Outline C++ exception handlers for MSVC targets.

[andrew.w.kaylor]

Summary

This patch adds code to outline the catch handlers for Windows C++ exception handling support.

These changes are obviously derived from my earlier patch D6556, but since the direction has changed (from SEH to C++EH) it seemed reasonable to start a new differential.

The test cases are based on clang-generated IR for the listed code using an x86_64-pc-linux target, but I have edited this IR to match expected windows-msvc output.

I edited the IR to remove redundant store and load of the EH object and to replace invokes within a catch block with equivalent calls if the unwind destination does nothing but resume. I have code to perform both of these transformations, but I am holding it back for a later review.

The following things are not yet implemented:

Intrinsic support for llvm.eh.begincatch/llvm.eh.endcatch
Removal of outlined catch handlers.
Use of frame variables within a catch block.
Removal (from the parent function) of frame variables which are only used in catch blocks.
Outlining of unwind handlers.
Chained catch handlers (catching an exception from within a catch handler).
Sharing of blocks between several landing pads.
Production of intrinsics to support .xdata table generation.

I think that making the begin/end catch calls intrinsics is the only thing that should block the current patch. I'll submit a separate patch for that shortly.

[rnk]

Looks like a good incremental step to me.

I added David Majnemer to see if he has anything.

lib/CodeGen/WinEHPrepare.cpp

61–93

I'd rather we went with a clang-format indentation here, as it's the dominant style across LLVM.

[andrew.w.kaylor]

Rebased and cleaned up formatting.
Updated to use llvm.eh.begincatch and llvm.eh.endcatch intrinsics.

I was waiting for that change before committing this, but I think it should be ready now. I also have outlining of cleanup handlers ready to review as soon as this lands and some other implementation details that should be ready soon thereafter.

[majnemer]

include/llvm/Transforms/Utils/Cloning.h

140–141

Style nit, please move the curly brace on the same line as the tag name.

lib/CodeGen/WinEHPrepare.cpp

54

I'd make this SmallVectorImpl.

123

Perhaps: This only returns true if...

150

SmallVectorImpl

156

You shouldn't have variables of type twine. They should be used directly in the expression which consumes them.

167–171

It would be more idiomatic to do:

if (auto *Call = dyn_cast<CallInst>(&Inst))
  if (Call->getCalledFunction->getName() == "llvm.eh.actions")

215

This might deserve a comment.

278–279

Please fold this into a single line.

295–296

Please fold this into a single line.

316–318

You can simplify this by using if (match(Inst, m_Intrinsic<Intrinsic::eh_begincatch>()))

328

Likewise here with if (match(Inst, m_Intrinsic<Intrinsic::eh_endcatch>()))

lib/Transforms/Utils/CloneFunction.cpp

684

SmallVectorImpl<ReturnInst *>

[andrew.w.kaylor]

Cleanup based on review feedback.

[rnk]

Looks good, please commit.

include/llvm/Transforms/Utils/Cloning.h

void CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
                        ValueToValueMapTy &VMap,
                        bool ModuleLevelChanges,
                        SmallVectorImpl<ReturnInst*> &Returns,
                        const char *NameSuffix = "",
                        ClonedCodeInfo *CodeInfo = nullptr,
                        ValueMapTypeRemapper *TypeMapper = nullptr,
                        ValueMaterializer *Materializer = nullptr);
 
+/// A helper class used with CloneAndPruneIntoFromInst to change the default
+/// behavior while instructions are being cloned.
+class CloningDirector
+{
+public:
+  /// This enumeration describes the way CloneAndPruneIntoFromInst should
+  /// proceed after the CloningDirector has examined an instruction.
+  enum CloningAction {
+    ///< Continue cloning the instruction (default behavior).
+    CloneInstruction,
+    ///< Skip this instruction but continue cloning the current basic block.
+    SkipInstruction,
+    ///< Skip this instruction and stop cloning the current basic block.
+    StopCloningBB
+  };
+
+  CloningDirector() {}
+  virtual ~CloningDirector() {}
+
+  /// Subclasses must override this function to customize cloning behavior.
+  virtual CloningAction handleInstruction(ValueToValueMapTy &VMap,
+                                          const Instruction *Inst,
+                                          BasicBlock        *NewBB) = 0;
+};
+
+void CloneAndPruneIntoFromInst(Function *NewFunc, const Function *OldFunc,
+                               const Instruction *StartingInst,
+                               ValueToValueMapTy &VMap,
+                               bool ModuleLevelChanges,
+                               SmallVectorImpl<ReturnInst*> &Returns,
+                               const char *NameSuffix = "", 
+                               ClonedCodeInfo *CodeInfo = nullptr,
+                               const DataLayout *DL = nullptr,
+                               CloningDirector *Director = nullptr);
+
+
 /// CloneAndPruneFunctionInto - This works exactly like CloneFunctionInto,
 /// except that it does some simple constant prop and DCE on the fly.  The
 /// effect of this is to copy significantly less code in cases where (for
 /// example) a function call with constant arguments is inlined, and those
 /// constant arguments cause a significant amount of code in the callee to be
 /// dead.  Since this doesn't produce an exactly copy of the input, it can't be
 /// used for things like CloneFunction or CloneModule.
 ///

