DeclareImplicitEqualityComparison(ClassDecl, FD);
+  }
+}
+
+unsigned
+Sema::ActOnReenterTemplateScope(Decl *D,
+                                llvm::function_ref<Scope *()> EnterScope) {
+  if (!D)
+    return 0;
+  AdjustDeclIfTemplate(D);
+
+  // In order to get name lookup right, reenter template scopes in order from
+  // outermost to innermost.
+  SmallVector<TemplateParameterList *, 4> ParameterLists;
+  DeclContext *LookupDC = dyn_cast<DeclContext>(D);
+
+  if (DeclaratorDecl *DD = dyn_cast<DeclaratorDecl>(D)) {
+    for (unsigned i = 0; i < DD->getNumTemplateParameterLists(); ++i)
+      ParameterLists.push_back(DD->getTemplateParameterList(i));
+
+    if (FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
+      if (FunctionTemplateDecl *FTD = FD->getDescribedFunctionTemplate())
+        ParameterLists.push_back(FTD->getTemplateParameters());
+    } else if (VarDecl *VD = dyn_cast<VarDecl>(D)) {
+      LookupDC = VD->getDeclContext();
+
+      if (VarTemplateDecl *VTD = VD->getDescribedVarTemplate())
+        ParameterLists.push_back(VTD->getTemplateParameters());
+      else if (auto *PSD = dyn_cast<VarTemplatePartialSpecializationDecl>(D))
+        ParameterLists.push_back(PSD->getTemplateParameters());
+    }
+  } else if (TagDecl *TD = dyn_cast<TagDecl>(D)) {
+    for (unsigned i = 0; i < TD->getNumTemplateParameterLists(); ++i)
+      ParameterLists.push_back(TD->getTemplateParameterList(i));
+
+    if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(TD)) {
+      if (ClassTemplateDecl *CTD = RD->getDescribedClassTemplate())
+        ParameterLists.push_back(CTD->getTemplateParameters());
+      else if (auto *PSD = dyn_cast<ClassTemplatePartialSpecializationDecl>(D))
+        ParameterLists.push_back(PSD->getTemplateParameters());
+    }
+  }
+  // FIXME: Alias declarations and concepts.
+
+  unsigned Count = 0;
+  Scope *InnermostTemplateScope = nullptr;
+  for (TemplateParameterList *Params : ParameterLists) {
+    // Ignore explicit specializations; they don't contribute to the template
+    // depth.
+    if (Params->size() == 0)
+      continue;
+
+    InnermostTemplateScope = EnterScope();
+    for (NamedDecl *Param : *Params) {
+      if (Param->getDeclName()) {
+        InnermostTemplateScope->AddDecl(Param);
+        IdResolver.AddDecl(Param);
+      }
+    }
+    ++Count;
+  }
+
+  // Associate the new template scopes with the corresponding entities.
+  if (InnermostTemplateScope) {
+    assert(LookupDC && "no enclosing DeclContext for template lookup");
+    EnterTemplatedContext(InnermostTemplateScope, LookupDC);
+  }
+
+  return Count;
+}
+
+void Sema::ActOnStartDelayedMemberDeclarations(Scope *S, Decl *RecordD) {
+  if (!RecordD) return;
+  AdjustDeclIfTemplate(RecordD);
+  CXXRecordDecl *Record = cast<CXXRecordDecl>(RecordD);
+  PushDeclContext(S, Record);
+}
+
+void Sema::ActOnFinishDelayedMemberDeclarations(Scope *S, Decl *RecordD) {
+  if (!RecordD) return;
+  PopDeclContext();
+}
+
+/// This is used to implement the constant expression evaluation part of the
+/// attribute enable_if extension. There is nothing in standard C++ which would
+/// require reentering parameters.
+void Sema::ActOnReenterCXXMethodParameter(Scope *S, ParmVarDecl *Param) {
+  if (!Param)
+    return;
+
+  S->AddDecl(Param);
+  if (Param->getDeclName())
+    IdResolver.AddDecl(Param);
+}
+
+/// ActOnStartDelayedCXXMethodDeclaration - We have completed
+/// parsing a top-level (non-nested) C++ class, and we are now
+/// parsing those parts of the given Method declaration that could
+/// not be parsed earlier (C++ [class.mem]p2), such as default
+/// arguments. This action should enter the scope of the given
+/// Method declaration as if we had just parsed the qualified method
+/// name. However, it should not bring the parameters into scope;
+/// that will be performed by ActOnDelayedCXXMethodParameter.
+void Sema::ActOnStartDelayedCXXMethodDeclaration(Scope *S, Decl *MethodD) {
+}
+
+/// ActOnDelayedCXXMethodParameter - We've already started a delayed
+/// C++ method declaration. We're (re-)introducing the given
+/// function parameter into scope for use in parsing later parts of
+/// the method declaration. For example, we could see an
+/// ActOnParamDefaultArgument event for this parameter.
+void Sema::ActOnDelayedCXXMethodParameter(Scope *S, Decl *ParamD) {
+  if (!ParamD)
+    return;
+
+  ParmVarDecl *Param = cast<ParmVarDecl>(ParamD);
+
+  S->AddDecl(Param);
+  if (Param->getDeclName())
+    IdResolver.AddDecl(Param);
+}
+
+/// ActOnFinishDelayedCXXMethodDeclaration - We have finished
+/// processing the delayed method declaration for Method. The method
+/// declaration is now considered finished. There may be a separate
+/// ActOnStartOfFunctionDef action later (not necessarily
+/// immediately!) for this method, if it was also defined inside the
+/// class body.
+void Sema::ActOnFinishDelayedCXXMethodDeclaration(Scope *S, Decl *MethodD) {
+  if (!MethodD)
+    return;
+
+  AdjustDeclIfTemplate(MethodD);
+
+  FunctionDecl *Method = cast<FunctionDecl>(MethodD);
+
+  // Now that we have our default arguments, check the constructor
+  // again. It could produce additional diagnostics or affect whether
+  // the class has implicitly-declared destructors, among other
+  // things.
+  if (CXXConstructorDecl *Constructor = dyn_cast<CXXConstructorDecl>(Method))
+    CheckConstructor(Constructor);
+
+  // Check the default arguments, which we may have added.
+  if (!Method->isInvalidDecl())
+    CheckCXXDefaultArguments(Method);
+}
+
+// Emit the given diagnostic for each non-address-space qualifier.
+// Common part of CheckConstructorDeclarator and CheckDestructorDeclarator.
+static void checkMethodTypeQualifiers(Sema &S, Declarator &D, unsigned DiagID) {
+  const DeclaratorChunk::FunctionTypeInfo &FTI = D.getFunctionTypeInfo();
+  if (FTI.hasMethodTypeQualifiers() && !D.isInvalidType()) {
+    bool DiagOccured = false;
+    FTI.MethodQualifiers->forEachQualifier(
+        [DiagID, &S, &DiagOccured](DeclSpec::TQ, StringRef QualName,
+                                   SourceLocation SL) {
+          // This diagnostic should be emitted on any qualifier except an addr
+          // space qualifier. However, forEachQualifier currently doesn't visit
+          // addr space qualifiers, so there's no way to write this condition
+          // right now; we just diagnose on everything.
+          S.Diag(SL, DiagID) << QualName << SourceRange(SL);
+          DiagOccured = true;
+        });
+    if (DiagOccured)
+      D.setInvalidType();
+  }
+}
+
+/// CheckConstructorDeclarator - Called by ActOnDeclarator to check
+/// the well-formedness of the constructor declarator @p D with type @p
+/// R. If there are any errors in the declarator, this routine will
+/// emit diagnostics and set the invalid bit to true.  In any case, the type
+/// will be updated to reflect a well-formed type for the constructor and
+/// returned.
+QualType Sema::CheckConstructorDeclarator(Declarator &D, QualType R,
+                                          StorageClass &SC) {
+  bool isVirtual = D.getDeclSpec().isVirtualSpecified();
+
+  // C++ [class.ctor]p3:
+  //   A constructor shall not be virtual (10.3) or static (9.4). A
+  //   constructor can be invoked for a const, volatile or const
+  //   volatile object. A constructor shall not be declared const,
+  //   volatile, or const volatile (9.3.2).
+  if (isVirtual) {
+    if (!D.isInvalidType())
+      Diag(D.getIdentifierLoc(), diag::err_constructor_cannot_be)
+        << "virtual" << SourceRange(D.getDeclSpec().getVirtualSpecLoc())
+        << SourceRange(D.getIdentifierLoc());
+    D.setInvalidType();
+  }
+  if (SC == SC_Static) {
+    if (!D.isInvalidType())
+      Diag(D.getIdentifierLoc(), diag::err_constructor_cannot_be)
+        << "static" << SourceRange(D.getDeclSpec().getStorageClassSpecLoc())
+        << SourceRange(D.getIdentifierLoc());
+    D.setInvalidType();
+    SC = SC_None;
+  }
+
+  if (unsigned TypeQuals = D.getDeclSpec().getTypeQualifiers()) {
+    diagnoseIgnoredQualifiers(
+        diag::err_constructor_return_type, TypeQuals, SourceLocation(),
+        D.getDeclSpec().getConstSpecLoc(), D.getDeclSpec().getVolatileSpecLoc(),
+        D.getDeclSpec().getRestrictSpecLoc(),
+        D.getDeclSpec().getAtomicSpecLoc());
+    D.setInvalidType();
+  }
+
+  checkMethodTypeQualifiers(*this, D, diag::err_invalid_qualified_constructor);
+
+  // C++0x [class.ctor]p4:
+  //   A constructor shall not be declared with a ref-qualifier.
+  DeclaratorChunk::FunctionTypeInfo &FTI = D.getFunctionTypeInfo();
+  if (FTI.hasRefQualifier()) {
+    Diag(FTI.getRefQualifierLoc(), diag::err_ref_qualifier_constructor)
+      << FTI.RefQualifierIsLValueRef
+      << FixItHint::CreateRemoval(FTI.getRefQualifierLoc());
+    D.setInvalidType();
+  }
+
+  // Rebuild the function type "R" without any type qualifiers (in
+  // case any of the errors above fired) and with "void" as the
+  // return type, since constructors don't have return types.
+  const FunctionProtoType *Proto = R->castAs<FunctionProtoType>();
+  if (Proto->getReturnType() == Context.VoidTy && !D.isInvalidType())
+    return R;
+
+  FunctionProtoType::ExtProtoInfo EPI = Proto->getExtProtoInfo();
+  EPI.TypeQuals = Qualifiers();
+  EPI.RefQualifier = RQ_None;
+
+  return Context.getFunctionType(Context.VoidTy, Proto->getParamTypes(), EPI);
+}
+
+/// CheckConstructor - Checks a fully-formed constructor for
+/// well-formedness, issuing any diagnostics required. Returns true if
+/// the constructor declarator is invalid.
+void Sema::CheckConstructor(CXXConstructorDecl *Constructor) {
+  CXXRecordDecl *ClassDecl
+    = dyn_cast<CXXRecordDecl>(Constructor->getDeclContext());
+  if (!ClassDecl)
+    return Constructor->setInvalidDecl();
+
+  // C++ [class.copy]p3:
+  //   A declaration of a constructor for a class X is ill-formed if
+  //   its first parameter is of type (optionally cv-qualified) X and
+  //   either there are no other parameters or else all other
+  //   parameters have default arguments.
+  if (!Constructor->isInvalidDecl() &&
+      Constructor->hasOneParamOrDefaultArgs() &&
+      Constructor->getTemplateSpecializationKind() !=
+          TSK_ImplicitInstantiation) {
+    QualType ParamType = Constructor->getParamDecl(0)->getType();
+    QualType ClassTy = Context.getTagDeclType(ClassDecl);
+    if (Context.getCanonicalType(ParamType).getUnqualifiedType() == ClassTy) {
+      SourceLocation ParamLoc = Constructor->getParamDecl(0)->getLocation();
+      const char *ConstRef
+        = Constructor->getParamDecl(0)->getIdentifier() ? "const &"
+                                                        : " const &";
+      Diag(ParamLoc, diag::err_constructor_byvalue_arg)
+        << FixItHint::CreateInsertion(ParamLoc, ConstRef);
+
+      // FIXME: Rather that making the constructor invalid, we should endeavor
+      // to fix the type.
+      Constructor->setInvalidDecl();
+    }
+  }
+}
+
+/// CheckDestructor - Checks a fully-formed destructor definition for
+/// well-formedness, issuing any diagnostics required.  Returns true
+/// on error.
+bool Sema::CheckDestructor(CXXDestructorDecl *Destructor) {
+  CXXRecordDecl *RD = Destructor->getParent();
+
+  if (!Destructor->getOperatorDelete() && Destructor->isVirtual()) {
+    SourceLocation Loc;
+
+    if (!Destructor->isImplicit())
+      Loc = Destructor->getLocation();
+    else
+      Loc = RD->getLocation();
+
+    // If we have a virtual destructor, look up the deallocation function
+    if (FunctionDecl *OperatorDelete =
+            FindDeallocationFunctionForDestructor(Loc, RD)) {
+      Expr *ThisArg = nullptr;
+
+      // If the notional 'delete this' expression requires a non-trivial
+      // conversion from 'this' to the type of a destroying operator delete's
+      // first parameter, perform that conversion now.
+      if (OperatorDelete->isDestroyingOperatorDelete()) {
+        QualType ParamType = OperatorDelete->getParamDecl(0)->getType();
+        if (!declaresSameEntity(ParamType->getAsCXXRecordDecl(), RD)) {
+          // C++ [class.dtor]p13:
+          //   ... as if for the expression 'delete this' appearing in a
+          //   non-virtual destructor of the destructor's class.
+          ContextRAII SwitchContext(*this, Destructor);
+          ExprResult This =
+              ActOnCXXThis(OperatorDelete->getParamDecl(0)->getLocation());
+          assert(!This.isInvalid() && "couldn't form 'this' expr in dtor?");
+          This = PerformImplicitConversion(This.get(), ParamType, AA_Passing);
+          if (This.isInvalid()) {
+            // FIXME: Register this as a context note so that it comes out
+            // in the right order.
+            Diag(Loc, diag::note_implicit_delete_this_in_destructor_here);
+            return true;
+          }
+          ThisArg = This.get();
+        }
+      }
+
+      DiagnoseUseOfDecl(OperatorDelete, Loc);
+      MarkFunctionReferenced(Loc, OperatorDelete);
+      Destructor->setOperatorDelete(OperatorDelete, ThisArg);
+    }
+  }
+
+  return false;
+}
+
+/// CheckDestructorDeclarator - Called by ActOnDeclarator to check
+/// the well-formednes of the destructor declarator @p D with type @p
+/// R. If there are any errors in the declarator, this routine will
+/// emit diagnostics and set the declarator to invalid.  Even if this happens,
+/// will be updated to reflect a well-formed type for the destructor and
+/// returned.
+QualType Sema::CheckDestructorDeclarator(Declarator &D, QualType R,
+                                         StorageClass& SC) {
+  // C++ [class.dtor]p1:
+  //   [...] A typedef-name that names a class is a class-name
+  //   (7.1.3); however, a typedef-name that names a class shall not
+  //   be used as the identifier in the declarator for a destructor
+  //   declaration.
+  QualType DeclaratorType = GetTypeFromParser(D.getName().DestructorName);
+  if (const TypedefType *TT = DeclaratorType->getAs<TypedefType>())
+    Diag(D.getIdentifierLoc(), diag::ext_destructor_typedef_name)
+      << DeclaratorType << isa<TypeAliasDecl>(TT->getDecl());
+  else if (const TemplateSpecializationType *TST =
+             DeclaratorType->getAs<TemplateSpecializationType>())
+    if (TST->isTypeAlias())
+      Diag(D.getIdentifierLoc(), diag::ext_destructor_typedef_name)
+        << DeclaratorType << 1;
+
+  // C++ [class.dtor]p2:
+  //   A destructor is used to destroy objects of its class type. A
+  //   destructor takes no parameters, and no return type can be
+  //   specified for it (not even void). The address of a destructor
+  //   shall not be taken. A destructor shall not be static. A
+  //   destructor can be invoked for a const, volatile or const
+  //   volatile object. A destructor shall not be declared const,
+  //   volatile or const volatile (9.3.2).
+  if (SC == SC_Static) {
+    if (!D.isInvalidType())
+      Diag(D.getIdentifierLoc(), diag::err_destructor_cannot_be)
+        << "static" << SourceRange(D.getDeclSpec().getStorageClassSpecLoc())
+        << SourceRange(D.getIdentifierLoc())
+        << FixItHint::CreateRemoval(D.getDeclSpec().getStorageClassSpecLoc());
+
+    SC = SC_None;
+  }
+  if (!D.isInvalidType()) {
+    // Destructors don't have return types, but the parser will
+    // happily parse something like:
+    //
+    //   class X {
+    //     float ~X();
+    //   };
+    //
+    // The return type will be eliminated later.
+    if (D.getDeclSpec().hasTypeSpecifier())
+      Diag(D.getIdentifierLoc(), diag::err_destructor_return_type)
+        << SourceRange(D.getDeclSpec().getTypeSpecTypeLoc())
+        << SourceRange(D.getIdentifierLoc());
+    else if (unsigned TypeQuals = D.getDeclSpec().getTypeQualifiers()) {
+      diagnoseIgnoredQualifiers(diag::err_destructor_return_type, TypeQuals,
+                                SourceLocation(),
+                                D.getDeclSpec().getConstSpecLoc(),
+                                D.getDeclSpec().getVolatileSpecLoc(),
+                                D.getDeclSpec().getRestrictSpecLoc(),
+                                D.getDeclSpec().getAtomicSpecLoc());
+      D.setInvalidType();
+    }
+  }
+
+  checkMethodTypeQualifiers(*this, D, diag::err_invalid_qualified_destructor);
+
+  // C++0x [class.dtor]p2:
+  //   A destructor shall not be declared with a ref-qualifier.
+  DeclaratorChunk::FunctionTypeInfo &FTI = D.getFunctionTypeInfo();
+  if (FTI.hasRefQualifier()) {
+    Diag(FTI.getRefQualifierLoc(), diag::err_ref_qualifier_destructor)
+      << FTI.RefQualifierIsLValueRef
+      << FixItHint::CreateRemoval(FTI.getRefQualifierLoc());
+    D.setInvalidType();
+  }
+
+  // Make sure we don't have any parameters.
+  if (FTIHasNonVoidParameters(FTI)) {
+    Diag(D.getIdentifierLoc(), diag::err_destructor_with_params);
+
+    // Delete the parameters.
+    FTI.freeParams();
+    D.setInvalidType();
+  }
+
+  // Make sure the destructor isn't variadic.
+  if (FTI.isVariadic) {
+    Diag(D.getIdentifierLoc(), diag::err_destructor_variadic);
+    D.setInvalidType();
+  }
+
+  // Rebuild the function type "R" without any type qualifiers or
+  // parameters (in case any of the errors above fired) and with
+  // "void" as the return type, since destructors don't have return
+  // types.
+  if (!D.isInvalidType())
+    return R;
+
+  const FunctionProtoType *Proto = R->castAs<FunctionProtoType>();
+  FunctionProtoType::ExtProtoInfo EPI = Proto->getExtProtoInfo();
+  EPI.Variadic = false;
+  EPI.TypeQuals = Qualifiers();
+  EPI.RefQualifier = RQ_None;
+  return Context.getFunctionType(Context.VoidTy, None, EPI);
+}
+
+static void extendLeft(SourceRange &R, SourceRange Before) {
+  if (Before.isInvalid())
+    return;
+  R.setBegin(Before.getBegin());
+  if (R.getEnd().isInvalid())
+    R.setEnd(Before.getEnd());
+}
+
+static void extendRight(SourceRange &R, SourceRange After) {
+  if (After.isInvalid())
+    return;
+  if (R.getBegin().isInvalid())
+    R.setBegin(After.getBegin());
+  R.setEnd(After.getEnd());
+}
+
+/// CheckConversionDeclarator - Called by ActOnDeclarator to check the
+/// well-formednes of the conversion function declarator @p D with
+/// type @p R. If there are any errors in the declarator, this routine
+/// will emit diagnostics and return true. Otherwise, it will return
+/// false. Either way, the type @p R will be updated to reflect a
+/// well-formed type for the conversion operator.
+void Sema::CheckConversionDeclarator(Declarator &D, QualType &R,
+                                     StorageClass& SC) {
+  // C++ [class.conv.fct]p1:
+  //   Neither parameter types nor return type can be specified. The
+  //   type of a conversion function (8.3.5) is "function taking no
+  //   parameter returning conversion-type-id."
+  if (SC == SC_Static) {
+    if (!D.isInvalidType())
+      Diag(D.getIdentifierLoc(), diag::err_conv_function_not_member)
+        << SourceRange(D.getDeclSpec().getStorageClassSpecLoc())
+        << D.getName().getSourceRange();
+    D.setInvalidType();
+    SC = SC_None;
+  }
+
+  TypeSourceInfo *ConvTSI = nullptr;
+  QualType ConvType =
+      GetTypeFromParser(D.getName().ConversionFunctionId, &ConvTSI);
+
+  const DeclSpec &DS = D.getDeclSpec();
+  if (DS.hasTypeSpecifier() && !D.isInvalidType()) {
+    // Conversion functions don't have return types, but the parser will
+    // happily parse something like:
+    //
+    //   class X {
+    //     float operator bool();
+    //   };
+    //
+    // The return type will be changed later anyway.
+    Diag(D.getIdentifierLoc(), diag::err_conv_function_return_type)
+      << SourceRange(DS.getTypeSpecTypeLoc())
+      << SourceRange(D.getIdentifierLoc());
+    D.setInvalidType();
+  } else if (DS.getTypeQualifiers() && !D.isInvalidType()) {
+    // It's also plausible that the user writes type qualifiers in the wrong
+    // place, such as:
+    //   struct S { const operator int(); };
+    // FIXME: we could provide a fixit to move the qualifiers onto the
+    // conversion type.
+    Diag(D.getIdentifierLoc(), diag::err_conv_function_with_complex_decl)
+        << SourceRange(D.getIdentifierLoc()) << 0;
+    D.setInvalidType();
+  }
+
+  const auto *Proto = R->castAs<FunctionProtoType>();
+
+  // Make sure we don't have any parameters.
+  if (Proto->getNumParams() > 0) {
+    Diag(D.getIdentifierLoc(), diag::err_conv_function_with_params);
+
+    // Delete the parameters.
+    D.getFunctionTypeInfo().freeParams();
+    D.setInvalidType();
+  } else if (Proto->isVariadic()) {
+    Diag(D.getIdentifierLoc(), diag::err_conv_function_variadic);
+    D.setInvalidType();
+  }
+
+  // Diagnose "&operator bool()" and other such nonsense.  This
+  // is actually a gcc extension which we don't support.
+  if (Proto->getReturnType() != ConvType) {
+    bool NeedsTypedef = false;
+    SourceRange Before, After;
+
+    // Walk the chunks and extract information on them for our diagnostic.
+    bool PastFunctionChunk = false;
+    for (auto &Chunk : D.type_objects()) {
+      switch (Chunk.Kind) {
+      case DeclaratorChunk::Function:
+        if (!PastFunctionChunk) {
+          if (Chunk.Fun.HasTrailingReturnType) {
+            TypeSourceInfo *TRT = nullptr;
+            GetTypeFromParser(Chunk.Fun.getTrailingReturnType(), &TRT);
+            if (TRT) extendRight(After, TRT->getTypeLoc().getSourceRange());
+          }
+          PastFunctionChunk = true;
+          break;
+        }
+        LLVM_FALLTHROUGH;
+      case DeclaratorChunk::Array:
+        NeedsTypedef = true;
+        extendRight(After, Chunk.getSourceRange());
+        break;
+
+      case DeclaratorChunk::Pointer:
+      case DeclaratorChunk::BlockPointer:
+      case DeclaratorChunk::Reference:
+      case DeclaratorChunk::MemberPointer:
+      case DeclaratorChunk::Pipe:
+        extendLeft(Before, Chunk.getSourceRange());
+        break;
+
+      case DeclaratorChunk::Paren:
+        extendLeft(Before, Chunk.Loc);
+        extendRight(After, Chunk.EndLoc);
+        break;
+      }
+    }
+
+    SourceLocation Loc = Before.isValid() ? Before.getBegin() :
+                         After.isValid()  ? After.getBegin() :
+                                            D.getIdentifierLoc();
+    auto &&DB = Diag(Loc, diag::err_conv_function_with_complex_decl);
+    DB << Before << After;
+
+    if (!NeedsTypedef) {
+      DB << /*don't need a typedef*/0;
+
+      // If we can provide a correct fix-it hint, do so.
+      if (After.isInvalid() && ConvTSI) {
+        SourceLocation InsertLoc =
+            getLocForEndOfToken(ConvTSI->getTypeLoc().getEndLoc());
+        DB << FixItHint::CreateInsertion(InsertLoc, " ")
+           << FixItHint::CreateInsertionFromRange(
+                  InsertLoc, CharSourceRange::getTokenRange(Before))
+           << FixItHint::CreateRemoval(Before);
+      }
+    } else if (!Proto->getReturnType()->isDependentType()) {
+      DB << /*typedef*/1 << Proto->getReturnType();
+    } else if (getLangOpts().CPlusPlus11) {
+      DB << /*alias template*/2 << Proto->getReturnType();
+    } else {
+      DB << /*might not be fixable*/3;
+    }
+
+    // Recover by incorporating the other type chunks into the result type.
+    // Note, this does *not* change the name of the function. This is compatible
+    // with the GCC extension:
+    //   struct S { &operator int(); } s;
+    //   int &r = s.operator int(); // ok in GCC
+    //   S::operator int&() {} // error in GCC, function name is 'operator int'.
+    ConvType = Proto->getReturnType();
+  }
+
+  // C++ [class.conv.fct]p4:
+  //   The conversion-type-id shall not represent a function type nor
+  //   an array type.
+  if (ConvType->isArrayType()) {
+    Diag(D.getIdentifierLoc(), diag::err_conv_function_to_array);
+    ConvType = Context.getPointerType(ConvType);
+    D.setInvalidType();
+  } else if (ConvType->isFunctionType()) {
+    Diag(D.getIdentifierLoc(), diag::err_conv_function_to_function);
+    ConvType = Context.getPointerType(ConvType);
+    D.setInvalidType();
+  }
+
+  // Rebuild the function type "R" without any parameters (in case any
+  // of the errors above fired) and with the conversion type as the
+  // return type.
+  if (D.isInvalidType())
+    R = Context.getFunctionType(ConvType, None, Proto->getExtProtoInfo());
+
+  // C++0x explicit conversion operators.
+  if (DS.hasExplicitSpecifier() && !getLangOpts().CPlusPlus20)
+    Diag(DS.getExplicitSpecLoc(),
+         getLangOpts().CPlusPlus11
+             ? diag::warn_cxx98_compat_explicit_conversion_functions
+             : diag::ext_explicit_conversion_functions)
+        << SourceRange(DS.getExplicitSpecRange());
+}
+
+/// ActOnConversionDeclarator - Called by ActOnDeclarator to complete
+/// the declaration of the given C++ conversion function. This routine
+/// is responsible for recording the conversion function in the C++
+/// class, if possible.
+Decl *Sema::ActOnConversionDeclarator(CXXConversionDecl *Conversion) {
+  assert(Conversion && "Expected to receive a conversion function declaration");
+
+  CXXRecordDecl *ClassDecl = cast<CXXRecordDecl>(Conversion->getDeclContext());
+
+  // Make sure we aren't redeclaring the conversion function.
+  QualType ConvType = Context.getCanonicalType(Conversion->getConversionType());
+  // C++ [class.conv.fct]p1:
+  //   [...] A conversion function is never used to convert a
+  //   (possibly cv-qualified) object to the (possibly cv-qualified)
+  //   same object type (or a reference to it), to a (possibly
+  //   cv-qualified) base class of that type (or a reference to it),
+  //   or to (possibly cv-qualified) void.
+  QualType ClassType
+    = Context.getCanonicalType(Context.getTypeDeclType(ClassDecl));
+  if (const ReferenceType *ConvTypeRef = ConvType->getAs<ReferenceType>())
+    ConvType = ConvTypeRef->getPointeeType();
+  if (Conversion->getTemplateSpecializationKind() != TSK_Undeclared &&
+      Conversion->getTemplateSpecializationKind() != TSK_ExplicitSpecialization)
+    /* Suppress diagnostics for instantiations. */;
+  else if (Conversion->size_overridden_methods() != 0)
+    /* Suppress diagnostics for overriding virtual function in a base class. */;
+  else if (ConvType->isRecordType()) {
+    ConvType = Context.getCanonicalType(ConvType).getUnqualifiedType();
+    if (ConvType == ClassType)
+      Diag(Conversion->getLocation(), diag::warn_conv_to_self_not_used)
+        << ClassType;
+    else if (IsDerivedFrom(Conversion->getLocation(), ClassType, ConvType))
+      Diag(Conversion->getLocation(), diag::warn_conv_to_base_not_used)
+        <<  ClassType << ConvType;
+  } else if (ConvType->isVoidType()) {
+    Diag(Conversion->getLocation(), diag::warn_conv_to_void_not_used)
+      << ClassType << ConvType;
+  }
+
+  if (FunctionTemplateDecl *ConversionTemplate
+                                = Conversion->getDescribedFunctionTemplate())
+    return ConversionTemplate;
+
+  return Conversion;
+}
+
+namespace {
+/// Utility class to accumulate and print a diagnostic listing the invalid
+/// specifier(s) on a declaration.
+struct BadSpecifierDiagnoser {
+  BadSpecifierDiagnoser(Sema &S, SourceLocation Loc, unsigned DiagID)
+      : S(S), Diagnostic(S.Diag(Loc, DiagID)) {}
+  ~BadSpecifierDiagnoser() {
+    Diagnostic << Specifiers;
+  }
+
+  template<typename T> void check(SourceLocation SpecLoc, T Spec) {
+    return check(SpecLoc, DeclSpec::getSpecifierName(Spec));
+  }
+  void check(SourceLocation SpecLoc, DeclSpec::TST Spec) {
+    return check(SpecLoc,
+                 DeclSpec::getSpecifierName(Spec, S.getPrintingPolicy()));
+  }
+  void check(SourceLocation SpecLoc, const char *Spec) {
+    if (SpecLoc.isInvalid()) return;
+    Diagnostic << SourceRange(SpecLoc, SpecLoc);
+    if (!Specifiers.empty()) Specifiers += " ";
+    Specifiers += Spec;
+  }
+
+  Sema &S;
+  Sema::SemaDiagnosticBuilder Diagnostic;
+  std::string Specifiers;
+};
+}
+
+/// Check the validity of a declarator that we parsed for a deduction-guide.
+/// These aren't actually declarators in the grammar, so we need to check that
+/// the user didn't specify any pieces that are not part of the deduction-guide
+/// grammar.
+void Sema::CheckDeductionGuideDeclarator(Declarator &D, QualType &R,
+                                         StorageClass &SC) {
+  TemplateName GuidedTemplate = D.getName().TemplateName.get().get();
+  TemplateDecl *GuidedTemplateDecl = GuidedTemplate.getAsTemplateDecl();
+  assert(GuidedTemplateDecl && "missing template decl for deduction guide");
+
+  // C++ [temp.deduct.guide]p3:
+  //   A deduction-gide shall be declared in the same scope as the
+  //   corresponding class template.
+  if (!CurContext->getRedeclContext()->Equals(
+          GuidedTemplateDecl->getDeclContext()->getRedeclContext())) {
+    Diag(D.getIdentifierLoc(), diag::err_deduction_guide_wrong_scope)
+      << GuidedTemplateDecl;
+    Diag(GuidedTemplateDecl->getLocation(), diag::note_template_decl_here);
+  }
+
+  auto &DS = D.getMutableDeclSpec();
+  // We leave 'friend' and 'virtual' to be rejected in the normal way.
+  if (DS.hasTypeSpecifier() || DS.getTypeQualifiers() ||
+      DS.getStorageClassSpecLoc().isValid() || DS.isInlineSpecified() ||
+      DS.isNoreturnSpecified() || DS.hasConstexprSpecifier()) {
+    BadSpecifierDiagnoser Diagnoser(
+        *this, D.getIdentifierLoc(),
+        diag::err_deduction_guide_invalid_specifier);
+
+    Diagnoser.check(DS.getStorageClassSpecLoc(), DS.getStorageClassSpec());
+    DS.ClearStorageClassSpecs();
+    SC = SC_None;
+
+    // 'explicit' is permitted.
+    Diagnoser.check(DS.getInlineSpecLoc(), "inline");
+    Diagnoser.check(DS.getNoreturnSpecLoc(), "_Noreturn");
+    Diagnoser.check(DS.getConstexprSpecLoc(), "constexpr");
+    DS.ClearConstexprSpec();
+
+    Diagnoser.check(DS.getConstSpecLoc(), "const");
+    Diagnoser.check(DS.getRestrictSpecLoc(), "__restrict");
+    Diagnoser.check(DS.getVolatileSpecLoc(), "volatile");
+    Diagnoser.check(DS.getAtomicSpecLoc(), "_Atomic");
+    Diagnoser.check(DS.getUnalignedSpecLoc(), "__unaligned");
+    DS.ClearTypeQualifiers();
+
+    Diagnoser.check(DS.getTypeSpecComplexLoc(), DS.getTypeSpecComplex());
+    Diagnoser.check(DS.getTypeSpecSignLoc(), DS.getTypeSpecSign());
+    Diagnoser.check(DS.getTypeSpecWidthLoc(), DS.getTypeSpecWidth());
+    Diagnoser.check(DS.getTypeSpecTypeLoc(), DS.getTypeSpecType());
+    DS.ClearTypeSpecType();
+  }
+
+  if (D.isInvalidType())
+    return;
+
+  // Check the declarator is simple enough.
+  bool FoundFunction = false;
+  for (const DeclaratorChunk &Chunk : llvm::reverse(D.type_objects())) {
+    if (Chunk.Kind == DeclaratorChunk::Paren)
+      continue;
+    if (Chunk.Kind != DeclaratorChunk::Function || FoundFunction) {
+      Diag(D.getDeclSpec().getBeginLoc(),
+           diag::err_deduction_guide_with_complex_decl)
+          << D.getSourceRange();
+      break;
+    }
+    if (!Chunk.Fun.hasTrailingReturnType()) {
+      Diag(D.getName().getBeginLoc(),
+           diag::err_deduction_guide_no_trailing_return_type);
+      break;
+    }
+
+    // Check that the return type is written as a specialization of
+    // the template specified as the deduction-guide's name.
+    ParsedType TrailingReturnType = Chunk.Fun.getTrailingReturnType();
+    TypeSourceInfo *TSI = nullptr;
+    QualType RetTy = GetTypeFromParser(TrailingReturnType, &TSI);
+    assert(TSI && "deduction guide has valid type but invalid return type?");
+    bool AcceptableReturnType = false;
+    bool MightInstantiateToSpecialization = false;
+    if (auto RetTST =
+            TSI->getTypeLoc().getAs<TemplateSpecializationTypeLoc>()) {
+      TemplateName SpecifiedName = RetTST.getTypePtr()->getTemplateName();
+      bool TemplateMatches =
+          Context.hasSameTemplateName(SpecifiedName, GuidedTemplate);
+      if (SpecifiedName.getKind() == TemplateName::Template && TemplateMatches)
+        AcceptableReturnType = true;
+      else {
+        // This could still instantiate to the right type, unless we know it
+        // names the wrong class template.
+        auto *TD = SpecifiedName.getAsTemplateDecl();
+        MightInstantiateToSpecialization = !(TD && isa<ClassTemplateDecl>(TD) &&
+                                             !TemplateMatches);
+      }
+    } else if (!RetTy.hasQualifiers() && RetTy->isDependentType()) {
+      MightInstantiateToSpecialization = true;
+    }
+
+    if (!AcceptableReturnType) {
+      Diag(TSI->getTypeLoc().getBeginLoc(),
+           diag::err_deduction_guide_bad_trailing_return_type)
+          << GuidedTemplate << TSI->getType()
+          << MightInstantiateToSpecialization
+          << TSI->getTypeLoc().getSourceRange();
+    }
+
+    // Keep going to check that we don't have any inner declarator pieces (we
+    // could still have a function returning a pointer to a function).
+    FoundFunction = true;
+  }
+
+  if (D.isFunctionDefinition())
+    Diag(D.getIdentifierLoc(), diag::err_deduction_guide_defines_function);
+}
+
+//===----------------------------------------------------------------------===//
+// Namespace Handling
+//===----------------------------------------------------------------------===//
+
+/// Diagnose a mismatch in 'inline' qualifiers when a namespace is
+/// reopened.
+static void DiagnoseNamespaceInlineMismatch(Sema &S, SourceLocation KeywordLoc,
+                                            SourceLocation Loc,
+                                            IdentifierInfo *II, bool *IsInline,
+                                            NamespaceDecl *PrevNS) {
+  assert(*IsInline != PrevNS->isInline());
+
+  if (PrevNS->isInline())
+    // The user probably just forgot the 'inline', so suggest that it
+    // be added back.
+    S.Diag(Loc, diag::warn_inline_namespace_reopened_noninline)
+      << FixItHint::CreateInsertion(KeywordLoc, "inline ");
+  else
+    S.Diag(Loc, diag::err_inline_namespace_mismatch);
+
+  S.Diag(PrevNS->getLocation(), diag::note_previous_definition);
+  *IsInline = PrevNS->isInline();
+}
+
+/// ActOnStartNamespaceDef - This is called at the start of a namespace
+/// definition.
+Decl *Sema::ActOnStartNamespaceDef(
+    Scope *NamespcScope, SourceLocation InlineLoc, SourceLocation NamespaceLoc,
+    SourceLocation IdentLoc, IdentifierInfo *II, SourceLocation LBrace,
+    const ParsedAttributesView &AttrList, UsingDirectiveDecl *&UD) {
+  SourceLocation StartLoc = InlineLoc.isValid() ? InlineLoc : NamespaceLoc;
+  // For anonymous namespace, take the location of the left brace.
+  SourceLocation Loc = II ? IdentLoc : LBrace;
+  bool IsInline = InlineLoc.isValid();
+  bool IsInvalid = false;
+  bool IsStd = false;
+  bool AddToKnown = false;
+  Scope *DeclRegionScope = NamespcScope->getParent();
+
+  NamespaceDecl *PrevNS = nullptr;
+  if (II) {
+    // C++ [namespace.def]p2:
+    //   The identifier in an original-namespace-definition shall not
+    //   have been previously defined in the declarative region in
+    //   which the original-namespace-definition appears. The
+    //   identifier in an original-namespace-definition is the name of
+    //   the namespace. Subsequently in that declarative region, it is
+    //   treated as an original-namespace-name.
+    //
+    // Since namespace names are unique in their scope, and we don't
+    // look through using directives, just look for any ordinary names
+    // as if by qualified name lookup.
+    LookupResult R(*this, II, IdentLoc, LookupOrdinaryName,
+                   ForExternalRedeclaration);
+    LookupQualifiedName(R, CurContext->getRedeclContext());
+    NamedDecl *PrevDecl =
+        R.isSingleResult() ? R.getRepresentativeDecl() : nullptr;
+    PrevNS = dyn_cast_or_null<NamespaceDecl>(PrevDecl);
+
+    if (PrevNS) {
+      // This is an extended namespace definition.
+      if (IsInline != PrevNS->isInline())
+        DiagnoseNamespaceInlineMismatch(*this, NamespaceLoc, Loc, II,
+                                        &IsInline, PrevNS);
+    } else if (PrevDecl) {
+      // This is an invalid name redefinition.
+      Diag(Loc, diag::err_redefinition_different_kind)
+        << II;
+      Diag(PrevDecl->getLocation(), diag::note_previous_definition);
+      IsInvalid = true;
+      // Continue on to push Namespc as current DeclContext and return it.
+    } else if (II->isStr("std") &&
+               CurContext->getRedeclContext()->isTranslationUnit()) {
+      // This is the first "real" definition of the namespace "std", so update
+      // our cache of the "std" namespace to point at this definition.
+      PrevNS = getStdNamespace();
+      IsStd = true;
+      AddToKnown = !IsInline;
+    } else {
+      // We've seen this namespace for the first time.
+      AddToKnown = !IsInline;
+    }
+  } else {
+    // Anonymous namespaces.
+
+    // Determine whether the parent already has an anonymous namespace.
+    DeclContext *Parent = CurContext->getRedeclContext();
+    if (TranslationUnitDecl *TU = dyn_cast<TranslationUnitDecl>(Parent)) {
+      PrevNS = TU->getAnonymousNamespace();
+    } else {
+      NamespaceDecl *ND = cast<NamespaceDecl>(Parent);
+      PrevNS = ND->getAnonymousNamespace();
+    }
+
+    if (PrevNS && IsInline != PrevNS->isInline())
+      DiagnoseNamespaceInlineMismatch(*this, NamespaceLoc, NamespaceLoc, II,
+                                      &IsInline, PrevNS);
+  }
+
+  NamespaceDecl *Namespc = NamespaceDecl::Create(Context, CurContext, IsInline,
+                                                 StartLoc, Loc, II, PrevNS);
+  if (IsInvalid)
+    Namespc->setInvalidDecl();
+
+  ProcessDeclAttributeList(DeclRegionScope, Namespc, AttrList);
+  AddPragmaAttributes(DeclRegionScope, Namespc);
+
+  // FIXME: Should we be merging attributes?
+  if (const VisibilityAttr *Attr = Namespc->getAttr<VisibilityAttr>())
+    PushNamespaceVisibilityAttr(Attr, Loc);
+
+  if (IsStd)
+    StdNamespace = Namespc;
+  if (AddToKnown)
+    KnownNamespaces[Namespc] = false;
+
+  if (II) {
+    PushOnScopeChains(Namespc, DeclRegionScope);
+  } else {
+    // Link the anonymous namespace into its parent.
+    DeclContext *Parent = CurContext->getRedeclContext();
+    if (TranslationUnitDecl *TU = dyn_cast<TranslationUnitDecl>(Parent)) {
+      TU->setAnonymousNamespace(Namespc);
+    } else {
+      cast<NamespaceDecl>(Parent)->setAnonymousNamespace(Namespc);
+    }
+
+    CurContext->addDecl(Namespc);
+
+    // C++ [namespace.unnamed]p1.  An unnamed-namespace-definition
+    //   behaves as if it were replaced by
+    //     namespace unique { /* empty body */ }
+    //     using namespace unique;
+    //     namespace unique { namespace-body }
+    //   where all occurrences of 'unique' in a translation unit are
+    //   replaced by the same identifier and this identifier differs
+    //   from all other identifiers in the entire program.
+
+    // We just create the namespace with an empty name and then add an
+    // implicit using declaration, just like the standard suggests.
+    //
+    // CodeGen enforces the "universally unique" aspect by giving all
+    // declarations semantically contained within an anonymous
+    // namespace internal linkage.
+
+    if (!PrevNS) {
+      UD = UsingDirectiveDecl::Create(Context, Parent,
+                                      /* 'using' */ LBrace,
+                                      /* 'namespace' */ SourceLocation(),
+                                      /* qualifier */ NestedNameSpecifierLoc(),
+                                      /* identifier */ SourceLocation(),
+                                      Namespc,
+                                      /* Ancestor */ Parent);
+      UD->setImplicit();
+      Parent->addDecl(UD);
+    }
+  }
+
+  ActOnDocumentableDecl(Namespc);
+
+  // Although we could have an invalid decl (i.e. the namespace name is a
+  // redefinition), push it as current DeclContext and try to continue parsing.
+  // FIXME: We should be able to push Namespc here, so that the each DeclContext
+  // for the namespace has the declarations that showed up in that particular
+  // namespace definition.
+  PushDeclContext(NamespcScope, Namespc);
+  return Namespc;
+}
+
+/// getNamespaceDecl - Returns the namespace a decl represents. If the decl
+/// is a namespace alias, returns the namespace it points to.
