vendor/clang/clang-r126079

1 files changed, 1144 insertions, 0 deletions

diff --git a/lib/CodeGen/CGCleanup.cpp b/lib/CodeGen/CGCleanup.cpp
new file mode 100644
index 000000000000..374ede880d20
--- /dev/null
+++ b/lib/CodeGen/CGCleanup.cpp
@@ -0,0 +1,1144 @@
+//===--- CGCleanup.cpp - Bookkeeping and code emission for cleanups -------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains code dealing with the IR generation for cleanups
+// and related information.
+//
+// A "cleanup" is a piece of code which needs to be executed whenever
+// control transfers out of a particular scope.  This can be
+// conditionalized to occur only on exceptional control flow, only on
+// normal control flow, or both.
+//
+//===----------------------------------------------------------------------===//
+
+#include "CodeGenFunction.h"
+#include "CGCleanup.h"
+
+using namespace clang;
+using namespace CodeGen;
+
+bool DominatingValue<RValue>::saved_type::needsSaving(RValue rv) {
+  if (rv.isScalar())
+    return DominatingLLVMValue::needsSaving(rv.getScalarVal());
+  if (rv.isAggregate())
+    return DominatingLLVMValue::needsSaving(rv.getAggregateAddr());
+  return true;
+}
+
+DominatingValue<RValue>::saved_type
+DominatingValue<RValue>::saved_type::save(CodeGenFunction &CGF, RValue rv) {
+  if (rv.isScalar()) {
+    llvm::Value *V = rv.getScalarVal();
+
+    // These automatically dominate and don't need to be saved.
+    if (!DominatingLLVMValue::needsSaving(V))
+      return saved_type(V, ScalarLiteral);
+
+    // Everything else needs an alloca.
+    llvm::Value *addr = CGF.CreateTempAlloca(V->getType(), "saved-rvalue");
+    CGF.Builder.CreateStore(V, addr);
+    return saved_type(addr, ScalarAddress);
+  }
+
+  if (rv.isComplex()) {
+    CodeGenFunction::ComplexPairTy V = rv.getComplexVal();
+    const llvm::Type *ComplexTy =
+      llvm::StructType::get(CGF.getLLVMContext(),
+                            V.first->getType(), V.second->getType(),
+                            (void*) 0);
+    llvm::Value *addr = CGF.CreateTempAlloca(ComplexTy, "saved-complex");
+    CGF.StoreComplexToAddr(V, addr, /*volatile*/ false);
+    return saved_type(addr, ComplexAddress);
+  }
+
+  assert(rv.isAggregate());
+  llvm::Value *V = rv.getAggregateAddr(); // TODO: volatile?
+  if (!DominatingLLVMValue::needsSaving(V))
+    return saved_type(V, AggregateLiteral);
+
+  llvm::Value *addr = CGF.CreateTempAlloca(V->getType(), "saved-rvalue");
+  CGF.Builder.CreateStore(V, addr);
+  return saved_type(addr, AggregateAddress);  
+}
+
+/// Given a saved r-value produced by SaveRValue, perform the code
+/// necessary to restore it to usability at the current insertion
+/// point.
+RValue DominatingValue<RValue>::saved_type::restore(CodeGenFunction &CGF) {
+  switch (K) {
+  case ScalarLiteral:
+    return RValue::get(Value);
+  case ScalarAddress:
+    return RValue::get(CGF.Builder.CreateLoad(Value));
+  case AggregateLiteral:
+    return RValue::getAggregate(Value);
+  case AggregateAddress:
+    return RValue::getAggregate(CGF.Builder.CreateLoad(Value));
+  case ComplexAddress:
+    return RValue::getComplex(CGF.LoadComplexFromAddr(Value, false));
+  }
+
+  llvm_unreachable("bad saved r-value kind");
+  return RValue();
+}
+
+/// Push an entry of the given size onto this protected-scope stack.
+char *EHScopeStack::allocate(size_t Size) {
+  if (!StartOfBuffer) {
+    unsigned Capacity = 1024;
+    while (Capacity < Size) Capacity *= 2;
+    StartOfBuffer = new char[Capacity];
+    StartOfData = EndOfBuffer = StartOfBuffer + Capacity;
+  } else if (static_cast<size_t>(StartOfData - StartOfBuffer) < Size) {
+    unsigned CurrentCapacity = EndOfBuffer - StartOfBuffer;
+    unsigned UsedCapacity = CurrentCapacity - (StartOfData - StartOfBuffer);
+
+    unsigned NewCapacity = CurrentCapacity;
+    do {
+      NewCapacity *= 2;
+    } while (NewCapacity < UsedCapacity + Size);
+
+    char *NewStartOfBuffer = new char[NewCapacity];
+    char *NewEndOfBuffer = NewStartOfBuffer + NewCapacity;
+    char *NewStartOfData = NewEndOfBuffer - UsedCapacity;
+    memcpy(NewStartOfData, StartOfData, UsedCapacity);
+    delete [] StartOfBuffer;
+    StartOfBuffer = NewStartOfBuffer;
+    EndOfBuffer = NewEndOfBuffer;
+    StartOfData = NewStartOfData;
+  }
+
+  assert(StartOfBuffer + Size <= StartOfData);
+  StartOfData -= Size;
+  return StartOfData;
+}
+
+EHScopeStack::stable_iterator
+EHScopeStack::getEnclosingEHCleanup(iterator it) const {
+  assert(it != end());
+  do {
+    if (isa<EHCleanupScope>(*it)) {
+      if (cast<EHCleanupScope>(*it).isEHCleanup())
+        return stabilize(it);
+      return cast<EHCleanupScope>(*it).getEnclosingEHCleanup();
+    }
+    ++it;
+  } while (it != end());
+  return stable_end();
+}
+
+
+void *EHScopeStack::pushCleanup(CleanupKind Kind, size_t Size) {
+  assert(((Size % sizeof(void*)) == 0) && "cleanup type is misaligned");
+  char *Buffer = allocate(EHCleanupScope::getSizeForCleanupSize(Size));
+  bool IsNormalCleanup = Kind & NormalCleanup;
+  bool IsEHCleanup = Kind & EHCleanup;
+  bool IsActive = !(Kind & InactiveCleanup);
+  EHCleanupScope *Scope =
+    new (Buffer) EHCleanupScope(IsNormalCleanup,
+                                IsEHCleanup,
+                                IsActive,
+                                Size,
+                                BranchFixups.size(),
+                                InnermostNormalCleanup,
+                                InnermostEHCleanup);
+  if (IsNormalCleanup)
+    InnermostNormalCleanup = stable_begin();
+  if (IsEHCleanup)
+    InnermostEHCleanup = stable_begin();
+
+  return Scope->getCleanupBuffer();
+}
+
+void EHScopeStack::popCleanup() {
+  assert(!empty() && "popping exception stack when not empty");
+
+  assert(isa<EHCleanupScope>(*begin()));
+  EHCleanupScope &Cleanup = cast<EHCleanupScope>(*begin());
+  InnermostNormalCleanup = Cleanup.getEnclosingNormalCleanup();
+  InnermostEHCleanup = Cleanup.getEnclosingEHCleanup();
+  StartOfData += Cleanup.getAllocatedSize();
+
+  if (empty()) NextEHDestIndex = FirstEHDestIndex;
+
+  // Destroy the cleanup.
