Restoring authorship annotation for <orivej@yandex-team.ru>. Commit 2 of 2.

1 files changed, 373 insertions, 373 deletions

diff --git a/contrib/libs/llvm12/lib/CodeGen/ShadowStackGCLowering.cpp b/contrib/libs/llvm12/lib/CodeGen/ShadowStackGCLowering.cpp
index c62912b11c..45427dc41e 100644
--- a/contrib/libs/llvm12/lib/CodeGen/ShadowStackGCLowering.cpp
+++ b/contrib/libs/llvm12/lib/CodeGen/ShadowStackGCLowering.cpp
@@ -1,373 +1,373 @@
-//===- ShadowStackGCLowering.cpp - Custom lowering for shadow-stack gc ----===// 
-// 
-// 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 contains the custom lowering code required by the shadow-stack GC 
-// strategy. 
-// 
-// This pass implements the code transformation described in this paper: 
-//   "Accurate Garbage Collection in an Uncooperative Environment" 
-//   Fergus Henderson, ISMM, 2002 
-// 
-//===----------------------------------------------------------------------===// 
- 
-#include "llvm/ADT/SmallVector.h" 
-#include "llvm/ADT/StringExtras.h" 
-#include "llvm/CodeGen/Passes.h" 
-#include "llvm/IR/BasicBlock.h" 
-#include "llvm/IR/Constant.h" 
-#include "llvm/IR/Constants.h" 
-#include "llvm/IR/DerivedTypes.h" 
-#include "llvm/IR/Function.h" 
-#include "llvm/IR/GlobalValue.h" 
-#include "llvm/IR/GlobalVariable.h" 
-#include "llvm/IR/IRBuilder.h" 
-#include "llvm/IR/Instructions.h" 
-#include "llvm/IR/IntrinsicInst.h" 
-#include "llvm/IR/Intrinsics.h" 
-#include "llvm/IR/Module.h" 
-#include "llvm/IR/Type.h" 
-#include "llvm/IR/Value.h" 
-#include "llvm/InitializePasses.h" 
-#include "llvm/Pass.h" 
-#include "llvm/Support/Casting.h" 
-#include "llvm/Transforms/Utils/EscapeEnumerator.h" 
-#include <cassert> 
-#include <cstddef> 
-#include <string> 
-#include <utility> 
-#include <vector> 
- 
-using namespace llvm; 
- 
-#define DEBUG_TYPE "shadow-stack-gc-lowering" 
- 
-namespace { 
- 
-class ShadowStackGCLowering : public FunctionPass { 
-  /// RootChain - This is the global linked-list that contains the chain of GC 
-  /// roots. 
-  GlobalVariable *Head = nullptr; 
- 
-  /// StackEntryTy - Abstract type of a link in the shadow stack. 
-  StructType *StackEntryTy = nullptr; 
-  StructType *FrameMapTy = nullptr; 
- 
-  /// Roots - GC roots in the current function. Each is a pair of the 
-  /// intrinsic call and its corresponding alloca. 
-  std::vector<std::pair<CallInst *, AllocaInst *>> Roots; 
- 
-public: 
-  static char ID; 
- 
-  ShadowStackGCLowering(); 
- 
-  bool doInitialization(Module &M) override; 
-  bool runOnFunction(Function &F) override; 
- 
-private: 
-  bool IsNullValue(Value *V); 
-  Constant *GetFrameMap(Function &F); 
-  Type *GetConcreteStackEntryType(Function &F); 
-  void CollectRoots(Function &F); 
- 
-  static GetElementPtrInst *CreateGEP(LLVMContext &Context, IRBuilder<> &B, 
-                                      Type *Ty, Value *BasePtr, int Idx1, 
-                                      const char *Name); 
-  static GetElementPtrInst *CreateGEP(LLVMContext &Context, IRBuilder<> &B, 
-                                      Type *Ty, Value *BasePtr, int Idx1, int Idx2, 
-                                      const char *Name); 
-}; 
- 
-} // end anonymous namespace 
- 
-char ShadowStackGCLowering::ID = 0; 
- 
-INITIALIZE_PASS_BEGIN(ShadowStackGCLowering, DEBUG_TYPE, 
-                      "Shadow Stack GC Lowering", false, false) 
-INITIALIZE_PASS_DEPENDENCY(GCModuleInfo) 
-INITIALIZE_PASS_END(ShadowStackGCLowering, DEBUG_TYPE, 
-                    "Shadow Stack GC Lowering", false, false) 
- 
-FunctionPass *llvm::createShadowStackGCLoweringPass() { return new ShadowStackGCLowering(); } 
- 
-ShadowStackGCLowering::ShadowStackGCLowering() : FunctionPass(ID) { 
-  initializeShadowStackGCLoweringPass(*PassRegistry::getPassRegistry()); 
-} 
- 
-Constant *ShadowStackGCLowering::GetFrameMap(Function &F) { 
-  // doInitialization creates the abstract type of this value. 