+static inline NamespaceDecl *getNamespaceDecl(NamedDecl *D) {
+  if (NamespaceAliasDecl *AD = dyn_cast_or_null<NamespaceAliasDecl>(D))
+    return AD->getNamespace();
+  return dyn_cast_or_null<NamespaceDecl>(D);
+}
+
+/// ActOnFinishNamespaceDef - This callback is called after a namespace is
+/// exited. Decl is the DeclTy returned by ActOnStartNamespaceDef.
+void Sema::ActOnFinishNamespaceDef(Decl *Dcl, SourceLocation RBrace) {
+  NamespaceDecl *Namespc = dyn_cast_or_null<NamespaceDecl>(Dcl);
+  assert(Namespc && "Invalid parameter, expected NamespaceDecl");
+  Namespc->setRBraceLoc(RBrace);
+  PopDeclContext();
+  if (Namespc->hasAttr<VisibilityAttr>())
+    PopPragmaVisibility(true, RBrace);
+  // If this namespace contains an export-declaration, export it now.
+  if (DeferredExportedNamespaces.erase(Namespc))
+    Dcl->setModuleOwnershipKind(Decl::ModuleOwnershipKind::VisibleWhenImported);
+}
+
+CXXRecordDecl *Sema::getStdBadAlloc() const {
+  return cast_or_null<CXXRecordDecl>(
+                                  StdBadAlloc.get(Context.getExternalSource()));
+}
+
+EnumDecl *Sema::getStdAlignValT() const {
+  return cast_or_null<EnumDecl>(StdAlignValT.get(Context.getExternalSource()));
+}
+
+NamespaceDecl *Sema::getStdNamespace() const {
+  return cast_or_null<NamespaceDecl>(
+                                 StdNamespace.get(Context.getExternalSource()));
+}
+
+NamespaceDecl *Sema::lookupStdExperimentalNamespace() {
+  if (!StdExperimentalNamespaceCache) {
+    if (auto Std = getStdNamespace()) {
+      LookupResult Result(*this, &PP.getIdentifierTable().get("experimental"),
+                          SourceLocation(), LookupNamespaceName);
+      if (!LookupQualifiedName(Result, Std) ||
+          !(StdExperimentalNamespaceCache =
+                Result.getAsSingle<NamespaceDecl>()))
+        Result.suppressDiagnostics();
+    }
+  }
+  return StdExperimentalNamespaceCache;
+}
+
+namespace {
+
+enum UnsupportedSTLSelect {
+  USS_InvalidMember,
+  USS_MissingMember,
+  USS_NonTrivial,
+  USS_Other
+};
+
+struct InvalidSTLDiagnoser {
+  Sema &S;
+  SourceLocation Loc;
+  QualType TyForDiags;
+
+  QualType operator()(UnsupportedSTLSelect Sel = USS_Other, StringRef Name = "",
+                      const VarDecl *VD = nullptr) {
+    {
+      auto D = S.Diag(Loc, diag::err_std_compare_type_not_supported)
+               << TyForDiags << ((int)Sel);
+      if (Sel == USS_InvalidMember || Sel == USS_MissingMember) {
+        assert(!Name.empty());
+        D << Name;
+      }
+    }
+    if (Sel == USS_InvalidMember) {
+      S.Diag(VD->getLocation(), diag::note_var_declared_here)
+          << VD << VD->getSourceRange();
+    }
+    return QualType();
+  }
+};
+} // namespace
+
+QualType Sema::CheckComparisonCategoryType(ComparisonCategoryType Kind,
+                                           SourceLocation Loc,
+                                           ComparisonCategoryUsage Usage) {
+  assert(getLangOpts().CPlusPlus &&
+         "Looking for comparison category type outside of C++.");
+
+  // Use an elaborated type for diagnostics which has a name containing the
+  // prepended 'std' namespace but not any inline namespace names.
+  auto TyForDiags = [&](ComparisonCategoryInfo *Info) {
+    auto *NNS =
+        NestedNameSpecifier::Create(Context, nullptr, getStdNamespace());
+    return Context.getElaboratedType(ETK_None, NNS, Info->getType());
+  };
+
+  // Check if we've already successfully checked the comparison category type
+  // before. If so, skip checking it again.
+  ComparisonCategoryInfo *Info = Context.CompCategories.lookupInfo(Kind);
+  if (Info && FullyCheckedComparisonCategories[static_cast<unsigned>(Kind)]) {
+    // The only thing we need to check is that the type has a reachable
+    // definition in the current context.
+    if (RequireCompleteType(Loc, TyForDiags(Info), diag::err_incomplete_type))
+      return QualType();
+
+    return Info->getType();
+  }
+
+  // If lookup failed
+  if (!Info) {
+    std::string NameForDiags = "std::";
+    NameForDiags += ComparisonCategories::getCategoryString(Kind);
+    Diag(Loc, diag::err_implied_comparison_category_type_not_found)
+        << NameForDiags << (int)Usage;
+    return QualType();
+  }
+
+  assert(Info->Kind == Kind);
+  assert(Info->Record);
+
+  // Update the Record decl in case we encountered a forward declaration on our
+  // first pass. FIXME: This is a bit of a hack.
+  if (Info->Record->hasDefinition())
+    Info->Record = Info->Record->getDefinition();
+
+  if (RequireCompleteType(Loc, TyForDiags(Info), diag::err_incomplete_type))
+    return QualType();
+
+  InvalidSTLDiagnoser UnsupportedSTLError{*this, Loc, TyForDiags(Info)};
+
+  if (!Info->Record->isTriviallyCopyable())
+    return UnsupportedSTLError(USS_NonTrivial);
+
+  for (const CXXBaseSpecifier &BaseSpec : Info->Record->bases()) {
+    CXXRecordDecl *Base = BaseSpec.getType()->getAsCXXRecordDecl();
+    // Tolerate empty base classes.
+    if (Base->isEmpty())
+      continue;
+    // Reject STL implementations which have at least one non-empty base.
+    return UnsupportedSTLError();
+  }
+
+  // Check that the STL has implemented the types using a single integer field.
+  // This expectation allows better codegen for builtin operators. We require:
+  //   (1) The class has exactly one field.
+  //   (2) The field is an integral or enumeration type.
+  auto FIt = Info->Record->field_begin(), FEnd = Info->Record->field_end();
+  if (std::distance(FIt, FEnd) != 1 ||
+      !FIt->getType()->isIntegralOrEnumerationType()) {
+    return UnsupportedSTLError();
+  }
+
+  // Build each of the require values and store them in Info.
+  for (ComparisonCategoryResult CCR :
+       ComparisonCategories::getPossibleResultsForType(Kind)) {
+    StringRef MemName = ComparisonCategories::getResultString(CCR);
+    ComparisonCategoryInfo::ValueInfo *ValInfo = Info->lookupValueInfo(CCR);
+
+    if (!ValInfo)
+      return UnsupportedSTLError(USS_MissingMember, MemName);
+
+    VarDecl *VD = ValInfo->VD;
+    assert(VD && "should not be null!");
+
+    // Attempt to diagnose reasons why the STL definition of this type
+    // might be foobar, including it failing to be a constant expression.
+    // TODO Handle more ways the lookup or result can be invalid.
+    if (!VD->isStaticDataMember() ||
+        !VD->isUsableInConstantExpressions(Context))
+      return UnsupportedSTLError(USS_InvalidMember, MemName, VD);
+
+    // Attempt to evaluate the var decl as a constant expression and extract
+    // the value of its first field as a ICE. If this fails, the STL
+    // implementation is not supported.
+    if (!ValInfo->hasValidIntValue())
+      return UnsupportedSTLError();
+
+    MarkVariableReferenced(Loc, VD);
+  }
+
+  // We've successfully built the required types and expressions. Update
+  // the cache and return the newly cached value.
+  FullyCheckedComparisonCategories[static_cast<unsigned>(Kind)] = true;
+  return Info->getType();
+}
+
+/// Retrieve the special "std" namespace, which may require us to
+/// implicitly define the namespace.
+NamespaceDecl *Sema::getOrCreateStdNamespace() {
+  if (!StdNamespace) {
+    // The "std" namespace has not yet been defined, so build one implicitly.
+    StdNamespace = NamespaceDecl::Create(Context,
+                                         Context.getTranslationUnitDecl(),
+                                         /*Inline=*/false,
+                                         SourceLocation(), SourceLocation(),
+                                         &PP.getIdentifierTable().get("std"),
+                                         /*PrevDecl=*/nullptr);
+    getStdNamespace()->setImplicit(true);
+  }
+
+  return getStdNamespace();
+}
+
+bool Sema::isStdInitializerList(QualType Ty, QualType *Element) {
+  assert(getLangOpts().CPlusPlus &&
+         "Looking for std::initializer_list outside of C++.");
+
+  // We're looking for implicit instantiations of
+  // template <typename E> class std::initializer_list.
+
+  if (!StdNamespace) // If we haven't seen namespace std yet, this can't be it.
+    return false;
+
+  ClassTemplateDecl *Template = nullptr;
+  const TemplateArgument *Arguments = nullptr;
+
+  if (const RecordType *RT = Ty->getAs<RecordType>()) {
+
+    ClassTemplateSpecializationDecl *Specialization =
+        dyn_cast<ClassTemplateSpecializationDecl>(RT->getDecl());
+    if (!Specialization)
+      return false;
+
+    Template = Specialization->getSpecializedTemplate();
+    Arguments = Specialization->getTemplateArgs().data();
+  } else if (const TemplateSpecializationType *TST =
+                 Ty->getAs<TemplateSpecializationType>()) {
+    Template = dyn_cast_or_null<ClassTemplateDecl>(
+        TST->getTemplateName().getAsTemplateDecl());
+    Arguments = TST->getArgs();
+  }
+  if (!Template)
+    return false;
+
+  if (!StdInitializerList) {
+    // Haven't recognized std::initializer_list yet, maybe this is it.
+    CXXRecordDecl *TemplateClass = Template->getTemplatedDecl();
+    if (TemplateClass->getIdentifier() !=
+            &PP.getIdentifierTable().get("initializer_list") ||
+        !getStdNamespace()->InEnclosingNamespaceSetOf(
+            TemplateClass->getDeclContext()))
+      return false;
+    // This is a template called std::initializer_list, but is it the right
+    // template?
+    TemplateParameterList *Params = Template->getTemplateParameters();
+    if (Params->getMinRequiredArguments() != 1)
+      return false;
+    if (!isa<TemplateTypeParmDecl>(Params->getParam(0)))
+      return false;
+
+    // It's the right template.
+    StdInitializerList = Template;
+  }
+
+  if (Template->getCanonicalDecl() != StdInitializerList->getCanonicalDecl())
+    return false;
+
+  // This is an instance of std::initializer_list. Find the argument type.
+  if (Element)
+    *Element = Arguments[0].getAsType();
+  return true;
+}
+
+static ClassTemplateDecl *LookupStdInitializerList(Sema &S, SourceLocation Loc){
+  NamespaceDecl *Std = S.getStdNamespace();
+  if (!Std) {
+    S.Diag(Loc, diag::err_implied_std_initializer_list_not_found);
+    return nullptr;
+  }
+
+  LookupResult Result(S, &S.PP.getIdentifierTable().get("initializer_list"),
+                      Loc, Sema::LookupOrdinaryName);
+  if (!S.LookupQualifiedName(Result, Std)) {
+    S.Diag(Loc, diag::err_implied_std_initializer_list_not_found);
+    return nullptr;
+  }
+  ClassTemplateDecl *Template = Result.getAsSingle<ClassTemplateDecl>();
+  if (!Template) {
+    Result.suppressDiagnostics();
+    // We found something weird. Complain about the first thing we found.
+    NamedDecl *Found = *Result.begin();
+    S.Diag(Found->getLocation(), diag::err_malformed_std_initializer_list);
+    return nullptr;
+  }
+
+  // We found some template called std::initializer_list. Now verify that it's
+  // correct.
+  TemplateParameterList *Params = Template->getTemplateParameters();
+  if (Params->getMinRequiredArguments() != 1 ||
+      !isa<TemplateTypeParmDecl>(Params->getParam(0))) {
+    S.Diag(Template->getLocation(), diag::err_malformed_std_initializer_list);
+    return nullptr;
+  }
+
+  return Template;
+}
+
+QualType Sema::BuildStdInitializerList(QualType Element, SourceLocation Loc) {
+  if (!StdInitializerList) {
+    StdInitializerList = LookupStdInitializerList(*this, Loc);
+    if (!StdInitializerList)
+      return QualType();
+  }
+
+  TemplateArgumentListInfo Args(Loc, Loc);
+  Args.addArgument(TemplateArgumentLoc(TemplateArgument(Element),
+                                       Context.getTrivialTypeSourceInfo(Element,
+                                                                        Loc)));
+  return Context.getCanonicalType(
+      CheckTemplateIdType(TemplateName(StdInitializerList), Loc, Args));
+}
+
+bool Sema::isInitListConstructor(const FunctionDecl *Ctor) {
+  // C++ [dcl.init.list]p2:
+  //   A constructor is an initializer-list constructor if its first parameter
+  //   is of type std::initializer_list<E> or reference to possibly cv-qualified
+  //   std::initializer_list<E> for some type E, and either there are no other
+  //   parameters or else all other parameters have default arguments.
+  if (!Ctor->hasOneParamOrDefaultArgs())
+    return false;
+
+  QualType ArgType = Ctor->getParamDecl(0)->getType();
+  if (const ReferenceType *RT = ArgType->getAs<ReferenceType>())
+    ArgType = RT->getPointeeType().getUnqualifiedType();
+
+  return isStdInitializerList(ArgType, nullptr);
+}
+
+/// Determine whether a using statement is in a context where it will be
+/// apply in all contexts.
+static bool IsUsingDirectiveInToplevelContext(DeclContext *CurContext) {
+  switch (CurContext->getDeclKind()) {
+    case Decl::TranslationUnit:
+      return true;
+    case Decl::LinkageSpec:
+      return IsUsingDirectiveInToplevelContext(CurContext->getParent());
+    default:
+      return false;
+  }
+}
+
+namespace {
+
+// Callback to only accept typo corrections that are namespaces.
+class NamespaceValidatorCCC final : public CorrectionCandidateCallback {
+public:
+  bool ValidateCandidate(const TypoCorrection &candidate) override {
+    if (NamedDecl *ND = candidate.getCorrectionDecl())
+      return isa<NamespaceDecl>(ND) || isa<NamespaceAliasDecl>(ND);
+    return false;
+  }
+
+  std::unique_ptr<CorrectionCandidateCallback> clone() override {
+    return std::make_unique<NamespaceValidatorCCC>(*this);
+  }
+};
+
+}
+
+static bool TryNamespaceTypoCorrection(Sema &S, LookupResult &R, Scope *Sc,
+                                       CXXScopeSpec &SS,
+                                       SourceLocation IdentLoc,
+                                       IdentifierInfo *Ident) {
+  R.clear();
+  NamespaceValidatorCCC CCC{};
+  if (TypoCorrection Corrected =
+          S.CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(), Sc, &SS, CCC,
+                        Sema::CTK_ErrorRecovery)) {
+    if (DeclContext *DC = S.computeDeclContext(SS, false)) {
+      std::string CorrectedStr(Corrected.getAsString(S.getLangOpts()));
+      bool DroppedSpecifier = Corrected.WillReplaceSpecifier() &&
+                              Ident->getName().equals(CorrectedStr);
+      S.diagnoseTypo(Corrected,
+                     S.PDiag(diag::err_using_directive_member_suggest)
+                       << Ident << DC << DroppedSpecifier << SS.getRange(),
+                     S.PDiag(diag::note_namespace_defined_here));
+    } else {
+      S.diagnoseTypo(Corrected,
+                     S.PDiag(diag::err_using_directive_suggest) << Ident,
+                     S.PDiag(diag::note_namespace_defined_here));
+    }
+    R.addDecl(Corrected.getFoundDecl());
+    return true;
+  }
+  return false;
+}
+
+Decl *Sema::ActOnUsingDirective(Scope *S, SourceLocation UsingLoc,
+                                SourceLocation NamespcLoc, CXXScopeSpec &SS,
+                                SourceLocation IdentLoc,
+                                IdentifierInfo *NamespcName,
+                                const ParsedAttributesView &AttrList) {
+  assert(!SS.isInvalid() && "Invalid CXXScopeSpec.");
+  assert(NamespcName && "Invalid NamespcName.");
+  assert(IdentLoc.isValid() && "Invalid NamespceName location.");
+
+  // This can only happen along a recovery path.
+  while (S->isTemplateParamScope())
+    S = S->getParent();
+  assert(S->getFlags() & Scope::DeclScope && "Invalid Scope.");
+
+  UsingDirectiveDecl *UDir = nullptr;
+  NestedNameSpecifier *Qualifier = nullptr;
+  if (SS.isSet())
+    Qualifier = SS.getScopeRep();
+
+  // Lookup namespace name.
+  LookupResult R(*this, NamespcName, IdentLoc, LookupNamespaceName);
+  LookupParsedName(R, S, &SS);
+  if (R.isAmbiguous())
+    return nullptr;
+
+  if (R.empty()) {
+    R.clear();
+    // Allow "using namespace std;" or "using namespace ::std;" even if
+    // "std" hasn't been defined yet, for GCC compatibility.
+    if ((!Qualifier || Qualifier->getKind() == NestedNameSpecifier::Global) &&
+        NamespcName->isStr("std")) {
+      Diag(IdentLoc, diag::ext_using_undefined_std);
+      R.addDecl(getOrCreateStdNamespace());
+      R.resolveKind();
+    }
+    // Otherwise, attempt typo correction.
+    else TryNamespaceTypoCorrection(*this, R, S, SS, IdentLoc, NamespcName);
+  }
+
+  if (!R.empty()) {
+    NamedDecl *Named = R.getRepresentativeDecl();
+    NamespaceDecl *NS = R.getAsSingle<NamespaceDecl>();
+    assert(NS && "expected namespace decl");
+
+    // The use of a nested name specifier may trigger deprecation warnings.
+    DiagnoseUseOfDecl(Named, IdentLoc);
+
+    // C++ [namespace.udir]p1:
+    //   A using-directive specifies that the names in the nominated
+    //   namespace can be used in the scope in which the
+    //   using-directive appears after the using-directive. During
+    //   unqualified name lookup (3.4.1), the names appear as if they
+    //   were declared in the nearest enclosing namespace which
+    //   contains both the using-directive and the nominated
+    //   namespace. [Note: in this context, "contains" means "contains
+    //   directly or indirectly". ]
+
+    // Find enclosing context containing both using-directive and
+    // nominated namespace.
+    DeclContext *CommonAncestor = NS;
+    while (CommonAncestor && !CommonAncestor->Encloses(CurContext))
+      CommonAncestor = CommonAncestor->getParent();
+
+    UDir = UsingDirectiveDecl::Create(Context, CurContext, UsingLoc, NamespcLoc,
+                                      SS.getWithLocInContext(Context),
+                                      IdentLoc, Named, CommonAncestor);
+
+    if (IsUsingDirectiveInToplevelContext(CurContext) &&
+        !SourceMgr.isInMainFile(SourceMgr.getExpansionLoc(IdentLoc))) {
+      Diag(IdentLoc, diag::warn_using_directive_in_header);
+    }
+
+    PushUsingDirective(S, UDir);
+  } else {
+    Diag(IdentLoc, diag::err_expected_namespace_name) << SS.getRange();
+  }
+
+  if (UDir)
+    ProcessDeclAttributeList(S, UDir, AttrList);
+
+  return UDir;
+}
+
+void Sema::PushUsingDirective(Scope *S, UsingDirectiveDecl *UDir) {
+  // If the scope has an associated entity and the using directive is at
+  // namespace or translation unit scope, add the UsingDirectiveDecl into
+  // its lookup structure so qualified name lookup can find it.
+  DeclContext *Ctx = S->getEntity();
+  if (Ctx && !Ctx->isFunctionOrMethod())
+    Ctx->addDecl(UDir);
+  else
+    // Otherwise, it is at block scope. The using-directives will affect lookup
+    // only to the end of the scope.
+    S->PushUsingDirective(UDir);
+}
+
+Decl *Sema::ActOnUsingDeclaration(Scope *S, AccessSpecifier AS,
+                                  SourceLocation UsingLoc,
+                                  SourceLocation TypenameLoc, CXXScopeSpec &SS,
+                                  UnqualifiedId &Name,
+                                  SourceLocation EllipsisLoc,
+                                  const ParsedAttributesView &AttrList) {
+  assert(S->getFlags() & Scope::DeclScope && "Invalid Scope.");
+
+  if (SS.isEmpty()) {
+    Diag(Name.getBeginLoc(), diag::err_using_requires_qualname);
+    return nullptr;
+  }
+
+  switch (Name.getKind()) {
+  case UnqualifiedIdKind::IK_ImplicitSelfParam:
+  case UnqualifiedIdKind::IK_Identifier:
+  case UnqualifiedIdKind::IK_OperatorFunctionId:
+  case UnqualifiedIdKind::IK_LiteralOperatorId:
+  case UnqualifiedIdKind::IK_ConversionFunctionId:
+    break;
+
+  case UnqualifiedIdKind::IK_ConstructorName:
+  case UnqualifiedIdKind::IK_ConstructorTemplateId:
+    // C++11 inheriting constructors.
+    Diag(Name.getBeginLoc(),
+         getLangOpts().CPlusPlus11
+             ? diag::warn_cxx98_compat_using_decl_constructor
+             : diag::err_using_decl_constructor)
+        << SS.getRange();
+
+    if (getLangOpts().CPlusPlus11) break;
+
+    return nullptr;
+
+  case UnqualifiedIdKind::IK_DestructorName:
+    Diag(Name.getBeginLoc(), diag::err_using_decl_destructor) << SS.getRange();
+    return nullptr;
+
+  case UnqualifiedIdKind::IK_TemplateId:
+    Diag(Name.getBeginLoc(), diag::err_using_decl_template_id)
+        << SourceRange(Name.TemplateId->LAngleLoc, Name.TemplateId->RAngleLoc);
+    return nullptr;
+
+  case UnqualifiedIdKind::IK_DeductionGuideName:
+    llvm_unreachable("cannot parse qualified deduction guide name");
+  }
+
+  DeclarationNameInfo TargetNameInfo = GetNameFromUnqualifiedId(Name);
+  DeclarationName TargetName = TargetNameInfo.getName();
+  if (!TargetName)
+    return nullptr;
+
+  // Warn about access declarations.
+  if (UsingLoc.isInvalid()) {
+    Diag(Name.getBeginLoc(), getLangOpts().CPlusPlus11
+                                 ? diag::err_access_decl
+                                 : diag::warn_access_decl_deprecated)
+        << FixItHint::CreateInsertion(SS.getRange().getBegin(), "using ");
+  }
+
+  if (EllipsisLoc.isInvalid()) {
+    if (DiagnoseUnexpandedParameterPack(SS, UPPC_UsingDeclaration) ||
+        DiagnoseUnexpandedParameterPack(TargetNameInfo, UPPC_UsingDeclaration))
+      return nullptr;
+  } else {
+    if (!SS.getScopeRep()->containsUnexpandedParameterPack() &&
+        !TargetNameInfo.containsUnexpandedParameterPack()) {
+      Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
+        << SourceRange(SS.getBeginLoc(), TargetNameInfo.getEndLoc());
+      EllipsisLoc = SourceLocation();
+    }
+  }
+
+  NamedDecl *UD =
+      BuildUsingDeclaration(S, AS, UsingLoc, TypenameLoc.isValid(), TypenameLoc,
+                            SS, TargetNameInfo, EllipsisLoc, AttrList,
+                            /*IsInstantiation*/ false,
+                            AttrList.hasAttribute(ParsedAttr::AT_UsingIfExists));
+  if (UD)
+    PushOnScopeChains(UD, S, /*AddToContext*/ false);
+
+  return UD;
+}
+
+Decl *Sema::ActOnUsingEnumDeclaration(Scope *S, AccessSpecifier AS,
+                                      SourceLocation UsingLoc,
+                                      SourceLocation EnumLoc,
+                                      const DeclSpec &DS) {
+  switch (DS.getTypeSpecType()) {
+  case DeclSpec::TST_error:
+    // This will already have been diagnosed
+    return nullptr;
+
+  case DeclSpec::TST_enum:
+    break;
+
+  case DeclSpec::TST_typename:
+    Diag(DS.getTypeSpecTypeLoc(), diag::err_using_enum_is_dependent);
+    return nullptr;
+
+  default:
+    llvm_unreachable("unexpected DeclSpec type");
+  }
+
+  // As with enum-decls, we ignore attributes for now.
+  auto *Enum = cast<EnumDecl>(DS.getRepAsDecl());
+  if (auto *Def = Enum->getDefinition())
+    Enum = Def;
+
+  auto *UD = BuildUsingEnumDeclaration(S, AS, UsingLoc, EnumLoc,
+                                       DS.getTypeSpecTypeNameLoc(), Enum);
+  if (UD)
+    PushOnScopeChains(UD, S, /*AddToContext*/ false);
+
+  return UD;
+}
+
+/// Determine whether a using declaration considers the given
+/// declarations as "equivalent", e.g., if they are redeclarations of
+/// the same entity or are both typedefs of the same type.
+static bool
+IsEquivalentForUsingDecl(ASTContext &Context, NamedDecl *D1, NamedDecl *D2) {
+  if (D1->getCanonicalDecl() == D2->getCanonicalDecl())
+    return true;
+
+  if (TypedefNameDecl *TD1 = dyn_cast<TypedefNameDecl>(D1))
+    if (TypedefNameDecl *TD2 = dyn_cast<TypedefNameDecl>(D2))
+      return Context.hasSameType(TD1->getUnderlyingType(),
+                                 TD2->getUnderlyingType());
+
+  // Two using_if_exists using-declarations are equivalent if both are
+  // unresolved.
+  if (isa<UnresolvedUsingIfExistsDecl>(D1) &&
+      isa<UnresolvedUsingIfExistsDecl>(D2))
+    return true;
+
+  return false;
+}
+
+
+/// Determines whether to create a using shadow decl for a particular
+/// decl, given the set of decls existing prior to this using lookup.
+bool Sema::CheckUsingShadowDecl(BaseUsingDecl *BUD, NamedDecl *Orig,
+                                const LookupResult &Previous,
+                                UsingShadowDecl *&PrevShadow) {
+  // Diagnose finding a decl which is not from a base class of the
+  // current class.  We do this now because there are cases where this
+  // function will silently decide not to build a shadow decl, which
+  // will pre-empt further diagnostics.
+  //
+  // We don't need to do this in C++11 because we do the check once on
+  // the qualifier.
+  //
+  // FIXME: diagnose the following if we care enough:
+  //   struct A { int foo; };
+  //   struct B : A { using A::foo; };
+  //   template <class T> struct C : A {};
+  //   template <class T> struct D : C<T> { using B::foo; } // <---
+  // This is invalid (during instantiation) in C++03 because B::foo
+  // resolves to the using decl in B, which is not a base class of D<T>.
+  // We can't diagnose it immediately because C<T> is an unknown
+  // specialization. The UsingShadowDecl in D<T> then points directly
+  // to A::foo, which will look well-formed when we instantiate.
+  // The right solution is to not collapse the shadow-decl chain.
+  if (!getLangOpts().CPlusPlus11 && CurContext->isRecord())
+    if (auto *Using = dyn_cast<UsingDecl>(BUD)) {
+      DeclContext *OrigDC = Orig->getDeclContext();
+
+      // Handle enums and anonymous structs.
+      if (isa<EnumDecl>(OrigDC))
+        OrigDC = OrigDC->getParent();
+      CXXRecordDecl *OrigRec = cast<CXXRecordDecl>(OrigDC);
+      while (OrigRec->isAnonymousStructOrUnion())
+        OrigRec = cast<CXXRecordDecl>(OrigRec->getDeclContext());
+
+      if (cast<CXXRecordDecl>(CurContext)->isProvablyNotDerivedFrom(OrigRec)) {
+        if (OrigDC == CurContext) {
+          Diag(Using->getLocation(),
+               diag::err_using_decl_nested_name_specifier_is_current_class)
+              << Using->getQualifierLoc().getSourceRange();
+          Diag(Orig->getLocation(), diag::note_using_decl_target);
+          Using->setInvalidDecl();
+          return true;
+        }
+
+        Diag(Using->getQualifierLoc().getBeginLoc(),
+             diag::err_using_decl_nested_name_specifier_is_not_base_class)
+            << Using->getQualifier() << cast<CXXRecordDecl>(CurContext)
+            << Using->getQualifierLoc().getSourceRange();
+        Diag(Orig->getLocation(), diag::note_using_decl_target);
+        Using->setInvalidDecl();
+        return true;
+      }
+    }
+
+  if (Previous.empty()) return false;
+
+  NamedDecl *Target = Orig;
+  if (isa<UsingShadowDecl>(Target))
+    Target = cast<UsingShadowDecl>(Target)->getTargetDecl();
+
+  // If the target happens to be one of the previous declarations, we
+  // don't have a conflict.
+  //
+  // FIXME: but we might be increasing its access, in which case we
+  // should redeclare it.
+  NamedDecl *NonTag = nullptr, *Tag = nullptr;
+  bool FoundEquivalentDecl = false;
+  for (LookupResult::iterator I = Previous.begin(), E = Previous.end();
+         I != E; ++I) {
+    NamedDecl *D = (*I)->getUnderlyingDecl();
+    // We can have UsingDecls in our Previous results because we use the same
+    // LookupResult for checking whether the UsingDecl itself is a valid
+    // redeclaration.
+    if (isa<UsingDecl>(D) || isa<UsingPackDecl>(D) || isa<UsingEnumDecl>(D))
+      continue;
+
+    if (auto *RD = dyn_cast<CXXRecordDecl>(D)) {
+      // C++ [class.mem]p19:
+      //   If T is the name of a class, then [every named member other than
+      //   a non-static data member] shall have a name different from T
+      if (RD->isInjectedClassName() && !isa<FieldDecl>(Target) &&
+          !isa<IndirectFieldDecl>(Target) &&
+          !isa<UnresolvedUsingValueDecl>(Target) &&
+          DiagnoseClassNameShadow(
+              CurContext,
+              DeclarationNameInfo(BUD->getDeclName(), BUD->getLocation())))
+        return true;
+    }
+
+    if (IsEquivalentForUsingDecl(Context, D, Target)) {
+      if (UsingShadowDecl *Shadow = dyn_cast<UsingShadowDecl>(*I))
+        PrevShadow = Shadow;
+      FoundEquivalentDecl = true;
+    } else if (isEquivalentInternalLinkageDeclaration(D, Target)) {
+      // We don't conflict with an existing using shadow decl of an equivalent
+      // declaration, but we're not a redeclaration of it.
+      FoundEquivalentDecl = true;
+    }
+
+    if (isVisible(D))
+      (isa<TagDecl>(D) ? Tag : NonTag) = D;
+  }
+
+  if (FoundEquivalentDecl)
+    return false;
+
+  // Always emit a diagnostic for a mismatch between an unresolved
+  // using_if_exists and a resolved using declaration in either direction.
+  if (isa<UnresolvedUsingIfExistsDecl>(Target) !=
+      (isa_and_nonnull<UnresolvedUsingIfExistsDecl>(NonTag))) {
+    if (!NonTag && !Tag)
+      return false;
+    Diag(BUD->getLocation(), diag::err_using_decl_conflict);
+    Diag(Target->getLocation(), diag::note_using_decl_target);
+    Diag((NonTag ? NonTag : Tag)->getLocation(),
+         diag::note_using_decl_conflict);
+    BUD->setInvalidDecl();
+    return true;
+  }
+
+  if (FunctionDecl *FD = Target->getAsFunction()) {
+    NamedDecl *OldDecl = nullptr;
+    switch (CheckOverload(nullptr, FD, Previous, OldDecl,
+                          /*IsForUsingDecl*/ true)) {
+    case Ovl_Overload:
+      return false;
+
+    case Ovl_NonFunction:
+      Diag(BUD->getLocation(), diag::err_using_decl_conflict);
+      break;
+
+    // We found a decl with the exact signature.
+    case Ovl_Match:
+      // If we're in a record, we want to hide the target, so we
+      // return true (without a diagnostic) to tell the caller not to
+      // build a shadow decl.
+      if (CurContext->isRecord())
+        return true;
+
+      // If we're not in a record, this is an error.
+      Diag(BUD->getLocation(), diag::err_using_decl_conflict);
+      break;
+    }
+
+    Diag(Target->getLocation(), diag::note_using_decl_target);
+    Diag(OldDecl->getLocation(), diag::note_using_decl_conflict);
+    BUD->setInvalidDecl();
+    return true;
+  }
+
+  // Target is not a function.
+
+  if (isa<TagDecl>(Target)) {
+    // No conflict between a tag and a non-tag.
+    if (!Tag) return false;
+
+    Diag(BUD->getLocation(), diag::err_using_decl_conflict);
+    Diag(Target->getLocation(), diag::note_using_decl_target);
+    Diag(Tag->getLocation(), diag::note_using_decl_conflict);
+    BUD->setInvalidDecl();
+    return true;
+  }
+
+  // No conflict between a tag and a non-tag.
+  if (!NonTag) return false;
+
+  Diag(BUD->getLocation(), diag::err_using_decl_conflict);
+  Diag(Target->getLocation(), diag::note_using_decl_target);
+  Diag(NonTag->getLocation(), diag::note_using_decl_conflict);
+  BUD->setInvalidDecl();
+  return true;
+}
+
+/// Determine whether a direct base class is a virtual base class.
+static bool isVirtualDirectBase(CXXRecordDecl *Derived, CXXRecordDecl *Base) {
+  if (!Derived->getNumVBases())
+    return false;
+  for (auto &B : Derived->bases())
+    if (B.getType()->getAsCXXRecordDecl() == Base)
+      return B.isVirtual();
+  llvm_unreachable("not a direct base class");
+}
+
+/// Builds a shadow declaration corresponding to a 'using' declaration.
+UsingShadowDecl *Sema::BuildUsingShadowDecl(Scope *S, BaseUsingDecl *BUD,
+                                            NamedDecl *Orig,
+                                            UsingShadowDecl *PrevDecl) {
+  // If we resolved to another shadow declaration, just coalesce them.
+  NamedDecl *Target = Orig;
+  if (isa<UsingShadowDecl>(Target)) {
+    Target = cast<UsingShadowDecl>(Target)->getTargetDecl();
+    assert(!isa<UsingShadowDecl>(Target) && "nested shadow declaration");
+  }
+
+  NamedDecl *NonTemplateTarget = Target;
+  if (auto *TargetTD = dyn_cast<TemplateDecl>(Target))
+    NonTemplateTarget = TargetTD->getTemplatedDecl();
+
+  UsingShadowDecl *Shadow;
+  if (NonTemplateTarget && isa<CXXConstructorDecl>(NonTemplateTarget)) {
+    UsingDecl *Using = cast<UsingDecl>(BUD);
+    bool IsVirtualBase =
+        isVirtualDirectBase(cast<CXXRecordDecl>(CurContext),
+                            Using->getQualifier()->getAsRecordDecl());
+    Shadow = ConstructorUsingShadowDecl::Create(
+        Context, CurContext, Using->getLocation(), Using, Orig, IsVirtualBase);
+  } else {
+    Shadow = UsingShadowDecl::Create(Context, CurContext, BUD->getLocation(),
+                                     Target->getDeclName(), BUD, Target);
+  }
+  BUD->addShadowDecl(Shadow);
+
+  Shadow->setAccess(BUD->getAccess());
+  if (Orig->isInvalidDecl() || BUD->isInvalidDecl())
+    Shadow->setInvalidDecl();
+
+  Shadow->setPreviousDecl(PrevDecl);
+
+  if (S)
+    PushOnScopeChains(Shadow, S);
+  else
+    CurContext->addDecl(Shadow);
+
+
+  return Shadow;
+}
+
+/// Hides a using shadow declaration.  This is required by the current
+/// using-decl implementation when a resolvable using declaration in a
+/// class is followed by a declaration which would hide or override
+/// one or more of the using decl's targets; for example:
+///
+///   struct Base { void foo(int); };
+///   struct Derived : Base {
+///     using Base::foo;
+///     void foo(int);
+///   };
+///
+/// The governing language is C++03 [namespace.udecl]p12:
+///
+///   When a using-declaration brings names from a base class into a
+///   derived class scope, member functions in the derived class
+///   override and/or hide member functions with the same name and
+///   parameter types in a base class (rather than conflicting).
+///
+/// There are two ways to implement this:
+///   (1) optimistically create shadow decls when they're not hidden
+///       by existing declarations, or
+///   (2) don't create any shadow decls (or at least don't make them
+///       visible) until we've fully parsed/instantiated the class.
+/// The problem with (1) is that we might have to retroactively remove
+/// a shadow decl, which requires several O(n) operations because the
+/// decl structures are (very reasonably) not designed for removal.
+/// (2) avoids this but is very fiddly and phase-dependent.
+void Sema::HideUsingShadowDecl(Scope *S, UsingShadowDecl *Shadow) {
+  if (Shadow->getDeclName().getNameKind() ==
+        DeclarationName::CXXConversionFunctionName)
+    cast<CXXRecordDecl>(Shadow->getDeclContext())->removeConversion(Shadow);
+
+  // Remove it from the DeclContext...
+  Shadow->getDeclContext()->removeDecl(Shadow);
+
+  // ...and the scope, if applicable...
+  if (S) {
+    S->RemoveDecl(Shadow);
+    IdResolver.RemoveDecl(Shadow);
+  }
+
+  // ...and the using decl.
+  Shadow->getIntroducer()->removeShadowDecl(Shadow);
+
+  // TODO: complain somehow if Shadow was used.  It shouldn't
+  // be possible for this to happen, because...?
+}
+
+/// Find the base specifier for a base class with the given type.
+static CXXBaseSpecifier *findDirectBaseWithType(CXXRecordDecl *Derived,
+                                                QualType DesiredBase,
+                                                bool &AnyDependentBases) {
+  // Check whether the named type is a direct base class.
+  CanQualType CanonicalDesiredBase = DesiredBase->getCanonicalTypeUnqualified()
+    .getUnqualifiedType();
+  for (auto &Base : Derived->bases()) {
+    CanQualType BaseType = Base.getType()->getCanonicalTypeUnqualified();
+    if (CanonicalDesiredBase == BaseType)
+      return &Base;
+    if (BaseType->isDependentType())
+      AnyDependentBases = true;
+  }
+  return nullptr;
+}
+
+namespace {
+class UsingValidatorCCC final : public CorrectionCandidateCallback {
+public:
+  UsingValidatorCCC(bool HasTypenameKeyword, bool IsInstantiation,
+                    NestedNameSpecifier *NNS, CXXRecordDecl *RequireMemberOf)
+      : HasTypenameKeyword(HasTypenameKeyword),
+        IsInstantiation(IsInstantiation), OldNNS(NNS),
+        RequireMemberOf(RequireMemberOf) {}
+
+  bool ValidateCandidate(const TypoCorrection &Candidate) override {
+    NamedDecl *ND = Candidate.getCorrectionDecl();
+
+    // Keywords are not valid here.
+    if (!ND || isa<NamespaceDecl>(ND))
+      return false;
+
+    // Completely unqualified names are invalid for a 'using' declaration.
+    if (Candidate.WillReplaceSpecifier() && !Candidate.getCorrectionSpecifier())
+      return false;
+
+    // FIXME: Don't correct to a name that CheckUsingDeclRedeclaration would
+    // reject.
+
+    if (RequireMemberOf) {
+      auto *FoundRecord = dyn_cast<CXXRecordDecl>(ND);
+      if (FoundRecord && FoundRecord->isInjectedClassName()) {
+        // No-one ever wants a using-declaration to name an injected-class-name
+        // of a base class, unless they're declaring an inheriting constructor.
+        ASTContext &Ctx = ND->getASTContext();
+        if (!Ctx.getLangOpts().CPlusPlus11)
+          return false;
+        QualType FoundType = Ctx.getRecordType(FoundRecord);
+
+        // Check that the injected-class-name is named as a member of its own
+        // type; we don't want to suggest 'using Derived::Base;', since that
+        // means something else.
+        NestedNameSpecifier *Specifier =
+            Candidate.WillReplaceSpecifier()
+                ? Candidate.getCorrectionSpecifier()
+                : OldNNS;
+        if (!Specifier->getAsType() ||
+            !Ctx.hasSameType(QualType(Specifier->getAsType(), 0), FoundType))
+          return false;
+
+        // Check that this inheriting constructor declaration actually names a
+        // direct base class of the current class.
+        bool AnyDependentBases = false;
+        if (!findDirectBaseWithType(RequireMemberOf,
+                                    Ctx.getRecordType(FoundRecord),
+                                    AnyDependentBases) &&
+            !AnyDependentBases)
+          return false;
+      } else {
+        auto *RD = dyn_cast<CXXRecordDecl>(ND->getDeclContext());
+        if (!RD || RequireMemberOf->isProvablyNotDerivedFrom(RD))
+          return false;
+
+        // FIXME: Check that the base class member is accessible?
+      }
+    } else {
+      auto *FoundRecord = dyn_cast<CXXRecordDecl>(ND);
+      if (FoundRecord && FoundRecord->isInjectedClassName())
+        return false;
+    }
+
+    if (isa<TypeDecl>(ND))
+      return HasTypenameKeyword || !IsInstantiation;
+
+    return !HasTypenameKeyword;
+  }
+
+  std::unique_ptr<CorrectionCandidateCallback> clone() override {
+    return std::make_unique<UsingValidatorCCC>(*this);
+  }
+
+private:
+  bool HasTypenameKeyword;
+  bool IsInstantiation;
+  NestedNameSpecifier *OldNNS;
+  CXXRecordDecl *RequireMemberOf;
+};
+} // end anonymous namespace
+
+/// Remove decls we can't actually see from a lookup being used to declare
+/// shadow using decls.
+///
+/// \param S - The scope of the potential shadow decl
+/// \param Previous - The lookup of a potential shadow decl's name.
+void Sema::FilterUsingLookup(Scope *S, LookupResult &Previous) {
+  // It is really dumb that we have to do this.
+  LookupResult::Filter F = Previous.makeFilter();
+  while (F.hasNext()) {
+    NamedDecl *D = F.next();
+    if (!isDeclInScope(D, CurContext, S))
+      F.erase();
+    // If we found a local extern declaration that's not ordinarily visible,
+    // and this declaration is being added to a non-block scope, ignore it.
+    // We're only checking for scope conflicts here, not also for violations
+    // of the linkage rules.
+    else if (!CurContext->isFunctionOrMethod() && D->isLocalExternDecl() &&
+             !(D->getIdentifierNamespace() & Decl::IDNS_Ordinary))
+      F.erase();
+  }
+  F.done();
+}
+
+/// Builds a using declaration.
+///
+/// \param IsInstantiation - Whether this call arises from an
+///   instantiation of an unresolved using declaration.  We treat
+///   the lookup differently for these declarations.
+NamedDecl *Sema::BuildUsingDeclaration(
+    Scope *S, AccessSpecifier AS, SourceLocation UsingLoc,
+    bool HasTypenameKeyword, SourceLocation TypenameLoc, CXXScopeSpec &SS,
+    DeclarationNameInfo NameInfo, SourceLocation EllipsisLoc,
+    const ParsedAttributesView &AttrList, bool IsInstantiation,
+    bool IsUsingIfExists) {
+  assert(!SS.isInvalid() && "Invalid CXXScopeSpec.");
+  SourceLocation IdentLoc = NameInfo.getLoc();
+  assert(IdentLoc.isValid() && "Invalid TargetName location.");
+
+  // FIXME: We ignore attributes for now.
+
+  // For an inheriting constructor declaration, the name of the using
+  // declaration is the name of a constructor in this class, not in the
+  // base class.