+  Cleanup.~EHCleanupScope();
+
+  // Check whether we can shrink the branch-fixups stack.
+  if (!BranchFixups.empty()) {
+    // If we no longer have any normal cleanups, all the fixups are
+    // complete.
+    if (!hasNormalCleanups())
+      BranchFixups.clear();
+
+    // Otherwise we can still trim out unnecessary nulls.
+    else
+      popNullFixups();
+  }
+}
+
+EHFilterScope *EHScopeStack::pushFilter(unsigned NumFilters) {
+  char *Buffer = allocate(EHFilterScope::getSizeForNumFilters(NumFilters));
+  CatchDepth++;
+  return new (Buffer) EHFilterScope(NumFilters);
+}
+
+void EHScopeStack::popFilter() {
+  assert(!empty() && "popping exception stack when not empty");
+
+  EHFilterScope &Filter = cast<EHFilterScope>(*begin());
+  StartOfData += EHFilterScope::getSizeForNumFilters(Filter.getNumFilters());
+
+  if (empty()) NextEHDestIndex = FirstEHDestIndex;
+
+  assert(CatchDepth > 0 && "mismatched filter push/pop");
+  CatchDepth--;
+}
+
+EHCatchScope *EHScopeStack::pushCatch(unsigned NumHandlers) {
+  char *Buffer = allocate(EHCatchScope::getSizeForNumHandlers(NumHandlers));
+  CatchDepth++;
+  EHCatchScope *Scope = new (Buffer) EHCatchScope(NumHandlers);
+  for (unsigned I = 0; I != NumHandlers; ++I)
+    Scope->getHandlers()[I].Index = getNextEHDestIndex();
+  return Scope;
+}
+
+void EHScopeStack::pushTerminate() {
+  char *Buffer = allocate(EHTerminateScope::getSize());
+  CatchDepth++;
+  new (Buffer) EHTerminateScope(getNextEHDestIndex());
+}
+
+/// Remove any 'null' fixups on the stack.  However, we can't pop more
+/// fixups than the fixup depth on the innermost normal cleanup, or
+/// else fixups that we try to add to that cleanup will end up in the
+/// wrong place.  We *could* try to shrink fixup depths, but that's
+/// actually a lot of work for little benefit.
+void EHScopeStack::popNullFixups() {
+  // We expect this to only be called when there's still an innermost
+  // normal cleanup;  otherwise there really shouldn't be any fixups.
+  assert(hasNormalCleanups());
+
+  EHScopeStack::iterator it = find(InnermostNormalCleanup);
+  unsigned MinSize = cast<EHCleanupScope>(*it).getFixupDepth();
+  assert(BranchFixups.size() >= MinSize && "fixup stack out of order");
+
+  while (BranchFixups.size() > MinSize &&
+         BranchFixups.back().Destination == 0)
+    BranchFixups.pop_back();
+}
+
+void CodeGenFunction::initFullExprCleanup() {
+  // Create a variable to decide whether the cleanup needs to be run.
+  llvm::AllocaInst *active
+    = CreateTempAlloca(Builder.getInt1Ty(), "cleanup.cond");
+
+  // Initialize it to false at a site that's guaranteed to be run
+  // before each evaluation.
+  llvm::BasicBlock *block = OutermostConditional->getStartingBlock();
+  new llvm::StoreInst(Builder.getFalse(), active, &block->back());
+
+  // Initialize it to true at the current location.
+  Builder.CreateStore(Builder.getTrue(), active);
+
+  // Set that as the active flag in the cleanup.
+  EHCleanupScope &cleanup = cast<EHCleanupScope>(*EHStack.begin());
+  assert(cleanup.getActiveFlag() == 0 && "cleanup already has active flag?");
+  cleanup.setActiveFlag(active);
+
+  if (cleanup.isNormalCleanup()) cleanup.setTestFlagInNormalCleanup();
+  if (cleanup.isEHCleanup()) cleanup.setTestFlagInEHCleanup();
+}
+
+EHScopeStack::Cleanup::~Cleanup() {
+  llvm_unreachable("Cleanup is indestructable");
+}
+
+/// All the branch fixups on the EH stack have propagated out past the
+/// outermost normal cleanup; resolve them all by adding cases to the
+/// given switch instruction.
+static void ResolveAllBranchFixups(CodeGenFunction &CGF,
+                                   llvm::SwitchInst *Switch,
+                                   llvm::BasicBlock *CleanupEntry) {
+  llvm::SmallPtrSet<llvm::BasicBlock*, 4> CasesAdded;
+
+  for (unsigned I = 0, E = CGF.EHStack.getNumBranchFixups(); I != E; ++I) {
+    // Skip this fixup if its destination isn't set.
