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//===--- ForRangeCopyCheck.cpp - clang-tidy--------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "ForRangeCopyCheck.h"
#include "../utils/DeclRefExprUtils.h"
#include "../utils/FixItHintUtils.h"
#include "../utils/Matchers.h"
#include "../utils/OptionsUtils.h"
#include "../utils/TypeTraits.h"
#include "clang/Analysis/Analyses/ExprMutationAnalyzer.h"
#include "clang/Basic/Diagnostic.h"
#include <optional>
using namespace clang::ast_matchers;
namespace clang::tidy::performance {
ForRangeCopyCheck::ForRangeCopyCheck(StringRef Name, ClangTidyContext *Context)
: ClangTidyCheck(Name, Context),
WarnOnAllAutoCopies(Options.get("WarnOnAllAutoCopies", false)),
AllowedTypes(
utils::options::parseStringList(Options.get("AllowedTypes", ""))) {}
void ForRangeCopyCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
Options.store(Opts, "WarnOnAllAutoCopies", WarnOnAllAutoCopies);
Options.store(Opts, "AllowedTypes",
utils::options::serializeStringList(AllowedTypes));
}
void ForRangeCopyCheck::registerMatchers(MatchFinder *Finder) {
// Match loop variables that are not references or pointers or are already
// initialized through MaterializeTemporaryExpr which indicates a type
// conversion.
auto HasReferenceOrPointerTypeOrIsAllowed = hasType(qualType(
unless(anyOf(hasCanonicalType(anyOf(referenceType(), pointerType())),
hasDeclaration(namedDecl(
matchers::matchesAnyListedName(AllowedTypes)))))));
auto IteratorReturnsValueType = cxxOperatorCallExpr(
hasOverloadedOperatorName("*"),
callee(
cxxMethodDecl(returns(unless(hasCanonicalType(referenceType()))))));
auto NotConstructedByCopy = cxxConstructExpr(
hasDeclaration(cxxConstructorDecl(unless(isCopyConstructor()))));
auto ConstructedByConversion = cxxMemberCallExpr(callee(cxxConversionDecl()));
auto LoopVar =
varDecl(HasReferenceOrPointerTypeOrIsAllowed,
unless(hasInitializer(expr(hasDescendant(expr(
anyOf(materializeTemporaryExpr(), IteratorReturnsValueType,
NotConstructedByCopy, ConstructedByConversion)))))));
Finder->addMatcher(
traverse(TK_AsIs,
cxxForRangeStmt(hasLoopVariable(LoopVar.bind("loopVar")))
.bind("forRange")),
this);
}
void ForRangeCopyCheck::check(const MatchFinder::MatchResult &Result) {
const auto *Var = Result.Nodes.getNodeAs<VarDecl>("loopVar");
// Ignore code in macros since we can't place the fixes correctly.
if (Var->getBeginLoc().isMacroID())
return;
if (handleConstValueCopy(*Var, *Result.Context))
return;
const auto *ForRange = Result.Nodes.getNodeAs<CXXForRangeStmt>("forRange");
handleCopyIsOnlyConstReferenced(*Var, *ForRange, *Result.Context);
}
bool ForRangeCopyCheck::handleConstValueCopy(const VarDecl &LoopVar,
ASTContext &Context) {
if (WarnOnAllAutoCopies) {
// For aggressive check just test that loop variable has auto type.
if (!isa<AutoType>(LoopVar.getType()))
return false;
} else if (!LoopVar.getType().isConstQualified()) {
return false;
}
std::optional<bool> Expensive =
utils::type_traits::isExpensiveToCopy(LoopVar.getType(), Context);
if (!Expensive || !*Expensive)
return false;
auto Diagnostic =
diag(LoopVar.getLocation(),
"the loop variable's type is not a reference type; this creates a "
"copy in each iteration; consider making this a reference")
<< utils::fixit::changeVarDeclToReference(LoopVar, Context);
if (!LoopVar.getType().isConstQualified()) {
if (std::optional<FixItHint> Fix = utils::fixit::addQualifierToVarDecl(
LoopVar, Context, DeclSpec::TQ::TQ_const))
Diagnostic << *Fix;
}
return true;
}
bool ForRangeCopyCheck::handleCopyIsOnlyConstReferenced(
const VarDecl &LoopVar, const CXXForRangeStmt &ForRange,
ASTContext &Context) {
std::optional<bool> Expensive =
utils::type_traits::isExpensiveToCopy(LoopVar.getType(), Context);
if (LoopVar.getType().isConstQualified() || !Expensive || !*Expensive)
return false;
// We omit the case where the loop variable is not used in the loop body. E.g.
//
// for (auto _ : benchmark_state) {
// }
//
// Because the fix (changing to `const auto &`) will introduce an unused
// compiler warning which can't be suppressed.
// Since this case is very rare, it is safe to ignore it.
if (!ExprMutationAnalyzer(*ForRange.getBody(), Context).isMutated(&LoopVar) &&
!utils::decl_ref_expr::allDeclRefExprs(LoopVar, *ForRange.getBody(),
Context)
.empty()) {
auto Diag = diag(
LoopVar.getLocation(),
"loop variable is copied but only used as const reference; consider "
"making it a const reference");
if (std::optional<FixItHint> Fix = utils::fixit::addQualifierToVarDecl(
LoopVar, Context, DeclSpec::TQ::TQ_const))
Diag << *Fix << utils::fixit::changeVarDeclToReference(LoopVar, Context);
return true;
}
return false;
}
} // namespace clang::tidy::performance
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