+  DeclarationNameInfo UsingName = NameInfo;
+  if (UsingName.getName().getNameKind() == DeclarationName::CXXConstructorName)
+    if (auto *RD = dyn_cast<CXXRecordDecl>(CurContext))
+      UsingName.setName(Context.DeclarationNames.getCXXConstructorName(
+          Context.getCanonicalType(Context.getRecordType(RD))));
+
+  // Do the redeclaration lookup in the current scope.
+  LookupResult Previous(*this, UsingName, LookupUsingDeclName,
+                        ForVisibleRedeclaration);
+  Previous.setHideTags(false);
+  if (S) {
+    LookupName(Previous, S);
+
+    FilterUsingLookup(S, Previous);
+  } else {
+    assert(IsInstantiation && "no scope in non-instantiation");
+    if (CurContext->isRecord())
+      LookupQualifiedName(Previous, CurContext);
+    else {
+      // No redeclaration check is needed here; in non-member contexts we
+      // diagnosed all possible conflicts with other using-declarations when
+      // building the template:
+      //
+      // For a dependent non-type using declaration, the only valid case is
+      // if we instantiate to a single enumerator. We check for conflicts
+      // between shadow declarations we introduce, and we check in the template
+      // definition for conflicts between a non-type using declaration and any
+      // other declaration, which together covers all cases.
+      //
+      // A dependent typename using declaration will never successfully
+      // instantiate, since it will always name a class member, so we reject
+      // that in the template definition.
+    }
+  }
+
+  // Check for invalid redeclarations.
+  if (CheckUsingDeclRedeclaration(UsingLoc, HasTypenameKeyword,
+                                  SS, IdentLoc, Previous))
+    return nullptr;
+
+  // 'using_if_exists' doesn't make sense on an inherited constructor.
+  if (IsUsingIfExists && UsingName.getName().getNameKind() ==
+                             DeclarationName::CXXConstructorName) {
+    Diag(UsingLoc, diag::err_using_if_exists_on_ctor);
+    return nullptr;
+  }
+
+  DeclContext *LookupContext = computeDeclContext(SS);
+  NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
+  if (!LookupContext || EllipsisLoc.isValid()) {
+    NamedDecl *D;
+    // Dependent scope, or an unexpanded pack
+    if (!LookupContext && CheckUsingDeclQualifier(UsingLoc, HasTypenameKeyword,
+                                                  SS, NameInfo, IdentLoc))
+      return nullptr;
+
+    if (HasTypenameKeyword) {
+      // FIXME: not all declaration name kinds are legal here
+      D = UnresolvedUsingTypenameDecl::Create(Context, CurContext,
+                                              UsingLoc, TypenameLoc,
+                                              QualifierLoc,
+                                              IdentLoc, NameInfo.getName(),
+                                              EllipsisLoc);
+    } else {
+      D = UnresolvedUsingValueDecl::Create(Context, CurContext, UsingLoc,
+                                           QualifierLoc, NameInfo, EllipsisLoc);
+    }
+    D->setAccess(AS);
+    CurContext->addDecl(D);
+    ProcessDeclAttributeList(S, D, AttrList);
+    return D;
+  }
+
+  auto Build = [&](bool Invalid) {
+    UsingDecl *UD =
+        UsingDecl::Create(Context, CurContext, UsingLoc, QualifierLoc,
+                          UsingName, HasTypenameKeyword);
+    UD->setAccess(AS);
+    CurContext->addDecl(UD);
+    ProcessDeclAttributeList(S, UD, AttrList);
+    UD->setInvalidDecl(Invalid);
+    return UD;
+  };
+  auto BuildInvalid = [&]{ return Build(true); };
+  auto BuildValid = [&]{ return Build(false); };
+
+  if (RequireCompleteDeclContext(SS, LookupContext))
+    return BuildInvalid();
+
+  // Look up the target name.
+  LookupResult R(*this, NameInfo, LookupOrdinaryName);
+
+  // Unlike most lookups, we don't always want to hide tag
+  // declarations: tag names are visible through the using declaration
+  // even if hidden by ordinary names, *except* in a dependent context
+  // where they may be used by two-phase lookup.
+  if (!IsInstantiation)
+    R.setHideTags(false);
+
+  // For the purposes of this lookup, we have a base object type
+  // equal to that of the current context.
+  if (CurContext->isRecord()) {
+    R.setBaseObjectType(
+                   Context.getTypeDeclType(cast<CXXRecordDecl>(CurContext)));
+  }
+
+  LookupQualifiedName(R, LookupContext);
+
+  // Validate the context, now we have a lookup
+  if (CheckUsingDeclQualifier(UsingLoc, HasTypenameKeyword, SS, NameInfo,
+                              IdentLoc, &R))
+    return nullptr;
+
+  if (R.empty() && IsUsingIfExists)
+    R.addDecl(UnresolvedUsingIfExistsDecl::Create(Context, CurContext, UsingLoc,
+                                                  UsingName.getName()),
+              AS_public);
+
+  // Try to correct typos if possible. If constructor name lookup finds no
+  // results, that means the named class has no explicit constructors, and we
+  // suppressed declaring implicit ones (probably because it's dependent or
+  // invalid).
+  if (R.empty() &&
+      NameInfo.getName().getNameKind() != DeclarationName::CXXConstructorName) {
+    // HACK 2017-01-08: Work around an issue with libstdc++'s detection of
+    // ::gets. Sometimes it believes that glibc provides a ::gets in cases where
+    // it does not. The issue was fixed in libstdc++ 6.3 (2016-12-21) and later.
+    auto *II = NameInfo.getName().getAsIdentifierInfo();
+    if (getLangOpts().CPlusPlus14 && II && II->isStr("gets") &&
+        CurContext->isStdNamespace() &&
+        isa<TranslationUnitDecl>(LookupContext) &&
+        getSourceManager().isInSystemHeader(UsingLoc))
+      return nullptr;
+    UsingValidatorCCC CCC(HasTypenameKeyword, IsInstantiation, SS.getScopeRep(),
+                          dyn_cast<CXXRecordDecl>(CurContext));
+    if (TypoCorrection Corrected =
+            CorrectTypo(R.getLookupNameInfo(), R.getLookupKind(), S, &SS, CCC,
+                        CTK_ErrorRecovery)) {
+      // We reject candidates where DroppedSpecifier == true, hence the
+      // literal '0' below.
+      diagnoseTypo(Corrected, PDiag(diag::err_no_member_suggest)
+                                << NameInfo.getName() << LookupContext << 0
+                                << SS.getRange());
+
+      // If we picked a correction with no attached Decl we can't do anything
+      // useful with it, bail out.
+      NamedDecl *ND = Corrected.getCorrectionDecl();
+      if (!ND)
+        return BuildInvalid();
+
+      // If we corrected to an inheriting constructor, handle it as one.
+      auto *RD = dyn_cast<CXXRecordDecl>(ND);
+      if (RD && RD->isInjectedClassName()) {
+        // The parent of the injected class name is the class itself.
+        RD = cast<CXXRecordDecl>(RD->getParent());
+
+        // Fix up the information we'll use to build the using declaration.
+        if (Corrected.WillReplaceSpecifier()) {
+          NestedNameSpecifierLocBuilder Builder;
+          Builder.MakeTrivial(Context, Corrected.getCorrectionSpecifier(),
+                              QualifierLoc.getSourceRange());
+          QualifierLoc = Builder.getWithLocInContext(Context);
+        }
+
+        // In this case, the name we introduce is the name of a derived class
+        // constructor.
+        auto *CurClass = cast<CXXRecordDecl>(CurContext);
+        UsingName.setName(Context.DeclarationNames.getCXXConstructorName(
+            Context.getCanonicalType(Context.getRecordType(CurClass))));
+        UsingName.setNamedTypeInfo(nullptr);
+        for (auto *Ctor : LookupConstructors(RD))
+          R.addDecl(Ctor);
+        R.resolveKind();
+      } else {
+        // FIXME: Pick up all the declarations if we found an overloaded
+        // function.
+        UsingName.setName(ND->getDeclName());
+        R.addDecl(ND);
+      }
+    } else {
+      Diag(IdentLoc, diag::err_no_member)
+        << NameInfo.getName() << LookupContext << SS.getRange();
+      return BuildInvalid();
+    }
+  }
+
+  if (R.isAmbiguous())
+    return BuildInvalid();
+
+  if (HasTypenameKeyword) {
+    // If we asked for a typename and got a non-type decl, error out.
+    if (!R.getAsSingle<TypeDecl>() &&
+        !R.getAsSingle<UnresolvedUsingIfExistsDecl>()) {
+      Diag(IdentLoc, diag::err_using_typename_non_type);
+      for (LookupResult::iterator I = R.begin(), E = R.end(); I != E; ++I)
+        Diag((*I)->getUnderlyingDecl()->getLocation(),
+             diag::note_using_decl_target);
+      return BuildInvalid();
+    }
+  } else {
+    // If we asked for a non-typename and we got a type, error out,
+    // but only if this is an instantiation of an unresolved using
+    // decl.  Otherwise just silently find the type name.
+    if (IsInstantiation && R.getAsSingle<TypeDecl>()) {
+      Diag(IdentLoc, diag::err_using_dependent_value_is_type);
+      Diag(R.getFoundDecl()->getLocation(), diag::note_using_decl_target);
+      return BuildInvalid();
+    }
+  }
+
+  // C++14 [namespace.udecl]p6:
+  // A using-declaration shall not name a namespace.
+  if (R.getAsSingle<NamespaceDecl>()) {
+    Diag(IdentLoc, diag::err_using_decl_can_not_refer_to_namespace)
+      << SS.getRange();
+    return BuildInvalid();
+  }
+
+  UsingDecl *UD = BuildValid();
+
+  // Some additional rules apply to inheriting constructors.
+  if (UsingName.getName().getNameKind() ==
+        DeclarationName::CXXConstructorName) {
+    // Suppress access diagnostics; the access check is instead performed at the
+    // point of use for an inheriting constructor.
+    R.suppressDiagnostics();
+    if (CheckInheritingConstructorUsingDecl(UD))
+      return UD;
+  }
+
+  for (LookupResult::iterator I = R.begin(), E = R.end(); I != E; ++I) {
+    UsingShadowDecl *PrevDecl = nullptr;
+    if (!CheckUsingShadowDecl(UD, *I, Previous, PrevDecl))
+      BuildUsingShadowDecl(S, UD, *I, PrevDecl);
+  }
+
+  return UD;
+}
+
+NamedDecl *Sema::BuildUsingEnumDeclaration(Scope *S, AccessSpecifier AS,
+                                           SourceLocation UsingLoc,
+                                           SourceLocation EnumLoc,
+                                           SourceLocation NameLoc,
+                                           EnumDecl *ED) {
+  bool Invalid = false;
+
+  if (CurContext->getRedeclContext()->isRecord()) {
+    /// In class scope, check if this is a duplicate, for better a diagnostic.
+    DeclarationNameInfo UsingEnumName(ED->getDeclName(), NameLoc);
+    LookupResult Previous(*this, UsingEnumName, LookupUsingDeclName,
+                          ForVisibleRedeclaration);
+
+    LookupName(Previous, S);
+
+    for (NamedDecl *D : Previous)
+      if (UsingEnumDecl *UED = dyn_cast<UsingEnumDecl>(D))
+        if (UED->getEnumDecl() == ED) {
+          Diag(UsingLoc, diag::err_using_enum_decl_redeclaration)
+              << SourceRange(EnumLoc, NameLoc);
+          Diag(D->getLocation(), diag::note_using_enum_decl) << 1;
+          Invalid = true;
+          break;
+        }
+  }
+
+  if (RequireCompleteEnumDecl(ED, NameLoc))
+    Invalid = true;
+
+  UsingEnumDecl *UD = UsingEnumDecl::Create(Context, CurContext, UsingLoc,
+                                            EnumLoc, NameLoc, ED);
+  UD->setAccess(AS);
+  CurContext->addDecl(UD);
+
+  if (Invalid) {
+    UD->setInvalidDecl();
+    return UD;
+  }
+
+  // Create the shadow decls for each enumerator
+  for (EnumConstantDecl *EC : ED->enumerators()) {
+    UsingShadowDecl *PrevDecl = nullptr;
+    DeclarationNameInfo DNI(EC->getDeclName(), EC->getLocation());
+    LookupResult Previous(*this, DNI, LookupOrdinaryName,
+                          ForVisibleRedeclaration);
+    LookupName(Previous, S);
+    FilterUsingLookup(S, Previous);
+
+    if (!CheckUsingShadowDecl(UD, EC, Previous, PrevDecl))
+      BuildUsingShadowDecl(S, UD, EC, PrevDecl);
+  }
+
+  return UD;
+}
+
+NamedDecl *Sema::BuildUsingPackDecl(NamedDecl *InstantiatedFrom,
+                                    ArrayRef<NamedDecl *> Expansions) {
+  assert(isa<UnresolvedUsingValueDecl>(InstantiatedFrom) ||
+         isa<UnresolvedUsingTypenameDecl>(InstantiatedFrom) ||
+         isa<UsingPackDecl>(InstantiatedFrom));
+
+  auto *UPD =
+      UsingPackDecl::Create(Context, CurContext, InstantiatedFrom, Expansions);
+  UPD->setAccess(InstantiatedFrom->getAccess());
+  CurContext->addDecl(UPD);
+  return UPD;
+}
+
+/// Additional checks for a using declaration referring to a constructor name.
+bool Sema::CheckInheritingConstructorUsingDecl(UsingDecl *UD) {
+  assert(!UD->hasTypename() && "expecting a constructor name");
+
+  const Type *SourceType = UD->getQualifier()->getAsType();
+  assert(SourceType &&
+         "Using decl naming constructor doesn't have type in scope spec.");
+  CXXRecordDecl *TargetClass = cast<CXXRecordDecl>(CurContext);
+
+  // Check whether the named type is a direct base class.
+  bool AnyDependentBases = false;
+  auto *Base = findDirectBaseWithType(TargetClass, QualType(SourceType, 0),
+                                      AnyDependentBases);
+  if (!Base && !AnyDependentBases) {
+    Diag(UD->getUsingLoc(),
+         diag::err_using_decl_constructor_not_in_direct_base)
+      << UD->getNameInfo().getSourceRange()
+      << QualType(SourceType, 0) << TargetClass;
+    UD->setInvalidDecl();
+    return true;
+  }
+
+  if (Base)
+    Base->setInheritConstructors();
+
+  return false;
+}
+
+/// Checks that the given using declaration is not an invalid
+/// redeclaration.  Note that this is checking only for the using decl
+/// itself, not for any ill-formedness among the UsingShadowDecls.
+bool Sema::CheckUsingDeclRedeclaration(SourceLocation UsingLoc,
+                                       bool HasTypenameKeyword,
+                                       const CXXScopeSpec &SS,
+                                       SourceLocation NameLoc,
+                                       const LookupResult &Prev) {
+  NestedNameSpecifier *Qual = SS.getScopeRep();
+
+  // C++03 [namespace.udecl]p8:
+  // C++0x [namespace.udecl]p10:
+  //   A using-declaration is a declaration and can therefore be used
+  //   repeatedly where (and only where) multiple declarations are
+  //   allowed.
+  //
+  // That's in non-member contexts.
+  if (!CurContext->getRedeclContext()->isRecord()) {
+    // A dependent qualifier outside a class can only ever resolve to an
+    // enumeration type. Therefore it conflicts with any other non-type
+    // declaration in the same scope.
+    // FIXME: How should we check for dependent type-type conflicts at block
+    // scope?
+    if (Qual->isDependent() && !HasTypenameKeyword) {
+      for (auto *D : Prev) {
+        if (!isa<TypeDecl>(D) && !isa<UsingDecl>(D) && !isa<UsingPackDecl>(D)) {
+          bool OldCouldBeEnumerator =
+              isa<UnresolvedUsingValueDecl>(D) || isa<EnumConstantDecl>(D);
+          Diag(NameLoc,
+               OldCouldBeEnumerator ? diag::err_redefinition
+                                    : diag::err_redefinition_different_kind)
+              << Prev.getLookupName();
+          Diag(D->getLocation(), diag::note_previous_definition);
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  const NestedNameSpecifier *CNNS =
+      Context.getCanonicalNestedNameSpecifier(Qual);
+  for (LookupResult::iterator I = Prev.begin(), E = Prev.end(); I != E; ++I) {
+    NamedDecl *D = *I;
+
+    bool DTypename;
+    NestedNameSpecifier *DQual;
+    if (UsingDecl *UD = dyn_cast<UsingDecl>(D)) {
+      DTypename = UD->hasTypename();
+      DQual = UD->getQualifier();
+    } else if (UnresolvedUsingValueDecl *UD
+                 = dyn_cast<UnresolvedUsingValueDecl>(D)) {
+      DTypename = false;
+      DQual = UD->getQualifier();
+    } else if (UnresolvedUsingTypenameDecl *UD
+                 = dyn_cast<UnresolvedUsingTypenameDecl>(D)) {
+      DTypename = true;
+      DQual = UD->getQualifier();
+    } else continue;
+
+    // using decls differ if one says 'typename' and the other doesn't.
+    // FIXME: non-dependent using decls?
+    if (HasTypenameKeyword != DTypename) continue;
+
+    // using decls differ if they name different scopes (but note that
+    // template instantiation can cause this check to trigger when it
+    // didn't before instantiation).
+    if (CNNS != Context.getCanonicalNestedNameSpecifier(DQual))
+      continue;
+
+    Diag(NameLoc, diag::err_using_decl_redeclaration) << SS.getRange();
+    Diag(D->getLocation(), diag::note_using_decl) << 1;
+    return true;
+  }
+
+  return false;
+}
+
+/// Checks that the given nested-name qualifier used in a using decl
+/// in the current context is appropriately related to the current
+/// scope.  If an error is found, diagnoses it and returns true.
+/// R is nullptr, if the caller has not (yet) done a lookup, otherwise it's the
+/// result of that lookup. UD is likewise nullptr, except when we have an
+/// already-populated UsingDecl whose shadow decls contain the same information
+/// (i.e. we're instantiating a UsingDecl with non-dependent scope).
+bool Sema::CheckUsingDeclQualifier(SourceLocation UsingLoc, bool HasTypename,
+                                   const CXXScopeSpec &SS,
+                                   const DeclarationNameInfo &NameInfo,
+                                   SourceLocation NameLoc,
+                                   const LookupResult *R, const UsingDecl *UD) {
+  DeclContext *NamedContext = computeDeclContext(SS);
+  assert(bool(NamedContext) == (R || UD) && !(R && UD) &&
+         "resolvable context must have exactly one set of decls");
+
+  // C++ 20 permits using an enumerator that does not have a class-hierarchy
+  // relationship.
+  bool Cxx20Enumerator = false;
+  if (NamedContext) {
+    EnumConstantDecl *EC = nullptr;
+    if (R)
+      EC = R->getAsSingle<EnumConstantDecl>();
+    else if (UD && UD->shadow_size() == 1)
+      EC = dyn_cast<EnumConstantDecl>(UD->shadow_begin()->getTargetDecl());
+    if (EC)
+      Cxx20Enumerator = getLangOpts().CPlusPlus20;
+
+    if (auto *ED = dyn_cast<EnumDecl>(NamedContext)) {
+      // C++14 [namespace.udecl]p7:
+      // A using-declaration shall not name a scoped enumerator.
+      // C++20 p1099 permits enumerators.
+      if (EC && R && ED->isScoped())
+        Diag(SS.getBeginLoc(),
+             getLangOpts().CPlusPlus20
+                 ? diag::warn_cxx17_compat_using_decl_scoped_enumerator
+                 : diag::ext_using_decl_scoped_enumerator)
+            << SS.getRange();
+
+      // We want to consider the scope of the enumerator
+      NamedContext = ED->getDeclContext();
+    }
+  }
+
+  if (!CurContext->isRecord()) {
+    // C++03 [namespace.udecl]p3:
+    // C++0x [namespace.udecl]p8:
+    //   A using-declaration for a class member shall be a member-declaration.
+    // C++20 [namespace.udecl]p7
+    //   ... other than an enumerator ...
+
+    // If we weren't able to compute a valid scope, it might validly be a
+    // dependent class or enumeration scope. If we have a 'typename' keyword,
+    // the scope must resolve to a class type.
+    if (NamedContext ? !NamedContext->getRedeclContext()->isRecord()
+                     : !HasTypename)
+      return false; // OK
+
+    Diag(NameLoc,
+         Cxx20Enumerator
+             ? diag::warn_cxx17_compat_using_decl_class_member_enumerator
+             : diag::err_using_decl_can_not_refer_to_class_member)
+        << SS.getRange();
+
+    if (Cxx20Enumerator)
+      return false; // OK
+
+    auto *RD = NamedContext
+                   ? cast<CXXRecordDecl>(NamedContext->getRedeclContext())
+                   : nullptr;
+    if (RD && !RequireCompleteDeclContext(const_cast<CXXScopeSpec &>(SS), RD)) {
+      // See if there's a helpful fixit
+
+      if (!R) {
+        // We will have already diagnosed the problem on the template
+        // definition,  Maybe we should do so again?
+      } else if (R->getAsSingle<TypeDecl>()) {
+        if (getLangOpts().CPlusPlus11) {
+          // Convert 'using X::Y;' to 'using Y = X::Y;'.
+          Diag(SS.getBeginLoc(), diag::note_using_decl_class_member_workaround)
+            << 0 // alias declaration
+            << FixItHint::CreateInsertion(SS.getBeginLoc(),
+                                          NameInfo.getName().getAsString() +
+                                              " = ");
+        } else {
+          // Convert 'using X::Y;' to 'typedef X::Y Y;'.
+          SourceLocation InsertLoc = getLocForEndOfToken(NameInfo.getEndLoc());
+          Diag(InsertLoc, diag::note_using_decl_class_member_workaround)
+            << 1 // typedef declaration
+            << FixItHint::CreateReplacement(UsingLoc, "typedef")
+            << FixItHint::CreateInsertion(
+                   InsertLoc, " " + NameInfo.getName().getAsString());
+        }
+      } else if (R->getAsSingle<VarDecl>()) {
+        // Don't provide a fixit outside C++11 mode; we don't want to suggest
+        // repeating the type of the static data member here.
+        FixItHint FixIt;
+        if (getLangOpts().CPlusPlus11) {
+          // Convert 'using X::Y;' to 'auto &Y = X::Y;'.
+          FixIt = FixItHint::CreateReplacement(
+              UsingLoc, "auto &" + NameInfo.getName().getAsString() + " = ");
+        }
+
+        Diag(UsingLoc, diag::note_using_decl_class_member_workaround)
+          << 2 // reference declaration
+          << FixIt;
+      } else if (R->getAsSingle<EnumConstantDecl>()) {
+        // Don't provide a fixit outside C++11 mode; we don't want to suggest
+        // repeating the type of the enumeration here, and we can't do so if
+        // the type is anonymous.
+        FixItHint FixIt;
+        if (getLangOpts().CPlusPlus11) {
+          // Convert 'using X::Y;' to 'auto &Y = X::Y;'.
+          FixIt = FixItHint::CreateReplacement(
+              UsingLoc,
+              "constexpr auto " + NameInfo.getName().getAsString() + " = ");
+        }
+
+        Diag(UsingLoc, diag::note_using_decl_class_member_workaround)
+          << (getLangOpts().CPlusPlus11 ? 4 : 3) // const[expr] variable
+          << FixIt;
+      }
+    }
+
+    return true; // Fail
+  }
+
+  // If the named context is dependent, we can't decide much.
+  if (!NamedContext) {
+    // FIXME: in C++0x, we can diagnose if we can prove that the
+    // nested-name-specifier does not refer to a base class, which is
+    // still possible in some cases.
+
+    // Otherwise we have to conservatively report that things might be
+    // okay.
+    return false;
+  }
+
+  // The current scope is a record.
+  if (!NamedContext->isRecord()) {
+    // Ideally this would point at the last name in the specifier,
+    // but we don't have that level of source info.
+    Diag(SS.getBeginLoc(),
+         Cxx20Enumerator
+             ? diag::warn_cxx17_compat_using_decl_non_member_enumerator
+             : diag::err_using_decl_nested_name_specifier_is_not_class)
+        << SS.getScopeRep() << SS.getRange();
+
+    if (Cxx20Enumerator)
+      return false; // OK
+
+    return true;
+  }
+
+  if (!NamedContext->isDependentContext() &&
+      RequireCompleteDeclContext(const_cast<CXXScopeSpec&>(SS), NamedContext))
+    return true;
+
+  if (getLangOpts().CPlusPlus11) {
+    // C++11 [namespace.udecl]p3:
+    //   In a using-declaration used as a member-declaration, the
+    //   nested-name-specifier shall name a base class of the class
+    //   being defined.
+
+    if (cast<CXXRecordDecl>(CurContext)->isProvablyNotDerivedFrom(
+                                 cast<CXXRecordDecl>(NamedContext))) {
+
+      if (Cxx20Enumerator) {
+        Diag(NameLoc, diag::warn_cxx17_compat_using_decl_non_member_enumerator)
+            << SS.getRange();
+        return false;
+      }
+
+      if (CurContext == NamedContext) {
+        Diag(SS.getBeginLoc(),
+             diag::err_using_decl_nested_name_specifier_is_current_class)
+            << SS.getRange();
+        return !getLangOpts().CPlusPlus20;
+      }
+
+      if (!cast<CXXRecordDecl>(NamedContext)->isInvalidDecl()) {
+        Diag(SS.getBeginLoc(),
+             diag::err_using_decl_nested_name_specifier_is_not_base_class)
+            << SS.getScopeRep() << cast<CXXRecordDecl>(CurContext)
+            << SS.getRange();
+      }
+      return true;
+    }
+
+    return false;
+  }
+
+  // C++03 [namespace.udecl]p4:
+  //   A using-declaration used as a member-declaration shall refer
+  //   to a member of a base class of the class being defined [etc.].
+
+  // Salient point: SS doesn't have to name a base class as long as
+  // lookup only finds members from base classes.  Therefore we can
+  // diagnose here only if we can prove that that can't happen,
+  // i.e. if the class hierarchies provably don't intersect.
+
+  // TODO: it would be nice if "definitely valid" results were cached
+  // in the UsingDecl and UsingShadowDecl so that these checks didn't
+  // need to be repeated.
+
+  llvm::SmallPtrSet<const CXXRecordDecl *, 4> Bases;
+  auto Collect = [&Bases](const CXXRecordDecl *Base) {
+    Bases.insert(Base);
+    return true;
+  };
+
+  // Collect all bases. Return false if we find a dependent base.
+  if (!cast<CXXRecordDecl>(CurContext)->forallBases(Collect))
+    return false;
+
+  // Returns true if the base is dependent or is one of the accumulated base
+  // classes.
+  auto IsNotBase = [&Bases](const CXXRecordDecl *Base) {
+    return !Bases.count(Base);
+  };
+
+  // Return false if the class has a dependent base or if it or one
+  // of its bases is present in the base set of the current context.
+  if (Bases.count(cast<CXXRecordDecl>(NamedContext)) ||
+      !cast<CXXRecordDecl>(NamedContext)->forallBases(IsNotBase))
+    return false;
+
+  Diag(SS.getRange().getBegin(),
+       diag::err_using_decl_nested_name_specifier_is_not_base_class)
+    << SS.getScopeRep()
+    << cast<CXXRecordDecl>(CurContext)
+    << SS.getRange();
+
+  return true;
+}
+
+Decl *Sema::ActOnAliasDeclaration(Scope *S, AccessSpecifier AS,
+                                  MultiTemplateParamsArg TemplateParamLists,
+                                  SourceLocation UsingLoc, UnqualifiedId &Name,
+                                  const ParsedAttributesView &AttrList,
+                                  TypeResult Type, Decl *DeclFromDeclSpec) {
+  // Skip up to the relevant declaration scope.
+  while (S->isTemplateParamScope())
+    S = S->getParent();
+  assert((S->getFlags() & Scope::DeclScope) &&
+         "got alias-declaration outside of declaration scope");
+
+  if (Type.isInvalid())
+    return nullptr;
+
+  bool Invalid = false;
+  DeclarationNameInfo NameInfo = GetNameFromUnqualifiedId(Name);
+  TypeSourceInfo *TInfo = nullptr;
+  GetTypeFromParser(Type.get(), &TInfo);
+
+  if (DiagnoseClassNameShadow(CurContext, NameInfo))
+    return nullptr;
+
+  if (DiagnoseUnexpandedParameterPack(Name.StartLocation, TInfo,
+                                      UPPC_DeclarationType)) {
+    Invalid = true;
+    TInfo = Context.getTrivialTypeSourceInfo(Context.IntTy,
+                                             TInfo->getTypeLoc().getBeginLoc());
+  }
+
+  LookupResult Previous(*this, NameInfo, LookupOrdinaryName,
+                        TemplateParamLists.size()
+                            ? forRedeclarationInCurContext()
+                            : ForVisibleRedeclaration);
+  LookupName(Previous, S);
+
+  // Warn about shadowing the name of a template parameter.
+  if (Previous.isSingleResult() &&
+      Previous.getFoundDecl()->isTemplateParameter()) {
+    DiagnoseTemplateParameterShadow(Name.StartLocation,Previous.getFoundDecl());
+    Previous.clear();
+  }
+
+  assert(Name.Kind == UnqualifiedIdKind::IK_Identifier &&
+         "name in alias declaration must be an identifier");
+  TypeAliasDecl *NewTD = TypeAliasDecl::Create(Context, CurContext, UsingLoc,
+                                               Name.StartLocation,
+                                               Name.Identifier, TInfo);
+
+  NewTD->setAccess(AS);
+
+  if (Invalid)
+    NewTD->setInvalidDecl();
+
+  ProcessDeclAttributeList(S, NewTD, AttrList);
+  AddPragmaAttributes(S, NewTD);
+
+  CheckTypedefForVariablyModifiedType(S, NewTD);
+  Invalid |= NewTD->isInvalidDecl();
+
+  bool Redeclaration = false;
+
+  NamedDecl *NewND;
+  if (TemplateParamLists.size()) {
+    TypeAliasTemplateDecl *OldDecl = nullptr;
+    TemplateParameterList *OldTemplateParams = nullptr;
+
+    if (TemplateParamLists.size() != 1) {
+      Diag(UsingLoc, diag::err_alias_template_extra_headers)
+        << SourceRange(TemplateParamLists[1]->getTemplateLoc(),
+         TemplateParamLists[TemplateParamLists.size()-1]->getRAngleLoc());
+    }
+    TemplateParameterList *TemplateParams = TemplateParamLists[0];
+
+    // Check that we can declare a template here.
+    if (CheckTemplateDeclScope(S, TemplateParams))
+      return nullptr;
+
+    // Only consider previous declarations in the same scope.
+    FilterLookupForScope(Previous, CurContext, S, /*ConsiderLinkage*/false,
+                         /*ExplicitInstantiationOrSpecialization*/false);
+    if (!Previous.empty()) {
+      Redeclaration = true;
+
+      OldDecl = Previous.getAsSingle<TypeAliasTemplateDecl>();
+      if (!OldDecl && !Invalid) {
+        Diag(UsingLoc, diag::err_redefinition_different_kind)
+          << Name.Identifier;
+
+        NamedDecl *OldD = Previous.getRepresentativeDecl();
+        if (OldD->getLocation().isValid())
+          Diag(OldD->getLocation(), diag::note_previous_definition);
+
+        Invalid = true;
+      }
+
+      if (!Invalid && OldDecl && !OldDecl->isInvalidDecl()) {
+        if (TemplateParameterListsAreEqual(TemplateParams,
+                                           OldDecl->getTemplateParameters(),
+                                           /*Complain=*/true,
+                                           TPL_TemplateMatch))
+          OldTemplateParams =
+              OldDecl->getMostRecentDecl()->getTemplateParameters();
+        else
+          Invalid = true;
+
+        TypeAliasDecl *OldTD = OldDecl->getTemplatedDecl();
+        if (!Invalid &&
+            !Context.hasSameType(OldTD->getUnderlyingType(),
+                                 NewTD->getUnderlyingType())) {
+          // FIXME: The C++0x standard does not clearly say this is ill-formed,
+          // but we can't reasonably accept it.
+          Diag(NewTD->getLocation(), diag::err_redefinition_different_typedef)
+            << 2 << NewTD->getUnderlyingType() << OldTD->getUnderlyingType();
+          if (OldTD->getLocation().isValid())
+            Diag(OldTD->getLocation(), diag::note_previous_definition);
+          Invalid = true;
+        }
+      }
+    }
+
+    // Merge any previous default template arguments into our parameters,
+    // and check the parameter list.
+    if (CheckTemplateParameterList(TemplateParams, OldTemplateParams,
+                                   TPC_TypeAliasTemplate))
+      return nullptr;
+
+    TypeAliasTemplateDecl *NewDecl =
+      TypeAliasTemplateDecl::Create(Context, CurContext, UsingLoc,
+                                    Name.Identifier, TemplateParams,
+                                    NewTD);
+    NewTD->setDescribedAliasTemplate(NewDecl);
+
+    NewDecl->setAccess(AS);
+
+    if (Invalid)
+      NewDecl->setInvalidDecl();
+    else if (OldDecl) {
+      NewDecl->setPreviousDecl(OldDecl);
+      CheckRedeclarationInModule(NewDecl, OldDecl);
+    }
+
+    NewND = NewDecl;
+  } else {
+    if (auto *TD = dyn_cast_or_null<TagDecl>(DeclFromDeclSpec)) {
+      setTagNameForLinkagePurposes(TD, NewTD);
+      handleTagNumbering(TD, S);
+    }
+    ActOnTypedefNameDecl(S, CurContext, NewTD, Previous, Redeclaration);
+    NewND = NewTD;
+  }
+
+  PushOnScopeChains(NewND, S);
+  ActOnDocumentableDecl(NewND);
+  return NewND;
+}
+
+Decl *Sema::ActOnNamespaceAliasDef(Scope *S, SourceLocation NamespaceLoc,
+                                   SourceLocation AliasLoc,
+                                   IdentifierInfo *Alias, CXXScopeSpec &SS,
+                                   SourceLocation IdentLoc,
+                                   IdentifierInfo *Ident) {
+
+  // Lookup the namespace name.
+  LookupResult R(*this, Ident, IdentLoc, LookupNamespaceName);
+  LookupParsedName(R, S, &SS);
+
+  if (R.isAmbiguous())
+    return nullptr;
+
+  if (R.empty()) {
+    if (!TryNamespaceTypoCorrection(*this, R, S, SS, IdentLoc, Ident)) {
+      Diag(IdentLoc, diag::err_expected_namespace_name) << SS.getRange();
+      return nullptr;
+    }
+  }
+  assert(!R.isAmbiguous() && !R.empty());
+  NamedDecl *ND = R.getRepresentativeDecl();
+
+  // Check if we have a previous declaration with the same name.
+  LookupResult PrevR(*this, Alias, AliasLoc, LookupOrdinaryName,
+                     ForVisibleRedeclaration);
+  LookupName(PrevR, S);
+
+  // Check we're not shadowing a template parameter.
+  if (PrevR.isSingleResult() && PrevR.getFoundDecl()->isTemplateParameter()) {
+    DiagnoseTemplateParameterShadow(AliasLoc, PrevR.getFoundDecl());
+    PrevR.clear();
+  }
+
+  // Filter out any other lookup result from an enclosing scope.
+  FilterLookupForScope(PrevR, CurContext, S, /*ConsiderLinkage*/false,
+                       /*AllowInlineNamespace*/false);
+
+  // Find the previous declaration and check that we can redeclare it.
+  NamespaceAliasDecl *Prev = nullptr;
+  if (PrevR.isSingleResult()) {
+    NamedDecl *PrevDecl = PrevR.getRepresentativeDecl();
+    if (NamespaceAliasDecl *AD = dyn_cast<NamespaceAliasDecl>(PrevDecl)) {
+      // We already have an alias with the same name that points to the same
+      // namespace; check that it matches.
+      if (AD->getNamespace()->Equals(getNamespaceDecl(ND))) {
+        Prev = AD;
+      } else if (isVisible(PrevDecl)) {
+        Diag(AliasLoc, diag::err_redefinition_different_namespace_alias)
+          << Alias;
+        Diag(AD->getLocation(), diag::note_previous_namespace_alias)
+          << AD->getNamespace();
+        return nullptr;
+      }
+    } else if (isVisible(PrevDecl)) {
+      unsigned DiagID = isa<NamespaceDecl>(PrevDecl->getUnderlyingDecl())
+                            ? diag::err_redefinition
+                            : diag::err_redefinition_different_kind;
+      Diag(AliasLoc, DiagID) << Alias;
+      Diag(PrevDecl->getLocation(), diag::note_previous_definition);
+      return nullptr;
+    }
+  }
+
+  // The use of a nested name specifier may trigger deprecation warnings.
+  DiagnoseUseOfDecl(ND, IdentLoc);
+
+  NamespaceAliasDecl *AliasDecl =
+    NamespaceAliasDecl::Create(Context, CurContext, NamespaceLoc, AliasLoc,
+                               Alias, SS.getWithLocInContext(Context),
+                               IdentLoc, ND);
+  if (Prev)
+    AliasDecl->setPreviousDecl(Prev);
+
+  PushOnScopeChains(AliasDecl, S);
+  return AliasDecl;
+}
+
+namespace {
+struct SpecialMemberExceptionSpecInfo
+    : SpecialMemberVisitor<SpecialMemberExceptionSpecInfo> {
+  SourceLocation Loc;
+  Sema::ImplicitExceptionSpecification ExceptSpec;
+
+  SpecialMemberExceptionSpecInfo(Sema &S, CXXMethodDecl *MD,
+                                 Sema::CXXSpecialMember CSM,
+                                 Sema::InheritedConstructorInfo *ICI,
+                                 SourceLocation Loc)
+      : SpecialMemberVisitor(S, MD, CSM, ICI), Loc(Loc), ExceptSpec(S) {}
+
+  bool visitBase(CXXBaseSpecifier *Base);
+  bool visitField(FieldDecl *FD);
+
+  void visitClassSubobject(CXXRecordDecl *Class, Subobject Subobj,
+                           unsigned Quals);
+
+  void visitSubobjectCall(Subobject Subobj,
+                          Sema::SpecialMemberOverloadResult SMOR);
+};
+}
+
+bool SpecialMemberExceptionSpecInfo::visitBase(CXXBaseSpecifier *Base) {
+  auto *RT = Base->getType()->getAs<RecordType>();
+  if (!RT)
+    return false;
+
+  auto *BaseClass = cast<CXXRecordDecl>(RT->getDecl());
+  Sema::SpecialMemberOverloadResult SMOR = lookupInheritedCtor(BaseClass);
+  if (auto *BaseCtor = SMOR.getMethod()) {
+    visitSubobjectCall(Base, BaseCtor);
+    return false;
+  }
+
+  visitClassSubobject(BaseClass, Base, 0);
+  return false;
+}
+
+bool SpecialMemberExceptionSpecInfo::visitField(FieldDecl *FD) {
+  if (CSM == Sema::CXXDefaultConstructor && FD->hasInClassInitializer()) {
+    Expr *E = FD->getInClassInitializer();
+    if (!E)
+      // FIXME: It's a little wasteful to build and throw away a
+      // CXXDefaultInitExpr here.
+      // FIXME: We should have a single context note pointing at Loc, and
+      // this location should be MD->getLocation() instead, since that's
+      // the location where we actually use the default init expression.
+      E = S.BuildCXXDefaultInitExpr(Loc, FD).get();
+    if (E)
+      ExceptSpec.CalledExpr(E);
+  } else if (auto *RT = S.Context.getBaseElementType(FD->getType())
+                            ->getAs<RecordType>()) {
+    visitClassSubobject(cast<CXXRecordDecl>(RT->getDecl()), FD,
+                        FD->getType().getCVRQualifiers());
+  }
+  return false;
+}
+
+void SpecialMemberExceptionSpecInfo::visitClassSubobject(CXXRecordDecl *Class,
+                                                         Subobject Subobj,
+                                                         unsigned Quals) {
+  FieldDecl *Field = Subobj.dyn_cast<FieldDecl*>();
+  bool IsMutable = Field && Field->isMutable();
+  visitSubobjectCall(Subobj, lookupIn(Class, Quals, IsMutable));
+}
+
+void SpecialMemberExceptionSpecInfo::visitSubobjectCall(
+    Subobject Subobj, Sema::SpecialMemberOverloadResult SMOR) {
+  // Note, if lookup fails, it doesn't matter what exception specification we
+  // choose because the special member will be deleted.
+  if (CXXMethodDecl *MD = SMOR.getMethod())
+    ExceptSpec.CalledDecl(getSubobjectLoc(Subobj), MD);
+}
+
+bool Sema::tryResolveExplicitSpecifier(ExplicitSpecifier &ExplicitSpec) {
+  llvm::APSInt Result;
+  ExprResult Converted = CheckConvertedConstantExpression(
+      ExplicitSpec.getExpr(), Context.BoolTy, Result, CCEK_ExplicitBool);
+  ExplicitSpec.setExpr(Converted.get());
+  if (Converted.isUsable() && !Converted.get()->isValueDependent()) {
+    ExplicitSpec.setKind(Result.getBoolValue()
+                             ? ExplicitSpecKind::ResolvedTrue
+                             : ExplicitSpecKind::ResolvedFalse);
+    return true;
+  }
+  ExplicitSpec.setKind(ExplicitSpecKind::Unresolved);
+  return false;
+}
+
+ExplicitSpecifier Sema::ActOnExplicitBoolSpecifier(Expr *ExplicitExpr) {
+  ExplicitSpecifier ES(ExplicitExpr, ExplicitSpecKind::Unresolved);
+  if (!ExplicitExpr->isTypeDependent())
+    tryResolveExplicitSpecifier(ES);
+  return ES;
+}
+
+static Sema::ImplicitExceptionSpecification
+ComputeDefaultedSpecialMemberExceptionSpec(
+    Sema &S, SourceLocation Loc, CXXMethodDecl *MD, Sema::CXXSpecialMember CSM,
+    Sema::InheritedConstructorInfo *ICI) {
+  ComputingExceptionSpec CES(S, MD, Loc);
+
+  CXXRecordDecl *ClassDecl = MD->getParent();
+
+  // C++ [except.spec]p14:
+  //   An implicitly declared special member function (Clause 12) shall have an
+  //   exception-specification. [...]
+  SpecialMemberExceptionSpecInfo Info(S, MD, CSM, ICI, MD->getLocation());
+  if (ClassDecl->isInvalidDecl())
+    return Info.ExceptSpec;
+
+  // FIXME: If this diagnostic fires, we're probably missing a check for
+  // attempting to resolve an exception specification before it's known
+  // at a higher level.
+  if (S.RequireCompleteType(MD->getLocation(),
+                            S.Context.getRecordType(ClassDecl),
+                            diag::err_exception_spec_incomplete_type))
+    return Info.ExceptSpec;
+
+  // C++1z [except.spec]p7:
+  //   [Look for exceptions thrown by] a constructor selected [...] to
+  //   initialize a potentially constructed subobject,
+  // C++1z [except.spec]p8:
+  //   The exception specification for an implicitly-declared destructor, or a
+  //   destructor without a noexcept-specifier, is potentially-throwing if and
+  //   only if any of the destructors for any of its potentially constructed
+  //   subojects is potentially throwing.
+  // FIXME: We respect the first rule but ignore the "potentially constructed"
+  // in the second rule to resolve a core issue (no number yet) that would have
+  // us reject:
+  //   struct A { virtual void f() = 0; virtual ~A() noexcept(false) = 0; };
+  //   struct B : A {};
+  //   struct C : B { void f(); };
+  // ... due to giving B::~B() a non-throwing exception specification.
+  Info.visit(Info.IsConstructor ? Info.VisitPotentiallyConstructedBases
+                                : Info.VisitAllBases);
+
+  return Info.ExceptSpec;
+}
+
+namespace {
+/// RAII object to register a special member as being currently declared.