+    BranchFixup &Fixup = CGF.EHStack.getBranchFixup(I);
+    if (Fixup.Destination == 0) continue;
+
+    // If there isn't an OptimisticBranchBlock, then InitialBranch is
+    // still pointing directly to its destination; forward it to the
+    // appropriate cleanup entry.  This is required in the specific
+    // case of
+    //   { std::string s; goto lbl; }
+    //   lbl:
+    // i.e. where there's an unresolved fixup inside a single cleanup
+    // entry which we're currently popping.
+    if (Fixup.OptimisticBranchBlock == 0) {
+      new llvm::StoreInst(CGF.Builder.getInt32(Fixup.DestinationIndex),
+                          CGF.getNormalCleanupDestSlot(),
+                          Fixup.InitialBranch);
+      Fixup.InitialBranch->setSuccessor(0, CleanupEntry);
+    }
+
+    // Don't add this case to the switch statement twice.
+    if (!CasesAdded.insert(Fixup.Destination)) continue;
+
+    Switch->addCase(CGF.Builder.getInt32(Fixup.DestinationIndex),
+                    Fixup.Destination);
+  }
+
+  CGF.EHStack.clearFixups();
+}
+
+/// Transitions the terminator of the given exit-block of a cleanup to
+/// be a cleanup switch.
+static llvm::SwitchInst *TransitionToCleanupSwitch(CodeGenFunction &CGF,
+                                                   llvm::BasicBlock *Block) {
+  // If it's a branch, turn it into a switch whose default
+  // destination is its original target.
+  llvm::TerminatorInst *Term = Block->getTerminator();
+  assert(Term && "can't transition block without terminator");
+
+  if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
+    assert(Br->isUnconditional());
+    llvm::LoadInst *Load =
+      new llvm::LoadInst(CGF.getNormalCleanupDestSlot(), "cleanup.dest", Term);
+    llvm::SwitchInst *Switch =
+      llvm::SwitchInst::Create(Load, Br->getSuccessor(0), 4, Block);
+    Br->eraseFromParent();
+    return Switch;
+  } else {
+    return cast<llvm::SwitchInst>(Term);
+  }
+}
+
+void CodeGenFunction::ResolveBranchFixups(llvm::BasicBlock *Block) {
+  assert(Block && "resolving a null target block");
+  if (!EHStack.getNumBranchFixups()) return;
+
+  assert(EHStack.hasNormalCleanups() &&
+         "branch fixups exist with no normal cleanups on stack");
+
+  llvm::SmallPtrSet<llvm::BasicBlock*, 4> ModifiedOptimisticBlocks;
+  bool ResolvedAny = false;
+
+  for (unsigned I = 0, E = EHStack.getNumBranchFixups(); I != E; ++I) {
+    // Skip this fixup if its destination doesn't match.
+    BranchFixup &Fixup = EHStack.getBranchFixup(I);
+    if (Fixup.Destination != Block) continue;
+
+    Fixup.Destination = 0;
+    ResolvedAny = true;
+
+    // If it doesn't have an optimistic branch block, LatestBranch is
+    // already pointing to the right place.
+    llvm::BasicBlock *BranchBB = Fixup.OptimisticBranchBlock;
+    if (!BranchBB)
+      continue;
+
+    // Don't process the same optimistic branch block twice.
+    if (!ModifiedOptimisticBlocks.insert(BranchBB))
+      continue;
+
+    llvm::SwitchInst *Switch = TransitionToCleanupSwitch(*this, BranchBB);
+
+    // Add a case to the switch.
+    Switch->addCase(Builder.getInt32(Fixup.DestinationIndex), Block);
+  }
+
+  if (ResolvedAny)
+    EHStack.popNullFixups();
+}
+
+/// Pops cleanup blocks until the given savepoint is reached.
+void CodeGenFunction::PopCleanupBlocks(EHScopeStack::stable_iterator Old) {
+  assert(Old.isValid());
+
+  while (EHStack.stable_begin() != Old) {
+    EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
+
+    // As long as Old strictly encloses the scope's enclosing normal
+    // cleanup, we're going to emit another normal cleanup which
+    // fallthrough can propagate through.
+    bool FallThroughIsBranchThrough =
+      Old.strictlyEncloses(Scope.getEnclosingNormalCleanup());
+
+    PopCleanupBlock(FallThroughIsBranchThrough);
+  }
+}
+
+static llvm::BasicBlock *CreateNormalEntry(CodeGenFunction &CGF,
+                                           EHCleanupScope &Scope) {
+  assert(Scope.isNormalCleanup());
+  llvm::BasicBlock *Entry = Scope.getNormalBlock();
+  if (!Entry) {
+    Entry = CGF.createBasicBlock("cleanup");
+    Scope.setNormalBlock(Entry);
+  }
+  return Entry;
+}
+
+static llvm::BasicBlock *CreateEHEntry(CodeGenFunction &CGF,
+                                       EHCleanupScope &Scope) {
+  assert(Scope.isEHCleanup());
+  llvm::BasicBlock *Entry = Scope.getEHBlock();
+  if (!Entry) {
+    Entry = CGF.createBasicBlock("eh.cleanup");
+    Scope.setEHBlock(Entry);
+  }
+  return Entry;
+}
+
+/// Attempts to reduce a cleanup's entry block to a fallthrough.  This
+/// is basically llvm::MergeBlockIntoPredecessor, except
+/// simplified/optimized for the tighter constraints on cleanup blocks.
+///
+/// Returns the new block, whatever it is.
+static llvm::BasicBlock *SimplifyCleanupEntry(CodeGenFunction &CGF,
+                                              llvm::BasicBlock *Entry) {
+  llvm::BasicBlock *Pred = Entry->getSinglePredecessor();
+  if (!Pred) return Entry;
+
+  llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Pred->getTerminator());
+  if (!Br || Br->isConditional()) return Entry;
+  assert(Br->getSuccessor(0) == Entry);
+
+  // If we were previously inserting at the end of the cleanup entry
+  // block, we'll need to continue inserting at the end of the
+  // predecessor.
+  bool WasInsertBlock = CGF.Builder.GetInsertBlock() == Entry;
+  assert(!WasInsertBlock || CGF.Builder.GetInsertPoint() == Entry->end());
+
+  // Kill the branch.