lib/CodeGen/WinEHPrepare.cpp

 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/Analysis/LibCallSemantics.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
 #include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/Cloning.h"
+#include "llvm/Transforms/Utils/Local.h"
 #include <memory>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "winehprepare"
 
 namespace {
 class WinEHPrepare : public FunctionPass {
   std::unique_ptr<FunctionPass> DwarfPrepare;
 
 public:
   static char ID; // Pass identification, replacement for typeid.
   WinEHPrepare(const TargetMachine *TM = nullptr)
       : FunctionPass(ID), DwarfPrepare(createDwarfEHPass(TM)) {}
 
   bool runOnFunction(Function &Fn) override;
 
   bool doFinalization(Module &M) override;
 
   void getAnalysisUsage(AnalysisUsage &AU) const override;
 
   const char *getPassName() const override {
     return "Windows exception handling preparation";
   }
+
+private:
+  bool prepareCPPEHHandlers(Function &F,
+                            SmallVector<LandingPadInst *, 4> &LPads);
+  bool outlineCatchHandler(Function *SrcFn, Constant *SelectorType,
+                           LandingPadInst *LPad, StructType *EHDataStructTy);
+};
+
+class WinEHCatchDirector : public CloningDirector {
+public:
+  WinEHCatchDirector(LandingPadInst *LPI, Function *CatchFn, Value *Selector,
+                     Value *EHObj)
+      : LPI(LPI), CatchFn(CatchFn),
+        CurrentSelector(Selector->stripPointerCasts()), EHObj(EHObj),
+        SelectorIDType(Type::getInt32Ty(LPI->getContext())),
+        Int8PtrType(Type::getInt8PtrTy(LPI->getContext())) {}
+  virtual ~WinEHCatchDirector() {}
+
+  CloningAction handleInstruction(ValueToValueMapTy &VMap,
+                                  const Instruction *Inst,
+                                  BasicBlock *NewBB) override;
+
+private:
+  LandingPadInst *LPI;
+  Function *CatchFn;
+  Value *CurrentSelector;
+  Value *EHObj;
+  Type *SelectorIDType;
+  Type *Int8PtrType;
+
+  const Value *ExtractedEHPtr;
+  const Value *ExtractedSelector;
+  const Value *EHPtrStoreAddr;
+  const Value *SelectorStoreAddr;
+  const Value *EHObjStoreAddr;
 };
 } // end anonymous namespace
 
 char WinEHPrepare::ID = 0;
-INITIALIZE_TM_PASS(WinEHPrepare, "winehprepare",
-                   "Prepare Windows exceptions", false, false)
+INITIALIZE_TM_PASS(WinEHPrepare, "winehprepare", "Prepare Windows exceptions",
+                   false, false)
 
 FunctionPass *llvm::createWinEHPass(const TargetMachine *TM) {
   return new WinEHPrepare(TM);
 }
 
 static bool isMSVCPersonality(EHPersonality Pers) {
   return Pers == EHPersonality::MSVC_Win64SEH ||
          Pers == EHPersonality::MSVC_CXX;
 }
 
bool WinEHPrepare::runOnFunction(Function &Fn) {
 
   // Classify the personality to see what kind of preparation we need.
   EHPersonality Pers = ClassifyEHPersonality(LPads.back()->getPersonalityFn());
 
   // Delegate through to the DWARF pass if this is unrecognized.
   if (!isMSVCPersonality(Pers))
     return DwarfPrepare->runOnFunction(Fn);
 
-  // FIXME: Cleanups are unimplemented. Replace them with unreachable.
+  // FIXME: This is only returning true if the C++ EH handlers were outlined.
+  //        When that code is complete, it should always return whatever
+  //        prepareCPPEHHandlers returns.
+  if (Pers == EHPersonality::MSVC_CXX && prepareCPPEHHandlers(Fn, LPads))
+    return true;
+
+  // FIXME: SEH Cleanups are unimplemented. Replace them with unreachable.
   if (Resumes.empty())
     return false;
 
   for (ResumeInst *Resume : Resumes) {
     IRBuilder<>(Resume).CreateUnreachable();
     Resume->eraseFromParent();
   }
 
   return true;
 }
 
 bool WinEHPrepare::doFinalization(Module &M) {
   return DwarfPrepare->doFinalization(M);
 }
 