-  Type *VoidPtr = Type::getInt8PtrTy(F.getContext()); 
- 
-  // Truncate the ShadowStackDescriptor if some metadata is null. 
-  unsigned NumMeta = 0; 
-  SmallVector<Constant *, 16> Metadata; 
-  for (unsigned I = 0; I != Roots.size(); ++I) { 
-    Constant *C = cast<Constant>(Roots[I].first->getArgOperand(1)); 
-    if (!C->isNullValue()) 
-      NumMeta = I + 1; 
-    Metadata.push_back(ConstantExpr::getBitCast(C, VoidPtr)); 
-  } 
-  Metadata.resize(NumMeta); 
- 
-  Type *Int32Ty = Type::getInt32Ty(F.getContext()); 
- 
-  Constant *BaseElts[] = { 
-      ConstantInt::get(Int32Ty, Roots.size(), false), 
-      ConstantInt::get(Int32Ty, NumMeta, false), 
-  }; 
- 
-  Constant *DescriptorElts[] = { 
-      ConstantStruct::get(FrameMapTy, BaseElts), 
-      ConstantArray::get(ArrayType::get(VoidPtr, NumMeta), Metadata)}; 
- 
-  Type *EltTys[] = {DescriptorElts[0]->getType(), DescriptorElts[1]->getType()}; 
-  StructType *STy = StructType::create(EltTys, "gc_map." + utostr(NumMeta)); 
- 
-  Constant *FrameMap = ConstantStruct::get(STy, DescriptorElts); 
- 
-  // FIXME: Is this actually dangerous as WritingAnLLVMPass.html claims? Seems 
-  //        that, short of multithreaded LLVM, it should be safe; all that is 
-  //        necessary is that a simple Module::iterator loop not be invalidated. 
-  //        Appending to the GlobalVariable list is safe in that sense. 
-  // 
-  //        All of the output passes emit globals last. The ExecutionEngine 
-  //        explicitly supports adding globals to the module after 
-  //        initialization. 
-  // 
-  //        Still, if it isn't deemed acceptable, then this transformation needs 
-  //        to be a ModulePass (which means it cannot be in the 'llc' pipeline 
-  //        (which uses a FunctionPassManager (which segfaults (not asserts) if 
-  //        provided a ModulePass))). 
-  Constant *GV = new GlobalVariable(*F.getParent(), FrameMap->getType(), true, 
-                                    GlobalVariable::InternalLinkage, FrameMap, 
-                                    "__gc_" + F.getName()); 
- 
-  Constant *GEPIndices[2] = { 
-      ConstantInt::get(Type::getInt32Ty(F.getContext()), 0), 
-      ConstantInt::get(Type::getInt32Ty(F.getContext()), 0)}; 
-  return ConstantExpr::getGetElementPtr(FrameMap->getType(), GV, GEPIndices); 
-} 
- 
-Type *ShadowStackGCLowering::GetConcreteStackEntryType(Function &F) { 
-  // doInitialization creates the generic version of this type. 
-  std::vector<Type *> EltTys; 
-  EltTys.push_back(StackEntryTy); 
-  for (size_t I = 0; I != Roots.size(); I++) 
-    EltTys.push_back(Roots[I].second->getAllocatedType()); 
- 
-  return StructType::create(EltTys, ("gc_stackentry." + F.getName()).str()); 
-} 
- 
-/// doInitialization - If this module uses the GC intrinsics, find them now. If 
-/// not, exit fast. 