+struct DeclaringSpecialMember {
+  Sema &S;
+  Sema::SpecialMemberDecl D;
+  Sema::ContextRAII SavedContext;
+  bool WasAlreadyBeingDeclared;
+
+  DeclaringSpecialMember(Sema &S, CXXRecordDecl *RD, Sema::CXXSpecialMember CSM)
+      : S(S), D(RD, CSM), SavedContext(S, RD) {
+    WasAlreadyBeingDeclared = !S.SpecialMembersBeingDeclared.insert(D).second;
+    if (WasAlreadyBeingDeclared)
+      // This almost never happens, but if it does, ensure that our cache
+      // doesn't contain a stale result.
+      S.SpecialMemberCache.clear();
+    else {
+      // Register a note to be produced if we encounter an error while
+      // declaring the special member.
+      Sema::CodeSynthesisContext Ctx;
+      Ctx.Kind = Sema::CodeSynthesisContext::DeclaringSpecialMember;
+      // FIXME: We don't have a location to use here. Using the class's
+      // location maintains the fiction that we declare all special members
+      // with the class, but (1) it's not clear that lying about that helps our
+      // users understand what's going on, and (2) there may be outer contexts
+      // on the stack (some of which are relevant) and printing them exposes
+      // our lies.
+      Ctx.PointOfInstantiation = RD->getLocation();
+      Ctx.Entity = RD;
+      Ctx.SpecialMember = CSM;
+      S.pushCodeSynthesisContext(Ctx);
+    }
+  }
+  ~DeclaringSpecialMember() {
+    if (!WasAlreadyBeingDeclared) {
+      S.SpecialMembersBeingDeclared.erase(D);
+      S.popCodeSynthesisContext();
+    }
+  }
+
+  /// Are we already trying to declare this special member?
+  bool isAlreadyBeingDeclared() const {
+    return WasAlreadyBeingDeclared;
+  }
+};
+}
+
+void Sema::CheckImplicitSpecialMemberDeclaration(Scope *S, FunctionDecl *FD) {
+  // Look up any existing declarations, but don't trigger declaration of all
+  // implicit special members with this name.
+  DeclarationName Name = FD->getDeclName();
+  LookupResult R(*this, Name, SourceLocation(), LookupOrdinaryName,
+                 ForExternalRedeclaration);
+  for (auto *D : FD->getParent()->lookup(Name))
+    if (auto *Acceptable = R.getAcceptableDecl(D))
+      R.addDecl(Acceptable);
+  R.resolveKind();
+  R.suppressDiagnostics();
+
+  CheckFunctionDeclaration(S, FD, R, /*IsMemberSpecialization*/false);
+}
+
+void Sema::setupImplicitSpecialMemberType(CXXMethodDecl *SpecialMem,
+                                          QualType ResultTy,
+                                          ArrayRef<QualType> Args) {
+  // Build an exception specification pointing back at this constructor.
+  FunctionProtoType::ExtProtoInfo EPI = getImplicitMethodEPI(*this, SpecialMem);
+
+  LangAS AS = getDefaultCXXMethodAddrSpace();
+  if (AS != LangAS::Default) {
+    EPI.TypeQuals.addAddressSpace(AS);
+  }
+
+  auto QT = Context.getFunctionType(ResultTy, Args, EPI);
+  SpecialMem->setType(QT);
+
+  // During template instantiation of implicit special member functions we need
+  // a reliable TypeSourceInfo for the function prototype in order to allow
+  // functions to be substituted.
+  if (inTemplateInstantiation() &&
+      cast<CXXRecordDecl>(SpecialMem->getParent())->isLambda()) {
+    TypeSourceInfo *TSI =
+        Context.getTrivialTypeSourceInfo(SpecialMem->getType());
+    SpecialMem->setTypeSourceInfo(TSI);
+  }
+}
+
+CXXConstructorDecl *Sema::DeclareImplicitDefaultConstructor(
+                                                     CXXRecordDecl *ClassDecl) {
+  // C++ [class.ctor]p5:
+  //   A default constructor for a class X is a constructor of class X
+  //   that can be called without an argument. If there is no
+  //   user-declared constructor for class X, a default constructor is
+  //   implicitly declared. An implicitly-declared default constructor
+  //   is an inline public member of its class.
+  assert(ClassDecl->needsImplicitDefaultConstructor() &&
+         "Should not build implicit default constructor!");
+
+  DeclaringSpecialMember DSM(*this, ClassDecl, CXXDefaultConstructor);
+  if (DSM.isAlreadyBeingDeclared())
+    return nullptr;
+
+  bool Constexpr = defaultedSpecialMemberIsConstexpr(*this, ClassDecl,
+                                                     CXXDefaultConstructor,
+                                                     false);
+
+  // Create the actual constructor declaration.
+  CanQualType ClassType
+    = Context.getCanonicalType(Context.getTypeDeclType(ClassDecl));
+  SourceLocation ClassLoc = ClassDecl->getLocation();
+  DeclarationName Name
+    = Context.DeclarationNames.getCXXConstructorName(ClassType);
+  DeclarationNameInfo NameInfo(Name, ClassLoc);
+  CXXConstructorDecl *DefaultCon = CXXConstructorDecl::Create(
+      Context, ClassDecl, ClassLoc, NameInfo, /*Type*/ QualType(),
+      /*TInfo=*/nullptr, ExplicitSpecifier(),
+      getCurFPFeatures().isFPConstrained(),
+      /*isInline=*/true, /*isImplicitlyDeclared=*/true,
+      Constexpr ? ConstexprSpecKind::Constexpr
+                : ConstexprSpecKind::Unspecified);
+  DefaultCon->setAccess(AS_public);
+  DefaultCon->setDefaulted();
+
+  if (getLangOpts().CUDA) {
+    inferCUDATargetForImplicitSpecialMember(ClassDecl, CXXDefaultConstructor,
+                                            DefaultCon,
+                                            /* ConstRHS */ false,
+                                            /* Diagnose */ false);
+  }
+
+  setupImplicitSpecialMemberType(DefaultCon, Context.VoidTy, None);
+
+  // We don't need to use SpecialMemberIsTrivial here; triviality for default
+  // constructors is easy to compute.
+  DefaultCon->setTrivial(ClassDecl->hasTrivialDefaultConstructor());
+
+  // Note that we have declared this constructor.
+  ++getASTContext().NumImplicitDefaultConstructorsDeclared;
+
+  Scope *S = getScopeForContext(ClassDecl);
+  CheckImplicitSpecialMemberDeclaration(S, DefaultCon);
+
+  if (ShouldDeleteSpecialMember(DefaultCon, CXXDefaultConstructor))
+    SetDeclDeleted(DefaultCon, ClassLoc);
+
+  if (S)
+    PushOnScopeChains(DefaultCon, S, false);
+  ClassDecl->addDecl(DefaultCon);
+
+  return DefaultCon;
+}
+
+void Sema::DefineImplicitDefaultConstructor(SourceLocation CurrentLocation,
+                                            CXXConstructorDecl *Constructor) {
+  assert((Constructor->isDefaulted() && Constructor->isDefaultConstructor() &&
+          !Constructor->doesThisDeclarationHaveABody() &&
+          !Constructor->isDeleted()) &&
+    "DefineImplicitDefaultConstructor - call it for implicit default ctor");
+  if (Constructor->willHaveBody() || Constructor->isInvalidDecl())
+    return;
+
+  CXXRecordDecl *ClassDecl = Constructor->getParent();
+  assert(ClassDecl && "DefineImplicitDefaultConstructor - invalid constructor");
+
+  SynthesizedFunctionScope Scope(*this, Constructor);
+
+  // The exception specification is needed because we are defining the
+  // function.
+  ResolveExceptionSpec(CurrentLocation,
+                       Constructor->getType()->castAs<FunctionProtoType>());
+  MarkVTableUsed(CurrentLocation, ClassDecl);
+
+  // Add a context note for diagnostics produced after this point.
+  Scope.addContextNote(CurrentLocation);
+
+  if (SetCtorInitializers(Constructor, /*AnyErrors=*/false)) {
+    Constructor->setInvalidDecl();
+    return;
+  }
+
+  SourceLocation Loc = Constructor->getEndLoc().isValid()
+                           ? Constructor->getEndLoc()
+                           : Constructor->getLocation();
+  Constructor->setBody(new (Context) CompoundStmt(Loc));
+  Constructor->markUsed(Context);
+
+  if (ASTMutationListener *L = getASTMutationListener()) {
+    L->CompletedImplicitDefinition(Constructor);
+  }
+
+  DiagnoseUninitializedFields(*this, Constructor);
+}
+
+void Sema::ActOnFinishDelayedMemberInitializers(Decl *D) {
+  // Perform any delayed checks on exception specifications.
+  CheckDelayedMemberExceptionSpecs();
+}
+
+/// Find or create the fake constructor we synthesize to model constructing an
+/// object of a derived class via a constructor of a base class.
+CXXConstructorDecl *
+Sema::findInheritingConstructor(SourceLocation Loc,
+                                CXXConstructorDecl *BaseCtor,
+                                ConstructorUsingShadowDecl *Shadow) {
+  CXXRecordDecl *Derived = Shadow->getParent();
+  SourceLocation UsingLoc = Shadow->getLocation();
+
+  // FIXME: Add a new kind of DeclarationName for an inherited constructor.
+  // For now we use the name of the base class constructor as a member of the
+  // derived class to indicate a (fake) inherited constructor name.
+  DeclarationName Name = BaseCtor->getDeclName();
+
+  // Check to see if we already have a fake constructor for this inherited
+  // constructor call.
+  for (NamedDecl *Ctor : Derived->lookup(Name))
+    if (declaresSameEntity(cast<CXXConstructorDecl>(Ctor)
+                               ->getInheritedConstructor()
+                               .getConstructor(),
+                           BaseCtor))
+      return cast<CXXConstructorDecl>(Ctor);
+
+  DeclarationNameInfo NameInfo(Name, UsingLoc);
+  TypeSourceInfo *TInfo =
+      Context.getTrivialTypeSourceInfo(BaseCtor->getType(), UsingLoc);
+  FunctionProtoTypeLoc ProtoLoc =
+      TInfo->getTypeLoc().IgnoreParens().castAs<FunctionProtoTypeLoc>();
+
+  // Check the inherited constructor is valid and find the list of base classes
+  // from which it was inherited.
+  InheritedConstructorInfo ICI(*this, Loc, Shadow);
+
+  bool Constexpr =
+      BaseCtor->isConstexpr() &&
+      defaultedSpecialMemberIsConstexpr(*this, Derived, CXXDefaultConstructor,
+                                        false, BaseCtor, &ICI);
+
+  CXXConstructorDecl *DerivedCtor = CXXConstructorDecl::Create(
+      Context, Derived, UsingLoc, NameInfo, TInfo->getType(), TInfo,
+      BaseCtor->getExplicitSpecifier(), getCurFPFeatures().isFPConstrained(),
+      /*isInline=*/true,
+      /*isImplicitlyDeclared=*/true,
+      Constexpr ? BaseCtor->getConstexprKind() : ConstexprSpecKind::Unspecified,
+      InheritedConstructor(Shadow, BaseCtor),
+      BaseCtor->getTrailingRequiresClause());
+  if (Shadow->isInvalidDecl())
+    DerivedCtor->setInvalidDecl();
+
+  // Build an unevaluated exception specification for this fake constructor.
+  const FunctionProtoType *FPT = TInfo->getType()->castAs<FunctionProtoType>();
+  FunctionProtoType::ExtProtoInfo EPI = FPT->getExtProtoInfo();
+  EPI.ExceptionSpec.Type = EST_Unevaluated;
+  EPI.ExceptionSpec.SourceDecl = DerivedCtor;
+  DerivedCtor->setType(Context.getFunctionType(FPT->getReturnType(),
+                                               FPT->getParamTypes(), EPI));
+
+  // Build the parameter declarations.
+  SmallVector<ParmVarDecl *, 16> ParamDecls;
+  for (unsigned I = 0, N = FPT->getNumParams(); I != N; ++I) {
+    TypeSourceInfo *TInfo =
+        Context.getTrivialTypeSourceInfo(FPT->getParamType(I), UsingLoc);
+    ParmVarDecl *PD = ParmVarDecl::Create(
+        Context, DerivedCtor, UsingLoc, UsingLoc, /*IdentifierInfo=*/nullptr,
+        FPT->getParamType(I), TInfo, SC_None, /*DefArg=*/nullptr);
+    PD->setScopeInfo(0, I);
+    PD->setImplicit();
+    // Ensure attributes are propagated onto parameters (this matters for
+    // format, pass_object_size, ...).
+    mergeDeclAttributes(PD, BaseCtor->getParamDecl(I));
+    ParamDecls.push_back(PD);
+    ProtoLoc.setParam(I, PD);
+  }
+
+  // Set up the new constructor.
+  assert(!BaseCtor->isDeleted() && "should not use deleted constructor");
+  DerivedCtor->setAccess(BaseCtor->getAccess());
+  DerivedCtor->setParams(ParamDecls);
+  Derived->addDecl(DerivedCtor);
+
+  if (ShouldDeleteSpecialMember(DerivedCtor, CXXDefaultConstructor, &ICI))
+    SetDeclDeleted(DerivedCtor, UsingLoc);
+
+  return DerivedCtor;
+}
+
+void Sema::NoteDeletedInheritingConstructor(CXXConstructorDecl *Ctor) {
+  InheritedConstructorInfo ICI(*this, Ctor->getLocation(),
+                               Ctor->getInheritedConstructor().getShadowDecl());
+  ShouldDeleteSpecialMember(Ctor, CXXDefaultConstructor, &ICI,
+                            /*Diagnose*/true);
+}
+
+void Sema::DefineInheritingConstructor(SourceLocation CurrentLocation,
+                                       CXXConstructorDecl *Constructor) {
+  CXXRecordDecl *ClassDecl = Constructor->getParent();
+  assert(Constructor->getInheritedConstructor() &&
+         !Constructor->doesThisDeclarationHaveABody() &&
+         !Constructor->isDeleted());
+  if (Constructor->willHaveBody() || Constructor->isInvalidDecl())
+    return;
+
+  // Initializations are performed "as if by a defaulted default constructor",
+  // so enter the appropriate scope.
+  SynthesizedFunctionScope Scope(*this, Constructor);
+
+  // The exception specification is needed because we are defining the
+  // function.
+  ResolveExceptionSpec(CurrentLocation,
+                       Constructor->getType()->castAs<FunctionProtoType>());
+  MarkVTableUsed(CurrentLocation, ClassDecl);
+
+  // Add a context note for diagnostics produced after this point.
+  Scope.addContextNote(CurrentLocation);
+
+  ConstructorUsingShadowDecl *Shadow =
+      Constructor->getInheritedConstructor().getShadowDecl();
+  CXXConstructorDecl *InheritedCtor =
+      Constructor->getInheritedConstructor().getConstructor();
+
+  // [class.inhctor.init]p1:
+  //   initialization proceeds as if a defaulted default constructor is used to
+  //   initialize the D object and each base class subobject from which the
+  //   constructor was inherited
+
+  InheritedConstructorInfo ICI(*this, CurrentLocation, Shadow);
+  CXXRecordDecl *RD = Shadow->getParent();
+  SourceLocation InitLoc = Shadow->getLocation();
+
+  // Build explicit initializers for all base classes from which the
+  // constructor was inherited.
+  SmallVector<CXXCtorInitializer*, 8> Inits;
+  for (bool VBase : {false, true}) {
+    for (CXXBaseSpecifier &B : VBase ? RD->vbases() : RD->bases()) {
+      if (B.isVirtual() != VBase)
+        continue;
+
+      auto *BaseRD = B.getType()->getAsCXXRecordDecl();
+      if (!BaseRD)
+        continue;
+
+      auto BaseCtor = ICI.findConstructorForBase(BaseRD, InheritedCtor);
+      if (!BaseCtor.first)
+        continue;
+
+      MarkFunctionReferenced(CurrentLocation, BaseCtor.first);
+      ExprResult Init = new (Context) CXXInheritedCtorInitExpr(
+          InitLoc, B.getType(), BaseCtor.first, VBase, BaseCtor.second);
+
+      auto *TInfo = Context.getTrivialTypeSourceInfo(B.getType(), InitLoc);
+      Inits.push_back(new (Context) CXXCtorInitializer(
+          Context, TInfo, VBase, InitLoc, Init.get(), InitLoc,
+          SourceLocation()));
+    }
+  }
+
+  // We now proceed as if for a defaulted default constructor, with the relevant
+  // initializers replaced.
+
+  if (SetCtorInitializers(Constructor, /*AnyErrors*/false, Inits)) {
+    Constructor->setInvalidDecl();
+    return;
+  }
+
+  Constructor->setBody(new (Context) CompoundStmt(InitLoc));
+  Constructor->markUsed(Context);
+
+  if (ASTMutationListener *L = getASTMutationListener()) {
+    L->CompletedImplicitDefinition(Constructor);
+  }
+
+  DiagnoseUninitializedFields(*this, Constructor);
+}
+
+CXXDestructorDecl *Sema::DeclareImplicitDestructor(CXXRecordDecl *ClassDecl) {
+  // C++ [class.dtor]p2:
+  //   If a class has no user-declared destructor, a destructor is
+  //   declared implicitly. An implicitly-declared destructor is an
+  //   inline public member of its class.
+  assert(ClassDecl->needsImplicitDestructor());
+
+  DeclaringSpecialMember DSM(*this, ClassDecl, CXXDestructor);
+  if (DSM.isAlreadyBeingDeclared())
+    return nullptr;
+
+  bool Constexpr = defaultedSpecialMemberIsConstexpr(*this, ClassDecl,
+                                                     CXXDestructor,
+                                                     false);
+
+  // Create the actual destructor declaration.
+  CanQualType ClassType
+    = Context.getCanonicalType(Context.getTypeDeclType(ClassDecl));
+  SourceLocation ClassLoc = ClassDecl->getLocation();
+  DeclarationName Name
+    = Context.DeclarationNames.getCXXDestructorName(ClassType);
+  DeclarationNameInfo NameInfo(Name, ClassLoc);
+  CXXDestructorDecl *Destructor = CXXDestructorDecl::Create(
+      Context, ClassDecl, ClassLoc, NameInfo, QualType(), nullptr,
+      getCurFPFeatures().isFPConstrained(),
+      /*isInline=*/true,
+      /*isImplicitlyDeclared=*/true,
+      Constexpr ? ConstexprSpecKind::Constexpr
+                : ConstexprSpecKind::Unspecified);
+  Destructor->setAccess(AS_public);
+  Destructor->setDefaulted();
+
+  if (getLangOpts().CUDA) {
+    inferCUDATargetForImplicitSpecialMember(ClassDecl, CXXDestructor,
+                                            Destructor,
+                                            /* ConstRHS */ false,
+                                            /* Diagnose */ false);
+  }
+
+  setupImplicitSpecialMemberType(Destructor, Context.VoidTy, None);
+
+  // We don't need to use SpecialMemberIsTrivial here; triviality for
+  // destructors is easy to compute.
+  Destructor->setTrivial(ClassDecl->hasTrivialDestructor());
+  Destructor->setTrivialForCall(ClassDecl->hasAttr<TrivialABIAttr>() ||
+                                ClassDecl->hasTrivialDestructorForCall());
+
+  // Note that we have declared this destructor.
+  ++getASTContext().NumImplicitDestructorsDeclared;
+
+  Scope *S = getScopeForContext(ClassDecl);
+  CheckImplicitSpecialMemberDeclaration(S, Destructor);
+
+  // We can't check whether an implicit destructor is deleted before we complete
+  // the definition of the class, because its validity depends on the alignment
+  // of the class. We'll check this from ActOnFields once the class is complete.
+  if (ClassDecl->isCompleteDefinition() &&
+      ShouldDeleteSpecialMember(Destructor, CXXDestructor))
+    SetDeclDeleted(Destructor, ClassLoc);
+
+  // Introduce this destructor into its scope.
+  if (S)
+    PushOnScopeChains(Destructor, S, false);
+  ClassDecl->addDecl(Destructor);
+
+  return Destructor;
+}
+
+void Sema::DefineImplicitDestructor(SourceLocation CurrentLocation,
+                                    CXXDestructorDecl *Destructor) {
+  assert((Destructor->isDefaulted() &&
+          !Destructor->doesThisDeclarationHaveABody() &&
+          !Destructor->isDeleted()) &&
+         "DefineImplicitDestructor - call it for implicit default dtor");
+  if (Destructor->willHaveBody() || Destructor->isInvalidDecl())
+    return;
+
+  CXXRecordDecl *ClassDecl = Destructor->getParent();
+  assert(ClassDecl && "DefineImplicitDestructor - invalid destructor");
+
+  SynthesizedFunctionScope Scope(*this, Destructor);
+
+  // The exception specification is needed because we are defining the
+  // function.
+  ResolveExceptionSpec(CurrentLocation,
+                       Destructor->getType()->castAs<FunctionProtoType>());
+  MarkVTableUsed(CurrentLocation, ClassDecl);
+
+  // Add a context note for diagnostics produced after this point.
+  Scope.addContextNote(CurrentLocation);
+
+  MarkBaseAndMemberDestructorsReferenced(Destructor->getLocation(),
+                                         Destructor->getParent());
+
+  if (CheckDestructor(Destructor)) {
+    Destructor->setInvalidDecl();
+    return;
+  }
+
+  SourceLocation Loc = Destructor->getEndLoc().isValid()
+                           ? Destructor->getEndLoc()
+                           : Destructor->getLocation();
+  Destructor->setBody(new (Context) CompoundStmt(Loc));
+  Destructor->markUsed(Context);
+
+  if (ASTMutationListener *L = getASTMutationListener()) {
+    L->CompletedImplicitDefinition(Destructor);
+  }
+}
+
+void Sema::CheckCompleteDestructorVariant(SourceLocation CurrentLocation,
+                                          CXXDestructorDecl *Destructor) {
+  if (Destructor->isInvalidDecl())
+    return;
+
+  CXXRecordDecl *ClassDecl = Destructor->getParent();
+  assert(Context.getTargetInfo().getCXXABI().isMicrosoft() &&
+         "implicit complete dtors unneeded outside MS ABI");
+  assert(ClassDecl->getNumVBases() > 0 &&
+         "complete dtor only exists for classes with vbases");
+
+  SynthesizedFunctionScope Scope(*this, Destructor);
+
+  // Add a context note for diagnostics produced after this point.
+  Scope.addContextNote(CurrentLocation);
+
+  MarkVirtualBaseDestructorsReferenced(Destructor->getLocation(), ClassDecl);
+}
+
+/// Perform any semantic analysis which needs to be delayed until all
+/// pending class member declarations have been parsed.
+void Sema::ActOnFinishCXXMemberDecls() {
+  // If the context is an invalid C++ class, just suppress these checks.
+  if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(CurContext)) {
+    if (Record->isInvalidDecl()) {
+      DelayedOverridingExceptionSpecChecks.clear();
+      DelayedEquivalentExceptionSpecChecks.clear();
+      return;
+    }
+    checkForMultipleExportedDefaultConstructors(*this, Record);
+  }
+}
+
+void Sema::ActOnFinishCXXNonNestedClass() {
+  referenceDLLExportedClassMethods();
+
+  if (!DelayedDllExportMemberFunctions.empty()) {
+    SmallVector<CXXMethodDecl*, 4> WorkList;
+    std::swap(DelayedDllExportMemberFunctions, WorkList);
+    for (CXXMethodDecl *M : WorkList) {
+      DefineDefaultedFunction(*this, M, M->getLocation());
+
+      // Pass the method to the consumer to get emitted. This is not necessary
+      // for explicit instantiation definitions, as they will get emitted
+      // anyway.
+      if (M->getParent()->getTemplateSpecializationKind() !=
+          TSK_ExplicitInstantiationDefinition)
+        ActOnFinishInlineFunctionDef(M);
+    }
+  }
+}
+
+void Sema::referenceDLLExportedClassMethods() {
+  if (!DelayedDllExportClasses.empty()) {
+    // Calling ReferenceDllExportedMembers might cause the current function to
+    // be called again, so use a local copy of DelayedDllExportClasses.
+    SmallVector<CXXRecordDecl *, 4> WorkList;
+    std::swap(DelayedDllExportClasses, WorkList);
+    for (CXXRecordDecl *Class : WorkList)
+      ReferenceDllExportedMembers(*this, Class);
+  }
+}
+
+void Sema::AdjustDestructorExceptionSpec(CXXDestructorDecl *Destructor) {
+  assert(getLangOpts().CPlusPlus11 &&
+         "adjusting dtor exception specs was introduced in c++11");
+
+  if (Destructor->isDependentContext())
+    return;
+
+  // C++11 [class.dtor]p3:
+  //   A declaration of a destructor that does not have an exception-
+  //   specification is implicitly considered to have the same exception-
+  //   specification as an implicit declaration.
+  const auto *DtorType = Destructor->getType()->castAs<FunctionProtoType>();
+  if (DtorType->hasExceptionSpec())
+    return;
+
+  // Replace the destructor's type, building off the existing one. Fortunately,
+  // the only thing of interest in the destructor type is its extended info.
+  // The return and arguments are fixed.
+  FunctionProtoType::ExtProtoInfo EPI = DtorType->getExtProtoInfo();
+  EPI.ExceptionSpec.Type = EST_Unevaluated;
+  EPI.ExceptionSpec.SourceDecl = Destructor;
+  Destructor->setType(Context.getFunctionType(Context.VoidTy, None, EPI));
+
+  // FIXME: If the destructor has a body that could throw, and the newly created
+  // spec doesn't allow exceptions, we should emit a warning, because this
+  // change in behavior can break conforming C++03 programs at runtime.
+  // However, we don't have a body or an exception specification yet, so it
+  // needs to be done somewhere else.
+}
+
+namespace {
+/// An abstract base class for all helper classes used in building the
+//  copy/move operators. These classes serve as factory functions and help us
+//  avoid using the same Expr* in the AST twice.
+class ExprBuilder {
+  ExprBuilder(const ExprBuilder&) = delete;
+  ExprBuilder &operator=(const ExprBuilder&) = delete;
+
+protected:
+  static Expr *assertNotNull(Expr *E) {
+    assert(E && "Expression construction must not fail.");
+    return E;
+  }
+
+public:
+  ExprBuilder() {}
+  virtual ~ExprBuilder() {}
+
+  virtual Expr *build(Sema &S, SourceLocation Loc) const = 0;
+};
+
+class RefBuilder: public ExprBuilder {
+  VarDecl *Var;
+  QualType VarType;
+
+public:
+  Expr *build(Sema &S, SourceLocation Loc) const override {
+    return assertNotNull(S.BuildDeclRefExpr(Var, VarType, VK_LValue, Loc));
+  }
+
+  RefBuilder(VarDecl *Var, QualType VarType)
+      : Var(Var), VarType(VarType) {}
+};
+
+class ThisBuilder: public ExprBuilder {
+public:
+  Expr *build(Sema &S, SourceLocation Loc) const override {
+    return assertNotNull(S.ActOnCXXThis(Loc).getAs<Expr>());
+  }
+};
+
+class CastBuilder: public ExprBuilder {
+  const ExprBuilder &Builder;
+  QualType Type;
+  ExprValueKind Kind;
+  const CXXCastPath &Path;
+
+public:
+  Expr *build(Sema &S, SourceLocation Loc) const override {
+    return assertNotNull(S.ImpCastExprToType(Builder.build(S, Loc), Type,
+                                             CK_UncheckedDerivedToBase, Kind,
+                                             &Path).get());
+  }
+
+  CastBuilder(const ExprBuilder &Builder, QualType Type, ExprValueKind Kind,
+              const CXXCastPath &Path)
+      : Builder(Builder), Type(Type), Kind(Kind), Path(Path) {}
+};
+
+class DerefBuilder: public ExprBuilder {
+  const ExprBuilder &Builder;
+
+public:
+  Expr *build(Sema &S, SourceLocation Loc) const override {
+    return assertNotNull(
+        S.CreateBuiltinUnaryOp(Loc, UO_Deref, Builder.build(S, Loc)).get());
+  }
+
+  DerefBuilder(const ExprBuilder &Builder) : Builder(Builder) {}
+};
+
+class MemberBuilder: public ExprBuilder {
+  const ExprBuilder &Builder;
+  QualType Type;
+  CXXScopeSpec SS;
+  bool IsArrow;
+  LookupResult &MemberLookup;
+
+public:
+  Expr *build(Sema &S, SourceLocation Loc) const override {
+    return assertNotNull(S.BuildMemberReferenceExpr(
+        Builder.build(S, Loc), Type, Loc, IsArrow, SS, SourceLocation(),
+        nullptr, MemberLookup, nullptr, nullptr).get());
+  }
+
+  MemberBuilder(const ExprBuilder &Builder, QualType Type, bool IsArrow,
+                LookupResult &MemberLookup)
+      : Builder(Builder), Type(Type), IsArrow(IsArrow),
+        MemberLookup(MemberLookup) {}
+};
+
+class MoveCastBuilder: public ExprBuilder {
+  const ExprBuilder &Builder;
+
+public:
+  Expr *build(Sema &S, SourceLocation Loc) const override {
+    return assertNotNull(CastForMoving(S, Builder.build(S, Loc)));
+  }
+
+  MoveCastBuilder(const ExprBuilder &Builder) : Builder(Builder) {}
+};
+
+class LvalueConvBuilder: public ExprBuilder {
+  const ExprBuilder &Builder;
+
+public:
+  Expr *build(Sema &S, SourceLocation Loc) const override {
+    return assertNotNull(
+        S.DefaultLvalueConversion(Builder.build(S, Loc)).get());
+  }
+
+  LvalueConvBuilder(const ExprBuilder &Builder) : Builder(Builder) {}
+};
+
+class SubscriptBuilder: public ExprBuilder {
+  const ExprBuilder &Base;
+  const ExprBuilder &Index;
+
+public:
+  Expr *build(Sema &S, SourceLocation Loc) const override {
+    return assertNotNull(S.CreateBuiltinArraySubscriptExpr(
+        Base.build(S, Loc), Loc, Index.build(S, Loc), Loc).get());
+  }
+
+  SubscriptBuilder(const ExprBuilder &Base, const ExprBuilder &Index)
+      : Base(Base), Index(Index) {}
+};
+
+} // end anonymous namespace
+
+/// When generating a defaulted copy or move assignment operator, if a field
+/// should be copied with __builtin_memcpy rather than via explicit assignments,
+/// do so. This optimization only applies for arrays of scalars, and for arrays
+/// of class type where the selected copy/move-assignment operator is trivial.
+static StmtResult
+buildMemcpyForAssignmentOp(Sema &S, SourceLocation Loc, QualType T,
+                           const ExprBuilder &ToB, const ExprBuilder &FromB) {
+  // Compute the size of the memory buffer to be copied.
+  QualType SizeType = S.Context.getSizeType();
+  llvm::APInt Size(S.Context.getTypeSize(SizeType),
+                   S.Context.getTypeSizeInChars(T).getQuantity());
+
+  // Take the address of the field references for "from" and "to". We
+  // directly construct UnaryOperators here because semantic analysis
+  // does not permit us to take the address of an xvalue.
+  Expr *From = FromB.build(S, Loc);
+  From = UnaryOperator::Create(
+      S.Context, From, UO_AddrOf, S.Context.getPointerType(From->getType()),
+      VK_PRValue, OK_Ordinary, Loc, false, S.CurFPFeatureOverrides());
+  Expr *To = ToB.build(S, Loc);
+  To = UnaryOperator::Create(
+      S.Context, To, UO_AddrOf, S.Context.getPointerType(To->getType()),
+      VK_PRValue, OK_Ordinary, Loc, false, S.CurFPFeatureOverrides());
+
+  const Type *E = T->getBaseElementTypeUnsafe();
+  bool NeedsCollectableMemCpy =
+      E->isRecordType() &&
+      E->castAs<RecordType>()->getDecl()->hasObjectMember();
+
+  // Create a reference to the __builtin_objc_memmove_collectable function
+  StringRef MemCpyName = NeedsCollectableMemCpy ?
+    "__builtin_objc_memmove_collectable" :
+    "__builtin_memcpy";
+  LookupResult R(S, &S.Context.Idents.get(MemCpyName), Loc,
+                 Sema::LookupOrdinaryName);
+  S.LookupName(R, S.TUScope, true);
+
+  FunctionDecl *MemCpy = R.getAsSingle<FunctionDecl>();
+  if (!MemCpy)
+    // Something went horribly wrong earlier, and we will have complained
+    // about it.
+    return StmtError();
+
+  ExprResult MemCpyRef = S.BuildDeclRefExpr(MemCpy, S.Context.BuiltinFnTy,
+                                            VK_PRValue, Loc, nullptr);
+  assert(MemCpyRef.isUsable() && "Builtin reference cannot fail");
+
+  Expr *CallArgs[] = {
+    To, From, IntegerLiteral::Create(S.Context, Size, SizeType, Loc)
+  };
+  ExprResult Call = S.BuildCallExpr(/*Scope=*/nullptr, MemCpyRef.get(),
+                                    Loc, CallArgs, Loc);
+
+  assert(!Call.isInvalid() && "Call to __builtin_memcpy cannot fail!");
+  return Call.getAs<Stmt>();
+}
+
+/// Builds a statement that copies/moves the given entity from \p From to
+/// \c To.
+///
+/// This routine is used to copy/move the members of a class with an
+/// implicitly-declared copy/move assignment operator. When the entities being
+/// copied are arrays, this routine builds for loops to copy them.
+///
+/// \param S The Sema object used for type-checking.
+///
+/// \param Loc The location where the implicit copy/move is being generated.
+///
+/// \param T The type of the expressions being copied/moved. Both expressions
+/// must have this type.
+///
+/// \param To The expression we are copying/moving to.
+///
+/// \param From The expression we are copying/moving from.
+///
+/// \param CopyingBaseSubobject Whether we're copying/moving a base subobject.
+/// Otherwise, it's a non-static member subobject.
+///
+/// \param Copying Whether we're copying or moving.
+///
+/// \param Depth Internal parameter recording the depth of the recursion.
+///
+/// \returns A statement or a loop that copies the expressions, or StmtResult(0)
+/// if a memcpy should be used instead.
+static StmtResult
+buildSingleCopyAssignRecursively(Sema &S, SourceLocation Loc, QualType T,
+                                 const ExprBuilder &To, const ExprBuilder &From,
+                                 bool CopyingBaseSubobject, bool Copying,
+                                 unsigned Depth = 0) {
+  // C++11 [class.copy]p28:
+  //   Each subobject is assigned in the manner appropriate to its type:
+  //
+  //     - if the subobject is of class type, as if by a call to operator= with
+  //       the subobject as the object expression and the corresponding
+  //       subobject of x as a single function argument (as if by explicit
+  //       qualification; that is, ignoring any possible virtual overriding
+  //       functions in more derived classes);
+  //
+  // C++03 [class.copy]p13:
+  //     - if the subobject is of class type, the copy assignment operator for
+  //       the class is used (as if by explicit qualification; that is,
+  //       ignoring any possible virtual overriding functions in more derived
+  //       classes);
+  if (const RecordType *RecordTy = T->getAs<RecordType>()) {
+    CXXRecordDecl *ClassDecl = cast<CXXRecordDecl>(RecordTy->getDecl());
+
+    // Look for operator=.
+    DeclarationName Name
+      = S.Context.DeclarationNames.getCXXOperatorName(OO_Equal);
+    LookupResult OpLookup(S, Name, Loc, Sema::LookupOrdinaryName);
+    S.LookupQualifiedName(OpLookup, ClassDecl, false);
+
+    // Prior to C++11, filter out any result that isn't a copy/move-assignment
+    // operator.
+    if (!S.getLangOpts().CPlusPlus11) {
+      LookupResult::Filter F = OpLookup.makeFilter();
+      while (F.hasNext()) {
+        NamedDecl *D = F.next();
+        if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(D))
+          if (Method->isCopyAssignmentOperator() ||
+              (!Copying && Method->isMoveAssignmentOperator()))
+            continue;
+
+        F.erase();
+      }
+      F.done();
+    }
+
+    // Suppress the protected check (C++ [class.protected]) for each of the
+    // assignment operators we found. This strange dance is required when
+    // we're assigning via a base classes's copy-assignment operator. To
+    // ensure that we're getting the right base class subobject (without
+    // ambiguities), we need to cast "this" to that subobject type; to
+    // ensure that we don't go through the virtual call mechanism, we need
+    // to qualify the operator= name with the base class (see below). However,
+    // this means that if the base class has a protected copy assignment
+    // operator, the protected member access check will fail. So, we
+    // rewrite "protected" access to "public" access in this case, since we
+    // know by construction that we're calling from a derived class.
+    if (CopyingBaseSubobject) {
+      for (LookupResult::iterator L = OpLookup.begin(), LEnd = OpLookup.end();
+           L != LEnd; ++L) {
+        if (L.getAccess() == AS_protected)
+          L.setAccess(AS_public);
+      }
+    }
+
+    // Create the nested-name-specifier that will be used to qualify the
+    // reference to operator=; this is required to suppress the virtual
+    // call mechanism.
+    CXXScopeSpec SS;
+    const Type *CanonicalT = S.Context.getCanonicalType(T.getTypePtr());
+    SS.MakeTrivial(S.Context,
+                   NestedNameSpecifier::Create(S.Context, nullptr, false,
+                                               CanonicalT),
+                   Loc);
+
+    // Create the reference to operator=.
+    ExprResult OpEqualRef
+      = S.BuildMemberReferenceExpr(To.build(S, Loc), T, Loc, /*IsArrow=*/false,
+                                   SS, /*TemplateKWLoc=*/SourceLocation(),
+                                   /*FirstQualifierInScope=*/nullptr,
+                                   OpLookup,
+                                   /*TemplateArgs=*/nullptr, /*S*/nullptr,
+                                   /*SuppressQualifierCheck=*/true);
+    if (OpEqualRef.isInvalid())
+      return StmtError();
+
+    // Build the call to the assignment operator.
+
+    Expr *FromInst = From.build(S, Loc);
+    ExprResult Call = S.BuildCallToMemberFunction(/*Scope=*/nullptr,
+                                                  OpEqualRef.getAs<Expr>(),
+                                                  Loc, FromInst, Loc);
+    if (Call.isInvalid())
+      return StmtError();
+
+    // If we built a call to a trivial 'operator=' while copying an array,
+    // bail out. We'll replace the whole shebang with a memcpy.
+    CXXMemberCallExpr *CE = dyn_cast<CXXMemberCallExpr>(Call.get());
+    if (CE && CE->getMethodDecl()->isTrivial() && Depth)
+      return StmtResult((Stmt*)nullptr);
+
+    // Convert to an expression-statement, and clean up any produced
+    // temporaries.
+    return S.ActOnExprStmt(Call);
+  }
+
+  //     - if the subobject is of scalar type, the built-in assignment
+  //       operator is used.
+  const ConstantArrayType *ArrayTy = S.Context.getAsConstantArrayType(T);
+  if (!ArrayTy) {
+    ExprResult Assignment = S.CreateBuiltinBinOp(
+        Loc, BO_Assign, To.build(S, Loc), From.build(S, Loc));
+    if (Assignment.isInvalid())
+      return StmtError();
+    return S.ActOnExprStmt(Assignment);
+  }
+
+  //     - if the subobject is an array, each element is assigned, in the
+  //       manner appropriate to the element type;
+
+  // Construct a loop over the array bounds, e.g.,
+  //
+  //   for (__SIZE_TYPE__ i0 = 0; i0 != array-size; ++i0)
+  //
+  // that will copy each of the array elements.
+  QualType SizeType = S.Context.getSizeType();
+
+  // Create the iteration variable.
+  IdentifierInfo *IterationVarName = nullptr;
+  {
+    SmallString<8> Str;
+    llvm::raw_svector_ostream OS(Str);
+    OS << "__i" << Depth;
+    IterationVarName = &S.Context.Idents.get(OS.str());
+  }
+  VarDecl *IterationVar = VarDecl::Create(S.Context, S.CurContext, Loc, Loc,
+                                          IterationVarName, SizeType,
+                            S.Context.getTrivialTypeSourceInfo(SizeType, Loc),
+                                          SC_None);
+
+  // Initialize the iteration variable to zero.
+  llvm::APInt Zero(S.Context.getTypeSize(SizeType), 0);
+  IterationVar->setInit(IntegerLiteral::Create(S.Context, Zero, SizeType, Loc));
+
+  // Creates a reference to the iteration variable.
+  RefBuilder IterationVarRef(IterationVar, SizeType);
+  LvalueConvBuilder IterationVarRefRVal(IterationVarRef);
+
+  // Create the DeclStmt that holds the iteration variable.
+  Stmt *InitStmt = new (S.Context) DeclStmt(DeclGroupRef(IterationVar),Loc,Loc);
+
+  // Subscript the "from" and "to" expressions with the iteration variable.
+  SubscriptBuilder FromIndexCopy(From, IterationVarRefRVal);
+  MoveCastBuilder FromIndexMove(FromIndexCopy);
+  const ExprBuilder *FromIndex;
+  if (Copying)
+    FromIndex = &FromIndexCopy;
+  else
+    FromIndex = &FromIndexMove;
+
+  SubscriptBuilder ToIndex(To, IterationVarRefRVal);
+
+  // Build the copy/move for an individual element of the array.
+  StmtResult Copy =
+    buildSingleCopyAssignRecursively(S, Loc, ArrayTy->getElementType(),
+                                     ToIndex, *FromIndex, CopyingBaseSubobject,
+                                     Copying, Depth + 1);
+  // Bail out if copying fails or if we determined that we should use memcpy.
+  if (Copy.isInvalid() || !Copy.get())
+    return Copy;
+
+  // Create the comparison against the array bound.
+  llvm::APInt Upper
+    = ArrayTy->getSize().zextOrTrunc(S.Context.getTypeSize(SizeType));
+  Expr *Comparison = BinaryOperator::Create(
+      S.Context, IterationVarRefRVal.build(S, Loc),
+      IntegerLiteral::Create(S.Context, Upper, SizeType, Loc), BO_NE,
+      S.Context.BoolTy, VK_PRValue, OK_Ordinary, Loc,
+      S.CurFPFeatureOverrides());
+
+  // Create the pre-increment of the iteration variable. We can determine
+  // whether the increment will overflow based on the value of the array
+  // bound.
+  Expr *Increment = UnaryOperator::Create(
+      S.Context, IterationVarRef.build(S, Loc), UO_PreInc, SizeType, VK_LValue,
+      OK_Ordinary, Loc, Upper.isMaxValue(), S.CurFPFeatureOverrides());
+
+  // Construct the loop that copies all elements of this array.
+  return S.ActOnForStmt(
+      Loc, Loc, InitStmt,
+      S.ActOnCondition(nullptr, Loc, Comparison, Sema::ConditionKind::Boolean),
+      S.MakeFullDiscardedValueExpr(Increment), Loc, Copy.get());
+}
+
+static StmtResult
+buildSingleCopyAssign(Sema &S, SourceLocation Loc, QualType T,
+                      const ExprBuilder &To, const ExprBuilder &From,
+                      bool CopyingBaseSubobject, bool Copying) {
+  // Maybe we should use a memcpy?
+  if (T->isArrayType() && !T.isConstQualified() && !T.isVolatileQualified() &&
+      T.isTriviallyCopyableType(S.Context))
+    return buildMemcpyForAssignmentOp(S, Loc, T, To, From);
+
+  StmtResult Result(buildSingleCopyAssignRecursively(S, Loc, T, To, From,
+                                                     CopyingBaseSubobject,
+                                                     Copying, 0));
+
+  // If we ended up picking a trivial assignment operator for an array of a
+  // non-trivially-copyable class type, just emit a memcpy.