 void WinEHPrepare::getAnalysisUsage(AnalysisUsage &AU) const {
   DwarfPrepare->getAnalysisUsage(AU);
 }
+
+bool WinEHPrepare::prepareCPPEHHandlers(
+    Function &F, SmallVector<LandingPadInst *, 4> &LPads) {
+  // FIXME: Find all frame variable references in the handlers
+  //        to populate the structure elements.
+  SmallVector<Type *, 2> AllocStructTys;
+  AllocStructTys.push_back(Type::getInt32Ty(F.getContext()));   // EH state
+  AllocStructTys.push_back(Type::getInt8PtrTy(F.getContext())); // EH object
+  Twine AllocStructName = "struct." + F.getName() + ".ehdata";
+  StructType *EHDataStructTy =
+      StructType::create(F.getContext(), AllocStructTys, AllocStructName.str());
+  bool HandlersOutlined = false;
+
+  for (LandingPadInst *LPad : LPads) {
+    // Look for evidence that this landingpad has already been processed.
+    bool LPadHasActionList = false;
+    BasicBlock *LPadBB = LPad->getParent();
+    for (Instruction &Inst : LPadBB->getInstList()) {
+      // FIXME: Make this an intrinsic.
+      CallInst *Call = dyn_cast<CallInst>(&Inst);
+      if (Call && Call->getCalledFunction()->getName() == "llvm.eh.actions") {
+        LPadHasActionList = true;
+        break;
+      }
+    }
+
+    // If we've already outlined the handlers for this landingpad,
+    // there's nothing more to do here.
+    if (LPadHasActionList)
+      continue;
+
+    for (unsigned Idx = 0, NumClauses = LPad->getNumClauses(); Idx < NumClauses;
+         ++Idx) {
+      if (LPad->isCatch(Idx))
+        HandlersOutlined =
+            outlineCatchHandler(&F, LPad->getClause(Idx), LPad, EHDataStructTy);
+    } // End for each clause
+  }   // End for each landingpad
+
+  return HandlersOutlined;
+}
+
+bool WinEHPrepare::outlineCatchHandler(Function *SrcFn, Constant *SelectorType,
+                                       LandingPadInst *LPad,
+                                       StructType *EHDataStructTy) {
+  Module *M = SrcFn->getParent();
+  LLVMContext &Context = M->getContext();
+
+  // Create a new function to receive the handler contents.
+  Type *Int8PtrType = Type::getInt8PtrTy(Context);
+  std::vector<Type *> ArgTys;
+  ArgTys.push_back(Int8PtrType);
+  ArgTys.push_back(Int8PtrType);
+  FunctionType *FnType = FunctionType::get(Int8PtrType, ArgTys, false);
+  Function *CatchHandler = Function::Create(
+      FnType, GlobalVariable::ExternalLinkage, SrcFn->getName() + ".catch", M);
+
+  // Generate a standard prolog to setup the frame recovery structure.
+  IRBuilder<> Builder(Context);
+  BasicBlock *Entry = BasicBlock::Create(Context, "catch.entry");
+  CatchHandler->getBasicBlockList().push_front(Entry);
+  Builder.SetInsertPoint(Entry);
+  Builder.SetCurrentDebugLocation(LPad->getDebugLoc());
+
+  Function *RecoverFrameFn =
+      Intrinsic::getDeclaration(M, Intrinsic::framerecover);
+  Value *RecoverArgs[] = {Builder.CreateBitCast(SrcFn, Int8PtrType, ""),
+                          &(CatchHandler->getArgumentList().back())};
+  CallInst *EHAlloc =
+      Builder.CreateCall(RecoverFrameFn, RecoverArgs, "eh.alloc");
+  Value *EHData =
+      Builder.CreateBitCast(EHAlloc, EHDataStructTy->getPointerTo(), "ehdata");
+  Value *EHObjPtr =
+      Builder.CreateConstInBoundsGEP2_32(EHData, 0, 1, "eh.obj.ptr");
+  Value *EHObj = Builder.CreateLoad(EHObjPtr, false, "eh.obj");
+
+  ValueToValueMapTy VMap;
+
+  // FIXME: Map other values referenced in the filter handler.
+
+  WinEHCatchDirector Director(LPad, CatchHandler, SelectorType, EHObj);
+
+  SmallVector<ReturnInst *, 8> Returns;
+  ClonedCodeInfo InlinedFunctionInfo;
+
+  BasicBlock::iterator II = LPad;
+
+  CloneAndPruneIntoFromInst(CatchHandler, SrcFn, ++II, VMap,
+                            /*ModuleLevelChanges=*/false, Returns, "",
+                            &InlinedFunctionInfo,
+                            SrcFn->getParent()->getDataLayout(), &Director);
+
+  // Move all the instructions in the first cloned block into our entry block.
+  BasicBlock *FirstClonedBB = std::next(Function::iterator(Entry));
+  Entry->getInstList().splice(Entry->end(), FirstClonedBB->getInstList());
+  FirstClonedBB->eraseFromParent();
+
+  return true;
+}
+
+CloningDirector::CloningAction WinEHCatchDirector::handleInstruction(
+    ValueToValueMapTy &VMap, const Instruction *Inst, BasicBlock *NewBB) {
+  // Intercept instructions which extract values from the landing pad aggregate.
+  const ExtractValueInst *Extract = dyn_cast<ExtractValueInst>(Inst);
+  if (Extract && Extract->getAggregateOperand() == LPI) {
+
+    assert(Extract->getNumIndices() == 1 &&
+           "Unexpected operation: extracting both landing pad values");
+    assert((*(Extract->idx_begin()) == 0 || *(Extract->idx_begin()) == 1) &&
+           "Unexpected operation: extracting an unknown landing pad element");
+
+    if (*(Extract->idx_begin()) == 0) {
+      // Element 0 doesn't directly corresponds to anything in the WinEH scheme.
+      // It will be stored to a memory location, then later loaded and finally
+      // the loaded value will be used as the argument to an llvm.eh.begincatch
+      // call.  We're tracking it here so that we can skip the store and load.