-bool ShadowStackGCLowering::doInitialization(Module &M) { 
-  bool Active = false; 
-  for (Function &F : M) { 
-    if (F.hasGC() && F.getGC() == std::string("shadow-stack")) { 
-      Active = true; 
-      break; 
-    } 
-  } 
-  if (!Active) 
-    return false; 
- 
-  // struct FrameMap { 
-  //   int32_t NumRoots; // Number of roots in stack frame. 
-  //   int32_t NumMeta;  // Number of metadata descriptors. May be < NumRoots. 
-  //   void *Meta[];     // May be absent for roots without metadata. 
-  // }; 
-  std::vector<Type *> EltTys; 
-  // 32 bits is ok up to a 32GB stack frame. :) 
-  EltTys.push_back(Type::getInt32Ty(M.getContext())); 
-  // Specifies length of variable length array. 
-  EltTys.push_back(Type::getInt32Ty(M.getContext())); 
-  FrameMapTy = StructType::create(EltTys, "gc_map"); 
-  PointerType *FrameMapPtrTy = PointerType::getUnqual(FrameMapTy); 
- 
-  // struct StackEntry { 
-  //   ShadowStackEntry *Next; // Caller's stack entry. 
-  //   FrameMap *Map;          // Pointer to constant FrameMap. 
-  //   void *Roots[];          // Stack roots (in-place array, so we pretend). 
-  // }; 
- 
-  StackEntryTy = StructType::create(M.getContext(), "gc_stackentry"); 
- 
-  EltTys.clear(); 
-  EltTys.push_back(PointerType::getUnqual(StackEntryTy)); 
-  EltTys.push_back(FrameMapPtrTy); 
-  StackEntryTy->setBody(EltTys); 
-  PointerType *StackEntryPtrTy = PointerType::getUnqual(StackEntryTy); 
- 
-  // Get the root chain if it already exists. 
-  Head = M.getGlobalVariable("llvm_gc_root_chain"); 
-  if (!Head) { 
-    // If the root chain does not exist, insert a new one with linkonce 
-    // linkage! 
-    Head = new GlobalVariable( 
-        M, StackEntryPtrTy, false, GlobalValue::LinkOnceAnyLinkage, 
-        Constant::getNullValue(StackEntryPtrTy), "llvm_gc_root_chain"); 
-  } else if (Head->hasExternalLinkage() && Head->isDeclaration()) { 
-    Head->setInitializer(Constant::getNullValue(StackEntryPtrTy)); 
-    Head->setLinkage(GlobalValue::LinkOnceAnyLinkage); 
-  } 
- 
-  return true; 
-} 
- 
-bool ShadowStackGCLowering::IsNullValue(Value *V) { 
-  if (Constant *C = dyn_cast<Constant>(V)) 
-    return C->isNullValue(); 
-  return false; 
-} 
- 
-void ShadowStackGCLowering::CollectRoots(Function &F) { 
-  // FIXME: Account for original alignment. Could fragment the root array. 
-  //   Approach 1: Null initialize empty slots at runtime. Yuck. 
-  //   Approach 2: Emit a map of the array instead of just a count. 
- 
-  assert(Roots.empty() && "Not cleaned up?"); 
- 
-  SmallVector<std::pair<CallInst *, AllocaInst *>, 16> MetaRoots; 
- 
-  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 
-    for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) 
-      if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) 
-        if (Function *F = CI->getCalledFunction()) 
-          if (F->getIntrinsicID() == Intrinsic::gcroot) { 
-            std::pair<CallInst *, AllocaInst *> Pair = std::make_pair( 
-                CI, 
-                cast<AllocaInst>(CI->getArgOperand(0)->stripPointerCasts())); 
-            if (IsNullValue(CI->getArgOperand(1))) 
-              Roots.push_back(Pair); 
-            else 
-              MetaRoots.push_back(Pair); 
-          } 
- 
-  // Number roots with metadata (usually empty) at the beginning, so that the 
-  // FrameMap::Meta array can be elided. 
