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      1 //===--- CGCleanup.cpp - Bookkeeping and code emission for cleanups -------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file contains code dealing with the IR generation for cleanups
     11 // and related information.
     12 //
     13 // A "cleanup" is a piece of code which needs to be executed whenever
     14 // control transfers out of a particular scope.  This can be
     15 // conditionalized to occur only on exceptional control flow, only on
     16 // normal control flow, or both.
     17 //
     18 //===----------------------------------------------------------------------===//
     19 
     20 #include "CGCleanup.h"
     21 #include "CodeGenFunction.h"
     22 #include "llvm/Support/SaveAndRestore.h"
     23 
     24 using namespace clang;
     25 using namespace CodeGen;
     26 
     27 bool DominatingValue<RValue>::saved_type::needsSaving(RValue rv) {
     28   if (rv.isScalar())
     29     return DominatingLLVMValue::needsSaving(rv.getScalarVal());
     30   if (rv.isAggregate())
     31     return DominatingLLVMValue::needsSaving(rv.getAggregatePointer());
     32   return true;
     33 }
     34 
     35 DominatingValue<RValue>::saved_type
     36 DominatingValue<RValue>::saved_type::save(CodeGenFunction &CGF, RValue rv) {
     37   if (rv.isScalar()) {
     38     llvm::Value *V = rv.getScalarVal();
     39 
     40     // These automatically dominate and don't need to be saved.
     41     if (!DominatingLLVMValue::needsSaving(V))
     42       return saved_type(V, ScalarLiteral);
     43 
     44     // Everything else needs an alloca.
     45     Address addr =
     46       CGF.CreateDefaultAlignTempAlloca(V->getType(), "saved-rvalue");
     47     CGF.Builder.CreateStore(V, addr);
     48     return saved_type(addr.getPointer(), ScalarAddress);
     49   }
     50 
     51   if (rv.isComplex()) {
     52     CodeGenFunction::ComplexPairTy V = rv.getComplexVal();
     53     llvm::Type *ComplexTy =
     54       llvm::StructType::get(V.first->getType(), V.second->getType(),
     55                             (void*) nullptr);
     56     Address addr = CGF.CreateDefaultAlignTempAlloca(ComplexTy, "saved-complex");
     57     CGF.Builder.CreateStore(V.first,
     58                             CGF.Builder.CreateStructGEP(addr, 0, CharUnits()));
     59     CharUnits offset = CharUnits::fromQuantity(
     60                CGF.CGM.getDataLayout().getTypeAllocSize(V.first->getType()));
     61     CGF.Builder.CreateStore(V.second,
     62                             CGF.Builder.CreateStructGEP(addr, 1, offset));
     63     return saved_type(addr.getPointer(), ComplexAddress);
     64   }
     65 
     66   assert(rv.isAggregate());
     67   Address V = rv.getAggregateAddress(); // TODO: volatile?
     68   if (!DominatingLLVMValue::needsSaving(V.getPointer()))
     69     return saved_type(V.getPointer(), AggregateLiteral,
     70                       V.getAlignment().getQuantity());
     71 
     72   Address addr =
     73     CGF.CreateTempAlloca(V.getType(), CGF.getPointerAlign(), "saved-rvalue");
     74   CGF.Builder.CreateStore(V.getPointer(), addr);
     75   return saved_type(addr.getPointer(), AggregateAddress,
     76                     V.getAlignment().getQuantity());
     77 }
     78 
     79 /// Given a saved r-value produced by SaveRValue, perform the code
     80 /// necessary to restore it to usability at the current insertion
     81 /// point.
     82 RValue DominatingValue<RValue>::saved_type::restore(CodeGenFunction &CGF) {
     83   auto getSavingAddress = [&](llvm::Value *value) {
     84     auto alignment = cast<llvm::AllocaInst>(value)->getAlignment();
     85     return Address(value, CharUnits::fromQuantity(alignment));
     86   };
     87   switch (K) {
     88   case ScalarLiteral:
     89     return RValue::get(Value);
     90   case ScalarAddress:
     91     return RValue::get(CGF.Builder.CreateLoad(getSavingAddress(Value)));
     92   case AggregateLiteral:
     93     return RValue::getAggregate(Address(Value, CharUnits::fromQuantity(Align)));
     94   case AggregateAddress: {
     95     auto addr = CGF.Builder.CreateLoad(getSavingAddress(Value));
     96     return RValue::getAggregate(Address(addr, CharUnits::fromQuantity(Align)));
     97   }
     98   case ComplexAddress: {
     99     Address address = getSavingAddress(Value);
    100     llvm::Value *real = CGF.Builder.CreateLoad(
    101                  CGF.Builder.CreateStructGEP(address, 0, CharUnits()));
    102     CharUnits offset = CharUnits::fromQuantity(
    103                  CGF.CGM.getDataLayout().getTypeAllocSize(real->getType()));
    104     llvm::Value *imag = CGF.Builder.CreateLoad(
    105                  CGF.Builder.CreateStructGEP(address, 1, offset));
    106     return RValue::getComplex(real, imag);
    107   }
    108   }
    109 
    110   llvm_unreachable("bad saved r-value kind");
    111 }
    112 
    113 /// Push an entry of the given size onto this protected-scope stack.