+      ExtractedEHPtr = Inst;
+    } else {
+      // Element 1 corresponds to the filter selector.  We'll map it to 1 for
+      // matching purposes, but it will also probably be stored to memory and
+      // reloaded, so we need to track the instuction so that we can map the
+      // loaded value too.
+      VMap[Inst] = ConstantInt::get(SelectorIDType, 1);
+      ExtractedSelector = Inst;
+    }
+
+    // Tell the caller not to clone this instruction.
+    return CloningDirector::SkipInstruction;
+  }
+
+  const StoreInst *Store = dyn_cast<StoreInst>(Inst);
+  if (Store) {
+    // Look for and suppress stores of the extracted landingpad values.
+    const Value *StoredValue = Store->getValueOperand();
+    if (StoredValue == ExtractedEHPtr) {
+      EHPtrStoreAddr = Store->getPointerOperand();
+      return CloningDirector::SkipInstruction;
+    }
+    if (StoredValue == ExtractedSelector) {
+      SelectorStoreAddr = Store->getPointerOperand();
+      return CloningDirector::SkipInstruction;
+    }
+
+    // Any other store just gets cloned.
+    return CloningDirector::CloneInstruction;
+  }
+
+  const LoadInst *Load = dyn_cast<LoadInst>(Inst);
+  if (Load) {
+    // Look for loads of (previously suppressed) landingpad values.
+    // The EHPtr load can be ignored (it should only be used as
+    // an argument to llvm.eh.begincatch), but the selector value
+    // needs to be mapped to a constant value of 1 to be used to
+    // simplify the branching to always flow to the current handler.
+    const Value *LoadAddr = Load->getPointerOperand();
+    if (LoadAddr == EHPtrStoreAddr) {
+      VMap[Inst] = UndefValue::get(Int8PtrType);
+      return CloningDirector::SkipInstruction;
+    }
+    if (LoadAddr == SelectorStoreAddr) {
+      VMap[Inst] = ConstantInt::get(SelectorIDType, 1);
+      return CloningDirector::SkipInstruction;
+    }
+
+    // Any other loads just get cloned.
+    return CloningDirector::CloneInstruction;
+  }
+
+  const IntrinsicInst *IntrinCall = dyn_cast<IntrinsicInst>(Inst);
+  if (IntrinCall) {
+    if (IntrinCall->getIntrinsicID() == llvm::Intrinsic::eh_begincatch) {
+      // The argument to the call is some form of the first element of the
+      // landingpad aggregate value, but that doesn't matter.  It isn't used
+      // here.
+      // The return value of this instruction, however, is used to access the
+      // EH object pointer.  We have generated an instruction to get that value
+      // from the EH alloc block, so we can just map to that here.
+      VMap[Inst] = EHObj;
+      return CloningDirector::SkipInstruction;
+    }
+    if (IntrinCall->getIntrinsicID() == llvm::Intrinsic::eh_endcatch) {
+      // It might be interesting to track whether or not we are inside a catch
+      // function, but that might make the algorithm more brittle than it needs
+      // to be.
+
+      // The end catch call can occur in one of two places: either in a
+      // landingpad
+      // block that is part of the catch handlers exception mechanism, or at the
+      // end of the catch block.  If it occurs in a landing pad, we must skip it
+      // and continue so that the landing pad gets cloned.
+      // FIXME: This case isn't fully supported yet and shouldn't turn up in any
+      //        of the test cases until it is.
+      if (IntrinCall->getParent()->isLandingPad())
+        return CloningDirector::SkipInstruction;
+
+      // If an end catch occurs anywhere else the next instruction should be an
+      // unconditional branch instruction that we want to replace with a return
+      // to the the address of the branch target.
+      const BasicBlock *EndCatchBB = IntrinCall->getParent();
+      const TerminatorInst *Terminator = EndCatchBB->getTerminator();
+      const BranchInst *Branch = dyn_cast<BranchInst>(Terminator);
+      assert(Branch && Branch->isUnconditional());
+      assert(std::next(BasicBlock::const_iterator(IntrinCall)) ==
+             BasicBlock::const_iterator(Branch));
+
+      ReturnInst::Create(NewBB->getContext(),
+                         BlockAddress::get(Branch->getSuccessor(0)), NewBB);
+
+      // We just added a terminator to the cloned block.
+      // Tell the caller to stop processing the current basic block so that
+      // the branch instruction will be skipped.
+      return CloningDirector::StopCloningBB;
+    }
+    if (IntrinCall->getIntrinsicID() == llvm::Intrinsic::eh_typeid_for) {
+      Value *Selector = IntrinCall->getArgOperand(0)->stripPointerCasts();
+      // This causes a replacement that will collapse the landing pad CFG based
+      // on the filter function we intend to match.
+      if (Selector == CurrentSelector)
+        VMap[Inst] = ConstantInt::get(SelectorIDType, 1);
+      else
+        VMap[Inst] = ConstantInt::get(SelectorIDType, 0);
+      // Tell the caller not to clone this instruction.
+      return CloningDirector::SkipInstruction;
+    }
+    // Any other intrinsics just get cloned.
+    return CloningDirector::CloneInstruction;
+  }
+
+  // Continue with the default cloning behavior.
+  return CloningDirector::CloneInstruction;
+}