-  Roots.insert(Roots.begin(), MetaRoots.begin(), MetaRoots.end()); 
-} 
- 
-GetElementPtrInst *ShadowStackGCLowering::CreateGEP(LLVMContext &Context, 
-                                                    IRBuilder<> &B, Type *Ty, 
-                                                    Value *BasePtr, int Idx, 
-                                                    int Idx2, 
-                                                    const char *Name) { 
-  Value *Indices[] = {ConstantInt::get(Type::getInt32Ty(Context), 0), 
-                      ConstantInt::get(Type::getInt32Ty(Context), Idx), 
-                      ConstantInt::get(Type::getInt32Ty(Context), Idx2)}; 
-  Value *Val = B.CreateGEP(Ty, BasePtr, Indices, Name); 
- 
-  assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant"); 
- 
-  return dyn_cast<GetElementPtrInst>(Val); 
-} 
- 
-GetElementPtrInst *ShadowStackGCLowering::CreateGEP(LLVMContext &Context, 
-                                            IRBuilder<> &B, Type *Ty, Value *BasePtr, 
-                                            int Idx, const char *Name) { 
-  Value *Indices[] = {ConstantInt::get(Type::getInt32Ty(Context), 0), 
-                      ConstantInt::get(Type::getInt32Ty(Context), Idx)}; 
-  Value *Val = B.CreateGEP(Ty, BasePtr, Indices, Name); 
- 
-  assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant"); 
- 
-  return dyn_cast<GetElementPtrInst>(Val); 
-} 
- 
-/// runOnFunction - Insert code to maintain the shadow stack. 
-bool ShadowStackGCLowering::runOnFunction(Function &F) { 
-  // Quick exit for functions that do not use the shadow stack GC. 
-  if (!F.hasGC() || 
-      F.getGC() != std::string("shadow-stack")) 
-    return false; 
- 
-  LLVMContext &Context = F.getContext(); 
- 
-  // Find calls to llvm.gcroot. 
-  CollectRoots(F); 
- 
-  // If there are no roots in this function, then there is no need to add a 
-  // stack map entry for it. 
-  if (Roots.empty()) 
-    return false; 
- 
-  // Build the constant map and figure the type of the shadow stack entry. 
-  Value *FrameMap = GetFrameMap(F); 
-  Type *ConcreteStackEntryTy = GetConcreteStackEntryType(F); 
- 
-  // Build the shadow stack entry at the very start of the function. 
-  BasicBlock::iterator IP = F.getEntryBlock().begin(); 
-  IRBuilder<> AtEntry(IP->getParent(), IP); 
- 
-  Instruction *StackEntry = 
-      AtEntry.CreateAlloca(ConcreteStackEntryTy, nullptr, "gc_frame"); 
- 
-  while (isa<AllocaInst>(IP)) 
-    ++IP; 
-  AtEntry.SetInsertPoint(IP->getParent(), IP); 
- 
-  // Initialize the map pointer and load the current head of the shadow stack. 
-  Instruction *CurrentHead = 
-      AtEntry.CreateLoad(StackEntryTy->getPointerTo(), Head, "gc_currhead"); 
-  Instruction *EntryMapPtr = CreateGEP(Context, AtEntry, ConcreteStackEntryTy, 
-                                       StackEntry, 0, 1, "gc_frame.map"); 
-  AtEntry.CreateStore(FrameMap, EntryMapPtr); 
- 
-  // After all the allocas... 
-  for (unsigned I = 0, E = Roots.size(); I != E; ++I) { 
-    // For each root, find the corresponding slot in the aggregate... 
-    Value *SlotPtr = CreateGEP(Context, AtEntry, ConcreteStackEntryTy, 
-                               StackEntry, 1 + I, "gc_root"); 
- 
-    // And use it in lieu of the alloca. 
-    AllocaInst *OriginalAlloca = Roots[I].second; 
-    SlotPtr->takeName(OriginalAlloca); 
-    OriginalAlloca->replaceAllUsesWith(SlotPtr); 
-  } 
- 
-  // Move past the original stores inserted by GCStrategy::InitRoots. This isn't 
-  // really necessary (the collector would never see the intermediate state at 
-  // runtime), but it's nicer not to push the half-initialized entry onto the 
-  // shadow stack. 
-  while (isa<StoreInst>(IP)) 
-    ++IP; 
-  AtEntry.SetInsertPoint(IP->getParent(), IP); 
- 
-  // Push the entry onto the shadow stack. 
-  Instruction *EntryNextPtr = CreateGEP(Context, AtEntry, ConcreteStackEntryTy, 
-                                        StackEntry, 0, 0, "gc_frame.next"); 
-  Instruction *NewHeadVal = CreateGEP(Context, AtEntry, ConcreteStackEntryTy, 
-                                      StackEntry, 0, "gc_newhead"); 
-  AtEntry.CreateStore(CurrentHead, EntryNextPtr); 
-  AtEntry.CreateStore(NewHeadVal, Head); 
- 
-  // For each instruction that escapes... 