+  Br->eraseFromParent();
+
+  // Merge the blocks.
+  Pred->getInstList().splice(Pred->end(), Entry->getInstList());
+
+  // Replace all uses of the entry with the predecessor, in case there
+  // are phis in the cleanup.
+  Entry->replaceAllUsesWith(Pred);
+
+  // Kill the entry block.
+  Entry->eraseFromParent();
+
+  if (WasInsertBlock)
+    CGF.Builder.SetInsertPoint(Pred);
+
+  return Pred;
+}
+
+static void EmitCleanup(CodeGenFunction &CGF,
+                        EHScopeStack::Cleanup *Fn,
+                        bool ForEH,
+                        llvm::Value *ActiveFlag) {
+  // EH cleanups always occur within a terminate scope.
+  if (ForEH) CGF.EHStack.pushTerminate();
+
+  // If there's an active flag, load it and skip the cleanup if it's
+  // false.
+  llvm::BasicBlock *ContBB = 0;
+  if (ActiveFlag) {
+    ContBB = CGF.createBasicBlock("cleanup.done");
+    llvm::BasicBlock *CleanupBB = CGF.createBasicBlock("cleanup.action");
+    llvm::Value *IsActive
+      = CGF.Builder.CreateLoad(ActiveFlag, "cleanup.is_active");
+    CGF.Builder.CreateCondBr(IsActive, CleanupBB, ContBB);
+    CGF.EmitBlock(CleanupBB);
+  }
+
+  // Ask the cleanup to emit itself.
+  Fn->Emit(CGF, ForEH);
+  assert(CGF.HaveInsertPoint() && "cleanup ended with no insertion point?");
+
+  // Emit the continuation block if there was an active flag.
+  if (ActiveFlag)
+    CGF.EmitBlock(ContBB);
+
+  // Leave the terminate scope.
+  if (ForEH) CGF.EHStack.popTerminate();
+}
+
+static void ForwardPrebranchedFallthrough(llvm::BasicBlock *Exit,
+                                          llvm::BasicBlock *From,
+                                          llvm::BasicBlock *To) {
+  // Exit is the exit block of a cleanup, so it always terminates in
+  // an unconditional branch or a switch.
+  llvm::TerminatorInst *Term = Exit->getTerminator();
+
+  if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
+    assert(Br->isUnconditional() && Br->getSuccessor(0) == From);
+    Br->setSuccessor(0, To);
+  } else {
+    llvm::SwitchInst *Switch = cast<llvm::SwitchInst>(Term);
+    for (unsigned I = 0, E = Switch->getNumSuccessors(); I != E; ++I)
+      if (Switch->getSuccessor(I) == From)
+        Switch->setSuccessor(I, To);
+  }
+}
+
+/// Pops a cleanup block.  If the block includes a normal cleanup, the
+/// current insertion point is threaded through the cleanup, as are
+/// any branch fixups on the cleanup.
+void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
+  assert(!EHStack.empty() && "cleanup stack is empty!");
+  assert(isa<EHCleanupScope>(*EHStack.begin()) && "top not a cleanup!");
+  EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
+  assert(Scope.getFixupDepth() <= EHStack.getNumBranchFixups());
+
+  // Remember activation information.
+  bool IsActive = Scope.isActive();
+  llvm::Value *NormalActiveFlag =
+    Scope.shouldTestFlagInNormalCleanup() ? Scope.getActiveFlag() : 0;
+  llvm::Value *EHActiveFlag = 
+    Scope.shouldTestFlagInEHCleanup() ? Scope.getActiveFlag() : 0;
+
+  // Check whether we need an EH cleanup.  This is only true if we've
+  // generated a lazy EH cleanup block.
+  bool RequiresEHCleanup = Scope.hasEHBranches();
+
+  // Check the three conditions which might require a normal cleanup:
+
+  // - whether there are branch fix-ups through this cleanup
+  unsigned FixupDepth = Scope.getFixupDepth();
+  bool HasFixups = EHStack.getNumBranchFixups() != FixupDepth;
+
+  // - whether there are branch-throughs or branch-afters
+  bool HasExistingBranches = Scope.hasBranches();
+
+  // - whether there's a fallthrough
+  llvm::BasicBlock *FallthroughSource = Builder.GetInsertBlock();
+  bool HasFallthrough = (FallthroughSource != 0 && IsActive);
+
+  // Branch-through fall-throughs leave the insertion point set to the
+  // end of the last cleanup, which points to the current scope.  The
+  // rest of IR gen doesn't need to worry about this; it only happens
+  // during the execution of PopCleanupBlocks().
+  bool HasPrebranchedFallthrough =
+    (FallthroughSource && FallthroughSource->getTerminator());
+
+  // If this is a normal cleanup, then having a prebranched
+  // fallthrough implies that the fallthrough source unconditionally
+  // jumps here.
+  assert(!Scope.isNormalCleanup() || !HasPrebranchedFallthrough ||
+         (Scope.getNormalBlock() &&
+          FallthroughSource->getTerminator()->getSuccessor(0)
+            == Scope.getNormalBlock()));
+
+  bool RequiresNormalCleanup = false;
+  if (Scope.isNormalCleanup() &&
+      (HasFixups || HasExistingBranches || HasFallthrough)) {
+    RequiresNormalCleanup = true;
+  }
+
+  // Even if we don't need the normal cleanup, we might still have
+  // prebranched fallthrough to worry about.
+  if (Scope.isNormalCleanup() && !RequiresNormalCleanup &&
+      HasPrebranchedFallthrough) {
+    assert(!IsActive);
+
+    llvm::BasicBlock *NormalEntry = Scope.getNormalBlock();
+
+    // If we're branching through this cleanup, just forward the
+    // prebranched fallthrough to the next cleanup, leaving the insert
+    // point in the old block.
+    if (FallthroughIsBranchThrough) {
+      EHScope &S = *EHStack.find(Scope.getEnclosingNormalCleanup());
+      llvm::BasicBlock *EnclosingEntry = 
+        CreateNormalEntry(*this, cast<EHCleanupScope>(S));
+
+      ForwardPrebranchedFallthrough(FallthroughSource,
+                                    NormalEntry, EnclosingEntry);
+      assert(NormalEntry->use_empty() &&
+             "uses of entry remain after forwarding?");
+      delete NormalEntry;
+
+    // Otherwise, we're branching out;  just emit the next block.