lib/Transforms/Utils/CloneFunction.cpp

namespace {
   struct PruningFunctionCloner {
     Function *NewFunc;
     const Function *OldFunc;
     ValueToValueMapTy &VMap;
     bool ModuleLevelChanges;
     const char *NameSuffix;
     ClonedCodeInfo *CodeInfo;
     const DataLayout *DL;
+    CloningDirector *Director;
+
   public:
     PruningFunctionCloner(Function *newFunc, const Function *oldFunc,
                           ValueToValueMapTy &valueMap,
                           bool moduleLevelChanges,
                           const char *nameSuffix, 
                           ClonedCodeInfo *codeInfo,
-                          const DataLayout *DL)
+                          const DataLayout *DL,
+                          CloningDirector *Director)
     : NewFunc(newFunc), OldFunc(oldFunc),
       VMap(valueMap), ModuleLevelChanges(moduleLevelChanges),
-      NameSuffix(nameSuffix), CodeInfo(codeInfo), DL(DL) {
+      NameSuffix(nameSuffix), CodeInfo(codeInfo), DL(DL),
+      Director(Director) {
     }
 
     /// CloneBlock - The specified block is found to be reachable, clone it and
     /// anything that it can reach.
-    void CloneBlock(const BasicBlock *BB,
+    void CloneBlock(const BasicBlock *BB, 
+                    BasicBlock::const_iterator StartingInst,
                     std::vector<const BasicBlock*> &ToClone);
   };
 }
 
 /// CloneBlock - The specified block is found to be reachable, clone it and
 /// anything that it can reach.
 void PruningFunctionCloner::CloneBlock(const BasicBlock *BB,
+                                       BasicBlock::const_iterator StartingInst,
                                        std::vector<const BasicBlock*> &ToClone){
   WeakVH &BBEntry = VMap[BB];
 
   // Have we already cloned this block?
   if (BBEntry) return;
   
   // Nope, clone it now.
   BasicBlock *NewBB;
void PruningFunctionCloner::CloneBlock(const BasicBlock *BB,
   //
   // Note that we don't need to fix the mapping for unreachable blocks;
   // the default mapping there is safe.
   if (BB->hasAddressTaken()) {
     Constant *OldBBAddr = BlockAddress::get(const_cast<Function*>(OldFunc),
                                             const_cast<BasicBlock*>(BB));
     VMap[OldBBAddr] = BlockAddress::get(NewFunc, NewBB);
   }
-    
-
   bool hasCalls = false, hasDynamicAllocas = false, hasStaticAllocas = false;
-  
   // Loop over all instructions, and copy them over, DCE'ing as we go.  This
   // loop doesn't include the terminator.
-  for (BasicBlock::const_iterator II = BB->begin(), IE = --BB->end();
+  for (BasicBlock::const_iterator II = StartingInst, IE = --BB->end();
        II != IE; ++II) {
+    // If the "Director" remaps the instruction, don't clone it.
+    if (Director) {
+      CloningDirector::CloningAction Action 
+                              = Director->handleInstruction(VMap, II, NewBB);
+      // If the cloning director says stop, we want to stop everything, not
+      // just break out of the loop (which would cause the terminator to be
+      // cloned).  The cloning director is responsible for inserting a proper
+      // terminator into the new basic block in this case.
+      if (Action == CloningDirector::StopCloningBB)
+        return;
+      // If the cloning director says skip, continue to the next instruction.
+      // In this case, the cloning director is responsible for mapping the
+      // skipped instruction to some value that is defined in the new
+      // basic block.
+      if (Action == CloningDirector::SkipInstruction)
+        continue;
+    }
+
     Instruction *NewInst = II->clone();
 
     // Eagerly remap operands to the newly cloned instruction, except for PHI
     // nodes for which we defer processing until we update the CFG.
     if (!isa<PHINode>(NewInst)) {
       RemapInstruction(NewInst, VMap,
                        ModuleLevelChanges ? RF_None : RF_NoModuleLevelChanges);
 
if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
       else
         hasDynamicAllocas = true;
     }
   }
   