-  EscapeEnumerator EE(F, "gc_cleanup"); 
-  while (IRBuilder<> *AtExit = EE.Next()) { 
-    // Pop the entry from the shadow stack. Don't reuse CurrentHead from 
-    // AtEntry, since that would make the value live for the entire function. 
-    Instruction *EntryNextPtr2 = 
-        CreateGEP(Context, *AtExit, ConcreteStackEntryTy, StackEntry, 0, 0, 
-                  "gc_frame.next"); 
-    Value *SavedHead = AtExit->CreateLoad(StackEntryTy->getPointerTo(), 
-                                          EntryNextPtr2, "gc_savedhead"); 
-    AtExit->CreateStore(SavedHead, Head); 
-  } 
- 
-  // Delete the original allocas (which are no longer used) and the intrinsic 
-  // calls (which are no longer valid). Doing this last avoids invalidating 
-  // iterators. 
-  for (unsigned I = 0, E = Roots.size(); I != E; ++I) { 
-    Roots[I].first->eraseFromParent(); 
-    Roots[I].second->eraseFromParent(); 
-  } 
- 
-  Roots.clear(); 
-  return true; 
-} 
+//===- ShadowStackGCLowering.cpp - Custom lowering for shadow-stack gc ----===//
+//
+// 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 contains the custom lowering code required by the shadow-stack GC
+// strategy.
+//
+// This pass implements the code transformation described in this paper:
+//   "Accurate Garbage Collection in an Uncooperative Environment"
+//   Fergus Henderson, ISMM, 2002
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/GlobalValue.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/Value.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Transforms/Utils/EscapeEnumerator.h"
+#include <cassert>
+#include <cstddef>
+#include <string>
+#include <utility>
+#include <vector>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "shadow-stack-gc-lowering"
+
+namespace {
+
+class ShadowStackGCLowering : public FunctionPass {
+  /// RootChain - This is the global linked-list that contains the chain of GC
+  /// roots.
+  GlobalVariable *Head = nullptr;
+
+  /// StackEntryTy - Abstract type of a link in the shadow stack.
+  StructType *StackEntryTy = nullptr;
+  StructType *FrameMapTy = nullptr;
+
+  /// Roots - GC roots in the current function. Each is a pair of the
+  /// intrinsic call and its corresponding alloca.
+  std::vector<std::pair<CallInst *, AllocaInst *>> Roots;
+
+public:
+  static char ID;
+
+  ShadowStackGCLowering();
+
+  bool doInitialization(Module &M) override;
+  bool runOnFunction(Function &F) override;
+
+private:
+  bool IsNullValue(Value *V);
+  Constant *GetFrameMap(Function &F);
+  Type *GetConcreteStackEntryType(Function &F);
+  void CollectRoots(Function &F);
+
+  static GetElementPtrInst *CreateGEP(LLVMContext &Context, IRBuilder<> &B,
+                                      Type *Ty, Value *BasePtr, int Idx1,
+                                      const char *Name);
+  static GetElementPtrInst *CreateGEP(LLVMContext &Context, IRBuilder<> &B,
+                                      Type *Ty, Value *BasePtr, int Idx1, int Idx2,
+                                      const char *Name);
+};
+
+} // end anonymous namespace
+
+char ShadowStackGCLowering::ID = 0;
+
+INITIALIZE_PASS_BEGIN(ShadowStackGCLowering, DEBUG_TYPE,
+                      "Shadow Stack GC Lowering", false, false)
+INITIALIZE_PASS_DEPENDENCY(GCModuleInfo)
+INITIALIZE_PASS_END(ShadowStackGCLowering, DEBUG_TYPE,
+                    "Shadow Stack GC Lowering", false, false)
+
+FunctionPass *llvm::createShadowStackGCLoweringPass() { return new ShadowStackGCLowering(); }
+
+ShadowStackGCLowering::ShadowStackGCLowering() : FunctionPass(ID) {
+  initializeShadowStackGCLoweringPass(*PassRegistry::getPassRegistry());
+}
+
+Constant *ShadowStackGCLowering::GetFrameMap(Function &F) {
+  // doInitialization creates the abstract type of this value.