+    } else {
+      EmitBlock(NormalEntry);
+      SimplifyCleanupEntry(*this, NormalEntry);
+    }
+  }
+
+  // If we don't need the cleanup at all, we're done.
+  if (!RequiresNormalCleanup && !RequiresEHCleanup) {
+    EHStack.popCleanup(); // safe because there are no fixups
+    assert(EHStack.getNumBranchFixups() == 0 ||
+           EHStack.hasNormalCleanups());
+    return;
+  }
+
+  // Copy the cleanup emission data out.  Note that SmallVector
+  // guarantees maximal alignment for its buffer regardless of its
+  // type parameter.
+  llvm::SmallVector<char, 8*sizeof(void*)> CleanupBuffer;
+  CleanupBuffer.reserve(Scope.getCleanupSize());
+  memcpy(CleanupBuffer.data(),
+         Scope.getCleanupBuffer(), Scope.getCleanupSize());
+  CleanupBuffer.set_size(Scope.getCleanupSize());
+  EHScopeStack::Cleanup *Fn =
+    reinterpret_cast<EHScopeStack::Cleanup*>(CleanupBuffer.data());
+
+  // We want to emit the EH cleanup after the normal cleanup, but go
+  // ahead and do the setup for the EH cleanup while the scope is still
+  // alive.
+  llvm::BasicBlock *EHEntry = 0;
+  llvm::SmallVector<llvm::Instruction*, 2> EHInstsToAppend;
+  if (RequiresEHCleanup) {
+    EHEntry = CreateEHEntry(*this, Scope);
+
+    // Figure out the branch-through dest if necessary.
+    llvm::BasicBlock *EHBranchThroughDest = 0;
+    if (Scope.hasEHBranchThroughs()) {
+      assert(Scope.getEnclosingEHCleanup() != EHStack.stable_end());
+      EHScope &S = *EHStack.find(Scope.getEnclosingEHCleanup());
+      EHBranchThroughDest = CreateEHEntry(*this, cast<EHCleanupScope>(S));
+    }
+
+    // If we have exactly one branch-after and no branch-throughs, we
+    // can dispatch it without a switch.
+    if (!Scope.hasEHBranchThroughs() &&
+        Scope.getNumEHBranchAfters() == 1) {
+      assert(!EHBranchThroughDest);
+
+      // TODO: remove the spurious eh.cleanup.dest stores if this edge
+      // never went through any switches.
+      llvm::BasicBlock *BranchAfterDest = Scope.getEHBranchAfterBlock(0);
+      EHInstsToAppend.push_back(llvm::BranchInst::Create(BranchAfterDest));
+    
+    // Otherwise, if we have any branch-afters, we need a switch.
+    } else if (Scope.getNumEHBranchAfters()) {
+      // The default of the switch belongs to the branch-throughs if
+      // they exist.
+      llvm::BasicBlock *Default =
+        (EHBranchThroughDest ? EHBranchThroughDest : getUnreachableBlock());
+
+      const unsigned SwitchCapacity = Scope.getNumEHBranchAfters();
+
+      llvm::LoadInst *Load =
+        new llvm::LoadInst(getEHCleanupDestSlot(), "cleanup.dest");
+      llvm::SwitchInst *Switch =
+        llvm::SwitchInst::Create(Load, Default, SwitchCapacity);
+
+      EHInstsToAppend.push_back(Load);
+      EHInstsToAppend.push_back(Switch);
+
+      for (unsigned I = 0, E = Scope.getNumEHBranchAfters(); I != E; ++I)
+        Switch->addCase(Scope.getEHBranchAfterIndex(I),
+                        Scope.getEHBranchAfterBlock(I));
+
+    // Otherwise, we have only branch-throughs; jump to the next EH
+    // cleanup.
+    } else {
+      assert(EHBranchThroughDest);
+      EHInstsToAppend.push_back(llvm::BranchInst::Create(EHBranchThroughDest));
+    }
+  }
+
+  if (!RequiresNormalCleanup) {
+    EHStack.popCleanup();
+  } else {
+    // If we have a fallthrough and no other need for the cleanup,
+    // emit it directly.
+    if (HasFallthrough && !HasPrebranchedFallthrough &&
+        !HasFixups && !HasExistingBranches) {
+
+      // Fixups can cause us to optimistically create a normal block,
+      // only to later have no real uses for it.  Just delete it in
+      // this case.
+      // TODO: we can potentially simplify all the uses after this.
+      if (Scope.getNormalBlock()) {
+        Scope.getNormalBlock()->replaceAllUsesWith(getUnreachableBlock());
+        delete Scope.getNormalBlock();
+      }
+
+      EHStack.popCleanup();
+
+      EmitCleanup(*this, Fn, /*ForEH*/ false, NormalActiveFlag);
+
+    // Otherwise, the best approach is to thread everything through
+    // the cleanup block and then try to clean up after ourselves.
+    } else {
+      // Force the entry block to exist.
+      llvm::BasicBlock *NormalEntry = CreateNormalEntry(*this, Scope);
+
+      // I.  Set up the fallthrough edge in.
+
+      // If there's a fallthrough, we need to store the cleanup
+      // destination index.  For fall-throughs this is always zero.
+      if (HasFallthrough) {
+        if (!HasPrebranchedFallthrough)
+          Builder.CreateStore(Builder.getInt32(0), getNormalCleanupDestSlot());
+
+      // Otherwise, clear the IP if we don't have fallthrough because
+      // the cleanup is inactive.  We don't need to save it because
+      // it's still just FallthroughSource.
+      } else if (FallthroughSource) {
+        assert(!IsActive && "source without fallthrough for active cleanup");
+        Builder.ClearInsertionPoint();
+      }
+
+      // II.  Emit the entry block.  This implicitly branches to it if
+      // we have fallthrough.  All the fixups and existing branches
+      // should already be branched to it.