+  if (!Result.isInvalid() && !Result.get())
+    return buildMemcpyForAssignmentOp(S, Loc, T, To, From);
+
+  return Result;
+}
+
+CXXMethodDecl *Sema::DeclareImplicitCopyAssignment(CXXRecordDecl *ClassDecl) {
+  // Note: The following rules are largely analoguous to the copy
+  // constructor rules. Note that virtual bases are not taken into account
+  // for determining the argument type of the operator. Note also that
+  // operators taking an object instead of a reference are allowed.
+  assert(ClassDecl->needsImplicitCopyAssignment());
+
+  DeclaringSpecialMember DSM(*this, ClassDecl, CXXCopyAssignment);
+  if (DSM.isAlreadyBeingDeclared())
+    return nullptr;
+
+  QualType ArgType = Context.getTypeDeclType(ClassDecl);
+  LangAS AS = getDefaultCXXMethodAddrSpace();
+  if (AS != LangAS::Default)
+    ArgType = Context.getAddrSpaceQualType(ArgType, AS);
+  QualType RetType = Context.getLValueReferenceType(ArgType);
+  bool Const = ClassDecl->implicitCopyAssignmentHasConstParam();
+  if (Const)
+    ArgType = ArgType.withConst();
+
+  ArgType = Context.getLValueReferenceType(ArgType);
+
+  bool Constexpr = defaultedSpecialMemberIsConstexpr(*this, ClassDecl,
+                                                     CXXCopyAssignment,
+                                                     Const);
+
+  //   An implicitly-declared copy assignment operator is an inline public
+  //   member of its class.
+  DeclarationName Name = Context.DeclarationNames.getCXXOperatorName(OO_Equal);
+  SourceLocation ClassLoc = ClassDecl->getLocation();
+  DeclarationNameInfo NameInfo(Name, ClassLoc);
+  CXXMethodDecl *CopyAssignment = CXXMethodDecl::Create(
+      Context, ClassDecl, ClassLoc, NameInfo, QualType(),
+      /*TInfo=*/nullptr, /*StorageClass=*/SC_None,
+      getCurFPFeatures().isFPConstrained(),
+      /*isInline=*/true,
+      Constexpr ? ConstexprSpecKind::Constexpr : ConstexprSpecKind::Unspecified,
+      SourceLocation());
+  CopyAssignment->setAccess(AS_public);
+  CopyAssignment->setDefaulted();
+  CopyAssignment->setImplicit();
+
+  if (getLangOpts().CUDA) {
+    inferCUDATargetForImplicitSpecialMember(ClassDecl, CXXCopyAssignment,
+                                            CopyAssignment,
+                                            /* ConstRHS */ Const,
+                                            /* Diagnose */ false);
+  }
+
+  setupImplicitSpecialMemberType(CopyAssignment, RetType, ArgType);
+
+  // Add the parameter to the operator.
+  ParmVarDecl *FromParam = ParmVarDecl::Create(Context, CopyAssignment,
+                                               ClassLoc, ClassLoc,
+                                               /*Id=*/nullptr, ArgType,
+                                               /*TInfo=*/nullptr, SC_None,
+                                               nullptr);
+  CopyAssignment->setParams(FromParam);
+
+  CopyAssignment->setTrivial(
+    ClassDecl->needsOverloadResolutionForCopyAssignment()
+      ? SpecialMemberIsTrivial(CopyAssignment, CXXCopyAssignment)
+      : ClassDecl->hasTrivialCopyAssignment());
+
+  // Note that we have added this copy-assignment operator.
+  ++getASTContext().NumImplicitCopyAssignmentOperatorsDeclared;
+
+  Scope *S = getScopeForContext(ClassDecl);
+  CheckImplicitSpecialMemberDeclaration(S, CopyAssignment);
+
+  if (ShouldDeleteSpecialMember(CopyAssignment, CXXCopyAssignment)) {
+    ClassDecl->setImplicitCopyAssignmentIsDeleted();
+    SetDeclDeleted(CopyAssignment, ClassLoc);
+  }
+
+  if (S)
+    PushOnScopeChains(CopyAssignment, S, false);
+  ClassDecl->addDecl(CopyAssignment);
+
+  return CopyAssignment;
+}
+
+/// Diagnose an implicit copy operation for a class which is odr-used, but
+/// which is deprecated because the class has a user-declared copy constructor,
+/// copy assignment operator, or destructor.
+static void diagnoseDeprecatedCopyOperation(Sema &S, CXXMethodDecl *CopyOp) {
+  assert(CopyOp->isImplicit());
+
+  CXXRecordDecl *RD = CopyOp->getParent();
+  CXXMethodDecl *UserDeclaredOperation = nullptr;
+
+  // In Microsoft mode, assignment operations don't affect constructors and
+  // vice versa.
+  if (RD->hasUserDeclaredDestructor()) {
+    UserDeclaredOperation = RD->getDestructor();
+  } else if (!isa<CXXConstructorDecl>(CopyOp) &&
+             RD->hasUserDeclaredCopyConstructor() &&
+             !S.getLangOpts().MSVCCompat) {
+    // Find any user-declared copy constructor.
+    for (auto *I : RD->ctors()) {
+      if (I->isCopyConstructor()) {
+        UserDeclaredOperation = I;
+        break;
+      }
+    }
+    assert(UserDeclaredOperation);
+  } else if (isa<CXXConstructorDecl>(CopyOp) &&
+             RD->hasUserDeclaredCopyAssignment() &&
+             !S.getLangOpts().MSVCCompat) {
+    // Find any user-declared move assignment operator.
+    for (auto *I : RD->methods()) {
+      if (I->isCopyAssignmentOperator()) {
+        UserDeclaredOperation = I;
+        break;
+      }
+    }
+    assert(UserDeclaredOperation);
+  }
+
+  if (UserDeclaredOperation) {
+    bool UDOIsUserProvided = UserDeclaredOperation->isUserProvided();
+    bool UDOIsDestructor = isa<CXXDestructorDecl>(UserDeclaredOperation);
+    bool IsCopyAssignment = !isa<CXXConstructorDecl>(CopyOp);
+    unsigned DiagID =
+        (UDOIsUserProvided && UDOIsDestructor)
+            ? diag::warn_deprecated_copy_with_user_provided_dtor
+        : (UDOIsUserProvided && !UDOIsDestructor)
+            ? diag::warn_deprecated_copy_with_user_provided_copy
+        : (!UDOIsUserProvided && UDOIsDestructor)
+            ? diag::warn_deprecated_copy_with_dtor
+            : diag::warn_deprecated_copy;
+    S.Diag(UserDeclaredOperation->getLocation(), DiagID)
+        << RD << IsCopyAssignment;
+  }
+}
+
+void Sema::DefineImplicitCopyAssignment(SourceLocation CurrentLocation,
+                                        CXXMethodDecl *CopyAssignOperator) {
+  assert((CopyAssignOperator->isDefaulted() &&
+          CopyAssignOperator->isOverloadedOperator() &&
+          CopyAssignOperator->getOverloadedOperator() == OO_Equal &&
+          !CopyAssignOperator->doesThisDeclarationHaveABody() &&
+          !CopyAssignOperator->isDeleted()) &&
+         "DefineImplicitCopyAssignment called for wrong function");
+  if (CopyAssignOperator->willHaveBody() || CopyAssignOperator->isInvalidDecl())
+    return;
+
+  CXXRecordDecl *ClassDecl = CopyAssignOperator->getParent();
+  if (ClassDecl->isInvalidDecl()) {
+    CopyAssignOperator->setInvalidDecl();
+    return;
+  }
+
+  SynthesizedFunctionScope Scope(*this, CopyAssignOperator);
+
+  // The exception specification is needed because we are defining the
+  // function.
+  ResolveExceptionSpec(CurrentLocation,
+                       CopyAssignOperator->getType()->castAs<FunctionProtoType>());
+
+  // Add a context note for diagnostics produced after this point.
+  Scope.addContextNote(CurrentLocation);
+
+  // C++11 [class.copy]p18:
+  //   The [definition of an implicitly declared copy assignment operator] is
+  //   deprecated if the class has a user-declared copy constructor or a
+  //   user-declared destructor.
+  if (getLangOpts().CPlusPlus11 && CopyAssignOperator->isImplicit())
+    diagnoseDeprecatedCopyOperation(*this, CopyAssignOperator);
+
+  // C++0x [class.copy]p30:
+  //   The implicitly-defined or explicitly-defaulted copy assignment operator
+  //   for a non-union class X performs memberwise copy assignment of its
+  //   subobjects. The direct base classes of X are assigned first, in the
+  //   order of their declaration in the base-specifier-list, and then the
+  //   immediate non-static data members of X are assigned, in the order in
+  //   which they were declared in the class definition.
+
+  // The statements that form the synthesized function body.
+  SmallVector<Stmt*, 8> Statements;
+
+  // The parameter for the "other" object, which we are copying from.
+  ParmVarDecl *Other = CopyAssignOperator->getParamDecl(0);
+  Qualifiers OtherQuals = Other->getType().getQualifiers();
+  QualType OtherRefType = Other->getType();
+  if (const LValueReferenceType *OtherRef
+                                = OtherRefType->getAs<LValueReferenceType>()) {
+    OtherRefType = OtherRef->getPointeeType();
+    OtherQuals = OtherRefType.getQualifiers();
+  }
+
+  // Our location for everything implicitly-generated.
+  SourceLocation Loc = CopyAssignOperator->getEndLoc().isValid()
+                           ? CopyAssignOperator->getEndLoc()
+                           : CopyAssignOperator->getLocation();
+
+  // Builds a DeclRefExpr for the "other" object.
+  RefBuilder OtherRef(Other, OtherRefType);
+
+  // Builds the "this" pointer.
+  ThisBuilder This;
+
+  // Assign base classes.
+  bool Invalid = false;
+  for (auto &Base : ClassDecl->bases()) {
+    // Form the assignment:
+    //   static_cast<Base*>(this)->Base::operator=(static_cast<Base&>(other));
+    QualType BaseType = Base.getType().getUnqualifiedType();
+    if (!BaseType->isRecordType()) {
+      Invalid = true;
+      continue;
+    }
+
+    CXXCastPath BasePath;
+    BasePath.push_back(&Base);
+
+    // Construct the "from" expression, which is an implicit cast to the
+    // appropriately-qualified base type.
+    CastBuilder From(OtherRef, Context.getQualifiedType(BaseType, OtherQuals),
+                     VK_LValue, BasePath);
+
+    // Dereference "this".
+    DerefBuilder DerefThis(This);
+    CastBuilder To(DerefThis,
+                   Context.getQualifiedType(
+                       BaseType, CopyAssignOperator->getMethodQualifiers()),
+                   VK_LValue, BasePath);
+
+    // Build the copy.
+    StmtResult Copy = buildSingleCopyAssign(*this, Loc, BaseType,
+                                            To, From,
+                                            /*CopyingBaseSubobject=*/true,
+                                            /*Copying=*/true);
+    if (Copy.isInvalid()) {
+      CopyAssignOperator->setInvalidDecl();
+      return;
+    }
+
+    // Success! Record the copy.
+    Statements.push_back(Copy.getAs<Expr>());
+  }
+
+  // Assign non-static members.
+  for (auto *Field : ClassDecl->fields()) {
+    // FIXME: We should form some kind of AST representation for the implied
+    // memcpy in a union copy operation.
+    if (Field->isUnnamedBitfield() || Field->getParent()->isUnion())
+      continue;
+
+    if (Field->isInvalidDecl()) {
+      Invalid = true;
+      continue;
+    }
+
+    // Check for members of reference type; we can't copy those.
+    if (Field->getType()->isReferenceType()) {
+      Diag(ClassDecl->getLocation(), diag::err_uninitialized_member_for_assign)
+        << Context.getTagDeclType(ClassDecl) << 0 << Field->getDeclName();
+      Diag(Field->getLocation(), diag::note_declared_at);
+      Invalid = true;
+      continue;
+    }
+
+    // Check for members of const-qualified, non-class type.
+    QualType BaseType = Context.getBaseElementType(Field->getType());
+    if (!BaseType->getAs<RecordType>() && BaseType.isConstQualified()) {
+      Diag(ClassDecl->getLocation(), diag::err_uninitialized_member_for_assign)
+        << Context.getTagDeclType(ClassDecl) << 1 << Field->getDeclName();
+      Diag(Field->getLocation(), diag::note_declared_at);
+      Invalid = true;
+      continue;
+    }
+
+    // Suppress assigning zero-width bitfields.
+    if (Field->isZeroLengthBitField(Context))
+      continue;
+
+    QualType FieldType = Field->getType().getNonReferenceType();
+    if (FieldType->isIncompleteArrayType()) {
+      assert(ClassDecl->hasFlexibleArrayMember() &&
+             "Incomplete array type is not valid");
+      continue;
+    }
+
+    // Build references to the field in the object we're copying from and to.
+    CXXScopeSpec SS; // Intentionally empty
+    LookupResult MemberLookup(*this, Field->getDeclName(), Loc,
+                              LookupMemberName);
+    MemberLookup.addDecl(Field);
+    MemberLookup.resolveKind();
+
+    MemberBuilder From(OtherRef, OtherRefType, /*IsArrow=*/false, MemberLookup);
+
+    MemberBuilder To(This, getCurrentThisType(), /*IsArrow=*/true, MemberLookup);
+
+    // Build the copy of this field.
+    StmtResult Copy = buildSingleCopyAssign(*this, Loc, FieldType,
+                                            To, From,
+                                            /*CopyingBaseSubobject=*/false,
+                                            /*Copying=*/true);
+    if (Copy.isInvalid()) {
+      CopyAssignOperator->setInvalidDecl();
+      return;
+    }
+
+    // Success! Record the copy.
+    Statements.push_back(Copy.getAs<Stmt>());
+  }
+
+  if (!Invalid) {
+    // Add a "return *this;"
+    ExprResult ThisObj = CreateBuiltinUnaryOp(Loc, UO_Deref, This.build(*this, Loc));
+
+    StmtResult Return = BuildReturnStmt(Loc, ThisObj.get());
+    if (Return.isInvalid())
+      Invalid = true;
+    else
+      Statements.push_back(Return.getAs<Stmt>());
+  }
+
+  if (Invalid) {
+    CopyAssignOperator->setInvalidDecl();
+    return;
+  }
+
+  StmtResult Body;
+  {
+    CompoundScopeRAII CompoundScope(*this);
+    Body = ActOnCompoundStmt(Loc, Loc, Statements,
+                             /*isStmtExpr=*/false);
+    assert(!Body.isInvalid() && "Compound statement creation cannot fail");
+  }
+  CopyAssignOperator->setBody(Body.getAs<Stmt>());
+  CopyAssignOperator->markUsed(Context);
+
+  if (ASTMutationListener *L = getASTMutationListener()) {
+    L->CompletedImplicitDefinition(CopyAssignOperator);
+  }
+}
+
+CXXMethodDecl *Sema::DeclareImplicitMoveAssignment(CXXRecordDecl *ClassDecl) {
+  assert(ClassDecl->needsImplicitMoveAssignment());
+
+  DeclaringSpecialMember DSM(*this, ClassDecl, CXXMoveAssignment);
+  if (DSM.isAlreadyBeingDeclared())
+    return nullptr;
+
+  // Note: The following rules are largely analoguous to the move
+  // constructor rules.
+
+  QualType ArgType = Context.getTypeDeclType(ClassDecl);
+  LangAS AS = getDefaultCXXMethodAddrSpace();
+  if (AS != LangAS::Default)
+    ArgType = Context.getAddrSpaceQualType(ArgType, AS);
+  QualType RetType = Context.getLValueReferenceType(ArgType);
+  ArgType = Context.getRValueReferenceType(ArgType);
+
+  bool Constexpr = defaultedSpecialMemberIsConstexpr(*this, ClassDecl,
+                                                     CXXMoveAssignment,
+                                                     false);
+
+  //   An implicitly-declared move assignment operator is an inline public
+  //   member of its class.
+  DeclarationName Name = Context.DeclarationNames.getCXXOperatorName(OO_Equal);
+  SourceLocation ClassLoc = ClassDecl->getLocation();
+  DeclarationNameInfo NameInfo(Name, ClassLoc);
+  CXXMethodDecl *MoveAssignment = CXXMethodDecl::Create(
+      Context, ClassDecl, ClassLoc, NameInfo, QualType(),
+      /*TInfo=*/nullptr, /*StorageClass=*/SC_None,
+      getCurFPFeatures().isFPConstrained(),
+      /*isInline=*/true,
+      Constexpr ? ConstexprSpecKind::Constexpr : ConstexprSpecKind::Unspecified,
+      SourceLocation());
+  MoveAssignment->setAccess(AS_public);
+  MoveAssignment->setDefaulted();
+  MoveAssignment->setImplicit();
+
+  if (getLangOpts().CUDA) {
+    inferCUDATargetForImplicitSpecialMember(ClassDecl, CXXMoveAssignment,
+                                            MoveAssignment,
+                                            /* ConstRHS */ false,
+                                            /* Diagnose */ false);
+  }
+
+  setupImplicitSpecialMemberType(MoveAssignment, RetType, ArgType);
+
+  // Add the parameter to the operator.
+  ParmVarDecl *FromParam = ParmVarDecl::Create(Context, MoveAssignment,
+                                               ClassLoc, ClassLoc,
+                                               /*Id=*/nullptr, ArgType,
+                                               /*TInfo=*/nullptr, SC_None,
+                                               nullptr);
+  MoveAssignment->setParams(FromParam);
+
+  MoveAssignment->setTrivial(
+    ClassDecl->needsOverloadResolutionForMoveAssignment()
+      ? SpecialMemberIsTrivial(MoveAssignment, CXXMoveAssignment)
+      : ClassDecl->hasTrivialMoveAssignment());
+
+  // Note that we have added this copy-assignment operator.
+  ++getASTContext().NumImplicitMoveAssignmentOperatorsDeclared;
+
+  Scope *S = getScopeForContext(ClassDecl);
+  CheckImplicitSpecialMemberDeclaration(S, MoveAssignment);
+
+  if (ShouldDeleteSpecialMember(MoveAssignment, CXXMoveAssignment)) {
+    ClassDecl->setImplicitMoveAssignmentIsDeleted();
+    SetDeclDeleted(MoveAssignment, ClassLoc);
+  }
+
+  if (S)
+    PushOnScopeChains(MoveAssignment, S, false);
+  ClassDecl->addDecl(MoveAssignment);
+
+  return MoveAssignment;
+}
+
+/// Check if we're implicitly defining a move assignment operator for a class
+/// with virtual bases. Such a move assignment might move-assign the virtual
+/// base multiple times.
+static void checkMoveAssignmentForRepeatedMove(Sema &S, CXXRecordDecl *Class,
+                                               SourceLocation CurrentLocation) {
+  assert(!Class->isDependentContext() && "should not define dependent move");
+
+  // Only a virtual base could get implicitly move-assigned multiple times.
+  // Only a non-trivial move assignment can observe this. We only want to
+  // diagnose if we implicitly define an assignment operator that assigns
+  // two base classes, both of which move-assign the same virtual base.
+  if (Class->getNumVBases() == 0 || Class->hasTrivialMoveAssignment() ||
+      Class->getNumBases() < 2)
+    return;
+
+  llvm::SmallVector<CXXBaseSpecifier *, 16> Worklist;
+  typedef llvm::DenseMap<CXXRecordDecl*, CXXBaseSpecifier*> VBaseMap;
+  VBaseMap VBases;
+
+  for (auto &BI : Class->bases()) {
+    Worklist.push_back(&BI);
+    while (!Worklist.empty()) {
+      CXXBaseSpecifier *BaseSpec = Worklist.pop_back_val();
+      CXXRecordDecl *Base = BaseSpec->getType()->getAsCXXRecordDecl();
+
+      // If the base has no non-trivial move assignment operators,
+      // we don't care about moves from it.
+      if (!Base->hasNonTrivialMoveAssignment())
+        continue;
+
+      // If there's nothing virtual here, skip it.
+      if (!BaseSpec->isVirtual() && !Base->getNumVBases())
+        continue;
+
+      // If we're not actually going to call a move assignment for this base,
+      // or the selected move assignment is trivial, skip it.
+      Sema::SpecialMemberOverloadResult SMOR =
+        S.LookupSpecialMember(Base, Sema::CXXMoveAssignment,
+                              /*ConstArg*/false, /*VolatileArg*/false,
+                              /*RValueThis*/true, /*ConstThis*/false,
+                              /*VolatileThis*/false);
+      if (!SMOR.getMethod() || SMOR.getMethod()->isTrivial() ||
+          !SMOR.getMethod()->isMoveAssignmentOperator())
+        continue;
+
+      if (BaseSpec->isVirtual()) {
+        // We're going to move-assign this virtual base, and its move
+        // assignment operator is not trivial. If this can happen for
+        // multiple distinct direct bases of Class, diagnose it. (If it
+        // only happens in one base, we'll diagnose it when synthesizing
+        // that base class's move assignment operator.)
+        CXXBaseSpecifier *&Existing =
+            VBases.insert(std::make_pair(Base->getCanonicalDecl(), &BI))
+                .first->second;
+        if (Existing && Existing != &BI) {
+          S.Diag(CurrentLocation, diag::warn_vbase_moved_multiple_times)
+            << Class << Base;
+          S.Diag(Existing->getBeginLoc(), diag::note_vbase_moved_here)
+              << (Base->getCanonicalDecl() ==
+                  Existing->getType()->getAsCXXRecordDecl()->getCanonicalDecl())
+              << Base << Existing->getType() << Existing->getSourceRange();
+          S.Diag(BI.getBeginLoc(), diag::note_vbase_moved_here)
+              << (Base->getCanonicalDecl() ==
+                  BI.getType()->getAsCXXRecordDecl()->getCanonicalDecl())
+              << Base << BI.getType() << BaseSpec->getSourceRange();
+
+          // Only diagnose each vbase once.
+          Existing = nullptr;
+        }
+      } else {
+        // Only walk over bases that have defaulted move assignment operators.
+        // We assume that any user-provided move assignment operator handles
+        // the multiple-moves-of-vbase case itself somehow.
+        if (!SMOR.getMethod()->isDefaulted())
+          continue;
+
+        // We're going to move the base classes of Base. Add them to the list.
+        for (auto &BI : Base->bases())
+          Worklist.push_back(&BI);
+      }
+    }
+  }
+}
+
+void Sema::DefineImplicitMoveAssignment(SourceLocation CurrentLocation,
+                                        CXXMethodDecl *MoveAssignOperator) {
+  assert((MoveAssignOperator->isDefaulted() &&
+          MoveAssignOperator->isOverloadedOperator() &&
+          MoveAssignOperator->getOverloadedOperator() == OO_Equal &&
+          !MoveAssignOperator->doesThisDeclarationHaveABody() &&
+          !MoveAssignOperator->isDeleted()) &&
+         "DefineImplicitMoveAssignment called for wrong function");
+  if (MoveAssignOperator->willHaveBody() || MoveAssignOperator->isInvalidDecl())
+    return;
+
+  CXXRecordDecl *ClassDecl = MoveAssignOperator->getParent();
+  if (ClassDecl->isInvalidDecl()) {
+    MoveAssignOperator->setInvalidDecl();
+    return;
+  }
+
+  // C++0x [class.copy]p28:
+  //   The implicitly-defined or move assignment operator for a non-union class
+  //   X performs memberwise move assignment of its subobjects. The direct base
+  //   classes of X are assigned first, in the order of their declaration in the
+  //   base-specifier-list, and then the immediate non-static data members of X
+  //   are assigned, in the order in which they were declared in the class
+  //   definition.
+
+  // Issue a warning if our implicit move assignment operator will move
+  // from a virtual base more than once.
+  checkMoveAssignmentForRepeatedMove(*this, ClassDecl, CurrentLocation);
+
+  SynthesizedFunctionScope Scope(*this, MoveAssignOperator);
+
+  // The exception specification is needed because we are defining the
+  // function.
+  ResolveExceptionSpec(CurrentLocation,
+                       MoveAssignOperator->getType()->castAs<FunctionProtoType>());
+
+  // Add a context note for diagnostics produced after this point.
+  Scope.addContextNote(CurrentLocation);
+
+  // The statements that form the synthesized function body.
+  SmallVector<Stmt*, 8> Statements;
+
+  // The parameter for the "other" object, which we are move from.
+  ParmVarDecl *Other = MoveAssignOperator->getParamDecl(0);
+  QualType OtherRefType =
+      Other->getType()->castAs<RValueReferenceType>()->getPointeeType();
+
+  // Our location for everything implicitly-generated.
+  SourceLocation Loc = MoveAssignOperator->getEndLoc().isValid()
+                           ? MoveAssignOperator->getEndLoc()
+                           : MoveAssignOperator->getLocation();
+
+  // Builds a reference to the "other" object.
+  RefBuilder OtherRef(Other, OtherRefType);
+  // Cast to rvalue.
+  MoveCastBuilder MoveOther(OtherRef);
+
+  // Builds the "this" pointer.
+  ThisBuilder This;
+
+  // Assign base classes.
+  bool Invalid = false;
+  for (auto &Base : ClassDecl->bases()) {
+    // C++11 [class.copy]p28:
+    //   It is unspecified whether subobjects representing virtual base classes
+    //   are assigned more than once by the implicitly-defined copy assignment
+    //   operator.
+    // FIXME: Do not assign to a vbase that will be assigned by some other base
+    // class. For a move-assignment, this can result in the vbase being moved
+    // multiple times.
+
+    // Form the assignment:
+    //   static_cast<Base*>(this)->Base::operator=(static_cast<Base&&>(other));
+    QualType BaseType = Base.getType().getUnqualifiedType();
+    if (!BaseType->isRecordType()) {
+      Invalid = true;
+      continue;
+    }
+
+    CXXCastPath BasePath;
+    BasePath.push_back(&Base);
+
+    // Construct the "from" expression, which is an implicit cast to the
+    // appropriately-qualified base type.
+    CastBuilder From(OtherRef, BaseType, VK_XValue, BasePath);
+
+    // Dereference "this".
+    DerefBuilder DerefThis(This);
+
+    // Implicitly cast "this" to the appropriately-qualified base type.
+    CastBuilder To(DerefThis,
+                   Context.getQualifiedType(
+                       BaseType, MoveAssignOperator->getMethodQualifiers()),
+                   VK_LValue, BasePath);
+
+    // Build the move.
+    StmtResult Move = buildSingleCopyAssign(*this, Loc, BaseType,
+                                            To, From,
+                                            /*CopyingBaseSubobject=*/true,
+                                            /*Copying=*/false);
+    if (Move.isInvalid()) {
+      MoveAssignOperator->setInvalidDecl();
+      return;
+    }
+
+    // Success! Record the move.
+    Statements.push_back(Move.getAs<Expr>());
+  }
+
+  // Assign non-static members.
+  for (auto *Field : ClassDecl->fields()) {
+    // FIXME: We should form some kind of AST representation for the implied
+    // memcpy in a union copy operation.
+    if (Field->isUnnamedBitfield() || Field->getParent()->isUnion())
+      continue;
+
+    if (Field->isInvalidDecl()) {
+      Invalid = true;
+      continue;
+    }
+
+    // Check for members of reference type; we can't move those.
+    if (Field->getType()->isReferenceType()) {
+      Diag(ClassDecl->getLocation(), diag::err_uninitialized_member_for_assign)
+        << Context.getTagDeclType(ClassDecl) << 0 << Field->getDeclName();
+      Diag(Field->getLocation(), diag::note_declared_at);
+      Invalid = true;
+      continue;
+    }
+
+    // Check for members of const-qualified, non-class type.
+    QualType BaseType = Context.getBaseElementType(Field->getType());
+    if (!BaseType->getAs<RecordType>() && BaseType.isConstQualified()) {
+      Diag(ClassDecl->getLocation(), diag::err_uninitialized_member_for_assign)
+        << Context.getTagDeclType(ClassDecl) << 1 << Field->getDeclName();
+      Diag(Field->getLocation(), diag::note_declared_at);
+      Invalid = true;
+      continue;
+    }
+
+    // Suppress assigning zero-width bitfields.
+    if (Field->isZeroLengthBitField(Context))
+      continue;
+
+    QualType FieldType = Field->getType().getNonReferenceType();
+    if (FieldType->isIncompleteArrayType()) {
+      assert(ClassDecl->hasFlexibleArrayMember() &&
+             "Incomplete array type is not valid");
+      continue;
+    }
+
+    // Build references to the field in the object we're copying from and to.
+    LookupResult MemberLookup(*this, Field->getDeclName(), Loc,
+                              LookupMemberName);
+    MemberLookup.addDecl(Field);
+    MemberLookup.resolveKind();
+    MemberBuilder From(MoveOther, OtherRefType,
+                       /*IsArrow=*/false, MemberLookup);
+    MemberBuilder To(This, getCurrentThisType(),
+                     /*IsArrow=*/true, MemberLookup);
+
+    assert(!From.build(*this, Loc)->isLValue() && // could be xvalue or prvalue
+        "Member reference with rvalue base must be rvalue except for reference "
+        "members, which aren't allowed for move assignment.");
+
+    // Build the move of this field.
+    StmtResult Move = buildSingleCopyAssign(*this, Loc, FieldType,
+                                            To, From,
+                                            /*CopyingBaseSubobject=*/false,
+                                            /*Copying=*/false);
+    if (Move.isInvalid()) {
+      MoveAssignOperator->setInvalidDecl();
+      return;
+    }
+
+    // Success! Record the copy.
+    Statements.push_back(Move.getAs<Stmt>());
+  }
+
+  if (!Invalid) {
+    // Add a "return *this;"
+    ExprResult ThisObj =
+        CreateBuiltinUnaryOp(Loc, UO_Deref, This.build(*this, Loc));
+
+    StmtResult Return = BuildReturnStmt(Loc, ThisObj.get());
+    if (Return.isInvalid())
+      Invalid = true;
+    else
+      Statements.push_back(Return.getAs<Stmt>());
+  }
+
+  if (Invalid) {
+    MoveAssignOperator->setInvalidDecl();
+    return;
+  }
+
+  StmtResult Body;
+  {
+    CompoundScopeRAII CompoundScope(*this);
+    Body = ActOnCompoundStmt(Loc, Loc, Statements,
+                             /*isStmtExpr=*/false);
+    assert(!Body.isInvalid() && "Compound statement creation cannot fail");
+  }
+  MoveAssignOperator->setBody(Body.getAs<Stmt>());
+  MoveAssignOperator->markUsed(Context);
+
+  if (ASTMutationListener *L = getASTMutationListener()) {
+    L->CompletedImplicitDefinition(MoveAssignOperator);
+  }
+}
+
+CXXConstructorDecl *Sema::DeclareImplicitCopyConstructor(
+                                                    CXXRecordDecl *ClassDecl) {
+  // C++ [class.copy]p4:
+  //   If the class definition does not explicitly declare a copy
+  //   constructor, one is declared implicitly.
+  assert(ClassDecl->needsImplicitCopyConstructor());
+
+  DeclaringSpecialMember DSM(*this, ClassDecl, CXXCopyConstructor);
+  if (DSM.isAlreadyBeingDeclared())
+    return nullptr;
+
+  QualType ClassType = Context.getTypeDeclType(ClassDecl);
+  QualType ArgType = ClassType;
+  bool Const = ClassDecl->implicitCopyConstructorHasConstParam();
+  if (Const)
+    ArgType = ArgType.withConst();
+
+  LangAS AS = getDefaultCXXMethodAddrSpace();
+  if (AS != LangAS::Default)
+    ArgType = Context.getAddrSpaceQualType(ArgType, AS);
+
+  ArgType = Context.getLValueReferenceType(ArgType);
+
+  bool Constexpr = defaultedSpecialMemberIsConstexpr(*this, ClassDecl,
+                                                     CXXCopyConstructor,
+                                                     Const);
+
+  DeclarationName Name
+    = Context.DeclarationNames.getCXXConstructorName(
+                                           Context.getCanonicalType(ClassType));
+  SourceLocation ClassLoc = ClassDecl->getLocation();
+  DeclarationNameInfo NameInfo(Name, ClassLoc);
+
+  //   An implicitly-declared copy constructor is an inline public
+  //   member of its class.
+  CXXConstructorDecl *CopyConstructor = CXXConstructorDecl::Create(
+      Context, ClassDecl, ClassLoc, NameInfo, QualType(), /*TInfo=*/nullptr,
+      ExplicitSpecifier(), getCurFPFeatures().isFPConstrained(),
+      /*isInline=*/true,
+      /*isImplicitlyDeclared=*/true,
+      Constexpr ? ConstexprSpecKind::Constexpr
+                : ConstexprSpecKind::Unspecified);
+  CopyConstructor->setAccess(AS_public);
+  CopyConstructor->setDefaulted();
+
+  if (getLangOpts().CUDA) {
+    inferCUDATargetForImplicitSpecialMember(ClassDecl, CXXCopyConstructor,
+                                            CopyConstructor,
+                                            /* ConstRHS */ Const,
+                                            /* Diagnose */ false);
+  }
+
+  setupImplicitSpecialMemberType(CopyConstructor, Context.VoidTy, ArgType);
+
+  // During template instantiation of special member functions we need a
+  // reliable TypeSourceInfo for the parameter types in order to allow functions
+  // to be substituted.
+  TypeSourceInfo *TSI = nullptr;
+  if (inTemplateInstantiation() && ClassDecl->isLambda())
+    TSI = Context.getTrivialTypeSourceInfo(ArgType);
+
+  // Add the parameter to the constructor.
+  ParmVarDecl *FromParam =
+      ParmVarDecl::Create(Context, CopyConstructor, ClassLoc, ClassLoc,
+                          /*IdentifierInfo=*/nullptr, ArgType,
+                          /*TInfo=*/TSI, SC_None, nullptr);
+  CopyConstructor->setParams(FromParam);
+
+  CopyConstructor->setTrivial(
+      ClassDecl->needsOverloadResolutionForCopyConstructor()
+          ? SpecialMemberIsTrivial(CopyConstructor, CXXCopyConstructor)
+          : ClassDecl->hasTrivialCopyConstructor());
+
+  CopyConstructor->setTrivialForCall(
+      ClassDecl->hasAttr<TrivialABIAttr>() ||
+      (ClassDecl->needsOverloadResolutionForCopyConstructor()
+           ? SpecialMemberIsTrivial(CopyConstructor, CXXCopyConstructor,
+             TAH_ConsiderTrivialABI)
+           : ClassDecl->hasTrivialCopyConstructorForCall()));
+
+  // Note that we have declared this constructor.
+  ++getASTContext().NumImplicitCopyConstructorsDeclared;
+
+  Scope *S = getScopeForContext(ClassDecl);
+  CheckImplicitSpecialMemberDeclaration(S, CopyConstructor);
+
+  if (ShouldDeleteSpecialMember(CopyConstructor, CXXCopyConstructor)) {
+    ClassDecl->setImplicitCopyConstructorIsDeleted();
+    SetDeclDeleted(CopyConstructor, ClassLoc);
+  }
+
+  if (S)
+    PushOnScopeChains(CopyConstructor, S, false);
+  ClassDecl->addDecl(CopyConstructor);
+
+  return CopyConstructor;
+}
+
+void Sema::DefineImplicitCopyConstructor(SourceLocation CurrentLocation,
+                                         CXXConstructorDecl *CopyConstructor) {
+  assert((CopyConstructor->isDefaulted() &&
+          CopyConstructor->isCopyConstructor() &&
+          !CopyConstructor->doesThisDeclarationHaveABody() &&
+          !CopyConstructor->isDeleted()) &&
+         "DefineImplicitCopyConstructor - call it for implicit copy ctor");
+  if (CopyConstructor->willHaveBody() || CopyConstructor->isInvalidDecl())
+    return;
+
+  CXXRecordDecl *ClassDecl = CopyConstructor->getParent();
+  assert(ClassDecl && "DefineImplicitCopyConstructor - invalid constructor");
+
+  SynthesizedFunctionScope Scope(*this, CopyConstructor);
+
+  // The exception specification is needed because we are defining the
+  // function.
+  ResolveExceptionSpec(CurrentLocation,
+                       CopyConstructor->getType()->castAs<FunctionProtoType>());
+  MarkVTableUsed(CurrentLocation, ClassDecl);
+
+  // Add a context note for diagnostics produced after this point.
+  Scope.addContextNote(CurrentLocation);
+
+  // C++11 [class.copy]p7:
+  //   The [definition of an implicitly declared copy constructor] is
+  //   deprecated if the class has a user-declared copy assignment operator
+  //   or a user-declared destructor.
+  if (getLangOpts().CPlusPlus11 && CopyConstructor->isImplicit())
+    diagnoseDeprecatedCopyOperation(*this, CopyConstructor);
+
+  if (SetCtorInitializers(CopyConstructor, /*AnyErrors=*/false)) {
+    CopyConstructor->setInvalidDecl();
+  }  else {
+    SourceLocation Loc = CopyConstructor->getEndLoc().isValid()
+                             ? CopyConstructor->getEndLoc()
+                             : CopyConstructor->getLocation();
+    Sema::CompoundScopeRAII CompoundScope(*this);
+    CopyConstructor->setBody(
+        ActOnCompoundStmt(Loc, Loc, None, /*isStmtExpr=*/false).getAs<Stmt>());
+    CopyConstructor->markUsed(Context);
+  }
+
+  if (ASTMutationListener *L = getASTMutationListener()) {
+    L->CompletedImplicitDefinition(CopyConstructor);
+  }
+}
+
+CXXConstructorDecl *Sema::DeclareImplicitMoveConstructor(
+                                                    CXXRecordDecl *ClassDecl) {
+  assert(ClassDecl->needsImplicitMoveConstructor());
+
+  DeclaringSpecialMember DSM(*this, ClassDecl, CXXMoveConstructor);
+  if (DSM.isAlreadyBeingDeclared())
+    return nullptr;
+
+  QualType ClassType = Context.getTypeDeclType(ClassDecl);
+
+  QualType ArgType = ClassType;
+  LangAS AS = getDefaultCXXMethodAddrSpace();
+  if (AS != LangAS::Default)
+    ArgType = Context.getAddrSpaceQualType(ClassType, AS);
+  ArgType = Context.getRValueReferenceType(ArgType);
+
+  bool Constexpr = defaultedSpecialMemberIsConstexpr(*this, ClassDecl,
+                                                     CXXMoveConstructor,
+                                                     false);
+
+  DeclarationName Name
+    = Context.DeclarationNames.getCXXConstructorName(
+                                           Context.getCanonicalType(ClassType));
+  SourceLocation ClassLoc = ClassDecl->getLocation();
+  DeclarationNameInfo NameInfo(Name, ClassLoc);
+
+  // C++11 [class.copy]p11:
+  //   An implicitly-declared copy/move constructor is an inline public
+  //   member of its class.
+  CXXConstructorDecl *MoveConstructor = CXXConstructorDecl::Create(
+      Context, ClassDecl, ClassLoc, NameInfo, QualType(), /*TInfo=*/nullptr,
+      ExplicitSpecifier(), getCurFPFeatures().isFPConstrained(),
+      /*isInline=*/true,
+      /*isImplicitlyDeclared=*/true,
+      Constexpr ? ConstexprSpecKind::Constexpr
+                : ConstexprSpecKind::Unspecified);
+  MoveConstructor->setAccess(AS_public);
+  MoveConstructor->setDefaulted();
+
+  if (getLangOpts().CUDA) {
+    inferCUDATargetForImplicitSpecialMember(ClassDecl, CXXMoveConstructor,
+                                            MoveConstructor,
+                                            /* ConstRHS */ false,
+                                            /* Diagnose */ false);
+  }
+
+  setupImplicitSpecialMemberType(MoveConstructor, Context.VoidTy, ArgType);
+
+  // Add the parameter to the constructor.
+  ParmVarDecl *FromParam = ParmVarDecl::Create(Context, MoveConstructor,
+                                               ClassLoc, ClassLoc,
+                                               /*IdentifierInfo=*/nullptr,
+                                               ArgType, /*TInfo=*/nullptr,
+                                               SC_None, nullptr);
+  MoveConstructor->setParams(FromParam);
+
+  MoveConstructor->setTrivial(
+      ClassDecl->needsOverloadResolutionForMoveConstructor()
+          ? SpecialMemberIsTrivial(MoveConstructor, CXXMoveConstructor)
+          : ClassDecl->hasTrivialMoveConstructor());
+
+  MoveConstructor->setTrivialForCall(
+      ClassDecl->hasAttr<TrivialABIAttr>() ||
+      (ClassDecl->needsOverloadResolutionForMoveConstructor()
+           ? SpecialMemberIsTrivial(MoveConstructor, CXXMoveConstructor,
+                                    TAH_ConsiderTrivialABI)
+           : ClassDecl->hasTrivialMoveConstructorForCall()));
+
+  // Note that we have declared this constructor.
+  ++getASTContext().NumImplicitMoveConstructorsDeclared;
+
+  Scope *S = getScopeForContext(ClassDecl);
+  CheckImplicitSpecialMemberDeclaration(S, MoveConstructor);
+
+  if (ShouldDeleteSpecialMember(MoveConstructor, CXXMoveConstructor)) {
+    ClassDecl->setImplicitMoveConstructorIsDeleted();
+    SetDeclDeleted(MoveConstructor, ClassLoc);
+  }
+
+  if (S)
+    PushOnScopeChains(MoveConstructor, S, false);
+  ClassDecl->addDecl(MoveConstructor);
+
+  return MoveConstructor;
+}
+
+void Sema::DefineImplicitMoveConstructor(SourceLocation CurrentLocation,
+                                         CXXConstructorDecl *MoveConstructor) {
+  assert((MoveConstructor->isDefaulted() &&
+          MoveConstructor->isMoveConstructor() &&
+          !MoveConstructor->doesThisDeclarationHaveABody() &&
+          !MoveConstructor->isDeleted()) &&
+         "DefineImplicitMoveConstructor - call it for implicit move ctor");
+  if (MoveConstructor->willHaveBody() || MoveConstructor->isInvalidDecl())
+    return;
+
+  CXXRecordDecl *ClassDecl = MoveConstructor->getParent();
+  assert(ClassDecl && "DefineImplicitMoveConstructor - invalid constructor");
+
+  SynthesizedFunctionScope Scope(*this, MoveConstructor);
+
+  // The exception specification is needed because we are defining the
+  // function.
+  ResolveExceptionSpec(CurrentLocation,
+                       MoveConstructor->getType()->castAs<FunctionProtoType>());
+  MarkVTableUsed(CurrentLocation, ClassDecl);
+
+  // Add a context note for diagnostics produced after this point.
+  Scope.addContextNote(CurrentLocation);
+
+  if (SetCtorInitializers(MoveConstructor, /*AnyErrors=*/false)) {
+    MoveConstructor->setInvalidDecl();
+  } else {
+    SourceLocation Loc = MoveConstructor->getEndLoc().isValid()
+                             ? MoveConstructor->getEndLoc()
+                             : MoveConstructor->getLocation();
+    Sema::CompoundScopeRAII CompoundScope(*this);
+    MoveConstructor->setBody(ActOnCompoundStmt(
+        Loc, Loc, None, /*isStmtExpr=*/ false).getAs<Stmt>());
+    MoveConstructor->markUsed(Context);
+  }
+
+  if (ASTMutationListener *L = getASTMutationListener()) {
+    L->CompletedImplicitDefinition(MoveConstructor);
+  }
+}
+
+bool Sema::isImplicitlyDeleted(FunctionDecl *FD) {
+  return FD->isDeleted() && FD->isDefaulted() && isa<CXXMethodDecl>(FD);
+}
+
+void Sema::DefineImplicitLambdaToFunctionPointerConversion(
+                            SourceLocation CurrentLocation,
+                            CXXConversionDecl *Conv) {
+  SynthesizedFunctionScope Scope(*this, Conv);
+  assert(!Conv->getReturnType()->isUndeducedType());
+
+  QualType ConvRT = Conv->getType()->castAs<FunctionType>()->getReturnType();
+  CallingConv CC =
+      ConvRT->getPointeeType()->castAs<FunctionType>()->getCallConv();
+
+  CXXRecordDecl *Lambda = Conv->getParent();
+  FunctionDecl *CallOp = Lambda->getLambdaCallOperator();
+  FunctionDecl *Invoker = Lambda->getLambdaStaticInvoker(CC);
+
+  if (auto *TemplateArgs = Conv->getTemplateSpecializationArgs()) {
+    CallOp = InstantiateFunctionDeclaration(
+        CallOp->getDescribedFunctionTemplate(), TemplateArgs, CurrentLocation);
+    if (!CallOp)
+      return;
+
+    Invoker = InstantiateFunctionDeclaration(
+        Invoker->getDescribedFunctionTemplate(), TemplateArgs, CurrentLocation);
+    if (!Invoker)
+      return;
+  }
+
+  if (CallOp->isInvalidDecl())
+    return;
+
+  // Mark the call operator referenced (and add to pending instantiations
+  // if necessary).
