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diff --git a/contrib/llvm/lib/CodeGen/ShadowStackGCLowering.cpp b/contrib/llvm/lib/CodeGen/ShadowStackGCLowering.cpp
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+++ b/contrib/llvm/lib/CodeGen/ShadowStackGCLowering.cpp
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+//===-- ShadowStackGCLowering.cpp - Custom lowering for shadow-stack gc ---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains the custom lowering code required by the shadow-stack GC
+// strategy.  
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/CodeGen/GCStrategy.h"
+#include "llvm/IR/CallSite.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "shadowstackgclowering"
+
+namespace {
+
+class ShadowStackGCLowering : public FunctionPass {
+  /// RootChain - This is the global linked-list that contains the chain of GC
+  /// roots.
+  GlobalVariable *Head;
+
+  /// StackEntryTy - Abstract type of a link in the shadow stack.
+  ///
+  StructType *StackEntryTy;
+  StructType *FrameMapTy;
+
+  /// 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);
+};
+}
+
+INITIALIZE_PASS_BEGIN(ShadowStackGCLowering, "shadow-stack-gc-lowering",
+                      "Shadow Stack GC Lowering", false, false)
+INITIALIZE_PASS_DEPENDENCY(GCModuleInfo)
+INITIALIZE_PASS_END(ShadowStackGCLowering, "shadow-stack-gc-lowering",
+                    "Shadow Stack GC Lowering", false, false)
+
+FunctionPass *llvm::createShadowStackGCLoweringPass() { return new ShadowStackGCLowering(); }
+
+char ShadowStackGCLowering::ID = 0;
+
+ShadowStackGCLowering::ShadowStackGCLowering()
+  : FunctionPass(ID), Head(nullptr), StackEntryTy(nullptr),
+    FrameMapTy(nullptr) {
+  initializeShadowStackGCLoweringPass(*PassRegistry::getPassRegistry());
+}
+
+namespace {
+/// EscapeEnumerator - This is a little algorithm to find all escape points
+/// from a function so that "finally"-style code can be inserted. In addition
+/// to finding the existing return and unwind instructions, it also (if
+/// necessary) transforms any call instructions into invokes and sends them to
+/// a landing pad.
+///
+/// It's wrapped up in a state machine using the same transform C# uses for
+/// 'yield return' enumerators, This transform allows it to be non-allocating.
+class EscapeEnumerator {
+  Function &F;
+  const char *CleanupBBName;
+
+  // State.
+  int State;
+  Function::iterator StateBB, StateE;
+  IRBuilder<> Builder;
+
+public:
+  EscapeEnumerator(Function &F, const char *N = "cleanup")
+      : F(F), CleanupBBName(N), State(0), Builder(F.getContext()) {}
+
+  IRBuilder<> *Next() {
+    switch (State) {
+    default:
+      return nullptr;
+
+    case 0:
+      StateBB = F.begin();
+      StateE = F.end();
+      State = 1;
+
+    case 1:
+      // Find all 'return', 'resume', and 'unwind' instructions.
+      while (StateBB != StateE) {
+        BasicBlock *CurBB = StateBB++;
+
+        // Branches and invokes do not escape, only unwind, resume, and return
+        // do.
+        TerminatorInst *TI = CurBB->getTerminator();
+        if (!isa<ReturnInst>(TI) && !isa<ResumeInst>(TI))
+          continue;
+
+        Builder.SetInsertPoint(TI->getParent(), TI);
+        return &Builder;
+      }
+
+      State = 2;
+
+      // Find all 'call' instructions.
+      SmallVector<Instruction *, 16> Calls;
+      for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+        for (BasicBlock::iterator II = BB->begin(), EE = BB->end(); II != EE;
+             ++II)
+          if (CallInst *CI = dyn_cast<CallInst>(II))
+            if (!CI->getCalledFunction() ||
+                !CI->getCalledFunction()->getIntrinsicID())
+              Calls.push_back(CI);
+
+      if (Calls.empty())
+        return nullptr;
+
+      // Create a cleanup block.
+      LLVMContext &C = F.getContext();
+      BasicBlock *CleanupBB = BasicBlock::Create(C, CleanupBBName, &F);
+      Type *ExnTy =
+          StructType::get(Type::getInt8PtrTy(C), Type::getInt32Ty(C), nullptr);
+      Constant *PersFn = F.getParent()->getOrInsertFunction(
+          "__gcc_personality_v0", FunctionType::get(Type::getInt32Ty(C), true));
+      LandingPadInst *LPad =
+          LandingPadInst::Create(ExnTy, PersFn, 1, "cleanup.lpad", CleanupBB);
+      LPad->setCleanup(true);
+      ResumeInst *RI = ResumeInst::Create(LPad, CleanupBB);
+
+      // Transform the 'call' instructions into 'invoke's branching to the
+      // cleanup block. Go in reverse order to make prettier BB names.
+      SmallVector<Value *, 16> Args;
+      for (unsigned I = Calls.size(); I != 0;) {
+        CallInst *CI = cast<CallInst>(Calls[--I]);
+
+        // Split the basic block containing the function call.
+        BasicBlock *CallBB = CI->getParent();
+        BasicBlock *NewBB =
+            CallBB->splitBasicBlock(CI, CallBB->getName() + ".cont");
+
+        // Remove the unconditional branch inserted at the end of CallBB.
+        CallBB->getInstList().pop_back();
+        NewBB->getInstList().remove(CI);
+
+        // Create a new invoke instruction.
+        Args.clear();
+        CallSite CS(CI);
+        Args.append(CS.arg_begin(), CS.arg_end());
+
+        InvokeInst *II =
+            InvokeInst::Create(CI->getCalledValue(), NewBB, CleanupBB, Args,
+                               CI->getName(), CallBB);
+        II->setCallingConv(CI->getCallingConv());
+        II->setAttributes(CI->getAttributes());
+        CI->replaceAllUsesWith(II);
+        delete CI;
+      }
+
+      Builder.SetInsertPoint(RI->getParent(), RI);
+      return &Builder;
+    }
+  }
+};
+}
+
+
+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(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(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;
+}