+      EmitBlock(NormalEntry);
+
+      // III.  Figure out where we're going and build the cleanup
+      // epilogue.
+
+      bool HasEnclosingCleanups =
+        (Scope.getEnclosingNormalCleanup() != EHStack.stable_end());
+
+      // Compute the branch-through dest if we need it:
+      //   - if there are branch-throughs threaded through the scope
+      //   - if fall-through is a branch-through
+      //   - if there are fixups that will be optimistically forwarded
+      //     to the enclosing cleanup
+      llvm::BasicBlock *BranchThroughDest = 0;
+      if (Scope.hasBranchThroughs() ||
+          (FallthroughSource && FallthroughIsBranchThrough) ||
+          (HasFixups && HasEnclosingCleanups)) {
+        assert(HasEnclosingCleanups);
+        EHScope &S = *EHStack.find(Scope.getEnclosingNormalCleanup());
+        BranchThroughDest = CreateNormalEntry(*this, cast<EHCleanupScope>(S));
+      }
+
+      llvm::BasicBlock *FallthroughDest = 0;
+      llvm::SmallVector<llvm::Instruction*, 2> InstsToAppend;
+
+      // If there's exactly one branch-after and no other threads,
+      // we can route it without a switch.
+      if (!Scope.hasBranchThroughs() && !HasFixups && !HasFallthrough &&
+          Scope.getNumBranchAfters() == 1) {
+        assert(!BranchThroughDest || !IsActive);
+
+        // TODO: clean up the possibly dead stores to the cleanup dest slot.
+        llvm::BasicBlock *BranchAfter = Scope.getBranchAfterBlock(0);
+        InstsToAppend.push_back(llvm::BranchInst::Create(BranchAfter));
+
+      // Build a switch-out if we need it:
+      //   - if there are branch-afters threaded through the scope
+      //   - if fall-through is a branch-after
+      //   - if there are fixups that have nowhere left to go and
+      //     so must be immediately resolved
+      } else if (Scope.getNumBranchAfters() ||
+                 (HasFallthrough && !FallthroughIsBranchThrough) ||
+                 (HasFixups && !HasEnclosingCleanups)) {
+
+        llvm::BasicBlock *Default =
+          (BranchThroughDest ? BranchThroughDest : getUnreachableBlock());
+
+        // TODO: base this on the number of branch-afters and fixups
+        const unsigned SwitchCapacity = 10;
+
+        llvm::LoadInst *Load =
+          new llvm::LoadInst(getNormalCleanupDestSlot(), "cleanup.dest");
+        llvm::SwitchInst *Switch =
+          llvm::SwitchInst::Create(Load, Default, SwitchCapacity);
+
+        InstsToAppend.push_back(Load);
+        InstsToAppend.push_back(Switch);
+
+        // Branch-after fallthrough.
+        if (FallthroughSource && !FallthroughIsBranchThrough) {
+          FallthroughDest = createBasicBlock("cleanup.cont");
+          if (HasFallthrough)
+            Switch->addCase(Builder.getInt32(0), FallthroughDest);
+        }
+
+        for (unsigned I = 0, E = Scope.getNumBranchAfters(); I != E; ++I) {
+          Switch->addCase(Scope.getBranchAfterIndex(I),
+                          Scope.getBranchAfterBlock(I));
+        }
+
+        // If there aren't any enclosing cleanups, we can resolve all
+        // the fixups now.
+        if (HasFixups && !HasEnclosingCleanups)
+          ResolveAllBranchFixups(*this, Switch, NormalEntry);
+      } else {
+        // We should always have a branch-through destination in this case.
+        assert(BranchThroughDest);
+        InstsToAppend.push_back(llvm::BranchInst::Create(BranchThroughDest));
+      }
+
+      // IV.  Pop the cleanup and emit it.
+      EHStack.popCleanup();
+      assert(EHStack.hasNormalCleanups() == HasEnclosingCleanups);
+
+      EmitCleanup(*this, Fn, /*ForEH*/ false, NormalActiveFlag);
+
+      // Append the prepared cleanup prologue from above.
+      llvm::BasicBlock *NormalExit = Builder.GetInsertBlock();
+      for (unsigned I = 0, E = InstsToAppend.size(); I != E; ++I)
+        NormalExit->getInstList().push_back(InstsToAppend[I]);
+
+      // Optimistically hope that any fixups will continue falling through.
+      for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
+           I < E; ++I) {
+        BranchFixup &Fixup = EHStack.getBranchFixup(I);
+        if (!Fixup.Destination) continue;
+        if (!Fixup.OptimisticBranchBlock) {
+          new llvm::StoreInst(Builder.getInt32(Fixup.DestinationIndex),
+                              getNormalCleanupDestSlot(),
+                              Fixup.InitialBranch);
+          Fixup.InitialBranch->setSuccessor(0, NormalEntry);
+        }
+        Fixup.OptimisticBranchBlock = NormalExit;
+      }
+
+      // V.  Set up the fallthrough edge out.
+      
+      // Case 1: a fallthrough source exists but shouldn't branch to
+      // the cleanup because the cleanup is inactive.
+      if (!HasFallthrough && FallthroughSource) {
+        assert(!IsActive);
+
+        // If we have a prebranched fallthrough, that needs to be
+        // forwarded to the right block.
+        if (HasPrebranchedFallthrough) {
+          llvm::BasicBlock *Next;
+          if (FallthroughIsBranchThrough) {
+            Next = BranchThroughDest;
+            assert(!FallthroughDest);
+          } else {
+            Next = FallthroughDest;
+          }
+
+          ForwardPrebranchedFallthrough(FallthroughSource, NormalEntry, Next);
+        }
+        Builder.SetInsertPoint(FallthroughSource);
+
+      // Case 2: a fallthrough source exists and should branch to the
+      // cleanup, but we're not supposed to branch through to the next
+      // cleanup.
+      } else if (HasFallthrough && FallthroughDest) {
+        assert(!FallthroughIsBranchThrough);
+        EmitBlock(FallthroughDest);
+
+      // Case 3: a fallthrough source exists and should branch to the
+      // cleanup and then through to the next.