   // Finally, clone over the terminator.
   const TerminatorInst *OldTI = BB->getTerminator();
   bool TerminatorDone = false;
+  if (Director) {
+    CloningDirector::CloningAction Action 
+                           = Director->handleInstruction(VMap, OldTI, NewBB);
+    // If the cloning director says stop, we want to stop everything, not
+    // just break out of the loop (which would cause the terminator to be
+    // cloned).  The cloning director is responsible for inserting a proper
+    // terminator into the new basic block in this case.
+    if (Action == CloningDirector::StopCloningBB)
+      return;
+    assert(Action != CloningDirector::SkipInstruction && 
+           "SkipInstruction is not valid for terminators.");
+  }
   if (const BranchInst *BI = dyn_cast<BranchInst>(OldTI)) {
     if (BI->isConditional()) {
       // If the condition was a known constant in the callee...
       ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition());
       // Or is a known constant in the caller...
       if (!Cond) {
         Value *V = VMap[BI->getCondition()];
         Cond = dyn_cast_or_null<ConstantInt>(V);
void PruningFunctionCloner::CloneBlock(const BasicBlock *BB,
   if (CodeInfo) {
     CodeInfo->ContainsCalls          |= hasCalls;
     CodeInfo->ContainsDynamicAllocas |= hasDynamicAllocas;
     CodeInfo->ContainsDynamicAllocas |= hasStaticAllocas && 
       BB != &BB->getParent()->front();
   }
 }
 
-/// CloneAndPruneFunctionInto - This works exactly like CloneFunctionInto,
-/// except that it does some simple constant prop and DCE on the fly.  The
-/// effect of this is to copy significantly less code in cases where (for
-/// example) a function call with constant arguments is inlined, and those
-/// constant arguments cause a significant amount of code in the callee to be
-/// dead.  Since this doesn't produce an exact copy of the input, it can't be
-/// used for things like CloneFunction or CloneModule.
-void llvm::CloneAndPruneFunctionInto(Function *NewFunc, const Function *OldFunc,
+/// CloneAndPruneIntoFromInst - This works like CloneAndPruneFunctionInto, except
+/// that it does not clone the entire function. Instead it starts at an
+/// instruction provided by the caller and copies (and prunes) only the code 
+/// reachable from that instruction.
+void llvm::CloneAndPruneIntoFromInst(Function *NewFunc, const Function *OldFunc,
+                                     const Instruction *StartingInst,
                                      ValueToValueMapTy &VMap,
                                      bool ModuleLevelChanges,
                                      SmallVectorImpl<ReturnInst*> &Returns,
                                      const char *NameSuffix, 
                                      ClonedCodeInfo *CodeInfo,
                                      const DataLayout *DL,
-                                     Instruction *TheCall) {
+                                     CloningDirector *Director) {
   assert(NameSuffix && "NameSuffix cannot be null!");
-  
 #ifndef NDEBUG
-  for (Function::const_arg_iterator II = OldFunc->arg_begin(), 
+  // If the cloning starts at the begining of the function, verify that
+  // the function arguments are mapped.
+  if (!StartingInst)
+    for (Function::const_arg_iterator II = OldFunc->arg_begin(),
          E = OldFunc->arg_end(); II != E; ++II)
       assert(VMap.count(II) && "No mapping from source argument specified!");
 #endif
 
   PruningFunctionCloner PFC(NewFunc, OldFunc, VMap, ModuleLevelChanges,
-                            NameSuffix, CodeInfo, DL);
+                            NameSuffix, CodeInfo, DL, Director);
+  const BasicBlock *StartingBB;
+  if (StartingInst)
+    StartingBB = StartingInst->getParent();
+  else {
+    StartingBB = &OldFunc->getEntryBlock();
+    StartingInst = StartingBB->begin();
+  }
 
   // Clone the entry block, and anything recursively reachable from it.
   std::vector<const BasicBlock*> CloneWorklist;
-  CloneWorklist.push_back(&OldFunc->getEntryBlock());
+  PFC.CloneBlock(StartingBB, StartingInst, CloneWorklist);
   while (!CloneWorklist.empty()) {
     const BasicBlock *BB = CloneWorklist.back();
     CloneWorklist.pop_back();
-    PFC.CloneBlock(BB, CloneWorklist);
+    PFC.CloneBlock(BB, BB->begin(), CloneWorklist);
   }
   
   // Loop over all of the basic blocks in the old function.  If the block was
   // reachable, we have cloned it and the old block is now in the value map:
   // insert it into the new function in the right order.  If not, ignore it.
   //
   // Defer PHI resolution until rest of function is resolved.
   SmallVector<const PHINode*, 16> PHIToResolve;
#endif
   for (unsigned Idx = 0, Size = PHIToResolve.size(); Idx != Size; ++Idx)
     if (PHINode *PN = dyn_cast<PHINode>(VMap[PHIToResolve[Idx]]))
       recursivelySimplifyInstruction(PN, DL);
 