+  Type *VoidPtr = Type::getInt8PtrTy(F.getContext());
+
+  // Truncate the ShadowStackDescriptor if some metadata is null.
+  unsigned NumMeta = 0;
+  SmallVector<Constant *, 16> Metadata;
+  for (unsigned I = 0; I != Roots.size(); ++I) {
+    Constant *C = cast<Constant>(Roots[I].first->getArgOperand(1));
+    if (!C->isNullValue())
+      NumMeta = I + 1;
+    Metadata.push_back(ConstantExpr::getBitCast(C, VoidPtr));
+  }
+  Metadata.resize(NumMeta);
+
+  Type *Int32Ty = Type::getInt32Ty(F.getContext());
+
+  Constant *BaseElts[] = {
+      ConstantInt::get(Int32Ty, Roots.size(), false),
+      ConstantInt::get(Int32Ty, NumMeta, false),
+  };
+
+  Constant *DescriptorElts[] = {
+      ConstantStruct::get(FrameMapTy, BaseElts),
+      ConstantArray::get(ArrayType::get(VoidPtr, NumMeta), Metadata)};
+
+  Type *EltTys[] = {DescriptorElts[0]->getType(), DescriptorElts[1]->getType()};
+  StructType *STy = StructType::create(EltTys, "gc_map." + utostr(NumMeta));
+
+  Constant *FrameMap = ConstantStruct::get(STy, DescriptorElts);
+
+  // FIXME: Is this actually dangerous as WritingAnLLVMPass.html claims? Seems
+  //        that, short of multithreaded LLVM, it should be safe; all that is
+  //        necessary is that a simple Module::iterator loop not be invalidated.
+  //        Appending to the GlobalVariable list is safe in that sense.
+  //
+  //        All of the output passes emit globals last. The ExecutionEngine
+  //        explicitly supports adding globals to the module after
+  //        initialization.
+  //
+  //        Still, if it isn't deemed acceptable, then this transformation needs
+  //        to be a ModulePass (which means it cannot be in the 'llc' pipeline
+  //        (which uses a FunctionPassManager (which segfaults (not asserts) if
+  //        provided a ModulePass))).
+  Constant *GV = new GlobalVariable(*F.getParent(), FrameMap->getType(), true,
+                                    GlobalVariable::InternalLinkage, FrameMap,
+                                    "__gc_" + F.getName());
+
+  Constant *GEPIndices[2] = {
+      ConstantInt::get(Type::getInt32Ty(F.getContext()), 0),
+      ConstantInt::get(Type::getInt32Ty(F.getContext()), 0)};
+  return ConstantExpr::getGetElementPtr(FrameMap->getType(), GV, GEPIndices);
+}
+
+Type *ShadowStackGCLowering::GetConcreteStackEntryType(Function &F) {
+  // doInitialization creates the generic version of this type.
+  std::vector<Type *> EltTys;
+  EltTys.push_back(StackEntryTy);
+  for (size_t I = 0; I != Roots.size(); I++)
+    EltTys.push_back(Roots[I].second->getAllocatedType());
+
+  return StructType::create(EltTys, ("gc_stackentry." + F.getName()).str());
+}
+
+/// doInitialization - If this module uses the GC intrinsics, find them now. If
+/// not, exit fast.
+bool ShadowStackGCLowering::doInitialization(Module &M) {
+  bool Active = false;
+  for (Function &F : M) {
+    if (F.hasGC() && F.getGC() == std::string("shadow-stack")) {
+      Active = true;
+      break;
+    }
+  }
+  if (!Active)
+    return false;
+
+  // struct FrameMap {
+  //   int32_t NumRoots; // Number of roots in stack frame.
+  //   int32_t NumMeta;  // Number of metadata descriptors. May be < NumRoots.
+  //   void *Meta[];     // May be absent for roots without metadata.
+  // };
+  std::vector<Type *> EltTys;
+  // 32 bits is ok up to a 32GB stack frame. :)
+  EltTys.push_back(Type::getInt32Ty(M.getContext()));
+  // Specifies length of variable length array.
+  EltTys.push_back(Type::getInt32Ty(M.getContext()));
+  FrameMapTy = StructType::create(EltTys, "gc_map");
+  PointerType *FrameMapPtrTy = PointerType::getUnqual(FrameMapTy);
+
+  // struct StackEntry {
+  //   ShadowStackEntry *Next; // Caller's stack entry.