+      } else if (HasFallthrough) {
+        // Everything is already set up for this.
+
+      // Case 4: no fallthrough source exists.
+      } else {
+        Builder.ClearInsertionPoint();
+      }
+
+      // VI.  Assorted cleaning.
+
+      // Check whether we can merge NormalEntry into a single predecessor.
+      // This might invalidate (non-IR) pointers to NormalEntry.
+      llvm::BasicBlock *NewNormalEntry =
+        SimplifyCleanupEntry(*this, NormalEntry);
+
+      // If it did invalidate those pointers, and NormalEntry was the same
+      // as NormalExit, go back and patch up the fixups.
+      if (NewNormalEntry != NormalEntry && NormalEntry == NormalExit)
+        for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
+               I < E; ++I)
+          EHStack.getBranchFixup(I).OptimisticBranchBlock = NewNormalEntry;
+    }
+  }
+
+  assert(EHStack.hasNormalCleanups() || EHStack.getNumBranchFixups() == 0);
+
+  // Emit the EH cleanup if required.
+  if (RequiresEHCleanup) {
+    CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
+
+    EmitBlock(EHEntry);
+    EmitCleanup(*this, Fn, /*ForEH*/ true, EHActiveFlag);
+
+    // Append the prepared cleanup prologue from above.
+    llvm::BasicBlock *EHExit = Builder.GetInsertBlock();
+    for (unsigned I = 0, E = EHInstsToAppend.size(); I != E; ++I)
+      EHExit->getInstList().push_back(EHInstsToAppend[I]);
+
+    Builder.restoreIP(SavedIP);
+
+    SimplifyCleanupEntry(*this, EHEntry);
+  }
+}
+
+/// Terminate the current block by emitting a branch which might leave
+/// the current cleanup-protected scope.  The target scope may not yet
+/// be known, in which case this will require a fixup.
+///
+/// As a side-effect, this method clears the insertion point.
+void CodeGenFunction::EmitBranchThroughCleanup(JumpDest Dest) {
+  assert(Dest.getScopeDepth().encloses(EHStack.getInnermostNormalCleanup())
+         && "stale jump destination");
+
+  if (!HaveInsertPoint())
+    return;
+
+  // Create the branch.
+  llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock());
+
+  // Calculate the innermost active normal cleanup.
+  EHScopeStack::stable_iterator
+    TopCleanup = EHStack.getInnermostActiveNormalCleanup();
+
+  // If we're not in an active normal cleanup scope, or if the
+  // destination scope is within the innermost active normal cleanup
+  // scope, we don't need to worry about fixups.
+  if (TopCleanup == EHStack.stable_end() ||
+      TopCleanup.encloses(Dest.getScopeDepth())) { // works for invalid
+    Builder.ClearInsertionPoint();
+    return;
+  }
+
+  // If we can't resolve the destination cleanup scope, just add this
+  // to the current cleanup scope as a branch fixup.
+  if (!Dest.getScopeDepth().isValid()) {
+    BranchFixup &Fixup = EHStack.addBranchFixup();
+    Fixup.Destination = Dest.getBlock();
+    Fixup.DestinationIndex = Dest.getDestIndex();
+    Fixup.InitialBranch = BI;
+    Fixup.OptimisticBranchBlock = 0;
+
+    Builder.ClearInsertionPoint();
+    return;
+  }
+
+  // Otherwise, thread through all the normal cleanups in scope.
+
+  // Store the index at the start.
+  llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex());
+  new llvm::StoreInst(Index, getNormalCleanupDestSlot(), BI);
+
+  // Adjust BI to point to the first cleanup block.
+  {
+    EHCleanupScope &Scope =
+      cast<EHCleanupScope>(*EHStack.find(TopCleanup));
+    BI->setSuccessor(0, CreateNormalEntry(*this, Scope));
+  }
+
+  // Add this destination to all the scopes involved.
+  EHScopeStack::stable_iterator I = TopCleanup;
+  EHScopeStack::stable_iterator E = Dest.getScopeDepth();
+  if (E.strictlyEncloses(I)) {
+    while (true) {
+      EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(I));
+      assert(Scope.isNormalCleanup());
+      I = Scope.getEnclosingNormalCleanup();
+
+      // If this is the last cleanup we're propagating through, tell it
+      // that there's a resolved jump moving through it.
+      if (!E.strictlyEncloses(I)) {
+        Scope.addBranchAfter(Index, Dest.getBlock());
+        break;
+      }
+
+      // Otherwise, tell the scope that there's a jump propoagating
+      // through it.  If this isn't new information, all the rest of
+      // the work has been done before.
+      if (!Scope.addBranchThrough(Dest.getBlock()))
+        break;
+    }
+  }
+  
+  Builder.ClearInsertionPoint();
+}
+
+void CodeGenFunction::EmitBranchThroughEHCleanup(UnwindDest Dest) {
+  // We should never get invalid scope depths for an UnwindDest; that
+  // implies that the destination wasn't set up correctly.
+  assert(Dest.getScopeDepth().isValid() && "invalid scope depth on EH dest?");
+
+  if (!HaveInsertPoint())
+    return;
+
+  // Create the branch.
+  llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock());
+
+  // Calculate the innermost active cleanup.
+  EHScopeStack::stable_iterator
+    InnermostCleanup = EHStack.getInnermostActiveEHCleanup();
+
+  // If the destination is in the same EH cleanup scope as us, we
+  // don't need to thread through anything.
+  if (InnermostCleanup.encloses(Dest.getScopeDepth())) {
+    Builder.ClearInsertionPoint();
+    return;
+  }
+  assert(InnermostCleanup != EHStack.stable_end());
+
+  // Store the index at the start.
+  llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex());
+  new llvm::StoreInst(Index, getEHCleanupDestSlot(), BI);
+
+  // Adjust BI to point to the first cleanup block.
+  {
+    EHCleanupScope &Scope =
+      cast<EHCleanupScope>(*EHStack.find(InnermostCleanup));
+    BI->setSuccessor(0, CreateEHEntry(*this, Scope));
+  }
+  
+  // Add this destination to all the scopes involved.