+  // For both the conversion and static-invoker template specializations
+  // we construct their body's in this function, so no need to add them
+  // to the PendingInstantiations.
+  MarkFunctionReferenced(CurrentLocation, CallOp);
+
+  // Fill in the __invoke function with a dummy implementation. IR generation
+  // will fill in the actual details. Update its type in case it contained
+  // an 'auto'.
+  Invoker->markUsed(Context);
+  Invoker->setReferenced();
+  Invoker->setType(Conv->getReturnType()->getPointeeType());
+  Invoker->setBody(new (Context) CompoundStmt(Conv->getLocation()));
+
+  // Construct the body of the conversion function { return __invoke; }.
+  Expr *FunctionRef = BuildDeclRefExpr(Invoker, Invoker->getType(),
+                                       VK_LValue, Conv->getLocation());
+  assert(FunctionRef && "Can't refer to __invoke function?");
+  Stmt *Return = BuildReturnStmt(Conv->getLocation(), FunctionRef).get();
+  Conv->setBody(CompoundStmt::Create(Context, Return, Conv->getLocation(),
+                                     Conv->getLocation()));
+  Conv->markUsed(Context);
+  Conv->setReferenced();
+
+  if (ASTMutationListener *L = getASTMutationListener()) {
+    L->CompletedImplicitDefinition(Conv);
+    L->CompletedImplicitDefinition(Invoker);
+  }
+}
+
+
+
+void Sema::DefineImplicitLambdaToBlockPointerConversion(
+       SourceLocation CurrentLocation,
+       CXXConversionDecl *Conv)
+{
+  assert(!Conv->getParent()->isGenericLambda());
+
+  SynthesizedFunctionScope Scope(*this, Conv);
+
+  // Copy-initialize the lambda object as needed to capture it.
+  Expr *This = ActOnCXXThis(CurrentLocation).get();
+  Expr *DerefThis =CreateBuiltinUnaryOp(CurrentLocation, UO_Deref, This).get();
+
+  ExprResult BuildBlock = BuildBlockForLambdaConversion(CurrentLocation,
+                                                        Conv->getLocation(),
+                                                        Conv, DerefThis);
+
+  // If we're not under ARC, make sure we still get the _Block_copy/autorelease
+  // behavior.  Note that only the general conversion function does this
+  // (since it's unusable otherwise); in the case where we inline the
+  // block literal, it has block literal lifetime semantics.
+  if (!BuildBlock.isInvalid() && !getLangOpts().ObjCAutoRefCount)
+    BuildBlock = ImplicitCastExpr::Create(
+        Context, BuildBlock.get()->getType(), CK_CopyAndAutoreleaseBlockObject,
+        BuildBlock.get(), nullptr, VK_PRValue, FPOptionsOverride());
+
+  if (BuildBlock.isInvalid()) {
+    Diag(CurrentLocation, diag::note_lambda_to_block_conv);
+    Conv->setInvalidDecl();
+    return;
+  }
+
+  // Create the return statement that returns the block from the conversion
+  // function.
+  StmtResult Return = BuildReturnStmt(Conv->getLocation(), BuildBlock.get());
+  if (Return.isInvalid()) {
+    Diag(CurrentLocation, diag::note_lambda_to_block_conv);
+    Conv->setInvalidDecl();
+    return;
+  }
+
+  // Set the body of the conversion function.
+  Stmt *ReturnS = Return.get();
+  Conv->setBody(CompoundStmt::Create(Context, ReturnS, Conv->getLocation(),
+                                     Conv->getLocation()));
+  Conv->markUsed(Context);
+
+  // We're done; notify the mutation listener, if any.
+  if (ASTMutationListener *L = getASTMutationListener()) {
+    L->CompletedImplicitDefinition(Conv);
+  }
+}
+
+/// Determine whether the given list arguments contains exactly one
+/// "real" (non-default) argument.
+static bool hasOneRealArgument(MultiExprArg Args) {
+  switch (Args.size()) {
+  case 0:
+    return false;
+
+  default:
+    if (!Args[1]->isDefaultArgument())
+      return false;
+
+    LLVM_FALLTHROUGH;
+  case 1:
+    return !Args[0]->isDefaultArgument();
+  }
+
+  return false;
+}
+
+ExprResult
+Sema::BuildCXXConstructExpr(SourceLocation ConstructLoc, QualType DeclInitType,
+                            NamedDecl *FoundDecl,
+                            CXXConstructorDecl *Constructor,
+                            MultiExprArg ExprArgs,
+                            bool HadMultipleCandidates,
+                            bool IsListInitialization,
+                            bool IsStdInitListInitialization,
+                            bool RequiresZeroInit,
+                            unsigned ConstructKind,
+                            SourceRange ParenRange) {
+  bool Elidable = false;
+
+  // C++0x [class.copy]p34:
+  //   When certain criteria are met, an implementation is allowed to
+  //   omit the copy/move construction of a class object, even if the
+  //   copy/move constructor and/or destructor for the object have
+  //   side effects. [...]
+  //     - when a temporary class object that has not been bound to a
+  //       reference (12.2) would be copied/moved to a class object
+  //       with the same cv-unqualified type, the copy/move operation
+  //       can be omitted by constructing the temporary object
+  //       directly into the target of the omitted copy/move
+  if (ConstructKind == CXXConstructExpr::CK_Complete && Constructor &&
+      // FIXME: Converting constructors should also be accepted.
+      // But to fix this, the logic that digs down into a CXXConstructExpr
+      // to find the source object needs to handle it.
+      // Right now it assumes the source object is passed directly as the
+      // first argument.
+      Constructor->isCopyOrMoveConstructor() && hasOneRealArgument(ExprArgs)) {
+    Expr *SubExpr = ExprArgs[0];
+    // FIXME: Per above, this is also incorrect if we want to accept
+    //        converting constructors, as isTemporaryObject will
+    //        reject temporaries with different type from the
+    //        CXXRecord itself.
+    Elidable = SubExpr->isTemporaryObject(
+        Context, cast<CXXRecordDecl>(FoundDecl->getDeclContext()));
+  }
+
+  return BuildCXXConstructExpr(ConstructLoc, DeclInitType,
+                               FoundDecl, Constructor,
+                               Elidable, ExprArgs, HadMultipleCandidates,
+                               IsListInitialization,
+                               IsStdInitListInitialization, RequiresZeroInit,
+                               ConstructKind, ParenRange);
+}
+
+ExprResult
+Sema::BuildCXXConstructExpr(SourceLocation ConstructLoc, QualType DeclInitType,
+                            NamedDecl *FoundDecl,
+                            CXXConstructorDecl *Constructor,
+                            bool Elidable,
+                            MultiExprArg ExprArgs,
+                            bool HadMultipleCandidates,
+                            bool IsListInitialization,
+                            bool IsStdInitListInitialization,
+                            bool RequiresZeroInit,
+                            unsigned ConstructKind,
+                            SourceRange ParenRange) {
+  if (auto *Shadow = dyn_cast<ConstructorUsingShadowDecl>(FoundDecl)) {
+    Constructor = findInheritingConstructor(ConstructLoc, Constructor, Shadow);
+    if (DiagnoseUseOfDecl(Constructor, ConstructLoc))
+      return ExprError();
+  }
+
+  return BuildCXXConstructExpr(
+      ConstructLoc, DeclInitType, Constructor, Elidable, ExprArgs,
+      HadMultipleCandidates, IsListInitialization, IsStdInitListInitialization,
+      RequiresZeroInit, ConstructKind, ParenRange);
+}
+
+/// BuildCXXConstructExpr - Creates a complete call to a constructor,
+/// including handling of its default argument expressions.
+ExprResult
+Sema::BuildCXXConstructExpr(SourceLocation ConstructLoc, QualType DeclInitType,
+                            CXXConstructorDecl *Constructor,
+                            bool Elidable,
+                            MultiExprArg ExprArgs,
+                            bool HadMultipleCandidates,
+                            bool IsListInitialization,
+                            bool IsStdInitListInitialization,
+                            bool RequiresZeroInit,
+                            unsigned ConstructKind,
+                            SourceRange ParenRange) {
+  assert(declaresSameEntity(
+             Constructor->getParent(),
+             DeclInitType->getBaseElementTypeUnsafe()->getAsCXXRecordDecl()) &&
+         "given constructor for wrong type");
+  MarkFunctionReferenced(ConstructLoc, Constructor);
+  if (getLangOpts().CUDA && !CheckCUDACall(ConstructLoc, Constructor))
+    return ExprError();
+  if (getLangOpts().SYCLIsDevice &&
+      !checkSYCLDeviceFunction(ConstructLoc, Constructor))
+    return ExprError();
+
+  return CheckForImmediateInvocation(
+      CXXConstructExpr::Create(
+          Context, DeclInitType, ConstructLoc, Constructor, Elidable, ExprArgs,
+          HadMultipleCandidates, IsListInitialization,
+          IsStdInitListInitialization, RequiresZeroInit,
+          static_cast<CXXConstructExpr::ConstructionKind>(ConstructKind),
+          ParenRange),
+      Constructor);
+}
+
+ExprResult Sema::BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field) {
+  assert(Field->hasInClassInitializer());
+
+  // If we already have the in-class initializer nothing needs to be done.
+  if (Field->getInClassInitializer())
+    return CXXDefaultInitExpr::Create(Context, Loc, Field, CurContext);
+
+  // If we might have already tried and failed to instantiate, don't try again.
+  if (Field->isInvalidDecl())
+    return ExprError();
+
+  // Maybe we haven't instantiated the in-class initializer. Go check the
+  // pattern FieldDecl to see if it has one.
+  CXXRecordDecl *ParentRD = cast<CXXRecordDecl>(Field->getParent());
+
+  if (isTemplateInstantiation(ParentRD->getTemplateSpecializationKind())) {
+    CXXRecordDecl *ClassPattern = ParentRD->getTemplateInstantiationPattern();
+    DeclContext::lookup_result Lookup =
+        ClassPattern->lookup(Field->getDeclName());
+
+    FieldDecl *Pattern = nullptr;
+    for (auto L : Lookup) {
+      if (isa<FieldDecl>(L)) {
+        Pattern = cast<FieldDecl>(L);
+        break;
+      }
+    }
+    assert(Pattern && "We must have set the Pattern!");
+
+    if (!Pattern->hasInClassInitializer() ||
+        InstantiateInClassInitializer(Loc, Field, Pattern,
+                                      getTemplateInstantiationArgs(Field))) {
+      // Don't diagnose this again.
+      Field->setInvalidDecl();
+      return ExprError();
+    }
+    return CXXDefaultInitExpr::Create(Context, Loc, Field, CurContext);
+  }
+
+  // DR1351:
+  //   If the brace-or-equal-initializer of a non-static data member
+  //   invokes a defaulted default constructor of its class or of an
+  //   enclosing class in a potentially evaluated subexpression, the
+  //   program is ill-formed.
+  //
+  // This resolution is unworkable: the exception specification of the
+  // default constructor can be needed in an unevaluated context, in
+  // particular, in the operand of a noexcept-expression, and we can be
+  // unable to compute an exception specification for an enclosed class.
+  //
+  // Any attempt to resolve the exception specification of a defaulted default
+  // constructor before the initializer is lexically complete will ultimately
+  // come here at which point we can diagnose it.
+  RecordDecl *OutermostClass = ParentRD->getOuterLexicalRecordContext();
+  Diag(Loc, diag::err_default_member_initializer_not_yet_parsed)
+      << OutermostClass << Field;
+  Diag(Field->getEndLoc(),
+       diag::note_default_member_initializer_not_yet_parsed);
+  // Recover by marking the field invalid, unless we're in a SFINAE context.
+  if (!isSFINAEContext())
+    Field->setInvalidDecl();
+  return ExprError();
+}
+
+void Sema::FinalizeVarWithDestructor(VarDecl *VD, const RecordType *Record) {
+  if (VD->isInvalidDecl()) return;
+  // If initializing the variable failed, don't also diagnose problems with
+  // the destructor, they're likely related.
+  if (VD->getInit() && VD->getInit()->containsErrors())
+    return;
+
+  CXXRecordDecl *ClassDecl = cast<CXXRecordDecl>(Record->getDecl());
+  if (ClassDecl->isInvalidDecl()) return;
+  if (ClassDecl->hasIrrelevantDestructor()) return;
+  if (ClassDecl->isDependentContext()) return;
+
+  if (VD->isNoDestroy(getASTContext()))
+    return;
+
+  CXXDestructorDecl *Destructor = LookupDestructor(ClassDecl);
+
+  // If this is an array, we'll require the destructor during initialization, so
+  // we can skip over this. We still want to emit exit-time destructor warnings
+  // though.
+  if (!VD->getType()->isArrayType()) {
+    MarkFunctionReferenced(VD->getLocation(), Destructor);
+    CheckDestructorAccess(VD->getLocation(), Destructor,
+                          PDiag(diag::err_access_dtor_var)
+                              << VD->getDeclName() << VD->getType());
+    DiagnoseUseOfDecl(Destructor, VD->getLocation());
+  }
+
+  if (Destructor->isTrivial()) return;
+
+  // If the destructor is constexpr, check whether the variable has constant
+  // destruction now.
+  if (Destructor->isConstexpr()) {
+    bool HasConstantInit = false;
+    if (VD->getInit() && !VD->getInit()->isValueDependent())
+      HasConstantInit = VD->evaluateValue();
+    SmallVector<PartialDiagnosticAt, 8> Notes;
+    if (!VD->evaluateDestruction(Notes) && VD->isConstexpr() &&
+        HasConstantInit) {
+      Diag(VD->getLocation(),
+           diag::err_constexpr_var_requires_const_destruction) << VD;
+      for (unsigned I = 0, N = Notes.size(); I != N; ++I)
+        Diag(Notes[I].first, Notes[I].second);
+    }
+  }
+
+  if (!VD->hasGlobalStorage()) return;
+
+  // Emit warning for non-trivial dtor in global scope (a real global,
+  // class-static, function-static).
+  Diag(VD->getLocation(), diag::warn_exit_time_destructor);
+
+  // TODO: this should be re-enabled for static locals by !CXAAtExit
+  if (!VD->isStaticLocal())
+    Diag(VD->getLocation(), diag::warn_global_destructor);
+}
+
+/// Given a constructor and the set of arguments provided for the
+/// constructor, convert the arguments and add any required default arguments
+/// to form a proper call to this constructor.
+///
+/// \returns true if an error occurred, false otherwise.
+bool Sema::CompleteConstructorCall(CXXConstructorDecl *Constructor,
+                                   QualType DeclInitType, MultiExprArg ArgsPtr,
+                                   SourceLocation Loc,
+                                   SmallVectorImpl<Expr *> &ConvertedArgs,
+                                   bool AllowExplicit,
+                                   bool IsListInitialization) {
+  // FIXME: This duplicates a lot of code from Sema::ConvertArgumentsForCall.
+  unsigned NumArgs = ArgsPtr.size();
+  Expr **Args = ArgsPtr.data();
+
+  const auto *Proto = Constructor->getType()->castAs<FunctionProtoType>();
+  unsigned NumParams = Proto->getNumParams();
+
+  // If too few arguments are available, we'll fill in the rest with defaults.
+  if (NumArgs < NumParams)
+    ConvertedArgs.reserve(NumParams);
+  else
+    ConvertedArgs.reserve(NumArgs);
+
+  VariadicCallType CallType =
+    Proto->isVariadic() ? VariadicConstructor : VariadicDoesNotApply;
+  SmallVector<Expr *, 8> AllArgs;
+  bool Invalid = GatherArgumentsForCall(Loc, Constructor,
+                                        Proto, 0,
+                                        llvm::makeArrayRef(Args, NumArgs),
+                                        AllArgs,
+                                        CallType, AllowExplicit,
+                                        IsListInitialization);
+  ConvertedArgs.append(AllArgs.begin(), AllArgs.end());
+
+  DiagnoseSentinelCalls(Constructor, Loc, AllArgs);
+
+  CheckConstructorCall(Constructor, DeclInitType,
+                       llvm::makeArrayRef(AllArgs.data(), AllArgs.size()),
+                       Proto, Loc);
+
+  return Invalid;
+}
+
+static inline bool
+CheckOperatorNewDeleteDeclarationScope(Sema &SemaRef,
+                                       const FunctionDecl *FnDecl) {
+  const DeclContext *DC = FnDecl->getDeclContext()->getRedeclContext();
+  if (isa<NamespaceDecl>(DC)) {
+    return SemaRef.Diag(FnDecl->getLocation(),
+                        diag::err_operator_new_delete_declared_in_namespace)
+      << FnDecl->getDeclName();
+  }
+
+  if (isa<TranslationUnitDecl>(DC) &&
+      FnDecl->getStorageClass() == SC_Static) {
+    return SemaRef.Diag(FnDecl->getLocation(),
+                        diag::err_operator_new_delete_declared_static)
+      << FnDecl->getDeclName();
+  }
+
+  return false;
+}
+
+static CanQualType RemoveAddressSpaceFromPtr(Sema &SemaRef,
+                                             const PointerType *PtrTy) {
+  auto &Ctx = SemaRef.Context;
+  Qualifiers PtrQuals = PtrTy->getPointeeType().getQualifiers();
+  PtrQuals.removeAddressSpace();
+  return Ctx.getPointerType(Ctx.getCanonicalType(Ctx.getQualifiedType(
+      PtrTy->getPointeeType().getUnqualifiedType(), PtrQuals)));
+}
+
+static inline bool
+CheckOperatorNewDeleteTypes(Sema &SemaRef, const FunctionDecl *FnDecl,
+                            CanQualType ExpectedResultType,
+                            CanQualType ExpectedFirstParamType,
+                            unsigned DependentParamTypeDiag,
+                            unsigned InvalidParamTypeDiag) {
+  QualType ResultType =
+      FnDecl->getType()->castAs<FunctionType>()->getReturnType();
+
+  if (SemaRef.getLangOpts().OpenCLCPlusPlus) {
+    // The operator is valid on any address space for OpenCL.
+    // Drop address space from actual and expected result types.
+    if (const auto *PtrTy = ResultType->getAs<PointerType>())
+      ResultType = RemoveAddressSpaceFromPtr(SemaRef, PtrTy);
+
+    if (auto ExpectedPtrTy = ExpectedResultType->getAs<PointerType>())
+      ExpectedResultType = RemoveAddressSpaceFromPtr(SemaRef, ExpectedPtrTy);
+  }
+
+  // Check that the result type is what we expect.
+  if (SemaRef.Context.getCanonicalType(ResultType) != ExpectedResultType) {
+    // Reject even if the type is dependent; an operator delete function is
+    // required to have a non-dependent result type.
+    return SemaRef.Diag(
+               FnDecl->getLocation(),
+               ResultType->isDependentType()
+                   ? diag::err_operator_new_delete_dependent_result_type
+                   : diag::err_operator_new_delete_invalid_result_type)
+           << FnDecl->getDeclName() << ExpectedResultType;
+  }
+
+  // A function template must have at least 2 parameters.
+  if (FnDecl->getDescribedFunctionTemplate() && FnDecl->getNumParams() < 2)
+    return SemaRef.Diag(FnDecl->getLocation(),
+                      diag::err_operator_new_delete_template_too_few_parameters)
+        << FnDecl->getDeclName();
+
+  // The function decl must have at least 1 parameter.
+  if (FnDecl->getNumParams() == 0)
+    return SemaRef.Diag(FnDecl->getLocation(),
+                        diag::err_operator_new_delete_too_few_parameters)
+      << FnDecl->getDeclName();
+
+  QualType FirstParamType = FnDecl->getParamDecl(0)->getType();
+  if (SemaRef.getLangOpts().OpenCLCPlusPlus) {
+    // The operator is valid on any address space for OpenCL.
+    // Drop address space from actual and expected first parameter types.
+    if (const auto *PtrTy =
+            FnDecl->getParamDecl(0)->getType()->getAs<PointerType>())
+      FirstParamType = RemoveAddressSpaceFromPtr(SemaRef, PtrTy);
+
+    if (auto ExpectedPtrTy = ExpectedFirstParamType->getAs<PointerType>())
+      ExpectedFirstParamType =
+          RemoveAddressSpaceFromPtr(SemaRef, ExpectedPtrTy);
+  }
+
+  // Check that the first parameter type is what we expect.
+  if (SemaRef.Context.getCanonicalType(FirstParamType).getUnqualifiedType() !=
+      ExpectedFirstParamType) {
+    // The first parameter type is not allowed to be dependent. As a tentative
+    // DR resolution, we allow a dependent parameter type if it is the right
+    // type anyway, to allow destroying operator delete in class templates.
+    return SemaRef.Diag(FnDecl->getLocation(), FirstParamType->isDependentType()
+                                                   ? DependentParamTypeDiag
+                                                   : InvalidParamTypeDiag)
+           << FnDecl->getDeclName() << ExpectedFirstParamType;
+  }
+
+  return false;
+}
+
+static bool
+CheckOperatorNewDeclaration(Sema &SemaRef, const FunctionDecl *FnDecl) {
+  // C++ [basic.stc.dynamic.allocation]p1:
+  //   A program is ill-formed if an allocation function is declared in a
+  //   namespace scope other than global scope or declared static in global
+  //   scope.
+  if (CheckOperatorNewDeleteDeclarationScope(SemaRef, FnDecl))
+    return true;
+
+  CanQualType SizeTy =
+    SemaRef.Context.getCanonicalType(SemaRef.Context.getSizeType());
+
+  // C++ [basic.stc.dynamic.allocation]p1:
+  //  The return type shall be void*. The first parameter shall have type
+  //  std::size_t.
+  if (CheckOperatorNewDeleteTypes(SemaRef, FnDecl, SemaRef.Context.VoidPtrTy,
+                                  SizeTy,
+                                  diag::err_operator_new_dependent_param_type,
+                                  diag::err_operator_new_param_type))
+    return true;
+
+  // C++ [basic.stc.dynamic.allocation]p1:
+  //  The first parameter shall not have an associated default argument.
+  if (FnDecl->getParamDecl(0)->hasDefaultArg())
+    return SemaRef.Diag(FnDecl->getLocation(),
+                        diag::err_operator_new_default_arg)
+      << FnDecl->getDeclName() << FnDecl->getParamDecl(0)->getDefaultArgRange();
+
+  return false;
+}
+
+static bool
+CheckOperatorDeleteDeclaration(Sema &SemaRef, FunctionDecl *FnDecl) {
+  // C++ [basic.stc.dynamic.deallocation]p1:
+  //   A program is ill-formed if deallocation functions are declared in a
+  //   namespace scope other than global scope or declared static in global
+  //   scope.
+  if (CheckOperatorNewDeleteDeclarationScope(SemaRef, FnDecl))
+    return true;
+
+  auto *MD = dyn_cast<CXXMethodDecl>(FnDecl);
+
+  // C++ P0722:
+  //   Within a class C, the first parameter of a destroying operator delete
+  //   shall be of type C *. The first parameter of any other deallocation
+  //   function shall be of type void *.
+  CanQualType ExpectedFirstParamType =
+      MD && MD->isDestroyingOperatorDelete()
+          ? SemaRef.Context.getCanonicalType(SemaRef.Context.getPointerType(
+                SemaRef.Context.getRecordType(MD->getParent())))
+          : SemaRef.Context.VoidPtrTy;
+
+  // C++ [basic.stc.dynamic.deallocation]p2:
+  //   Each deallocation function shall return void
+  if (CheckOperatorNewDeleteTypes(
+          SemaRef, FnDecl, SemaRef.Context.VoidTy, ExpectedFirstParamType,
+          diag::err_operator_delete_dependent_param_type,
+          diag::err_operator_delete_param_type))
+    return true;
+
+  // C++ P0722:
+  //   A destroying operator delete shall be a usual deallocation function.
+  if (MD && !MD->getParent()->isDependentContext() &&
+      MD->isDestroyingOperatorDelete() &&
+      !SemaRef.isUsualDeallocationFunction(MD)) {
+    SemaRef.Diag(MD->getLocation(),
+                 diag::err_destroying_operator_delete_not_usual);
+    return true;
+  }
+
+  return false;
+}
+
+/// CheckOverloadedOperatorDeclaration - Check whether the declaration
+/// of this overloaded operator is well-formed. If so, returns false;
+/// otherwise, emits appropriate diagnostics and returns true.
+bool Sema::CheckOverloadedOperatorDeclaration(FunctionDecl *FnDecl) {
+  assert(FnDecl && FnDecl->isOverloadedOperator() &&
+         "Expected an overloaded operator declaration");
+
+  OverloadedOperatorKind Op = FnDecl->getOverloadedOperator();
+
+  // C++ [over.oper]p5:
+  //   The allocation and deallocation functions, operator new,
+  //   operator new[], operator delete and operator delete[], are
+  //   described completely in 3.7.3. The attributes and restrictions
+  //   found in the rest of this subclause do not apply to them unless
+  //   explicitly stated in 3.7.3.
+  if (Op == OO_Delete || Op == OO_Array_Delete)
+    return CheckOperatorDeleteDeclaration(*this, FnDecl);
+
+  if (Op == OO_New || Op == OO_Array_New)
+    return CheckOperatorNewDeclaration(*this, FnDecl);
+
+  // C++ [over.oper]p6:
+  //   An operator function shall either be a non-static member
+  //   function or be a non-member function and have at least one
+  //   parameter whose type is a class, a reference to a class, an
+  //   enumeration, or a reference to an enumeration.
+  if (CXXMethodDecl *MethodDecl = dyn_cast<CXXMethodDecl>(FnDecl)) {
+    if (MethodDecl->isStatic())
+      return Diag(FnDecl->getLocation(),
+                  diag::err_operator_overload_static) << FnDecl->getDeclName();
+  } else {
+    bool ClassOrEnumParam = false;
+    for (auto Param : FnDecl->parameters()) {
+      QualType ParamType = Param->getType().getNonReferenceType();
+      if (ParamType->isDependentType() || ParamType->isRecordType() ||
+          ParamType->isEnumeralType()) {
+        ClassOrEnumParam = true;
+        break;
+      }
+    }
+
+    if (!ClassOrEnumParam)
+      return Diag(FnDecl->getLocation(),
+                  diag::err_operator_overload_needs_class_or_enum)
+        << FnDecl->getDeclName();
+  }
+
+  // C++ [over.oper]p8:
+  //   An operator function cannot have default arguments (8.3.6),
+  //   except where explicitly stated below.
+  //
+  // Only the function-call operator allows default arguments
+  // (C++ [over.call]p1).
+  if (Op != OO_Call) {
+    for (auto Param : FnDecl->parameters()) {
+      if (Param->hasDefaultArg())
+        return Diag(Param->getLocation(),
+                    diag::err_operator_overload_default_arg)
+          << FnDecl->getDeclName() << Param->getDefaultArgRange();
+    }
+  }
+
+  static const bool OperatorUses[NUM_OVERLOADED_OPERATORS][3] = {
+    { false, false, false }
+#define OVERLOADED_OPERATOR(Name,Spelling,Token,Unary,Binary,MemberOnly) \
+    , { Unary, Binary, MemberOnly }
+#include "clang/Basic/OperatorKinds.def"
+  };
+
+  bool CanBeUnaryOperator = OperatorUses[Op][0];
+  bool CanBeBinaryOperator = OperatorUses[Op][1];
+  bool MustBeMemberOperator = OperatorUses[Op][2];
+
+  // C++ [over.oper]p8:
+  //   [...] Operator functions cannot have more or fewer parameters
+  //   than the number required for the corresponding operator, as
+  //   described in the rest of this subclause.
+  unsigned NumParams = FnDecl->getNumParams()
+                     + (isa<CXXMethodDecl>(FnDecl)? 1 : 0);
+  if (Op != OO_Call &&
+      ((NumParams == 1 && !CanBeUnaryOperator) ||
+       (NumParams == 2 && !CanBeBinaryOperator) ||
+       (NumParams < 1) || (NumParams > 2))) {
+    // We have the wrong number of parameters.
+    unsigned ErrorKind;
+    if (CanBeUnaryOperator && CanBeBinaryOperator) {
+      ErrorKind = 2;  // 2 -> unary or binary.
+    } else if (CanBeUnaryOperator) {
+      ErrorKind = 0;  // 0 -> unary
+    } else {
+      assert(CanBeBinaryOperator &&
+             "All non-call overloaded operators are unary or binary!");
+      ErrorKind = 1;  // 1 -> binary
+    }
+
+    return Diag(FnDecl->getLocation(), diag::err_operator_overload_must_be)
+      << FnDecl->getDeclName() << NumParams << ErrorKind;
+  }
+
+  // Overloaded operators other than operator() cannot be variadic.
+  if (Op != OO_Call &&
+      FnDecl->getType()->castAs<FunctionProtoType>()->isVariadic()) {
+    return Diag(FnDecl->getLocation(), diag::err_operator_overload_variadic)
+      << FnDecl->getDeclName();
+  }
+
+  // Some operators must be non-static member functions.
+  if (MustBeMemberOperator && !isa<CXXMethodDecl>(FnDecl)) {
+    return Diag(FnDecl->getLocation(),
+                diag::err_operator_overload_must_be_member)
+      << FnDecl->getDeclName();
+  }
+
+  // C++ [over.inc]p1:
+  //   The user-defined function called operator++ implements the
+  //   prefix and postfix ++ operator. If this function is a member
+  //   function with no parameters, or a non-member function with one
+  //   parameter of class or enumeration type, it defines the prefix
+  //   increment operator ++ for objects of that type. If the function
+  //   is a member function with one parameter (which shall be of type
+  //   int) or a non-member function with two parameters (the second
+  //   of which shall be of type int), it defines the postfix
+  //   increment operator ++ for objects of that type.
+  if ((Op == OO_PlusPlus || Op == OO_MinusMinus) && NumParams == 2) {
+    ParmVarDecl *LastParam = FnDecl->getParamDecl(FnDecl->getNumParams() - 1);
+    QualType ParamType = LastParam->getType();
+
+    if (!ParamType->isSpecificBuiltinType(BuiltinType::Int) &&
+        !ParamType->isDependentType())
+      return Diag(LastParam->getLocation(),
+                  diag::err_operator_overload_post_incdec_must_be_int)
+        << LastParam->getType() << (Op == OO_MinusMinus);
+  }
+
+  return false;
+}
+
+static bool
+checkLiteralOperatorTemplateParameterList(Sema &SemaRef,
+                                          FunctionTemplateDecl *TpDecl) {
+  TemplateParameterList *TemplateParams = TpDecl->getTemplateParameters();
+
+  // Must have one or two template parameters.
+  if (TemplateParams->size() == 1) {
+    NonTypeTemplateParmDecl *PmDecl =
+        dyn_cast<NonTypeTemplateParmDecl>(TemplateParams->getParam(0));
+
+    // The template parameter must be a char parameter pack.
+    if (PmDecl && PmDecl->isTemplateParameterPack() &&
+        SemaRef.Context.hasSameType(PmDecl->getType(), SemaRef.Context.CharTy))
+      return false;
+
+    // C++20 [over.literal]p5:
+    //   A string literal operator template is a literal operator template
+    //   whose template-parameter-list comprises a single non-type
+    //   template-parameter of class type.
+    //
+    // As a DR resolution, we also allow placeholders for deduced class
+    // template specializations.
+    if (SemaRef.getLangOpts().CPlusPlus20 && PmDecl &&
+        !PmDecl->isTemplateParameterPack() &&
+        (PmDecl->getType()->isRecordType() ||
+         PmDecl->getType()->getAs<DeducedTemplateSpecializationType>()))
+      return false;
+  } else if (TemplateParams->size() == 2) {
+    TemplateTypeParmDecl *PmType =
+        dyn_cast<TemplateTypeParmDecl>(TemplateParams->getParam(0));
+    NonTypeTemplateParmDecl *PmArgs =
+        dyn_cast<NonTypeTemplateParmDecl>(TemplateParams->getParam(1));
+
+    // The second template parameter must be a parameter pack with the
+    // first template parameter as its type.
+    if (PmType && PmArgs && !PmType->isTemplateParameterPack() &&
+        PmArgs->isTemplateParameterPack()) {
+      const TemplateTypeParmType *TArgs =
+          PmArgs->getType()->getAs<TemplateTypeParmType>();
+      if (TArgs && TArgs->getDepth() == PmType->getDepth() &&
+          TArgs->getIndex() == PmType->getIndex()) {
+        if (!SemaRef.inTemplateInstantiation())
+          SemaRef.Diag(TpDecl->getLocation(),
+                       diag::ext_string_literal_operator_template);
+        return false;
+      }
+    }
+  }
+
+  SemaRef.Diag(TpDecl->getTemplateParameters()->getSourceRange().getBegin(),
+               diag::err_literal_operator_template)
+      << TpDecl->getTemplateParameters()->getSourceRange();
+  return true;
+}
+
+/// CheckLiteralOperatorDeclaration - Check whether the declaration
+/// of this literal operator function is well-formed. If so, returns
+/// false; otherwise, emits appropriate diagnostics and returns true.
+bool Sema::CheckLiteralOperatorDeclaration(FunctionDecl *FnDecl) {
+  if (isa<CXXMethodDecl>(FnDecl)) {
+    Diag(FnDecl->getLocation(), diag::err_literal_operator_outside_namespace)
+      << FnDecl->getDeclName();
+    return true;
+  }
+
+  if (FnDecl->isExternC()) {
+    Diag(FnDecl->getLocation(), diag::err_literal_operator_extern_c);
+    if (const LinkageSpecDecl *LSD =
+            FnDecl->getDeclContext()->getExternCContext())
+      Diag(LSD->getExternLoc(), diag::note_extern_c_begins_here);
+    return true;
+  }
+
+  // This might be the definition of a literal operator template.
+  FunctionTemplateDecl *TpDecl = FnDecl->getDescribedFunctionTemplate();
+
+  // This might be a specialization of a literal operator template.
+  if (!TpDecl)
+    TpDecl = FnDecl->getPrimaryTemplate();
+
+  // template <char...> type operator "" name() and
+  // template <class T, T...> type operator "" name() are the only valid
+  // template signatures, and the only valid signatures with no parameters.
+  //
+  // C++20 also allows template <SomeClass T> type operator "" name().
+  if (TpDecl) {
+    if (FnDecl->param_size() != 0) {
+      Diag(FnDecl->getLocation(),
+           diag::err_literal_operator_template_with_params);
+      return true;
+    }
+
+    if (checkLiteralOperatorTemplateParameterList(*this, TpDecl))
+      return true;
+
+  } else if (FnDecl->param_size() == 1) {
+    const ParmVarDecl *Param = FnDecl->getParamDecl(0);
+
+    QualType ParamType = Param->getType().getUnqualifiedType();
+
+    // Only unsigned long long int, long double, any character type, and const
+    // char * are allowed as the only parameters.
+    if (ParamType->isSpecificBuiltinType(BuiltinType::ULongLong) ||
+        ParamType->isSpecificBuiltinType(BuiltinType::LongDouble) ||
+        Context.hasSameType(ParamType, Context.CharTy) ||
+        Context.hasSameType(ParamType, Context.WideCharTy) ||
+        Context.hasSameType(ParamType, Context.Char8Ty) ||
+        Context.hasSameType(ParamType, Context.Char16Ty) ||
+        Context.hasSameType(ParamType, Context.Char32Ty)) {
+    } else if (const PointerType *Ptr = ParamType->getAs<PointerType>()) {
+      QualType InnerType = Ptr->getPointeeType();
+
+      // Pointer parameter must be a const char *.
+      if (!(Context.hasSameType(InnerType.getUnqualifiedType(),
+                                Context.CharTy) &&
+            InnerType.isConstQualified() && !InnerType.isVolatileQualified())) {
+        Diag(Param->getSourceRange().getBegin(),
+             diag::err_literal_operator_param)
+            << ParamType << "'const char *'" << Param->getSourceRange();
+        return true;
+      }
+
+    } else if (ParamType->isRealFloatingType()) {
+      Diag(Param->getSourceRange().getBegin(), diag::err_literal_operator_param)
+          << ParamType << Context.LongDoubleTy << Param->getSourceRange();
+      return true;
+
+    } else if (ParamType->isIntegerType()) {
+      Diag(Param->getSourceRange().getBegin(), diag::err_literal_operator_param)
+          << ParamType << Context.UnsignedLongLongTy << Param->getSourceRange();
+      return true;
+
+    } else {
+      Diag(Param->getSourceRange().getBegin(),
+           diag::err_literal_operator_invalid_param)
+          << ParamType << Param->getSourceRange();
+      return true;
+    }
+
+  } else if (FnDecl->param_size() == 2) {
+    FunctionDecl::param_iterator Param = FnDecl->param_begin();
+
+    // First, verify that the first parameter is correct.
+
+    QualType FirstParamType = (*Param)->getType().getUnqualifiedType();
+
+    // Two parameter function must have a pointer to const as a
+    // first parameter; let's strip those qualifiers.
+    const PointerType *PT = FirstParamType->getAs<PointerType>();
+
+    if (!PT) {
+      Diag((*Param)->getSourceRange().getBegin(),
+           diag::err_literal_operator_param)
+          << FirstParamType << "'const char *'" << (*Param)->getSourceRange();
+      return true;
+    }
+
+    QualType PointeeType = PT->getPointeeType();
+    // First parameter must be const
+    if (!PointeeType.isConstQualified() || PointeeType.isVolatileQualified()) {
+      Diag((*Param)->getSourceRange().getBegin(),
+           diag::err_literal_operator_param)
+          << FirstParamType << "'const char *'" << (*Param)->getSourceRange();
+      return true;
+    }
+
+    QualType InnerType = PointeeType.getUnqualifiedType();
+    // Only const char *, const wchar_t*, const char8_t*, const char16_t*, and
+    // const char32_t* are allowed as the first parameter to a two-parameter
+    // function
+    if (!(Context.hasSameType(InnerType, Context.CharTy) ||
+          Context.hasSameType(InnerType, Context.WideCharTy) ||
+          Context.hasSameType(InnerType, Context.Char8Ty) ||
+          Context.hasSameType(InnerType, Context.Char16Ty) ||
+          Context.hasSameType(InnerType, Context.Char32Ty))) {
+      Diag((*Param)->getSourceRange().getBegin(),
+           diag::err_literal_operator_param)
+          << FirstParamType << "'const char *'" << (*Param)->getSourceRange();
+      return true;
+    }
+
+    // Move on to the second and final parameter.
+    ++Param;
+
+    // The second parameter must be a std::size_t.
+    QualType SecondParamType = (*Param)->getType().getUnqualifiedType();
+    if (!Context.hasSameType(SecondParamType, Context.getSizeType())) {
+      Diag((*Param)->getSourceRange().getBegin(),
+           diag::err_literal_operator_param)
+          << SecondParamType << Context.getSizeType()
+          << (*Param)->getSourceRange();
+      return true;
+    }
+  } else {
+    Diag(FnDecl->getLocation(), diag::err_literal_operator_bad_param_count);
+    return true;
+  }
+
+  // Parameters are good.
+
+  // A parameter-declaration-clause containing a default argument is not
+  // equivalent to any of the permitted forms.
+  for (auto Param : FnDecl->parameters()) {
+    if (Param->hasDefaultArg()) {
+      Diag(Param->getDefaultArgRange().getBegin(),
+           diag::err_literal_operator_default_argument)
+        << Param->getDefaultArgRange();
+      break;
+    }
+  }
+
+  StringRef LiteralName
+    = FnDecl->getDeclName().getCXXLiteralIdentifier()->getName();
+  if (LiteralName[0] != '_' &&
+      !getSourceManager().isInSystemHeader(FnDecl->getLocation())) {
+    // C++11 [usrlit.suffix]p1:
+    //   Literal suffix identifiers that do not start with an underscore
+    //   are reserved for future standardization.
+    Diag(FnDecl->getLocation(), diag::warn_user_literal_reserved)
+      << StringLiteralParser::isValidUDSuffix(getLangOpts(), LiteralName);
+  }
+
+  return false;
+}
+
+/// ActOnStartLinkageSpecification - Parsed the beginning of a C++
+/// linkage specification, including the language and (if present)
+/// the '{'. ExternLoc is the location of the 'extern', Lang is the
+/// language string literal. LBraceLoc, if valid, provides the location of
+/// the '{' brace. Otherwise, this linkage specification does not
+/// have any braces.
+Decl *Sema::ActOnStartLinkageSpecification(Scope *S, SourceLocation ExternLoc,
+                                           Expr *LangStr,
+                                           SourceLocation LBraceLoc) {
+  StringLiteral *Lit = cast<StringLiteral>(LangStr);
+  if (!Lit->isAscii()) {
+    Diag(LangStr->getExprLoc(), diag::err_language_linkage_spec_not_ascii)
+      << LangStr->getSourceRange();
+    return nullptr;
+  }
+
+  StringRef Lang = Lit->getString();
+  LinkageSpecDecl::LanguageIDs Language;
+  if (Lang == "C")
+    Language = LinkageSpecDecl::lang_c;
+  else if (Lang == "C++")
+    Language = LinkageSpecDecl::lang_cxx;
+  else {
+    Diag(LangStr->getExprLoc(), diag::err_language_linkage_spec_unknown)
+      << LangStr->getSourceRange();
+    return nullptr;
+  }
+
+  // FIXME: Add all the various semantics of linkage specifications
+
+  LinkageSpecDecl *D = LinkageSpecDecl::Create(Context, CurContext, ExternLoc,
+                                               LangStr->getExprLoc(), Language,
+                                               LBraceLoc.isValid());
+
+  /// C++ [module.unit]p7.2.3
+  /// - Otherwise, if the declaration
+  ///   - ...
+  ///   - ...
+  ///   - appears within a linkage-specification,
+  ///   it is attached to the global module.
+  ///
+  /// If the declaration is already in global module fragment, we don't
+  /// need to attach it again.
+  if (getLangOpts().CPlusPlusModules && isCurrentModulePurview()) {
+    Module *GlobalModule =
+        PushGlobalModuleFragment(ExternLoc, /*IsImplicit=*/true);
+    D->setModuleOwnershipKind(Decl::ModuleOwnershipKind::ModulePrivate);
+    D->setLocalOwningModule(GlobalModule);
+  }
+
+  CurContext->addDecl(D);
+  PushDeclContext(S, D);
+  return D;
+}
+
+/// ActOnFinishLinkageSpecification - Complete the definition of
+/// the C++ linkage specification LinkageSpec. If RBraceLoc is
+/// valid, it's the position of the closing '}' brace in a linkage
+/// specification that uses braces.
+Decl *Sema::ActOnFinishLinkageSpecification(Scope *S,
+                                            Decl *LinkageSpec,
+                                            SourceLocation RBraceLoc) {
+  if (RBraceLoc.isValid()) {
+    LinkageSpecDecl* LSDecl = cast<LinkageSpecDecl>(LinkageSpec);
+    LSDecl->setRBraceLoc(RBraceLoc);
+  }
+
+  // If the current module doesn't has Parent, it implies that the
+  // LinkageSpec isn't in the module created by itself. So we don't
+  // need to pop it.