    114 char *EHScopeStack::allocate(size_t Size) {
    115   Size = llvm::RoundUpToAlignment(Size, ScopeStackAlignment);
    116   if (!StartOfBuffer) {
    117     unsigned Capacity = 1024;
    118     while (Capacity < Size) Capacity *= 2;
    119     StartOfBuffer = new char[Capacity];
    120     StartOfData = EndOfBuffer = StartOfBuffer + Capacity;
    121   } else if (static_cast<size_t>(StartOfData - StartOfBuffer) < Size) {
    122     unsigned CurrentCapacity = EndOfBuffer - StartOfBuffer;
    123     unsigned UsedCapacity = CurrentCapacity - (StartOfData - StartOfBuffer);
    124 
    125     unsigned NewCapacity = CurrentCapacity;
    126     do {
    127       NewCapacity *= 2;
    128     } while (NewCapacity < UsedCapacity + Size);
    129 
    130     char *NewStartOfBuffer = new char[NewCapacity];
    131     char *NewEndOfBuffer = NewStartOfBuffer + NewCapacity;
    132     char *NewStartOfData = NewEndOfBuffer - UsedCapacity;
    133     memcpy(NewStartOfData, StartOfData, UsedCapacity);
    134     delete [] StartOfBuffer;
    135     StartOfBuffer = NewStartOfBuffer;
    136     EndOfBuffer = NewEndOfBuffer;
    137     StartOfData = NewStartOfData;
    138   }
    139 
    140   assert(StartOfBuffer + Size <= StartOfData);
    141   StartOfData -= Size;
    142   return StartOfData;
    143 }
    144 
    145 void EHScopeStack::deallocate(size_t Size) {
    146   StartOfData += llvm::RoundUpToAlignment(Size, ScopeStackAlignment);
    147 }
    148 
    149 bool EHScopeStack::containsOnlyLifetimeMarkers(
    150     EHScopeStack::stable_iterator Old) const {
    151   for (EHScopeStack::iterator it = begin(); stabilize(it) != Old; it++) {
    152     EHCleanupScope *cleanup = dyn_cast<EHCleanupScope>(&*it);
    153     if (!cleanup || !cleanup->isLifetimeMarker())
    154       return false;
    155   }
    156 
    157   return true;
    158 }
    159 
    160 EHScopeStack::stable_iterator
    161 EHScopeStack::getInnermostActiveNormalCleanup() const {
    162   for (stable_iterator si = getInnermostNormalCleanup(), se = stable_end();
    163          si != se; ) {
    164     EHCleanupScope &cleanup = cast<EHCleanupScope>(*find(si));
    165     if (cleanup.isActive()) return si;
    166     si = cleanup.getEnclosingNormalCleanup();
    167   }
    168   return stable_end();
    169 }
    170 
    171 
    172 void *EHScopeStack::pushCleanup(CleanupKind Kind, size_t Size) {
    173   char *Buffer = allocate(EHCleanupScope::getSizeForCleanupSize(Size));
    174   bool IsNormalCleanup = Kind & NormalCleanup;
    175   bool IsEHCleanup = Kind & EHCleanup;
    176   bool IsActive = !(Kind & InactiveCleanup);
    177   EHCleanupScope *Scope =
    178     new (Buffer) EHCleanupScope(IsNormalCleanup,
    179                                 IsEHCleanup,
    180                                 IsActive,
    181                                 Size,
    182                                 BranchFixups.size(),
    183                                 InnermostNormalCleanup,
    184                                 InnermostEHScope);
    185   if (IsNormalCleanup)
    186     InnermostNormalCleanup = stable_begin();
    187   if (IsEHCleanup)
    188     InnermostEHScope = stable_begin();
    189 
    190   return Scope->getCleanupBuffer();
    191 }
    192 
    193 void EHScopeStack::popCleanup() {
    194   assert(!empty() && "popping exception stack when not empty");
    195 
    196   assert(isa<EHCleanupScope>(*begin()));
    197   EHCleanupScope &Cleanup = cast<EHCleanupScope>(*begin());
    198   InnermostNormalCleanup = Cleanup.getEnclosingNormalCleanup();
    199   InnermostEHScope = Cleanup.getEnclosingEHScope();
    200   deallocate(Cleanup.getAllocatedSize());
    201 
    202   // Destroy the cleanup.