+  for (EHScopeStack::stable_iterator
+         I = InnermostCleanup, E = Dest.getScopeDepth(); ; ) {
+    assert(E.strictlyEncloses(I));
+    EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(I));
+    assert(Scope.isEHCleanup());
+    I = Scope.getEnclosingEHCleanup();
+
+    // If this is the last cleanup we're propagating through, add this
+    // as a branch-after.
+    if (I == E) {
+      Scope.addEHBranchAfter(Index, Dest.getBlock());
+      break;
+    }
+
+    // Otherwise, add it as a branch-through.  If this isn't new
+    // information, all the rest of the work has been done before.
+    if (!Scope.addEHBranchThrough(Dest.getBlock()))
+      break;
+  }
+  
+  Builder.ClearInsertionPoint();
+}
+
+static bool IsUsedAsNormalCleanup(EHScopeStack &EHStack,
+                                  EHScopeStack::stable_iterator C) {
+  // If we needed a normal block for any reason, that counts.
+  if (cast<EHCleanupScope>(*EHStack.find(C)).getNormalBlock())
+    return true;
+
+  // Check whether any enclosed cleanups were needed.
+  for (EHScopeStack::stable_iterator
+         I = EHStack.getInnermostNormalCleanup();
+         I != C; ) {
+    assert(C.strictlyEncloses(I));
+    EHCleanupScope &S = cast<EHCleanupScope>(*EHStack.find(I));
+    if (S.getNormalBlock()) return true;
+    I = S.getEnclosingNormalCleanup();
+  }
+
+  return false;
+}
+
+static bool IsUsedAsEHCleanup(EHScopeStack &EHStack,
+                              EHScopeStack::stable_iterator C) {
+  // If we needed an EH block for any reason, that counts.
+  if (cast<EHCleanupScope>(*EHStack.find(C)).getEHBlock())
+    return true;
+
+  // Check whether any enclosed cleanups were needed.
+  for (EHScopeStack::stable_iterator
+         I = EHStack.getInnermostEHCleanup(); I != C; ) {
+    assert(C.strictlyEncloses(I));
+    EHCleanupScope &S = cast<EHCleanupScope>(*EHStack.find(I));
+    if (S.getEHBlock()) return true;
+    I = S.getEnclosingEHCleanup();
+  }
+
+  return false;
+}
+
+enum ForActivation_t {
+  ForActivation,
+  ForDeactivation
+};
+
+/// The given cleanup block is changing activation state.  Configure a
+/// cleanup variable if necessary.
+///
+/// It would be good if we had some way of determining if there were
+/// extra uses *after* the change-over point.
+static void SetupCleanupBlockActivation(CodeGenFunction &CGF,
+                                        EHScopeStack::stable_iterator C,
+                                        ForActivation_t Kind) {
+  EHCleanupScope &Scope = cast<EHCleanupScope>(*CGF.EHStack.find(C));
+
+  // We always need the flag if we're activating the cleanup, because
+  // we have to assume that the current location doesn't necessarily
+  // dominate all future uses of the cleanup.
+  bool NeedFlag = (Kind == ForActivation);
+
+  // Calculate whether the cleanup was used:
+
+  //   - as a normal cleanup
+  if (Scope.isNormalCleanup() && IsUsedAsNormalCleanup(CGF.EHStack, C)) {
+    Scope.setTestFlagInNormalCleanup();
+    NeedFlag = true;
+  }
+
+  //  - as an EH cleanup
+  if (Scope.isEHCleanup() && IsUsedAsEHCleanup(CGF.EHStack, C)) {
+    Scope.setTestFlagInEHCleanup();
+    NeedFlag = true;
+  }
+
+  // If it hasn't yet been used as either, we're done.
+  if (!NeedFlag) return;
+
+  llvm::AllocaInst *Var = Scope.getActiveFlag();
+  if (!Var) {
+    Var = CGF.CreateTempAlloca(CGF.Builder.getInt1Ty(), "cleanup.isactive");
+    Scope.setActiveFlag(Var);
+
+    // Initialize to true or false depending on whether it was
+    // active up to this point.
+    CGF.InitTempAlloca(Var, CGF.Builder.getInt1(Kind == ForDeactivation));
+  }
+
+  CGF.Builder.CreateStore(CGF.Builder.getInt1(Kind == ForActivation), Var);
+}
+
+/// Activate a cleanup that was created in an inactivated state.
+void CodeGenFunction::ActivateCleanupBlock(EHScopeStack::stable_iterator C) {
+  assert(C != EHStack.stable_end() && "activating bottom of stack?");
+  EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
+  assert(!Scope.isActive() && "double activation");
+
+  SetupCleanupBlockActivation(*this, C, ForActivation);
+
+  Scope.setActive(true);
+}
+
+/// Deactive a cleanup that was created in an active state.
+void CodeGenFunction::DeactivateCleanupBlock(EHScopeStack::stable_iterator C) {
+  assert(C != EHStack.stable_end() && "deactivating bottom of stack?");
+  EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
+  assert(Scope.isActive() && "double deactivation");
+
+  // If it's the top of the stack, just pop it.
+  if (C == EHStack.stable_begin()) {
+    // If it's a normal cleanup, we need to pretend that the
+    // fallthrough is unreachable.
+    CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
+    PopCleanupBlock();
+    Builder.restoreIP(SavedIP);
+    return;
+  }
+
+  // Otherwise, follow the general case.
+  SetupCleanupBlockActivation(*this, C, ForDeactivation);
+
+  Scope.setActive(false);
+}
+
+llvm::Value *CodeGenFunction::getNormalCleanupDestSlot() {
+  if (!NormalCleanupDest)
+    NormalCleanupDest =
+      CreateTempAlloca(Builder.getInt32Ty(), "cleanup.dest.slot");
+  return NormalCleanupDest;
+}
+
+llvm::Value *CodeGenFunction::getEHCleanupDestSlot() {
+  if (!EHCleanupDest)
+    EHCleanupDest =
+      CreateTempAlloca(Builder.getInt32Ty(), "eh.cleanup.dest.slot");
+  return EHCleanupDest;
+}