+  if (getLangOpts().CPlusPlusModules && getCurrentModule() &&
+      getCurrentModule()->isGlobalModule() && getCurrentModule()->Parent)
+    PopGlobalModuleFragment();
+
+  PopDeclContext();
+  return LinkageSpec;
+}
+
+Decl *Sema::ActOnEmptyDeclaration(Scope *S,
+                                  const ParsedAttributesView &AttrList,
+                                  SourceLocation SemiLoc) {
+  Decl *ED = EmptyDecl::Create(Context, CurContext, SemiLoc);
+  // Attribute declarations appertain to empty declaration so we handle
+  // them here.
+  ProcessDeclAttributeList(S, ED, AttrList);
+
+  CurContext->addDecl(ED);
+  return ED;
+}
+
+/// Perform semantic analysis for the variable declaration that
+/// occurs within a C++ catch clause, returning the newly-created
+/// variable.
+VarDecl *Sema::BuildExceptionDeclaration(Scope *S,
+                                         TypeSourceInfo *TInfo,
+                                         SourceLocation StartLoc,
+                                         SourceLocation Loc,
+                                         IdentifierInfo *Name) {
+  bool Invalid = false;
+  QualType ExDeclType = TInfo->getType();
+
+  // Arrays and functions decay.
+  if (ExDeclType->isArrayType())
+    ExDeclType = Context.getArrayDecayedType(ExDeclType);
+  else if (ExDeclType->isFunctionType())
+    ExDeclType = Context.getPointerType(ExDeclType);
+
+  // C++ 15.3p1: The exception-declaration shall not denote an incomplete type.
+  // The exception-declaration shall not denote a pointer or reference to an
+  // incomplete type, other than [cv] void*.
+  // N2844 forbids rvalue references.
+  if (!ExDeclType->isDependentType() && ExDeclType->isRValueReferenceType()) {
+    Diag(Loc, diag::err_catch_rvalue_ref);
+    Invalid = true;
+  }
+
+  if (ExDeclType->isVariablyModifiedType()) {
+    Diag(Loc, diag::err_catch_variably_modified) << ExDeclType;
+    Invalid = true;
+  }
+
+  QualType BaseType = ExDeclType;
+  int Mode = 0; // 0 for direct type, 1 for pointer, 2 for reference
+  unsigned DK = diag::err_catch_incomplete;
+  if (const PointerType *Ptr = BaseType->getAs<PointerType>()) {
+    BaseType = Ptr->getPointeeType();
+    Mode = 1;
+    DK = diag::err_catch_incomplete_ptr;
+  } else if (const ReferenceType *Ref = BaseType->getAs<ReferenceType>()) {
+    // For the purpose of error recovery, we treat rvalue refs like lvalue refs.
+    BaseType = Ref->getPointeeType();
+    Mode = 2;
+    DK = diag::err_catch_incomplete_ref;
+  }
+  if (!Invalid && (Mode == 0 || !BaseType->isVoidType()) &&
+      !BaseType->isDependentType() && RequireCompleteType(Loc, BaseType, DK))
+    Invalid = true;
+
+  if (!Invalid && Mode != 1 && BaseType->isSizelessType()) {
+    Diag(Loc, diag::err_catch_sizeless) << (Mode == 2 ? 1 : 0) << BaseType;
+    Invalid = true;
+  }
+
+  if (!Invalid && !ExDeclType->isDependentType() &&
+      RequireNonAbstractType(Loc, ExDeclType,
+                             diag::err_abstract_type_in_decl,
+                             AbstractVariableType))
+    Invalid = true;
+
+  // Only the non-fragile NeXT runtime currently supports C++ catches
+  // of ObjC types, and no runtime supports catching ObjC types by value.
+  if (!Invalid && getLangOpts().ObjC) {
+    QualType T = ExDeclType;
+    if (const ReferenceType *RT = T->getAs<ReferenceType>())
+      T = RT->getPointeeType();
+
+    if (T->isObjCObjectType()) {
+      Diag(Loc, diag::err_objc_object_catch);
+      Invalid = true;
+    } else if (T->isObjCObjectPointerType()) {
+      // FIXME: should this be a test for macosx-fragile specifically?
+      if (getLangOpts().ObjCRuntime.isFragile())
+        Diag(Loc, diag::warn_objc_pointer_cxx_catch_fragile);
+    }
+  }
+
+  VarDecl *ExDecl = VarDecl::Create(Context, CurContext, StartLoc, Loc, Name,
+                                    ExDeclType, TInfo, SC_None);
+  ExDecl->setExceptionVariable(true);
+
+  // In ARC, infer 'retaining' for variables of retainable type.
+  if (getLangOpts().ObjCAutoRefCount && inferObjCARCLifetime(ExDecl))
+    Invalid = true;
+
+  if (!Invalid && !ExDeclType->isDependentType()) {
+    if (const RecordType *recordType = ExDeclType->getAs<RecordType>()) {
+      // Insulate this from anything else we might currently be parsing.
+      EnterExpressionEvaluationContext scope(
+          *this, ExpressionEvaluationContext::PotentiallyEvaluated);
+
+      // C++ [except.handle]p16:
+      //   The object declared in an exception-declaration or, if the
+      //   exception-declaration does not specify a name, a temporary (12.2) is
+      //   copy-initialized (8.5) from the exception object. [...]
+      //   The object is destroyed when the handler exits, after the destruction
+      //   of any automatic objects initialized within the handler.
+      //
+      // We just pretend to initialize the object with itself, then make sure
+      // it can be destroyed later.
+      QualType initType = Context.getExceptionObjectType(ExDeclType);
+
+      InitializedEntity entity =
+        InitializedEntity::InitializeVariable(ExDecl);
+      InitializationKind initKind =
+        InitializationKind::CreateCopy(Loc, SourceLocation());
+
+      Expr *opaqueValue =
+        new (Context) OpaqueValueExpr(Loc, initType, VK_LValue, OK_Ordinary);
+      InitializationSequence sequence(*this, entity, initKind, opaqueValue);
+      ExprResult result = sequence.Perform(*this, entity, initKind, opaqueValue);
+      if (result.isInvalid())
+        Invalid = true;
+      else {
+        // If the constructor used was non-trivial, set this as the
+        // "initializer".
+        CXXConstructExpr *construct = result.getAs<CXXConstructExpr>();
+        if (!construct->getConstructor()->isTrivial()) {
+          Expr *init = MaybeCreateExprWithCleanups(construct);
+          ExDecl->setInit(init);
+        }
+
+        // And make sure it's destructable.
+        FinalizeVarWithDestructor(ExDecl, recordType);
+      }
+    }
+  }
+
+  if (Invalid)
+    ExDecl->setInvalidDecl();
+
+  return ExDecl;
+}
+
+/// ActOnExceptionDeclarator - Parsed the exception-declarator in a C++ catch
+/// handler.
+Decl *Sema::ActOnExceptionDeclarator(Scope *S, Declarator &D) {
+  TypeSourceInfo *TInfo = GetTypeForDeclarator(D, S);
+  bool Invalid = D.isInvalidType();
+
+  // Check for unexpanded parameter packs.
+  if (DiagnoseUnexpandedParameterPack(D.getIdentifierLoc(), TInfo,
+                                      UPPC_ExceptionType)) {
+    TInfo = Context.getTrivialTypeSourceInfo(Context.IntTy,
+                                             D.getIdentifierLoc());
+    Invalid = true;
+  }
+
+  IdentifierInfo *II = D.getIdentifier();
+  if (NamedDecl *PrevDecl = LookupSingleName(S, II, D.getIdentifierLoc(),
+                                             LookupOrdinaryName,
+                                             ForVisibleRedeclaration)) {
+    // The scope should be freshly made just for us. There is just no way
+    // it contains any previous declaration, except for function parameters in
+    // a function-try-block's catch statement.
+    assert(!S->isDeclScope(PrevDecl));
+    if (isDeclInScope(PrevDecl, CurContext, S)) {
+      Diag(D.getIdentifierLoc(), diag::err_redefinition)
+        << D.getIdentifier();
+      Diag(PrevDecl->getLocation(), diag::note_previous_definition);
+      Invalid = true;
+    } else if (PrevDecl->isTemplateParameter())
+      // Maybe we will complain about the shadowed template parameter.
+      DiagnoseTemplateParameterShadow(D.getIdentifierLoc(), PrevDecl);
+  }
+
+  if (D.getCXXScopeSpec().isSet() && !Invalid) {
+    Diag(D.getIdentifierLoc(), diag::err_qualified_catch_declarator)
+      << D.getCXXScopeSpec().getRange();
+    Invalid = true;
+  }
+
+  VarDecl *ExDecl = BuildExceptionDeclaration(
+      S, TInfo, D.getBeginLoc(), D.getIdentifierLoc(), D.getIdentifier());
+  if (Invalid)
+    ExDecl->setInvalidDecl();
+
+  // Add the exception declaration into this scope.
+  if (II)
+    PushOnScopeChains(ExDecl, S);
+  else
+    CurContext->addDecl(ExDecl);
+
+  ProcessDeclAttributes(S, ExDecl, D);
+  return ExDecl;
+}
+
+Decl *Sema::ActOnStaticAssertDeclaration(SourceLocation StaticAssertLoc,
+                                         Expr *AssertExpr,
+                                         Expr *AssertMessageExpr,
+                                         SourceLocation RParenLoc) {
+  StringLiteral *AssertMessage =
+      AssertMessageExpr ? cast<StringLiteral>(AssertMessageExpr) : nullptr;
+
+  if (DiagnoseUnexpandedParameterPack(AssertExpr, UPPC_StaticAssertExpression))
+    return nullptr;
+
+  return BuildStaticAssertDeclaration(StaticAssertLoc, AssertExpr,
+                                      AssertMessage, RParenLoc, false);
+}
+
+Decl *Sema::BuildStaticAssertDeclaration(SourceLocation StaticAssertLoc,
+                                         Expr *AssertExpr,
+                                         StringLiteral *AssertMessage,
+                                         SourceLocation RParenLoc,
+                                         bool Failed) {
+  assert(AssertExpr != nullptr && "Expected non-null condition");
+  if (!AssertExpr->isTypeDependent() && !AssertExpr->isValueDependent() &&
+      !Failed) {
+    // In a static_assert-declaration, the constant-expression shall be a
+    // constant expression that can be contextually converted to bool.
+    ExprResult Converted = PerformContextuallyConvertToBool(AssertExpr);
+    if (Converted.isInvalid())
+      Failed = true;
+
+    ExprResult FullAssertExpr =
+        ActOnFinishFullExpr(Converted.get(), StaticAssertLoc,
+                            /*DiscardedValue*/ false,
+                            /*IsConstexpr*/ true);
+    if (FullAssertExpr.isInvalid())
+      Failed = true;
+    else
+      AssertExpr = FullAssertExpr.get();
+
+    llvm::APSInt Cond;
+    if (!Failed && VerifyIntegerConstantExpression(
+                       AssertExpr, &Cond,
+                       diag::err_static_assert_expression_is_not_constant)
+                       .isInvalid())
+      Failed = true;
+
+    if (!Failed && !Cond) {
+      SmallString<256> MsgBuffer;
+      llvm::raw_svector_ostream Msg(MsgBuffer);
+      if (AssertMessage)
+        AssertMessage->printPretty(Msg, nullptr, getPrintingPolicy());
+
+      Expr *InnerCond = nullptr;
+      std::string InnerCondDescription;
+      std::tie(InnerCond, InnerCondDescription) =
+        findFailedBooleanCondition(Converted.get());
+      if (InnerCond && isa<ConceptSpecializationExpr>(InnerCond)) {
+        // Drill down into concept specialization expressions to see why they
+        // weren't satisfied.
+        Diag(StaticAssertLoc, diag::err_static_assert_failed)
+          << !AssertMessage << Msg.str() << AssertExpr->getSourceRange();
+        ConstraintSatisfaction Satisfaction;
+        if (!CheckConstraintSatisfaction(InnerCond, Satisfaction))
+          DiagnoseUnsatisfiedConstraint(Satisfaction);
+      } else if (InnerCond && !isa<CXXBoolLiteralExpr>(InnerCond)
+                           && !isa<IntegerLiteral>(InnerCond)) {
+        Diag(StaticAssertLoc, diag::err_static_assert_requirement_failed)
+          << InnerCondDescription << !AssertMessage
+          << Msg.str() << InnerCond->getSourceRange();
+      } else {
+        Diag(StaticAssertLoc, diag::err_static_assert_failed)
+          << !AssertMessage << Msg.str() << AssertExpr->getSourceRange();
+      }
+      Failed = true;
+    }
+  } else {
+    ExprResult FullAssertExpr = ActOnFinishFullExpr(AssertExpr, StaticAssertLoc,
+                                                    /*DiscardedValue*/false,
+                                                    /*IsConstexpr*/true);
+    if (FullAssertExpr.isInvalid())
+      Failed = true;
+    else
+      AssertExpr = FullAssertExpr.get();
+  }
+
+  Decl *Decl = StaticAssertDecl::Create(Context, CurContext, StaticAssertLoc,
+                                        AssertExpr, AssertMessage, RParenLoc,
+                                        Failed);
+
+  CurContext->addDecl(Decl);
+  return Decl;
+}
+
+/// Perform semantic analysis of the given friend type declaration.
+///
+/// \returns A friend declaration that.
+FriendDecl *Sema::CheckFriendTypeDecl(SourceLocation LocStart,
+                                      SourceLocation FriendLoc,
+                                      TypeSourceInfo *TSInfo) {
+  assert(TSInfo && "NULL TypeSourceInfo for friend type declaration");
+
+  QualType T = TSInfo->getType();
+  SourceRange TypeRange = TSInfo->getTypeLoc().getLocalSourceRange();
+
+  // C++03 [class.friend]p2:
+  //   An elaborated-type-specifier shall be used in a friend declaration
+  //   for a class.*
+  //
+  //   * The class-key of the elaborated-type-specifier is required.
+  if (!CodeSynthesisContexts.empty()) {
+    // Do not complain about the form of friend template types during any kind
+    // of code synthesis. For template instantiation, we will have complained
+    // when the template was defined.
+  } else {
+    if (!T->isElaboratedTypeSpecifier()) {
+      // If we evaluated the type to a record type, suggest putting
+      // a tag in front.
+      if (const RecordType *RT = T->getAs<RecordType>()) {
+        RecordDecl *RD = RT->getDecl();
+
+        SmallString<16> InsertionText(" ");
+        InsertionText += RD->getKindName();
+
+        Diag(TypeRange.getBegin(),
+             getLangOpts().CPlusPlus11 ?
+               diag::warn_cxx98_compat_unelaborated_friend_type :
+               diag::ext_unelaborated_friend_type)
+          << (unsigned) RD->getTagKind()
+          << T
+          << FixItHint::CreateInsertion(getLocForEndOfToken(FriendLoc),
+                                        InsertionText);
+      } else {
+        Diag(FriendLoc,
+             getLangOpts().CPlusPlus11 ?
+               diag::warn_cxx98_compat_nonclass_type_friend :
+               diag::ext_nonclass_type_friend)
+          << T
+          << TypeRange;
+      }
+    } else if (T->getAs<EnumType>()) {
+      Diag(FriendLoc,
+           getLangOpts().CPlusPlus11 ?
+             diag::warn_cxx98_compat_enum_friend :
+             diag::ext_enum_friend)
+        << T
+        << TypeRange;
+    }
+
+    // C++11 [class.friend]p3:
+    //   A friend declaration that does not declare a function shall have one
+    //   of the following forms:
+    //     friend elaborated-type-specifier ;
+    //     friend simple-type-specifier ;
+    //     friend typename-specifier ;
+    if (getLangOpts().CPlusPlus11 && LocStart != FriendLoc)
+      Diag(FriendLoc, diag::err_friend_not_first_in_declaration) << T;
+  }
+
+  //   If the type specifier in a friend declaration designates a (possibly
+  //   cv-qualified) class type, that class is declared as a friend; otherwise,
+  //   the friend declaration is ignored.
+  return FriendDecl::Create(Context, CurContext,
+                            TSInfo->getTypeLoc().getBeginLoc(), TSInfo,
+                            FriendLoc);
+}
+
+/// Handle a friend tag declaration where the scope specifier was
+/// templated.
+Decl *Sema::ActOnTemplatedFriendTag(Scope *S, SourceLocation FriendLoc,
+                                    unsigned TagSpec, SourceLocation TagLoc,
+                                    CXXScopeSpec &SS, IdentifierInfo *Name,
+                                    SourceLocation NameLoc,
+                                    const ParsedAttributesView &Attr,
+                                    MultiTemplateParamsArg TempParamLists) {
+  TagTypeKind Kind = TypeWithKeyword::getTagTypeKindForTypeSpec(TagSpec);
+
+  bool IsMemberSpecialization = false;
+  bool Invalid = false;
+
+  if (TemplateParameterList *TemplateParams =
+          MatchTemplateParametersToScopeSpecifier(
+              TagLoc, NameLoc, SS, nullptr, TempParamLists, /*friend*/ true,
+              IsMemberSpecialization, Invalid)) {
+    if (TemplateParams->size() > 0) {
+      // This is a declaration of a class template.
+      if (Invalid)
+        return nullptr;
+
+      return CheckClassTemplate(S, TagSpec, TUK_Friend, TagLoc, SS, Name,
+                                NameLoc, Attr, TemplateParams, AS_public,
+                                /*ModulePrivateLoc=*/SourceLocation(),
+                                FriendLoc, TempParamLists.size() - 1,
+                                TempParamLists.data()).get();
+    } else {
+      // The "template<>" header is extraneous.
+      Diag(TemplateParams->getTemplateLoc(), diag::err_template_tag_noparams)
+        << TypeWithKeyword::getTagTypeKindName(Kind) << Name;
+      IsMemberSpecialization = true;
+    }
+  }
+
+  if (Invalid) return nullptr;
+
+  bool isAllExplicitSpecializations = true;
+  for (unsigned I = TempParamLists.size(); I-- > 0; ) {
+    if (TempParamLists[I]->size()) {
+      isAllExplicitSpecializations = false;
+      break;
+    }
+  }
+
+  // FIXME: don't ignore attributes.
+
+  // If it's explicit specializations all the way down, just forget
+  // about the template header and build an appropriate non-templated
+  // friend.  TODO: for source fidelity, remember the headers.
+  if (isAllExplicitSpecializations) {
+    if (SS.isEmpty()) {
+      bool Owned = false;
+      bool IsDependent = false;
+      return ActOnTag(S, TagSpec, TUK_Friend, TagLoc, SS, Name, NameLoc,
+                      Attr, AS_public,
+                      /*ModulePrivateLoc=*/SourceLocation(),
+                      MultiTemplateParamsArg(), Owned, IsDependent,
+                      /*ScopedEnumKWLoc=*/SourceLocation(),
+                      /*ScopedEnumUsesClassTag=*/false,
+                      /*UnderlyingType=*/TypeResult(),
+                      /*IsTypeSpecifier=*/false,
+                      /*IsTemplateParamOrArg=*/false);
+    }
+
+    NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
+    ElaboratedTypeKeyword Keyword
+      = TypeWithKeyword::getKeywordForTagTypeKind(Kind);
+    QualType T = CheckTypenameType(Keyword, TagLoc, QualifierLoc,
+                                   *Name, NameLoc);
+    if (T.isNull())
+      return nullptr;
+
+    TypeSourceInfo *TSI = Context.CreateTypeSourceInfo(T);
+    if (isa<DependentNameType>(T)) {
+      DependentNameTypeLoc TL =
+          TSI->getTypeLoc().castAs<DependentNameTypeLoc>();
+      TL.setElaboratedKeywordLoc(TagLoc);
+      TL.setQualifierLoc(QualifierLoc);
+      TL.setNameLoc(NameLoc);
+    } else {
+      ElaboratedTypeLoc TL = TSI->getTypeLoc().castAs<ElaboratedTypeLoc>();
+      TL.setElaboratedKeywordLoc(TagLoc);
+      TL.setQualifierLoc(QualifierLoc);
+      TL.getNamedTypeLoc().castAs<TypeSpecTypeLoc>().setNameLoc(NameLoc);
+    }
+
+    FriendDecl *Friend = FriendDecl::Create(Context, CurContext, NameLoc,
+                                            TSI, FriendLoc, TempParamLists);
+    Friend->setAccess(AS_public);
+    CurContext->addDecl(Friend);
+    return Friend;
+  }
+
+  assert(SS.isNotEmpty() && "valid templated tag with no SS and no direct?");
+
+
+
+  // Handle the case of a templated-scope friend class.  e.g.
+  //   template <class T> class A<T>::B;
+  // FIXME: we don't support these right now.
+  Diag(NameLoc, diag::warn_template_qualified_friend_unsupported)
+    << SS.getScopeRep() << SS.getRange() << cast<CXXRecordDecl>(CurContext);
+  ElaboratedTypeKeyword ETK = TypeWithKeyword::getKeywordForTagTypeKind(Kind);
+  QualType T = Context.getDependentNameType(ETK, SS.getScopeRep(), Name);
+  TypeSourceInfo *TSI = Context.CreateTypeSourceInfo(T);
+  DependentNameTypeLoc TL = TSI->getTypeLoc().castAs<DependentNameTypeLoc>();
+  TL.setElaboratedKeywordLoc(TagLoc);
+  TL.setQualifierLoc(SS.getWithLocInContext(Context));
+  TL.setNameLoc(NameLoc);
+
+  FriendDecl *Friend = FriendDecl::Create(Context, CurContext, NameLoc,
+                                          TSI, FriendLoc, TempParamLists);
+  Friend->setAccess(AS_public);
+  Friend->setUnsupportedFriend(true);
+  CurContext->addDecl(Friend);
+  return Friend;
+}
+
+/// Handle a friend type declaration.  This works in tandem with
+/// ActOnTag.
+///
+/// Notes on friend class templates:
+///
+/// We generally treat friend class declarations as if they were
+/// declaring a class.  So, for example, the elaborated type specifier
+/// in a friend declaration is required to obey the restrictions of a
+/// class-head (i.e. no typedefs in the scope chain), template
+/// parameters are required to match up with simple template-ids, &c.
+/// However, unlike when declaring a template specialization, it's
+/// okay to refer to a template specialization without an empty
+/// template parameter declaration, e.g.
+///   friend class A<T>::B<unsigned>;
+/// We permit this as a special case; if there are any template
+/// parameters present at all, require proper matching, i.e.
+///   template <> template \<class T> friend class A<int>::B;
+Decl *Sema::ActOnFriendTypeDecl(Scope *S, const DeclSpec &DS,
+                                MultiTemplateParamsArg TempParams) {
+  SourceLocation Loc = DS.getBeginLoc();
+
+  assert(DS.isFriendSpecified());
+  assert(DS.getStorageClassSpec() == DeclSpec::SCS_unspecified);
+
+  // C++ [class.friend]p3:
+  // A friend declaration that does not declare a function shall have one of
+  // the following forms:
+  //     friend elaborated-type-specifier ;
+  //     friend simple-type-specifier ;
+  //     friend typename-specifier ;
+  //
+  // Any declaration with a type qualifier does not have that form. (It's
+  // legal to specify a qualified type as a friend, you just can't write the
+  // keywords.)
+  if (DS.getTypeQualifiers()) {
+    if (DS.getTypeQualifiers() & DeclSpec::TQ_const)
+      Diag(DS.getConstSpecLoc(), diag::err_friend_decl_spec) << "const";
+    if (DS.getTypeQualifiers() & DeclSpec::TQ_volatile)
+      Diag(DS.getVolatileSpecLoc(), diag::err_friend_decl_spec) << "volatile";
+    if (DS.getTypeQualifiers() & DeclSpec::TQ_restrict)
+      Diag(DS.getRestrictSpecLoc(), diag::err_friend_decl_spec) << "restrict";
+    if (DS.getTypeQualifiers() & DeclSpec::TQ_atomic)
+      Diag(DS.getAtomicSpecLoc(), diag::err_friend_decl_spec) << "_Atomic";
+    if (DS.getTypeQualifiers() & DeclSpec::TQ_unaligned)
+      Diag(DS.getUnalignedSpecLoc(), diag::err_friend_decl_spec) << "__unaligned";
+  }
+
+  // Try to convert the decl specifier to a type.  This works for
+  // friend templates because ActOnTag never produces a ClassTemplateDecl
+  // for a TUK_Friend.
+  Declarator TheDeclarator(DS, DeclaratorContext::Member);
+  TypeSourceInfo *TSI = GetTypeForDeclarator(TheDeclarator, S);
+  QualType T = TSI->getType();
+  if (TheDeclarator.isInvalidType())
+    return nullptr;
+
+  if (DiagnoseUnexpandedParameterPack(Loc, TSI, UPPC_FriendDeclaration))
+    return nullptr;
+
+  // This is definitely an error in C++98.  It's probably meant to
+  // be forbidden in C++0x, too, but the specification is just
+  // poorly written.
+  //
+  // The problem is with declarations like the following:
+  //   template <T> friend A<T>::foo;
+  // where deciding whether a class C is a friend or not now hinges
+  // on whether there exists an instantiation of A that causes
+  // 'foo' to equal C.  There are restrictions on class-heads
+  // (which we declare (by fiat) elaborated friend declarations to
+  // be) that makes this tractable.
+  //
+  // FIXME: handle "template <> friend class A<T>;", which
+  // is possibly well-formed?  Who even knows?
+  if (TempParams.size() && !T->isElaboratedTypeSpecifier()) {
+    Diag(Loc, diag::err_tagless_friend_type_template)
+      << DS.getSourceRange();
+    return nullptr;
+  }
+
+  // C++98 [class.friend]p1: A friend of a class is a function
+  //   or class that is not a member of the class . . .
+  // This is fixed in DR77, which just barely didn't make the C++03
+  // deadline.  It's also a very silly restriction that seriously
+  // affects inner classes and which nobody else seems to implement;
+  // thus we never diagnose it, not even in -pedantic.
+  //
+  // But note that we could warn about it: it's always useless to
+  // friend one of your own members (it's not, however, worthless to
+  // friend a member of an arbitrary specialization of your template).
+
+  Decl *D;
+  if (!TempParams.empty())
+    D = FriendTemplateDecl::Create(Context, CurContext, Loc,
+                                   TempParams,
+                                   TSI,
+                                   DS.getFriendSpecLoc());
+  else
+    D = CheckFriendTypeDecl(Loc, DS.getFriendSpecLoc(), TSI);
+
+  if (!D)
+    return nullptr;
+
+  D->setAccess(AS_public);
+  CurContext->addDecl(D);
+
+  return D;
+}
+
+NamedDecl *Sema::ActOnFriendFunctionDecl(Scope *S, Declarator &D,
+                                        MultiTemplateParamsArg TemplateParams) {
+  const DeclSpec &DS = D.getDeclSpec();
+
+  assert(DS.isFriendSpecified());
+  assert(DS.getStorageClassSpec() == DeclSpec::SCS_unspecified);
+
+  SourceLocation Loc = D.getIdentifierLoc();
+  TypeSourceInfo *TInfo = GetTypeForDeclarator(D, S);
+
+  // C++ [class.friend]p1
+  //   A friend of a class is a function or class....
+  // Note that this sees through typedefs, which is intended.
+  // It *doesn't* see through dependent types, which is correct
+  // according to [temp.arg.type]p3:
+  //   If a declaration acquires a function type through a
+  //   type dependent on a template-parameter and this causes
+  //   a declaration that does not use the syntactic form of a
+  //   function declarator to have a function type, the program
+  //   is ill-formed.
+  if (!TInfo->getType()->isFunctionType()) {
+    Diag(Loc, diag::err_unexpected_friend);
+
+    // It might be worthwhile to try to recover by creating an
+    // appropriate declaration.
+    return nullptr;
+  }
+
+  // C++ [namespace.memdef]p3
+  //  - If a friend declaration in a non-local class first declares a
+  //    class or function, the friend class or function is a member
+  //    of the innermost enclosing namespace.
+  //  - The name of the friend is not found by simple name lookup
+  //    until a matching declaration is provided in that namespace
+  //    scope (either before or after the class declaration granting
+  //    friendship).
+  //  - If a friend function is called, its name may be found by the
+  //    name lookup that considers functions from namespaces and
+  //    classes associated with the types of the function arguments.
+  //  - When looking for a prior declaration of a class or a function
+  //    declared as a friend, scopes outside the innermost enclosing
+  //    namespace scope are not considered.
+
+  CXXScopeSpec &SS = D.getCXXScopeSpec();
+  DeclarationNameInfo NameInfo = GetNameForDeclarator(D);
+  assert(NameInfo.getName());
+
+  // Check for unexpanded parameter packs.
+  if (DiagnoseUnexpandedParameterPack(Loc, TInfo, UPPC_FriendDeclaration) ||
+      DiagnoseUnexpandedParameterPack(NameInfo, UPPC_FriendDeclaration) ||
+      DiagnoseUnexpandedParameterPack(SS, UPPC_FriendDeclaration))
+    return nullptr;
+
+  // The context we found the declaration in, or in which we should
+  // create the declaration.
+  DeclContext *DC;
+  Scope *DCScope = S;
+  LookupResult Previous(*this, NameInfo, LookupOrdinaryName,
+                        ForExternalRedeclaration);
+
+  // There are five cases here.
+  //   - There's no scope specifier and we're in a local class. Only look
+  //     for functions declared in the immediately-enclosing block scope.
+  // We recover from invalid scope qualifiers as if they just weren't there.
+  FunctionDecl *FunctionContainingLocalClass = nullptr;
+  if ((SS.isInvalid() || !SS.isSet()) &&
+      (FunctionContainingLocalClass =
+           cast<CXXRecordDecl>(CurContext)->isLocalClass())) {
+    // C++11 [class.friend]p11:
+    //   If a friend declaration appears in a local class and the name
+    //   specified is an unqualified name, a prior declaration is
+    //   looked up without considering scopes that are outside the
+    //   innermost enclosing non-class scope. For a friend function
+    //   declaration, if there is no prior declaration, the program is
+    //   ill-formed.
+
+    // Find the innermost enclosing non-class scope. This is the block
+    // scope containing the local class definition (or for a nested class,
+    // the outer local class).
+    DCScope = S->getFnParent();
+
+    // Look up the function name in the scope.
+    Previous.clear(LookupLocalFriendName);
+    LookupName(Previous, S, /*AllowBuiltinCreation*/false);
+
+    if (!Previous.empty()) {
+      // All possible previous declarations must have the same context:
+      // either they were declared at block scope or they are members of
+      // one of the enclosing local classes.
+      DC = Previous.getRepresentativeDecl()->getDeclContext();
+    } else {
+      // This is ill-formed, but provide the context that we would have
+      // declared the function in, if we were permitted to, for error recovery.
+      DC = FunctionContainingLocalClass;
+    }
+    adjustContextForLocalExternDecl(DC);
+
+    // C++ [class.friend]p6:
+    //   A function can be defined in a friend declaration of a class if and
+    //   only if the class is a non-local class (9.8), the function name is
+    //   unqualified, and the function has namespace scope.
+    if (D.isFunctionDefinition()) {
+      Diag(NameInfo.getBeginLoc(), diag::err_friend_def_in_local_class);
+    }
+
+  //   - There's no scope specifier, in which case we just go to the
+  //     appropriate scope and look for a function or function template
+  //     there as appropriate.
+  } else if (SS.isInvalid() || !SS.isSet()) {
+    // C++11 [namespace.memdef]p3:
+    //   If the name in a friend declaration is neither qualified nor
+    //   a template-id and the declaration is a function or an
+    //   elaborated-type-specifier, the lookup to determine whether
+    //   the entity has been previously declared shall not consider
+    //   any scopes outside the innermost enclosing namespace.
+    bool isTemplateId =
+        D.getName().getKind() == UnqualifiedIdKind::IK_TemplateId;
+
+    // Find the appropriate context according to the above.
+    DC = CurContext;
+
+    // Skip class contexts.  If someone can cite chapter and verse
+    // for this behavior, that would be nice --- it's what GCC and
+    // EDG do, and it seems like a reasonable intent, but the spec
+    // really only says that checks for unqualified existing
+    // declarations should stop at the nearest enclosing namespace,
+    // not that they should only consider the nearest enclosing
+    // namespace.
+    while (DC->isRecord())
+      DC = DC->getParent();
+
+    DeclContext *LookupDC = DC->getNonTransparentContext();
+    while (true) {
+      LookupQualifiedName(Previous, LookupDC);
+
+      if (!Previous.empty()) {
+        DC = LookupDC;
+        break;
+      }
+
+      if (isTemplateId) {
+        if (isa<TranslationUnitDecl>(LookupDC)) break;
+      } else {
+        if (LookupDC->isFileContext()) break;
+      }
+      LookupDC = LookupDC->getParent();
+    }
+
+    DCScope = getScopeForDeclContext(S, DC);
+
+  //   - There's a non-dependent scope specifier, in which case we
+  //     compute it and do a previous lookup there for a function
+  //     or function template.
+  } else if (!SS.getScopeRep()->isDependent()) {
+    DC = computeDeclContext(SS);
+    if (!DC) return nullptr;
+
+    if (RequireCompleteDeclContext(SS, DC)) return nullptr;
+
+    LookupQualifiedName(Previous, DC);
+
+    // C++ [class.friend]p1: A friend of a class is a function or
+    //   class that is not a member of the class . . .
+    if (DC->Equals(CurContext))
+      Diag(DS.getFriendSpecLoc(),
+           getLangOpts().CPlusPlus11 ?
+             diag::warn_cxx98_compat_friend_is_member :
+             diag::err_friend_is_member);
+
+    if (D.isFunctionDefinition()) {
+      // C++ [class.friend]p6:
+      //   A function can be defined in a friend declaration of a class if and
+      //   only if the class is a non-local class (9.8), the function name is
+      //   unqualified, and the function has namespace scope.
+      //
+      // FIXME: We should only do this if the scope specifier names the
+      // innermost enclosing namespace; otherwise the fixit changes the
+      // meaning of the code.
+      SemaDiagnosticBuilder DB
+        = Diag(SS.getRange().getBegin(), diag::err_qualified_friend_def);
+
+      DB << SS.getScopeRep();
+      if (DC->isFileContext())
+        DB << FixItHint::CreateRemoval(SS.getRange());
+      SS.clear();
+    }
+
+  //   - There's a scope specifier that does not match any template
+  //     parameter lists, in which case we use some arbitrary context,
+  //     create a method or method template, and wait for instantiation.
+  //   - There's a scope specifier that does match some template
+  //     parameter lists, which we don't handle right now.
+  } else {
+    if (D.isFunctionDefinition()) {
+      // C++ [class.friend]p6:
+      //   A function can be defined in a friend declaration of a class if and
+      //   only if the class is a non-local class (9.8), the function name is
+      //   unqualified, and the function has namespace scope.
+      Diag(SS.getRange().getBegin(), diag::err_qualified_friend_def)
+        << SS.getScopeRep();
+    }
+
+    DC = CurContext;
+    assert(isa<CXXRecordDecl>(DC) && "friend declaration not in class?");
+  }
+
+  if (!DC->isRecord()) {
+    int DiagArg = -1;
+    switch (D.getName().getKind()) {
+    case UnqualifiedIdKind::IK_ConstructorTemplateId:
+    case UnqualifiedIdKind::IK_ConstructorName:
+      DiagArg = 0;
+      break;
+    case UnqualifiedIdKind::IK_DestructorName:
+      DiagArg = 1;
+      break;
+    case UnqualifiedIdKind::IK_ConversionFunctionId:
+      DiagArg = 2;
+      break;
+    case UnqualifiedIdKind::IK_DeductionGuideName:
+      DiagArg = 3;
+      break;
+    case UnqualifiedIdKind::IK_Identifier:
+    case UnqualifiedIdKind::IK_ImplicitSelfParam:
+    case UnqualifiedIdKind::IK_LiteralOperatorId:
+    case UnqualifiedIdKind::IK_OperatorFunctionId:
+    case UnqualifiedIdKind::IK_TemplateId:
+      break;
+    }
+    // This implies that it has to be an operator or function.
+    if (DiagArg >= 0) {
+      Diag(Loc, diag::err_introducing_special_friend) << DiagArg;
+      return nullptr;
+    }
+  }
+
+  // FIXME: This is an egregious hack to cope with cases where the scope stack
+  // does not contain the declaration context, i.e., in an out-of-line
+  // definition of a class.
+  Scope FakeDCScope(S, Scope::DeclScope, Diags);
+  if (!DCScope) {
+    FakeDCScope.setEntity(DC);
+    DCScope = &FakeDCScope;
+  }
+
+  bool AddToScope = true;
+  NamedDecl *ND = ActOnFunctionDeclarator(DCScope, D, DC, TInfo, Previous,
+                                          TemplateParams, AddToScope);
+  if (!ND) return nullptr;
+
+  assert(ND->getLexicalDeclContext() == CurContext);
+
+  // If we performed typo correction, we might have added a scope specifier
+  // and changed the decl context.
+  DC = ND->getDeclContext();
+
+  // Add the function declaration to the appropriate lookup tables,
+  // adjusting the redeclarations list as necessary.  We don't
+  // want to do this yet if the friending class is dependent.
+  //
+  // Also update the scope-based lookup if the target context's
+  // lookup context is in lexical scope.
+  if (!CurContext->isDependentContext()) {
+    DC = DC->getRedeclContext();
+    DC->makeDeclVisibleInContext(ND);
+    if (Scope *EnclosingScope = getScopeForDeclContext(S, DC))
+      PushOnScopeChains(ND, EnclosingScope, /*AddToContext=*/ false);
+  }
+
+  FriendDecl *FrD = FriendDecl::Create(Context, CurContext,
+                                       D.getIdentifierLoc(), ND,
+                                       DS.getFriendSpecLoc());
+  FrD->setAccess(AS_public);
+  CurContext->addDecl(FrD);
+
+  if (ND->isInvalidDecl()) {
+    FrD->setInvalidDecl();
+  } else {
+    if (DC->isRecord()) CheckFriendAccess(ND);
+
+    FunctionDecl *FD;
+    if (FunctionTemplateDecl *FTD = dyn_cast<FunctionTemplateDecl>(ND))
+      FD = FTD->getTemplatedDecl();
+    else
+      FD = cast<FunctionDecl>(ND);
+
+    // C++11 [dcl.fct.default]p4: If a friend declaration specifies a
+    // default argument expression, that declaration shall be a definition
+    // and shall be the only declaration of the function or function
+    // template in the translation unit.
+    if (functionDeclHasDefaultArgument(FD)) {
+      // We can't look at FD->getPreviousDecl() because it may not have been set
+      // if we're in a dependent context. If the function is known to be a
+      // redeclaration, we will have narrowed Previous down to the right decl.
+      if (D.isRedeclaration()) {
+        Diag(FD->getLocation(), diag::err_friend_decl_with_def_arg_redeclared);
+        Diag(Previous.getRepresentativeDecl()->getLocation(),
+             diag::note_previous_declaration);
+      } else if (!D.isFunctionDefinition())
+        Diag(FD->getLocation(), diag::err_friend_decl_with_def_arg_must_be_def);
+    }
+
+    // Mark templated-scope function declarations as unsupported.
+    if (FD->getNumTemplateParameterLists() && SS.isValid()) {
+      Diag(FD->getLocation(), diag::warn_template_qualified_friend_unsupported)
+        << SS.getScopeRep() << SS.getRange()
+        << cast<CXXRecordDecl>(CurContext);
+      FrD->setUnsupportedFriend(true);
+    }
+  }
+
+  warnOnReservedIdentifier(ND);
+
+  return ND;
+}
+
+void Sema::SetDeclDeleted(Decl *Dcl, SourceLocation DelLoc) {
+  AdjustDeclIfTemplate(Dcl);
+
+  FunctionDecl *Fn = dyn_cast_or_null<FunctionDecl>(Dcl);
+  if (!Fn) {
+    Diag(DelLoc, diag::err_deleted_non_function);
+    return;
+  }
+
+  // Deleted function does not have a body.
+  Fn->setWillHaveBody(false);
+
+  if (const FunctionDecl *Prev = Fn->getPreviousDecl()) {
+    // Don't consider the implicit declaration we generate for explicit
+    // specializations. FIXME: Do not generate these implicit declarations.
+    if ((Prev->getTemplateSpecializationKind() != TSK_ExplicitSpecialization ||
+         Prev->getPreviousDecl()) &&
+        !Prev->isDefined()) {
+      Diag(DelLoc, diag::err_deleted_decl_not_first);
+      Diag(Prev->getLocation().isInvalid() ? DelLoc : Prev->getLocation(),
+           Prev->isImplicit() ? diag::note_previous_implicit_declaration
+                              : diag::note_previous_declaration);
+      // We can't recover from this; the declaration might have already
+      // been used.
+      Fn->setInvalidDecl();
+      return;
+    }
+
+    // To maintain the invariant that functions are only deleted on their first
+    // declaration, mark the implicitly-instantiated declaration of the
+    // explicitly-specialized function as deleted instead of marking the
+    // instantiated redeclaration.
+    Fn = Fn->getCanonicalDecl();
+  }
+
+  // dllimport/dllexport cannot be deleted.
+  if (const InheritableAttr *DLLAttr = getDLLAttr(Fn)) {
+    Diag(Fn->getLocation(), diag::err_attribute_dll_deleted) << DLLAttr;
+    Fn->setInvalidDecl();
+  }
+
+  // C++11 [basic.start.main]p3:
+  //   A program that defines main as deleted [...] is ill-formed.
+  if (Fn->isMain())
+    Diag(DelLoc, diag::err_deleted_main);
+
+  // C++11 [dcl.fct.def.delete]p4:
+  //  A deleted function is implicitly inline.
+  Fn->setImplicitlyInline();
+  Fn->setDeletedAsWritten();
+}
+
+void Sema::SetDeclDefaulted(Decl *Dcl, SourceLocation DefaultLoc) {
+  if (!Dcl || Dcl->isInvalidDecl())
+    return;
+
+  auto *FD = dyn_cast<FunctionDecl>(Dcl);
+  if (!FD) {
+    if (auto *FTD = dyn_cast<FunctionTemplateDecl>(Dcl)) {
+      if (getDefaultedFunctionKind(FTD->getTemplatedDecl()).isComparison()) {
+        Diag(DefaultLoc, diag::err_defaulted_comparison_template);
+        return;
+      }
+    }
+
+    Diag(DefaultLoc, diag::err_default_special_members)
+        << getLangOpts().CPlusPlus20;
+    return;
+  }
+
+  // Reject if this can't possibly be a defaultable function.
+  DefaultedFunctionKind DefKind = getDefaultedFunctionKind(FD);
+  if (!DefKind &&
+      // A dependent function that doesn't locally look defaultable can
+      // still instantiate to a defaultable function if it's a constructor
+      // or assignment operator.
+      (!FD->isDependentContext() ||
+       (!isa<CXXConstructorDecl>(FD) &&
+        FD->getDeclName().getCXXOverloadedOperator() != OO_Equal))) {
+    Diag(DefaultLoc, diag::err_default_special_members)
+        << getLangOpts().CPlusPlus20;
+    return;
+  }
+
+  // Issue compatibility warning. We already warned if the operator is
+  // 'operator<=>' when parsing the '<=>' token.
+  if (DefKind.isComparison() &&
+      DefKind.asComparison() != DefaultedComparisonKind::ThreeWay) {
+    Diag(DefaultLoc, getLangOpts().CPlusPlus20
+                         ? diag::warn_cxx17_compat_defaulted_comparison
+                         : diag::ext_defaulted_comparison);
+  }
+
+  FD->setDefaulted();
+  FD->setExplicitlyDefaulted();
+
+  // Defer checking functions that are defaulted in a dependent context.
+  if (FD->isDependentContext())
+    return;
+
+  // Unset that we will have a body for this function. We might not,
+  // if it turns out to be trivial, and we don't need this marking now
+  // that we've marked it as defaulted.
+  FD->setWillHaveBody(false);
+
+  if (DefKind.isComparison()) {
+    // If this comparison's defaulting occurs within the definition of its
+    // lexical class context, we have to do the checking when complete.