   // Now that the inlined function body has been fully constructed, go through
   // and zap unconditional fall-through branches.  This happen all the time when
   // specializing code: code specialization turns conditional branches into
   // uncond branches, and this code folds them.
-  Function::iterator Begin = cast<BasicBlock>(VMap[&OldFunc->getEntryBlock()]);
+  Function::iterator Begin = cast<BasicBlock>(VMap[StartingBB]);
   Function::iterator I = Begin;
   while (I != NewFunc->end()) {
     // Check if this block has become dead during inlining or other
     // simplifications. Note that the first block will appear dead, as it has
     // not yet been wired up properly.
     if (I != Begin && (pred_begin(I) == pred_end(I) ||
                        I->getSinglePredecessor() == I)) {
       BasicBlock *DeadBB = I++;
while (I != NewFunc->end()) {
     Dest->eraseFromParent();
     
     // Do not increment I, iteratively merge all things this block branches to.
   }
 
   // Make a final pass over the basic blocks from theh old function to gather
   // any return instructions which survived folding. We have to do this here
   // because we can iteratively remove and merge returns above.
-  for (Function::iterator I = cast<BasicBlock>(VMap[&OldFunc->getEntryBlock()]),
+  for (Function::iterator I = cast<BasicBlock>(VMap[StartingBB]),
                           E = NewFunc->end();
        I != E; ++I)
     if (ReturnInst *RI = dyn_cast<ReturnInst>(I->getTerminator()))
       Returns.push_back(RI);
 }
+
+
+/// CloneAndPruneFunctionInto - This works exactly like CloneFunctionInto,
+/// except that it does some simple constant prop and DCE on the fly.  The
+/// effect of this is to copy significantly less code in cases where (for
+/// example) a function call with constant arguments is inlined, and those
+/// constant arguments cause a significant amount of code in the callee to be
+/// dead.  Since this doesn't produce an exact copy of the input, it can't be
+/// used for things like CloneFunction or CloneModule.
+void llvm::CloneAndPruneFunctionInto(Function *NewFunc, const Function *OldFunc,
+                                     ValueToValueMapTy &VMap,
+                                     bool ModuleLevelChanges,
+                                     SmallVectorImpl<ReturnInst*> &Returns,
+                                     const char *NameSuffix, 
+                                     ClonedCodeInfo *CodeInfo,
+                                     const DataLayout *DL,
+                                     Instruction *TheCall) {
+  CloneAndPruneIntoFromInst(NewFunc, OldFunc, OldFunc->front().begin(),
+                            VMap, ModuleLevelChanges, Returns, NameSuffix,
+                            CodeInfo, DL, nullptr);
+}

test/CodeGen/X86/cppeh-catch-all.ll

+; RUN: opt -mtriple=x86_64-pc-windows-msvc -winehprepare -S -o - < %s | FileCheck %s
+
+; This test is based on the following code:
+;
+; void test()
+; {
+;   try {
+;     may_throw();
+;   } catch (...) {
+;     handle_exception();
+;   }
+; }
+;
+; Parts of the IR have been hand-edited to simplify the test case.
+; The full IR will be restored when Windows C++ EH support is complete.
+
+; ModuleID = 'catch-all.cpp'
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+; Function Attrs: uwtable
+define void @_Z4testv() #0 {
+entry:
+  %exn.slot = alloca i8*
+  %ehselector.slot = alloca i32
+  invoke void @_Z9may_throwv()
+          to label %invoke.cont unwind label %lpad
+
+invoke.cont:                                      ; preds = %entry
+  br label %try.cont
+
+lpad:                                             ; preds = %entry
+  %0 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)* @__CxxFrameHandler3 to i8*)
+          catch i8* null
+  %1 = extractvalue { i8*, i32 } %0, 0
+  store i8* %1, i8** %exn.slot
+  %2 = extractvalue { i8*, i32 } %0, 1
+  store i32 %2, i32* %ehselector.slot
+  br label %catch
+
+catch:                                            ; preds = %lpad
+  %exn = load i8** %exn.slot
+  %3 = call i8* @llvm.eh.begincatch(i8* %exn) #3
+  call void @_Z16handle_exceptionv()
+  br label %invoke.cont2
+
+invoke.cont2:                                     ; preds = %catch
+  call void @llvm.eh.endcatch()
+  br label %try.cont
+
+try.cont:                                         ; preds = %invoke.cont2, %invoke.cont
+  ret void
+}
+
+; CHECK: define i8* @_Z4testv.catch(i8*, i8*) {
+; CHECK: catch.entry:
+; CHECK:   %eh.alloc = call i8* @llvm.framerecover(i8* bitcast (void ()* @_Z4testv to i8*), i8* %1)
+; CHECK:   %ehdata = bitcast i8* %eh.alloc to %struct._Z4testv.ehdata*
+; CHECK:   %eh.obj.ptr = getelementptr inbounds %struct._Z4testv.ehdata* %ehdata, i32 0, i32 1
+; CHECK:   %eh.obj = load i8** %eh.obj.ptr
+; CHECK:   call void @_Z16handle_exceptionv()
+; CHECK:   ret i8* blockaddress(@_Z4testv, %try.cont)
+; CHECK: }
+
+declare void @_Z9may_throwv() #1
+
+declare i32 @__CxxFrameHandler3(...)
+
+declare i8* @llvm.eh.begincatch(i8*)
+
+declare void @_Z16handle_exceptionv() #1
+
+declare void @llvm.eh.endcatch()
+
+attributes #0 = { uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { noinline noreturn nounwind }
+attributes #3 = { nounwind }
+attributes #4 = { noreturn nounwind }
+
+!llvm.ident = !{!0}
+
+!0 = !{!"clang version 3.7.0 (trunk 226027)"}