+  //   FrameMap *Map;          // Pointer to constant FrameMap.
+  //   void *Roots[];          // Stack roots (in-place array, so we pretend).
+  // };
+
+  StackEntryTy = StructType::create(M.getContext(), "gc_stackentry");
+
+  EltTys.clear();
+  EltTys.push_back(PointerType::getUnqual(StackEntryTy));
+  EltTys.push_back(FrameMapPtrTy);
+  StackEntryTy->setBody(EltTys);
+  PointerType *StackEntryPtrTy = PointerType::getUnqual(StackEntryTy);
+
+  // Get the root chain if it already exists.
+  Head = M.getGlobalVariable("llvm_gc_root_chain");
+  if (!Head) {
+    // If the root chain does not exist, insert a new one with linkonce
+    // linkage!
+    Head = new GlobalVariable(
+        M, StackEntryPtrTy, false, GlobalValue::LinkOnceAnyLinkage,
+        Constant::getNullValue(StackEntryPtrTy), "llvm_gc_root_chain");
+  } else if (Head->hasExternalLinkage() && Head->isDeclaration()) {
+    Head->setInitializer(Constant::getNullValue(StackEntryPtrTy));
+    Head->setLinkage(GlobalValue::LinkOnceAnyLinkage);
+  }
+
+  return true;
+}
+
+bool ShadowStackGCLowering::IsNullValue(Value *V) {
+  if (Constant *C = dyn_cast<Constant>(V))
+    return C->isNullValue();
+  return false;
+}
+
+void ShadowStackGCLowering::CollectRoots(Function &F) {
+  // FIXME: Account for original alignment. Could fragment the root array.
+  //   Approach 1: Null initialize empty slots at runtime. Yuck.
+  //   Approach 2: Emit a map of the array instead of just a count.
+
+  assert(Roots.empty() && "Not cleaned up?");
+
+  SmallVector<std::pair<CallInst *, AllocaInst *>, 16> MetaRoots;
+
+  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+    for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;)
+      if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++))
+        if (Function *F = CI->getCalledFunction())
+          if (F->getIntrinsicID() == Intrinsic::gcroot) {
+            std::pair<CallInst *, AllocaInst *> Pair = std::make_pair(
+                CI,
+                cast<AllocaInst>(CI->getArgOperand(0)->stripPointerCasts()));
+            if (IsNullValue(CI->getArgOperand(1)))
+              Roots.push_back(Pair);
+            else
+              MetaRoots.push_back(Pair);
+          }
+
+  // Number roots with metadata (usually empty) at the beginning, so that the
+  // FrameMap::Meta array can be elided.
+  Roots.insert(Roots.begin(), MetaRoots.begin(), MetaRoots.end());
+}
+
+GetElementPtrInst *ShadowStackGCLowering::CreateGEP(LLVMContext &Context,
+                                                    IRBuilder<> &B, Type *Ty,
+                                                    Value *BasePtr, int Idx,
+                                                    int Idx2,
+                                                    const char *Name) {
+  Value *Indices[] = {ConstantInt::get(Type::getInt32Ty(Context), 0),
+                      ConstantInt::get(Type::getInt32Ty(Context), Idx),
+                      ConstantInt::get(Type::getInt32Ty(Context), Idx2)};
+  Value *Val = B.CreateGEP(Ty, BasePtr, Indices, Name);
+
+  assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant");
+
+  return dyn_cast<GetElementPtrInst>(Val);
+}
+
+GetElementPtrInst *ShadowStackGCLowering::CreateGEP(LLVMContext &Context,
+                                            IRBuilder<> &B, Type *Ty, Value *BasePtr,
+                                            int Idx, const char *Name) {
+  Value *Indices[] = {ConstantInt::get(Type::getInt32Ty(Context), 0),
+                      ConstantInt::get(Type::getInt32Ty(Context), Idx)};
+  Value *Val = B.CreateGEP(Ty, BasePtr, Indices, Name);
+
+  assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant");
+
+  return dyn_cast<GetElementPtrInst>(Val);
+}
+
+/// runOnFunction - Insert code to maintain the shadow stack.