+    if (auto const *RD = dyn_cast<CXXRecordDecl>(FD->getLexicalDeclContext()))
+      if (!RD->isCompleteDefinition())
+        return;
+  }
+
+  // If this member fn was defaulted on its first declaration, we will have
+  // already performed the checking in CheckCompletedCXXClass. Such a
+  // declaration doesn't trigger an implicit definition.
+  if (isa<CXXMethodDecl>(FD)) {
+    const FunctionDecl *Primary = FD;
+    if (const FunctionDecl *Pattern = FD->getTemplateInstantiationPattern())
+      // Ask the template instantiation pattern that actually had the
+      // '= default' on it.
+      Primary = Pattern;
+    if (Primary->getCanonicalDecl()->isDefaulted())
+      return;
+  }
+
+  if (DefKind.isComparison()) {
+    if (CheckExplicitlyDefaultedComparison(nullptr, FD, DefKind.asComparison()))
+      FD->setInvalidDecl();
+    else
+      DefineDefaultedComparison(DefaultLoc, FD, DefKind.asComparison());
+  } else {
+    auto *MD = cast<CXXMethodDecl>(FD);
+
+    if (CheckExplicitlyDefaultedSpecialMember(MD, DefKind.asSpecialMember()))
+      MD->setInvalidDecl();
+    else
+      DefineDefaultedFunction(*this, MD, DefaultLoc);
+  }
+}
+
+static void SearchForReturnInStmt(Sema &Self, Stmt *S) {
+  for (Stmt *SubStmt : S->children()) {
+    if (!SubStmt)
+      continue;
+    if (isa<ReturnStmt>(SubStmt))
+      Self.Diag(SubStmt->getBeginLoc(),
+                diag::err_return_in_constructor_handler);
+    if (!isa<Expr>(SubStmt))
+      SearchForReturnInStmt(Self, SubStmt);
+  }
+}
+
+void Sema::DiagnoseReturnInConstructorExceptionHandler(CXXTryStmt *TryBlock) {
+  for (unsigned I = 0, E = TryBlock->getNumHandlers(); I != E; ++I) {
+    CXXCatchStmt *Handler = TryBlock->getHandler(I);
+    SearchForReturnInStmt(*this, Handler);
+  }
+}
+
+bool Sema::CheckOverridingFunctionAttributes(const CXXMethodDecl *New,
+                                             const CXXMethodDecl *Old) {
+  const auto *NewFT = New->getType()->castAs<FunctionProtoType>();
+  const auto *OldFT = Old->getType()->castAs<FunctionProtoType>();
+
+  if (OldFT->hasExtParameterInfos()) {
+    for (unsigned I = 0, E = OldFT->getNumParams(); I != E; ++I)
+      // A parameter of the overriding method should be annotated with noescape
+      // if the corresponding parameter of the overridden method is annotated.
+      if (OldFT->getExtParameterInfo(I).isNoEscape() &&
+          !NewFT->getExtParameterInfo(I).isNoEscape()) {
+        Diag(New->getParamDecl(I)->getLocation(),
+             diag::warn_overriding_method_missing_noescape);
+        Diag(Old->getParamDecl(I)->getLocation(),
+             diag::note_overridden_marked_noescape);
+      }
+  }
+
+  // Virtual overrides must have the same code_seg.
+  const auto *OldCSA = Old->getAttr<CodeSegAttr>();
+  const auto *NewCSA = New->getAttr<CodeSegAttr>();
+  if ((NewCSA || OldCSA) &&
+      (!OldCSA || !NewCSA || NewCSA->getName() != OldCSA->getName())) {
+    Diag(New->getLocation(), diag::err_mismatched_code_seg_override);
+    Diag(Old->getLocation(), diag::note_previous_declaration);
+    return true;
+  }
+
+  CallingConv NewCC = NewFT->getCallConv(), OldCC = OldFT->getCallConv();
+
+  // If the calling conventions match, everything is fine
+  if (NewCC == OldCC)
+    return false;
+
+  // If the calling conventions mismatch because the new function is static,
+  // suppress the calling convention mismatch error; the error about static
+  // function override (err_static_overrides_virtual from
+  // Sema::CheckFunctionDeclaration) is more clear.
+  if (New->getStorageClass() == SC_Static)
+    return false;
+
+  Diag(New->getLocation(),
+       diag::err_conflicting_overriding_cc_attributes)
+    << New->getDeclName() << New->getType() << Old->getType();
+  Diag(Old->getLocation(), diag::note_overridden_virtual_function);
+  return true;
+}
+
+bool Sema::CheckOverridingFunctionReturnType(const CXXMethodDecl *New,
+                                             const CXXMethodDecl *Old) {
+  QualType NewTy = New->getType()->castAs<FunctionType>()->getReturnType();
+  QualType OldTy = Old->getType()->castAs<FunctionType>()->getReturnType();
+
+  if (Context.hasSameType(NewTy, OldTy) ||
+      NewTy->isDependentType() || OldTy->isDependentType())
+    return false;
+
+  // Check if the return types are covariant
+  QualType NewClassTy, OldClassTy;
+
+  /// Both types must be pointers or references to classes.
+  if (const PointerType *NewPT = NewTy->getAs<PointerType>()) {
+    if (const PointerType *OldPT = OldTy->getAs<PointerType>()) {
+      NewClassTy = NewPT->getPointeeType();
+      OldClassTy = OldPT->getPointeeType();
+    }
+  } else if (const ReferenceType *NewRT = NewTy->getAs<ReferenceType>()) {
+    if (const ReferenceType *OldRT = OldTy->getAs<ReferenceType>()) {
+      if (NewRT->getTypeClass() == OldRT->getTypeClass()) {
+        NewClassTy = NewRT->getPointeeType();
+        OldClassTy = OldRT->getPointeeType();
+      }
+    }
+  }
+
+  // The return types aren't either both pointers or references to a class type.
+  if (NewClassTy.isNull()) {
+    Diag(New->getLocation(),
+         diag::err_different_return_type_for_overriding_virtual_function)
+        << New->getDeclName() << NewTy << OldTy
+        << New->getReturnTypeSourceRange();
+    Diag(Old->getLocation(), diag::note_overridden_virtual_function)
+        << Old->getReturnTypeSourceRange();
+
+    return true;
+  }
+
+  if (!Context.hasSameUnqualifiedType(NewClassTy, OldClassTy)) {
+    // C++14 [class.virtual]p8:
+    //   If the class type in the covariant return type of D::f differs from
+    //   that of B::f, the class type in the return type of D::f shall be
+    //   complete at the point of declaration of D::f or shall be the class
+    //   type D.
+    if (const RecordType *RT = NewClassTy->getAs<RecordType>()) {
+      if (!RT->isBeingDefined() &&
+          RequireCompleteType(New->getLocation(), NewClassTy,
+                              diag::err_covariant_return_incomplete,
+                              New->getDeclName()))
+        return true;
+    }
+
+    // Check if the new class derives from the old class.
+    if (!IsDerivedFrom(New->getLocation(), NewClassTy, OldClassTy)) {
+      Diag(New->getLocation(), diag::err_covariant_return_not_derived)
+          << New->getDeclName() << NewTy << OldTy
+          << New->getReturnTypeSourceRange();
+      Diag(Old->getLocation(), diag::note_overridden_virtual_function)
+          << Old->getReturnTypeSourceRange();
+      return true;
+    }
+
+    // Check if we the conversion from derived to base is valid.
+    if (CheckDerivedToBaseConversion(
+            NewClassTy, OldClassTy,
+            diag::err_covariant_return_inaccessible_base,
+            diag::err_covariant_return_ambiguous_derived_to_base_conv,
+            New->getLocation(), New->getReturnTypeSourceRange(),
+            New->getDeclName(), nullptr)) {
+      // FIXME: this note won't trigger for delayed access control
+      // diagnostics, and it's impossible to get an undelayed error
+      // here from access control during the original parse because
+      // the ParsingDeclSpec/ParsingDeclarator are still in scope.
+      Diag(Old->getLocation(), diag::note_overridden_virtual_function)
+          << Old->getReturnTypeSourceRange();
+      return true;
+    }
+  }
+
+  // The qualifiers of the return types must be the same.
+  if (NewTy.getLocalCVRQualifiers() != OldTy.getLocalCVRQualifiers()) {
+    Diag(New->getLocation(),
+         diag::err_covariant_return_type_different_qualifications)
+        << New->getDeclName() << NewTy << OldTy
+        << New->getReturnTypeSourceRange();
+    Diag(Old->getLocation(), diag::note_overridden_virtual_function)
+        << Old->getReturnTypeSourceRange();
+    return true;
+  }
+
+
+  // The new class type must have the same or less qualifiers as the old type.
+  if (NewClassTy.isMoreQualifiedThan(OldClassTy)) {
+    Diag(New->getLocation(),
+         diag::err_covariant_return_type_class_type_more_qualified)
+        << New->getDeclName() << NewTy << OldTy
+        << New->getReturnTypeSourceRange();
+    Diag(Old->getLocation(), diag::note_overridden_virtual_function)
+        << Old->getReturnTypeSourceRange();
+    return true;
+  }
+
+  return false;
+}
+
+/// Mark the given method pure.
+///
+/// \param Method the method to be marked pure.
+///
+/// \param InitRange the source range that covers the "0" initializer.
+bool Sema::CheckPureMethod(CXXMethodDecl *Method, SourceRange InitRange) {
+  SourceLocation EndLoc = InitRange.getEnd();
+  if (EndLoc.isValid())
+    Method->setRangeEnd(EndLoc);
+
+  if (Method->isVirtual() || Method->getParent()->isDependentContext()) {
+    Method->setPure();
+    return false;
+  }
+
+  if (!Method->isInvalidDecl())
+    Diag(Method->getLocation(), diag::err_non_virtual_pure)
+      << Method->getDeclName() << InitRange;
+  return true;
+}
+
+void Sema::ActOnPureSpecifier(Decl *D, SourceLocation ZeroLoc) {
+  if (D->getFriendObjectKind())
+    Diag(D->getLocation(), diag::err_pure_friend);
+  else if (auto *M = dyn_cast<CXXMethodDecl>(D))
+    CheckPureMethod(M, ZeroLoc);
+  else
+    Diag(D->getLocation(), diag::err_illegal_initializer);
+}
+
+/// Determine whether the given declaration is a global variable or
+/// static data member.
+static bool isNonlocalVariable(const Decl *D) {
+  if (const VarDecl *Var = dyn_cast_or_null<VarDecl>(D))
+    return Var->hasGlobalStorage();
+
+  return false;
+}
+
+/// Invoked when we are about to parse an initializer for the declaration
+/// 'Dcl'.
+///
+/// After this method is called, according to [C++ 3.4.1p13], if 'Dcl' is a
+/// static data member of class X, names should be looked up in the scope of
+/// class X. If the declaration had a scope specifier, a scope will have
+/// been created and passed in for this purpose. Otherwise, S will be null.
+void Sema::ActOnCXXEnterDeclInitializer(Scope *S, Decl *D) {
+  // If there is no declaration, there was an error parsing it.
+  if (!D || D->isInvalidDecl())
+    return;
+
+  // We will always have a nested name specifier here, but this declaration
+  // might not be out of line if the specifier names the current namespace:
+  //   extern int n;
+  //   int ::n = 0;
+  if (S && D->isOutOfLine())
+    EnterDeclaratorContext(S, D->getDeclContext());
+
+  // If we are parsing the initializer for a static data member, push a
+  // new expression evaluation context that is associated with this static
+  // data member.
+  if (isNonlocalVariable(D))
+    PushExpressionEvaluationContext(
+        ExpressionEvaluationContext::PotentiallyEvaluated, D);
+}
+
+/// Invoked after we are finished parsing an initializer for the declaration D.
+void Sema::ActOnCXXExitDeclInitializer(Scope *S, Decl *D) {
+  // If there is no declaration, there was an error parsing it.
+  if (!D || D->isInvalidDecl())
+    return;
+
+  if (isNonlocalVariable(D))
+    PopExpressionEvaluationContext();
+
+  if (S && D->isOutOfLine())
+    ExitDeclaratorContext(S);
+}
+
+/// ActOnCXXConditionDeclarationExpr - Parsed a condition declaration of a
+/// C++ if/switch/while/for statement.
+/// e.g: "if (int x = f()) {...}"
+DeclResult Sema::ActOnCXXConditionDeclaration(Scope *S, Declarator &D) {
+  // C++ 6.4p2:
+  // The declarator shall not specify a function or an array.
+  // The type-specifier-seq shall not contain typedef and shall not declare a
+  // new class or enumeration.
+  assert(D.getDeclSpec().getStorageClassSpec() != DeclSpec::SCS_typedef &&
+         "Parser allowed 'typedef' as storage class of condition decl.");
+
+  Decl *Dcl = ActOnDeclarator(S, D);
+  if (!Dcl)
+    return true;
+
+  if (isa<FunctionDecl>(Dcl)) { // The declarator shall not specify a function.
+    Diag(Dcl->getLocation(), diag::err_invalid_use_of_function_type)
+      << D.getSourceRange();
+    return true;
+  }
+
+  return Dcl;
+}
+
+void Sema::LoadExternalVTableUses() {
+  if (!ExternalSource)
+    return;
+
+  SmallVector<ExternalVTableUse, 4> VTables;
+  ExternalSource->ReadUsedVTables(VTables);
+  SmallVector<VTableUse, 4> NewUses;
+  for (unsigned I = 0, N = VTables.size(); I != N; ++I) {
+    llvm::DenseMap<CXXRecordDecl *, bool>::iterator Pos
+      = VTablesUsed.find(VTables[I].Record);
+    // Even if a definition wasn't required before, it may be required now.
+    if (Pos != VTablesUsed.end()) {
+      if (!Pos->second && VTables[I].DefinitionRequired)
+        Pos->second = true;
+      continue;
+    }
+
+    VTablesUsed[VTables[I].Record] = VTables[I].DefinitionRequired;
+    NewUses.push_back(VTableUse(VTables[I].Record, VTables[I].Location));
+  }
+
+  VTableUses.insert(VTableUses.begin(), NewUses.begin(), NewUses.end());
+}
+
+void Sema::MarkVTableUsed(SourceLocation Loc, CXXRecordDecl *Class,
+                          bool DefinitionRequired) {
+  // Ignore any vtable uses in unevaluated operands or for classes that do
+  // not have a vtable.
+  if (!Class->isDynamicClass() || Class->isDependentContext() ||
+      CurContext->isDependentContext() || isUnevaluatedContext())
+    return;
+  // Do not mark as used if compiling for the device outside of the target
+  // region.
+  if (TUKind != TU_Prefix && LangOpts.OpenMP && LangOpts.OpenMPIsDevice &&
+      !isInOpenMPDeclareTargetContext() &&
+      !isInOpenMPTargetExecutionDirective()) {
+    if (!DefinitionRequired)
+      MarkVirtualMembersReferenced(Loc, Class);
+    return;
+  }
+
+  // Try to insert this class into the map.
+  LoadExternalVTableUses();
+  Class = Class->getCanonicalDecl();
+  std::pair<llvm::DenseMap<CXXRecordDecl *, bool>::iterator, bool>
+    Pos = VTablesUsed.insert(std::make_pair(Class, DefinitionRequired));
+  if (!Pos.second) {
+    // If we already had an entry, check to see if we are promoting this vtable
+    // to require a definition. If so, we need to reappend to the VTableUses
+    // list, since we may have already processed the first entry.
+    if (DefinitionRequired && !Pos.first->second) {
+      Pos.first->second = true;
+    } else {
+      // Otherwise, we can early exit.
+      return;
+    }
+  } else {
+    // The Microsoft ABI requires that we perform the destructor body
+    // checks (i.e. operator delete() lookup) when the vtable is marked used, as
+    // the deleting destructor is emitted with the vtable, not with the
+    // destructor definition as in the Itanium ABI.
+    if (Context.getTargetInfo().getCXXABI().isMicrosoft()) {
+      CXXDestructorDecl *DD = Class->getDestructor();
+      if (DD && DD->isVirtual() && !DD->isDeleted()) {
+        if (Class->hasUserDeclaredDestructor() && !DD->isDefined()) {
+          // If this is an out-of-line declaration, marking it referenced will
+          // not do anything. Manually call CheckDestructor to look up operator
+          // delete().
+          ContextRAII SavedContext(*this, DD);
+          CheckDestructor(DD);
+        } else {
+          MarkFunctionReferenced(Loc, Class->getDestructor());
+        }
+      }
+    }
+  }
+
+  // Local classes need to have their virtual members marked
+  // immediately. For all other classes, we mark their virtual members
+  // at the end of the translation unit.
+  if (Class->isLocalClass())
+    MarkVirtualMembersReferenced(Loc, Class);
+  else
+    VTableUses.push_back(std::make_pair(Class, Loc));
+}
+
+bool Sema::DefineUsedVTables() {
+  LoadExternalVTableUses();
+  if (VTableUses.empty())
+    return false;
+
+  // Note: The VTableUses vector could grow as a result of marking
+  // the members of a class as "used", so we check the size each
+  // time through the loop and prefer indices (which are stable) to
+  // iterators (which are not).
+  bool DefinedAnything = false;
+  for (unsigned I = 0; I != VTableUses.size(); ++I) {
+    CXXRecordDecl *Class = VTableUses[I].first->getDefinition();
+    if (!Class)
+      continue;
+    TemplateSpecializationKind ClassTSK =
+        Class->getTemplateSpecializationKind();
+
+    SourceLocation Loc = VTableUses[I].second;
+
+    bool DefineVTable = true;
+
+    // If this class has a key function, but that key function is
+    // defined in another translation unit, we don't need to emit the
+    // vtable even though we're using it.
+    const CXXMethodDecl *KeyFunction = Context.getCurrentKeyFunction(Class);
+    if (KeyFunction && !KeyFunction->hasBody()) {
+      // The key function is in another translation unit.
+      DefineVTable = false;
+      TemplateSpecializationKind TSK =
+          KeyFunction->getTemplateSpecializationKind();
+      assert(TSK != TSK_ExplicitInstantiationDefinition &&
+             TSK != TSK_ImplicitInstantiation &&
+             "Instantiations don't have key functions");
+      (void)TSK;
+    } else if (!KeyFunction) {
+      // If we have a class with no key function that is the subject
+      // of an explicit instantiation declaration, suppress the
+      // vtable; it will live with the explicit instantiation
+      // definition.
+      bool IsExplicitInstantiationDeclaration =
+          ClassTSK == TSK_ExplicitInstantiationDeclaration;
+      for (auto R : Class->redecls()) {
+        TemplateSpecializationKind TSK
+          = cast<CXXRecordDecl>(R)->getTemplateSpecializationKind();
+        if (TSK == TSK_ExplicitInstantiationDeclaration)
+          IsExplicitInstantiationDeclaration = true;
+        else if (TSK == TSK_ExplicitInstantiationDefinition) {
+          IsExplicitInstantiationDeclaration = false;
+          break;
+        }
+      }
+
+      if (IsExplicitInstantiationDeclaration)
+        DefineVTable = false;
+    }
+
+    // The exception specifications for all virtual members may be needed even
+    // if we are not providing an authoritative form of the vtable in this TU.
+    // We may choose to emit it available_externally anyway.
+    if (!DefineVTable) {
+      MarkVirtualMemberExceptionSpecsNeeded(Loc, Class);
+      continue;
+    }
+
+    // Mark all of the virtual members of this class as referenced, so
+    // that we can build a vtable. Then, tell the AST consumer that a
+    // vtable for this class is required.
+    DefinedAnything = true;
+    MarkVirtualMembersReferenced(Loc, Class);
+    CXXRecordDecl *Canonical = Class->getCanonicalDecl();
+    if (VTablesUsed[Canonical])
+      Consumer.HandleVTable(Class);
+
+    // Warn if we're emitting a weak vtable. The vtable will be weak if there is
+    // no key function or the key function is inlined. Don't warn in C++ ABIs
+    // that lack key functions, since the user won't be able to make one.
+    if (Context.getTargetInfo().getCXXABI().hasKeyFunctions() &&
+        Class->isExternallyVisible() && ClassTSK != TSK_ImplicitInstantiation &&
+        ClassTSK != TSK_ExplicitInstantiationDefinition) {
+      const FunctionDecl *KeyFunctionDef = nullptr;
+      if (!KeyFunction || (KeyFunction->hasBody(KeyFunctionDef) &&
+                           KeyFunctionDef->isInlined()))
+        Diag(Class->getLocation(), diag::warn_weak_vtable) << Class;
+    }
+  }
+  VTableUses.clear();
+
+  return DefinedAnything;
+}
+
+void Sema::MarkVirtualMemberExceptionSpecsNeeded(SourceLocation Loc,
+                                                 const CXXRecordDecl *RD) {
+  for (const auto *I : RD->methods())
+    if (I->isVirtual() && !I->isPure())
+      ResolveExceptionSpec(Loc, I->getType()->castAs<FunctionProtoType>());
+}
+
+void Sema::MarkVirtualMembersReferenced(SourceLocation Loc,
+                                        const CXXRecordDecl *RD,
+                                        bool ConstexprOnly) {
+  // Mark all functions which will appear in RD's vtable as used.
+  CXXFinalOverriderMap FinalOverriders;
+  RD->getFinalOverriders(FinalOverriders);
+  for (CXXFinalOverriderMap::const_iterator I = FinalOverriders.begin(),
+                                            E = FinalOverriders.end();
+       I != E; ++I) {
+    for (OverridingMethods::const_iterator OI = I->second.begin(),
+                                           OE = I->second.end();
+         OI != OE; ++OI) {
+      assert(OI->second.size() > 0 && "no final overrider");
+      CXXMethodDecl *Overrider = OI->second.front().Method;
+
+      // C++ [basic.def.odr]p2:
+      //   [...] A virtual member function is used if it is not pure. [...]
+      if (!Overrider->isPure() && (!ConstexprOnly || Overrider->isConstexpr()))
+        MarkFunctionReferenced(Loc, Overrider);
+    }
+  }
+
+  // Only classes that have virtual bases need a VTT.
+  if (RD->getNumVBases() == 0)
+    return;
+
+  for (const auto &I : RD->bases()) {
+    const auto *Base =
+        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+    if (Base->getNumVBases() == 0)
+      continue;
+    MarkVirtualMembersReferenced(Loc, Base);
+  }
+}
+
+/// SetIvarInitializers - This routine builds initialization ASTs for the
+/// Objective-C implementation whose ivars need be initialized.
+void Sema::SetIvarInitializers(ObjCImplementationDecl *ObjCImplementation) {
+  if (!getLangOpts().CPlusPlus)
+    return;
+  if (ObjCInterfaceDecl *OID = ObjCImplementation->getClassInterface()) {
+    SmallVector<ObjCIvarDecl*, 8> ivars;
+    CollectIvarsToConstructOrDestruct(OID, ivars);
+    if (ivars.empty())
+      return;
+    SmallVector<CXXCtorInitializer*, 32> AllToInit;
+    for (unsigned i = 0; i < ivars.size(); i++) {
+      FieldDecl *Field = ivars[i];
+      if (Field->isInvalidDecl())
+        continue;
+
+      CXXCtorInitializer *Member;
+      InitializedEntity InitEntity = InitializedEntity::InitializeMember(Field);
+      InitializationKind InitKind =
+        InitializationKind::CreateDefault(ObjCImplementation->getLocation());
+
+      InitializationSequence InitSeq(*this, InitEntity, InitKind, None);
+      ExprResult MemberInit =
+        InitSeq.Perform(*this, InitEntity, InitKind, None);
+      MemberInit = MaybeCreateExprWithCleanups(MemberInit);
+      // Note, MemberInit could actually come back empty if no initialization
+      // is required (e.g., because it would call a trivial default constructor)
+      if (!MemberInit.get() || MemberInit.isInvalid())
+        continue;
+
+      Member =
+        new (Context) CXXCtorInitializer(Context, Field, SourceLocation(),
+                                         SourceLocation(),
+                                         MemberInit.getAs<Expr>(),
+                                         SourceLocation());
+      AllToInit.push_back(Member);
+
+      // Be sure that the destructor is accessible and is marked as referenced.
+      if (const RecordType *RecordTy =
+              Context.getBaseElementType(Field->getType())
+                  ->getAs<RecordType>()) {
+        CXXRecordDecl *RD = cast<CXXRecordDecl>(RecordTy->getDecl());
+        if (CXXDestructorDecl *Destructor = LookupDestructor(RD)) {
+          MarkFunctionReferenced(Field->getLocation(), Destructor);
+          CheckDestructorAccess(Field->getLocation(), Destructor,
+                            PDiag(diag::err_access_dtor_ivar)
+                              << Context.getBaseElementType(Field->getType()));
+        }
+      }
+    }
+    ObjCImplementation->setIvarInitializers(Context,
+                                            AllToInit.data(), AllToInit.size());
+  }
+}
+
+static
+void DelegatingCycleHelper(CXXConstructorDecl* Ctor,
+                           llvm::SmallPtrSet<CXXConstructorDecl*, 4> &Valid,
+                           llvm::SmallPtrSet<CXXConstructorDecl*, 4> &Invalid,
+                           llvm::SmallPtrSet<CXXConstructorDecl*, 4> &Current,
+                           Sema &S) {
+  if (Ctor->isInvalidDecl())
+    return;
+
+  CXXConstructorDecl *Target = Ctor->getTargetConstructor();
+
+  // Target may not be determinable yet, for instance if this is a dependent
+  // call in an uninstantiated template.
+  if (Target) {
+    const FunctionDecl *FNTarget = nullptr;
+    (void)Target->hasBody(FNTarget);
+    Target = const_cast<CXXConstructorDecl*>(
+      cast_or_null<CXXConstructorDecl>(FNTarget));
+  }
+
+  CXXConstructorDecl *Canonical = Ctor->getCanonicalDecl(),
+                     // Avoid dereferencing a null pointer here.
+                     *TCanonical = Target? Target->getCanonicalDecl() : nullptr;
+
+  if (!Current.insert(Canonical).second)
+    return;
+
+  // We know that beyond here, we aren't chaining into a cycle.
+  if (!Target || !Target->isDelegatingConstructor() ||
+      Target->isInvalidDecl() || Valid.count(TCanonical)) {
+    Valid.insert(Current.begin(), Current.end());
+    Current.clear();
+  // We've hit a cycle.
+  } else if (TCanonical == Canonical || Invalid.count(TCanonical) ||
+             Current.count(TCanonical)) {
+    // If we haven't diagnosed this cycle yet, do so now.
+    if (!Invalid.count(TCanonical)) {
+      S.Diag((*Ctor->init_begin())->getSourceLocation(),
+             diag::warn_delegating_ctor_cycle)
+        << Ctor;
+
+      // Don't add a note for a function delegating directly to itself.
+      if (TCanonical != Canonical)
+        S.Diag(Target->getLocation(), diag::note_it_delegates_to);
+
+      CXXConstructorDecl *C = Target;
+      while (C->getCanonicalDecl() != Canonical) {
+        const FunctionDecl *FNTarget = nullptr;
+        (void)C->getTargetConstructor()->hasBody(FNTarget);
+        assert(FNTarget && "Ctor cycle through bodiless function");
+
+        C = const_cast<CXXConstructorDecl*>(
+          cast<CXXConstructorDecl>(FNTarget));
+        S.Diag(C->getLocation(), diag::note_which_delegates_to);
+      }
+    }
+
+    Invalid.insert(Current.begin(), Current.end());
+    Current.clear();
+  } else {
+    DelegatingCycleHelper(Target, Valid, Invalid, Current, S);
+  }
+}
+
+
+void Sema::CheckDelegatingCtorCycles() {
+  llvm::SmallPtrSet<CXXConstructorDecl*, 4> Valid, Invalid, Current;
+
+  for (DelegatingCtorDeclsType::iterator
+         I = DelegatingCtorDecls.begin(ExternalSource),
+         E = DelegatingCtorDecls.end();
+       I != E; ++I)
+    DelegatingCycleHelper(*I, Valid, Invalid, Current, *this);
+
+  for (auto CI = Invalid.begin(), CE = Invalid.end(); CI != CE; ++CI)
+    (*CI)->setInvalidDecl();
+}
+
+namespace {
+  /// AST visitor that finds references to the 'this' expression.
+  class FindCXXThisExpr : public RecursiveASTVisitor<FindCXXThisExpr> {
+    Sema &S;
+
+  public:
+    explicit FindCXXThisExpr(Sema &S) : S(S) { }
+
+    bool VisitCXXThisExpr(CXXThisExpr *E) {
+      S.Diag(E->getLocation(), diag::err_this_static_member_func)
+        << E->isImplicit();
+      return false;
+    }
+  };
+}
+
+bool Sema::checkThisInStaticMemberFunctionType(CXXMethodDecl *Method) {
+  TypeSourceInfo *TSInfo = Method->getTypeSourceInfo();
+  if (!TSInfo)
+    return false;
+
+  TypeLoc TL = TSInfo->getTypeLoc();
+  FunctionProtoTypeLoc ProtoTL = TL.getAs<FunctionProtoTypeLoc>();
+  if (!ProtoTL)
+    return false;
+
+  // C++11 [expr.prim.general]p3:
+  //   [The expression this] shall not appear before the optional
+  //   cv-qualifier-seq and it shall not appear within the declaration of a
+  //   static member function (although its type and value category are defined
+  //   within a static member function as they are within a non-static member
+  //   function). [ Note: this is because declaration matching does not occur
+  //  until the complete declarator is known. - end note ]
+  const FunctionProtoType *Proto = ProtoTL.getTypePtr();
+  FindCXXThisExpr Finder(*this);
+
+  // If the return type came after the cv-qualifier-seq, check it now.
+  if (Proto->hasTrailingReturn() &&
+      !Finder.TraverseTypeLoc(ProtoTL.getReturnLoc()))
+    return true;
+
+  // Check the exception specification.
+  if (checkThisInStaticMemberFunctionExceptionSpec(Method))
+    return true;
+
+  // Check the trailing requires clause
+  if (Expr *E = Method->getTrailingRequiresClause())
+    if (!Finder.TraverseStmt(E))
+      return true;
+
+  return checkThisInStaticMemberFunctionAttributes(Method);
+}
+
+bool Sema::checkThisInStaticMemberFunctionExceptionSpec(CXXMethodDecl *Method) {
+  TypeSourceInfo *TSInfo = Method->getTypeSourceInfo();
+  if (!TSInfo)
+    return false;
+
+  TypeLoc TL = TSInfo->getTypeLoc();
+  FunctionProtoTypeLoc ProtoTL = TL.getAs<FunctionProtoTypeLoc>();
+  if (!ProtoTL)
+    return false;
+
+  const FunctionProtoType *Proto = ProtoTL.getTypePtr();
+  FindCXXThisExpr Finder(*this);
+
+  switch (Proto->getExceptionSpecType()) {
+  case EST_Unparsed:
+  case EST_Uninstantiated:
+  case EST_Unevaluated:
+  case EST_BasicNoexcept:
+  case EST_NoThrow:
+  case EST_DynamicNone:
+  case EST_MSAny:
+  case EST_None:
+    break;
+
+  case EST_DependentNoexcept:
+  case EST_NoexceptFalse:
+  case EST_NoexceptTrue:
+    if (!Finder.TraverseStmt(Proto->getNoexceptExpr()))
+      return true;
+    LLVM_FALLTHROUGH;
+
+  case EST_Dynamic:
+    for (const auto &E : Proto->exceptions()) {
+      if (!Finder.TraverseType(E))
+        return true;
+    }
+    break;
+  }
+
+  return false;
+}
+
+bool Sema::checkThisInStaticMemberFunctionAttributes(CXXMethodDecl *Method) {
+  FindCXXThisExpr Finder(*this);
+
+  // Check attributes.
+  for (const auto *A : Method->attrs()) {
+    // FIXME: This should be emitted by tblgen.
+    Expr *Arg = nullptr;
+    ArrayRef<Expr *> Args;
+    if (const auto *G = dyn_cast<GuardedByAttr>(A))
+      Arg = G->getArg();
+    else if (const auto *G = dyn_cast<PtGuardedByAttr>(A))
+      Arg = G->getArg();
+    else if (const auto *AA = dyn_cast<AcquiredAfterAttr>(A))
+      Args = llvm::makeArrayRef(AA->args_begin(), AA->args_size());
+    else if (const auto *AB = dyn_cast<AcquiredBeforeAttr>(A))
+      Args = llvm::makeArrayRef(AB->args_begin(), AB->args_size());
+    else if (const auto *ETLF = dyn_cast<ExclusiveTrylockFunctionAttr>(A)) {
+      Arg = ETLF->getSuccessValue();
+      Args = llvm::makeArrayRef(ETLF->args_begin(), ETLF->args_size());
+    } else if (const auto *STLF = dyn_cast<SharedTrylockFunctionAttr>(A)) {
+      Arg = STLF->getSuccessValue();
+      Args = llvm::makeArrayRef(STLF->args_begin(), STLF->args_size());
+    } else if (const auto *LR = dyn_cast<LockReturnedAttr>(A))
+      Arg = LR->getArg();
+    else if (const auto *LE = dyn_cast<LocksExcludedAttr>(A))
+      Args = llvm::makeArrayRef(LE->args_begin(), LE->args_size());
+    else if (const auto *RC = dyn_cast<RequiresCapabilityAttr>(A))
+      Args = llvm::makeArrayRef(RC->args_begin(), RC->args_size());
+    else if (const auto *AC = dyn_cast<AcquireCapabilityAttr>(A))
+      Args = llvm::makeArrayRef(AC->args_begin(), AC->args_size());
+    else if (const auto *AC = dyn_cast<TryAcquireCapabilityAttr>(A))
+      Args = llvm::makeArrayRef(AC->args_begin(), AC->args_size());
+    else if (const auto *RC = dyn_cast<ReleaseCapabilityAttr>(A))
+      Args = llvm::makeArrayRef(RC->args_begin(), RC->args_size());
+
+    if (Arg && !Finder.TraverseStmt(Arg))
+      return true;
+
+    for (unsigned I = 0, N = Args.size(); I != N; ++I) {
+      if (!Finder.TraverseStmt(Args[I]))
+        return true;
+    }
+  }
+
+  return false;
+}
+
+void Sema::checkExceptionSpecification(
+    bool IsTopLevel, ExceptionSpecificationType EST,
+    ArrayRef<ParsedType> DynamicExceptions,
+    ArrayRef<SourceRange> DynamicExceptionRanges, Expr *NoexceptExpr,
+    SmallVectorImpl<QualType> &Exceptions,
+    FunctionProtoType::ExceptionSpecInfo &ESI) {
+  Exceptions.clear();
+  ESI.Type = EST;
+  if (EST == EST_Dynamic) {
+    Exceptions.reserve(DynamicExceptions.size());
+    for (unsigned ei = 0, ee = DynamicExceptions.size(); ei != ee; ++ei) {
+      // FIXME: Preserve type source info.
+      QualType ET = GetTypeFromParser(DynamicExceptions[ei]);
+
+      if (IsTopLevel) {
+        SmallVector<UnexpandedParameterPack, 2> Unexpanded;
+        collectUnexpandedParameterPacks(ET, Unexpanded);
+        if (!Unexpanded.empty()) {
+          DiagnoseUnexpandedParameterPacks(
+              DynamicExceptionRanges[ei].getBegin(), UPPC_ExceptionType,
+              Unexpanded);
+          continue;
+        }
+      }
+
+      // Check that the type is valid for an exception spec, and
+      // drop it if not.
+      if (!CheckSpecifiedExceptionType(ET, DynamicExceptionRanges[ei]))
+        Exceptions.push_back(ET);
+    }
+    ESI.Exceptions = Exceptions;
+    return;
+  }
+
+  if (isComputedNoexcept(EST)) {
+    assert((NoexceptExpr->isTypeDependent() ||
+            NoexceptExpr->getType()->getCanonicalTypeUnqualified() ==
+            Context.BoolTy) &&
+           "Parser should have made sure that the expression is boolean");
+    if (IsTopLevel && DiagnoseUnexpandedParameterPack(NoexceptExpr)) {
+      ESI.Type = EST_BasicNoexcept;
+      return;
+    }
+
+    ESI.NoexceptExpr = NoexceptExpr;
+    return;
+  }
+}
+
+void Sema::actOnDelayedExceptionSpecification(Decl *MethodD,
+             ExceptionSpecificationType EST,
+             SourceRange SpecificationRange,
+             ArrayRef<ParsedType> DynamicExceptions,
+             ArrayRef<SourceRange> DynamicExceptionRanges,
+             Expr *NoexceptExpr) {
+  if (!MethodD)
+    return;
+
+  // Dig out the method we're referring to.
+  if (FunctionTemplateDecl *FunTmpl = dyn_cast<FunctionTemplateDecl>(MethodD))
+    MethodD = FunTmpl->getTemplatedDecl();
+
+  CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(MethodD);
+  if (!Method)
+    return;
+
+  // Check the exception specification.
+  llvm::SmallVector<QualType, 4> Exceptions;
+  FunctionProtoType::ExceptionSpecInfo ESI;
+  checkExceptionSpecification(/*IsTopLevel*/true, EST, DynamicExceptions,
+                              DynamicExceptionRanges, NoexceptExpr, Exceptions,
+                              ESI);
+
+  // Update the exception specification on the function type.
+  Context.adjustExceptionSpec(Method, ESI, /*AsWritten*/true);
+
+  if (Method->isStatic())
+    checkThisInStaticMemberFunctionExceptionSpec(Method);
+
+  if (Method->isVirtual()) {
+    // Check overrides, which we previously had to delay.
+    for (const CXXMethodDecl *O : Method->overridden_methods())
+      CheckOverridingFunctionExceptionSpec(Method, O);
+  }
+}
+
+/// HandleMSProperty - Analyze a __delcspec(property) field of a C++ class.
+///
+MSPropertyDecl *Sema::HandleMSProperty(Scope *S, RecordDecl *Record,
+                                       SourceLocation DeclStart, Declarator &D,
+                                       Expr *BitWidth,
+                                       InClassInitStyle InitStyle,
+                                       AccessSpecifier AS,
+                                       const ParsedAttr &MSPropertyAttr) {
+  IdentifierInfo *II = D.getIdentifier();
+  if (!II) {
+    Diag(DeclStart, diag::err_anonymous_property);
+    return nullptr;
+  }
+  SourceLocation Loc = D.getIdentifierLoc();
+
+  TypeSourceInfo *TInfo = GetTypeForDeclarator(D, S);
+  QualType T = TInfo->getType();
+  if (getLangOpts().CPlusPlus) {
+    CheckExtraCXXDefaultArguments(D);
+
+    if (DiagnoseUnexpandedParameterPack(D.getIdentifierLoc(), TInfo,
+                                        UPPC_DataMemberType)) {
+      D.setInvalidType();
+      T = Context.IntTy;
+      TInfo = Context.getTrivialTypeSourceInfo(T, Loc);
+    }
+  }
+
+  DiagnoseFunctionSpecifiers(D.getDeclSpec());
+
+  if (D.getDeclSpec().isInlineSpecified())
+    Diag(D.getDeclSpec().getInlineSpecLoc(), diag::err_inline_non_function)
+        << getLangOpts().CPlusPlus17;
+  if (DeclSpec::TSCS TSCS = D.getDeclSpec().getThreadStorageClassSpec())
+    Diag(D.getDeclSpec().getThreadStorageClassSpecLoc(),
+         diag::err_invalid_thread)
+      << DeclSpec::getSpecifierName(TSCS);
+
+  // Check to see if this name was declared as a member previously
+  NamedDecl *PrevDecl = nullptr;
+  LookupResult Previous(*this, II, Loc, LookupMemberName,
+                        ForVisibleRedeclaration);
+  LookupName(Previous, S);
+  switch (Previous.getResultKind()) {
+  case LookupResult::Found:
+  case LookupResult::FoundUnresolvedValue:
+    PrevDecl = Previous.getAsSingle<NamedDecl>();
+    break;
+
+  case LookupResult::FoundOverloaded:
+    PrevDecl = Previous.getRepresentativeDecl();
+    break;
+
+  case LookupResult::NotFound:
+  case LookupResult::NotFoundInCurrentInstantiation:
+  case LookupResult::Ambiguous:
+    break;
+  }
+
+  if (PrevDecl && PrevDecl->isTemplateParameter()) {
+    // Maybe we will complain about the shadowed template parameter.
+    DiagnoseTemplateParameterShadow(D.getIdentifierLoc(), PrevDecl);
+    // Just pretend that we didn't see the previous declaration.
+    PrevDecl = nullptr;
+  }
+
+  if (PrevDecl && !isDeclInScope(PrevDecl, Record, S))
+    PrevDecl = nullptr;
+
+  SourceLocation TSSL = D.getBeginLoc();
+  MSPropertyDecl *NewPD =
+      MSPropertyDecl::Create(Context, Record, Loc, II, T, TInfo, TSSL,
+                             MSPropertyAttr.getPropertyDataGetter(),
+                             MSPropertyAttr.getPropertyDataSetter());
+  ProcessDeclAttributes(TUScope, NewPD, D);
+  NewPD->setAccess(AS);
+
+  if (NewPD->isInvalidDecl())
+    Record->setInvalidDecl();
+
+  if (D.getDeclSpec().isModulePrivateSpecified())
+    NewPD->setModulePrivate();
+
+  if (NewPD->isInvalidDecl() && PrevDecl) {
+    // Don't introduce NewFD into scope; there's already something
+    // with the same name in the same scope.
+  } else if (II) {
+    PushOnScopeChains(NewPD, S);
+  } else
+    Record->addDecl(NewPD);
+
+  return NewPD;
+}
+
+void Sema::ActOnStartFunctionDeclarationDeclarator(
+    Declarator &Declarator, unsigned TemplateParameterDepth) {
+  auto &Info = InventedParameterInfos.emplace_back();
+  TemplateParameterList *ExplicitParams = nullptr;
+  ArrayRef<TemplateParameterList *> ExplicitLists =
+      Declarator.getTemplateParameterLists();
+  if (!ExplicitLists.empty()) {
+    bool IsMemberSpecialization, IsInvalid;
+    ExplicitParams = MatchTemplateParametersToScopeSpecifier(
+        Declarator.getBeginLoc(), Declarator.getIdentifierLoc(),
+        Declarator.getCXXScopeSpec(), /*TemplateId=*/nullptr,
+        ExplicitLists, /*IsFriend=*/false, IsMemberSpecialization, IsInvalid,
+        /*SuppressDiagnostic=*/true);
+  }
+  if (ExplicitParams) {
+    Info.AutoTemplateParameterDepth = ExplicitParams->getDepth();
+    for (NamedDecl *Param : *ExplicitParams)
+      Info.TemplateParams.push_back(Param);
+    Info.NumExplicitTemplateParams = ExplicitParams->size();
+  } else {
+    Info.AutoTemplateParameterDepth = TemplateParameterDepth;
+    Info.NumExplicitTemplateParams = 0;
+  }
+}
+
+void Sema::ActOnFinishFunctionDeclarationDeclarator(Declarator &Declarator) {
+  auto &FSI = InventedParameterInfos.back();
+  if (FSI.TemplateParams.size() > FSI.NumExplicitTemplateParams) {
+    if (FSI.NumExplicitTemplateParams != 0) {
+      TemplateParameterList *ExplicitParams =
+          Declarator.getTemplateParameterLists().back();
+      Declarator.setInventedTemplateParameterList(
+          TemplateParameterList::Create(
+              Context, ExplicitParams->getTemplateLoc(),
+              ExplicitParams->getLAngleLoc(), FSI.TemplateParams,
+              ExplicitParams->getRAngleLoc(),
+              ExplicitParams->getRequiresClause()));
+    } else {
+      Declarator.setInventedTemplateParameterList(
+          TemplateParameterList::Create(
+              Context, SourceLocation(), SourceLocation(), FSI.TemplateParams,
+              SourceLocation(), /*RequiresClause=*/nullptr));
+    }
+  }
+  InventedParameterInfos.pop_back();
+}