test/CodeGen/X86/cppeh-catch-scalar.ll

+; RUN: opt -mtriple=x86_64-pc-windows-msvc -winehprepare -S -o - < %s | FileCheck %s
+
+; This test is based on the following code:
+;
+; void test()
+; {
+;   try {
+;     may_throw();
+;   } catch (int) {
+;     handle_int();
+;   }
+; }
+;
+; Parts of the IR have been hand-edited to simplify the test case.
+; The full IR will be restored when Windows C++ EH support is complete.
+
+;ModuleID = 'cppeh-catch-scalar.cpp'
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+@_ZTIi = external constant i8*
+
+; Function Attrs: uwtable
+define void @_Z4testv() #0 {
+entry:
+  %exn.slot = alloca i8*
+  %ehselector.slot = alloca i32
+  invoke void @_Z9may_throwv()
+          to label %invoke.cont unwind label %lpad
+
+invoke.cont:                                      ; preds = %entry
+  br label %try.cont
+
+lpad:                                             ; preds = %entry
+  %0 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)* @__CxxFrameHandler3 to i8*)
+          catch i8* bitcast (i8** @_ZTIi to i8*)
+  %1 = extractvalue { i8*, i32 } %0, 0
+  store i8* %1, i8** %exn.slot
+  %2 = extractvalue { i8*, i32 } %0, 1
+  store i32 %2, i32* %ehselector.slot
+  br label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %lpad
+  %sel = load i32* %ehselector.slot
+  %3 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIi to i8*)) #3
+  %matches = icmp eq i32 %sel, %3
+  br i1 %matches, label %catch, label %eh.resume
+
+catch:                                            ; preds = %catch.dispatch
+  %exn11 = load i8** %exn.slot
+  %4 = call i8* @llvm.eh.begincatch(i8* %exn11) #3
+  %5 = bitcast i8* %4 to i32*
+  call void @_Z10handle_intv()
+  br label %invoke.cont2
+
+invoke.cont2:                                     ; preds = %catch
+  call void @llvm.eh.endcatch() #3
+  br label %try.cont
+
+try.cont:                                         ; preds = %invoke.cont2, %invoke.cont
+  ret void
+
+eh.resume:                                        ; preds = %catch.dispatch
+  %exn3 = load i8** %exn.slot
+  %sel4 = load i32* %ehselector.slot
+  %lpad.val = insertvalue { i8*, i32 } undef, i8* %exn3, 0
+  %lpad.val5 = insertvalue { i8*, i32 } %lpad.val, i32 %sel4, 1
+  resume { i8*, i32 } %lpad.val5
+}
+
+; CHECK: define i8* @_Z4testv.catch(i8*, i8*) {
+; CHECK: catch.entry:
+; CHECK:   %eh.alloc = call i8* @llvm.framerecover(i8* bitcast (void ()* @_Z4testv to i8*), i8* %1)
+; CHECK:   %ehdata = bitcast i8* %eh.alloc to %struct._Z4testv.ehdata*
+; CHECK:   %eh.obj.ptr = getelementptr inbounds %struct._Z4testv.ehdata* %ehdata, i32 0, i32 1
+; CHECK:   %eh.obj = load i8** %eh.obj.ptr
+; CHECK:   %2 = bitcast i8* %eh.obj to i32*
+; CHECK:   call void @_Z10handle_intv()
+; CHECK:   ret i8* blockaddress(@_Z4testv, %try.cont)
+; CHECK: }
+
+declare void @_Z9may_throwv() #1
+
+declare i32 @__CxxFrameHandler3(...)
+
+; Function Attrs: nounwind readnone
+declare i32 @llvm.eh.typeid.for(i8*) #2
+
+declare i8* @llvm.eh.begincatch(i8*)
+
+declare void @llvm.eh.endcatch()
+
+declare void @_Z10handle_intv() #1
+
+attributes #0 = { uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind readnone }
+attributes #3 = { nounwind }
+
+!llvm.ident = !{!0}
+
+!0 = !{!"clang version 3.7.0 (trunk 227474) (llvm/trunk 227508)"}