+bool ShadowStackGCLowering::runOnFunction(Function &F) {
+  // Quick exit for functions that do not use the shadow stack GC.
+  if (!F.hasGC() ||
+      F.getGC() != std::string("shadow-stack"))
+    return false;
+
+  LLVMContext &Context = F.getContext();
+
+  // Find calls to llvm.gcroot.
+  CollectRoots(F);
+
+  // If there are no roots in this function, then there is no need to add a
+  // stack map entry for it.
+  if (Roots.empty())
+    return false;
+
+  // Build the constant map and figure the type of the shadow stack entry.
+  Value *FrameMap = GetFrameMap(F);
+  Type *ConcreteStackEntryTy = GetConcreteStackEntryType(F);
+
+  // Build the shadow stack entry at the very start of the function.
+  BasicBlock::iterator IP = F.getEntryBlock().begin();
+  IRBuilder<> AtEntry(IP->getParent(), IP);
+
+  Instruction *StackEntry =
+      AtEntry.CreateAlloca(ConcreteStackEntryTy, nullptr, "gc_frame");
+
+  while (isa<AllocaInst>(IP))
+    ++IP;
+  AtEntry.SetInsertPoint(IP->getParent(), IP);
+
+  // Initialize the map pointer and load the current head of the shadow stack.
+  Instruction *CurrentHead =
+      AtEntry.CreateLoad(StackEntryTy->getPointerTo(), Head, "gc_currhead");
+  Instruction *EntryMapPtr = CreateGEP(Context, AtEntry, ConcreteStackEntryTy,
+                                       StackEntry, 0, 1, "gc_frame.map");
+  AtEntry.CreateStore(FrameMap, EntryMapPtr);
+
+  // After all the allocas...
+  for (unsigned I = 0, E = Roots.size(); I != E; ++I) {
+    // For each root, find the corresponding slot in the aggregate...
+    Value *SlotPtr = CreateGEP(Context, AtEntry, ConcreteStackEntryTy,
+                               StackEntry, 1 + I, "gc_root");
+
+    // And use it in lieu of the alloca.
+    AllocaInst *OriginalAlloca = Roots[I].second;
+    SlotPtr->takeName(OriginalAlloca);
+    OriginalAlloca->replaceAllUsesWith(SlotPtr);
+  }
+
+  // Move past the original stores inserted by GCStrategy::InitRoots. This isn't
+  // really necessary (the collector would never see the intermediate state at
+  // runtime), but it's nicer not to push the half-initialized entry onto the
+  // shadow stack.
+  while (isa<StoreInst>(IP))
+    ++IP;
+  AtEntry.SetInsertPoint(IP->getParent(), IP);
+
+  // Push the entry onto the shadow stack.
+  Instruction *EntryNextPtr = CreateGEP(Context, AtEntry, ConcreteStackEntryTy,
+                                        StackEntry, 0, 0, "gc_frame.next");
+  Instruction *NewHeadVal = CreateGEP(Context, AtEntry, ConcreteStackEntryTy,
+                                      StackEntry, 0, "gc_newhead");
+  AtEntry.CreateStore(CurrentHead, EntryNextPtr);
+  AtEntry.CreateStore(NewHeadVal, Head);
+
+  // For each instruction that escapes...
+  EscapeEnumerator EE(F, "gc_cleanup");
+  while (IRBuilder<> *AtExit = EE.Next()) {
+    // Pop the entry from the shadow stack. Don't reuse CurrentHead from
+    // AtEntry, since that would make the value live for the entire function.
+    Instruction *EntryNextPtr2 =
+        CreateGEP(Context, *AtExit, ConcreteStackEntryTy, StackEntry, 0, 0,
+                  "gc_frame.next");
+    Value *SavedHead = AtExit->CreateLoad(StackEntryTy->getPointerTo(),
+                                          EntryNextPtr2, "gc_savedhead");
+    AtExit->CreateStore(SavedHead, Head);
+  }
+
+  // Delete the original allocas (which are no longer used) and the intrinsic
+  // calls (which are no longer valid). Doing this last avoids invalidating
+  // iterators.
+  for (unsigned I = 0, E = Roots.size(); I != E; ++I) {
+    Roots[I].first->eraseFromParent();
+    Roots[I].second->eraseFromParent();
+  }
+
+  Roots.clear();
+  return true;
+}