    203   Cleanup.Destroy();
    204 
    205   // Check whether we can shrink the branch-fixups stack.
    206   if (!BranchFixups.empty()) {
    207     // If we no longer have any normal cleanups, all the fixups are
    208     // complete.
    209     if (!hasNormalCleanups())
    210       BranchFixups.clear();
    211 
    212     // Otherwise we can still trim out unnecessary nulls.
    213     else
    214       popNullFixups();
    215   }
    216 }
    217 
    218 EHFilterScope *EHScopeStack::pushFilter(unsigned numFilters) {
    219   assert(getInnermostEHScope() == stable_end());
    220   char *buffer = allocate(EHFilterScope::getSizeForNumFilters(numFilters));
    221   EHFilterScope *filter = new (buffer) EHFilterScope(numFilters);
    222   InnermostEHScope = stable_begin();
    223   return filter;
    224 }
    225 
    226 void EHScopeStack::popFilter() {
    227   assert(!empty() && "popping exception stack when not empty");
    228 
    229   EHFilterScope &filter = cast<EHFilterScope>(*begin());
    230   deallocate(EHFilterScope::getSizeForNumFilters(filter.getNumFilters()));
    231 
    232   InnermostEHScope = filter.getEnclosingEHScope();
    233 }
    234 
    235 EHCatchScope *EHScopeStack::pushCatch(unsigned numHandlers) {
    236   char *buffer = allocate(EHCatchScope::getSizeForNumHandlers(numHandlers));
    237   EHCatchScope *scope =
    238     new (buffer) EHCatchScope(numHandlers, InnermostEHScope);
    239   InnermostEHScope = stable_begin();
    240   return scope;
    241 }
    242 
    243 void EHScopeStack::pushTerminate() {
    244   char *Buffer = allocate(EHTerminateScope::getSize());
    245   new (Buffer) EHTerminateScope(InnermostEHScope);
    246   InnermostEHScope = stable_begin();
    247 }
    248 
    249 /// Remove any 'null' fixups on the stack.  However, we can't pop more
    250 /// fixups than the fixup depth on the innermost normal cleanup, or
    251 /// else fixups that we try to add to that cleanup will end up in the
    252 /// wrong place.  We *could* try to shrink fixup depths, but that's
    253 /// actually a lot of work for little benefit.
    254 void EHScopeStack::popNullFixups() {
    255   // We expect this to only be called when there's still an innermost
    256   // normal cleanup;  otherwise there really shouldn't be any fixups.
    257   assert(hasNormalCleanups());
    258 
    259   EHScopeStack::iterator it = find(InnermostNormalCleanup);
    260   unsigned MinSize = cast<EHCleanupScope>(*it).getFixupDepth();
    261   assert(BranchFixups.size() >= MinSize && "fixup stack out of order");
    262 
    263   while (BranchFixups.size() > MinSize &&
    264          BranchFixups.back().Destination == nullptr)
    265     BranchFixups.pop_back();
    266 }
    267 
    268 void CodeGenFunction::initFullExprCleanup() {
    269   // Create a variable to decide whether the cleanup needs to be run.
    270   Address active = CreateTempAlloca(Builder.getInt1Ty(), CharUnits::One(),
    271                                     "cleanup.cond");
    272 
    273   // Initialize it to false at a site that's guaranteed to be run
    274   // before each evaluation.
    275   setBeforeOutermostConditional(Builder.getFalse(), active);
    276 
    277   // Initialize it to true at the current location.
    278   Builder.CreateStore(Builder.getTrue(), active);
    279 
    280   // Set that as the active flag in the cleanup.
    281   EHCleanupScope &cleanup = cast<EHCleanupScope>(*EHStack.begin());
    282   assert(!cleanup.hasActiveFlag() && "cleanup already has active flag?");
    283   cleanup.setActiveFlag(active);
    284 
    285   if (cleanup.isNormalCleanup()) cleanup.setTestFlagInNormalCleanup();
    286   if (cleanup.isEHCleanup()) cleanup.setTestFlagInEHCleanup();
    287 }
    288 
    289 void EHScopeStack::Cleanup::anchor() {}
    290 
    291 static void createStoreInstBefore(llvm::Value *value, Address addr,
    292                                   llvm::Instruction *beforeInst) {
    293   auto store = new llvm::StoreInst(value, addr.getPointer(), beforeInst);
    294   store->setAlignment(addr.getAlignment().getQuantity());
    295 }
    296 
    297 static llvm::LoadInst *createLoadInstBefore(Address addr, const Twine &name,
    298                                             llvm::Instruction *beforeInst) {
    299   auto load = new llvm::LoadInst(addr.getPointer(), name, beforeInst);
    300   load->setAlignment(addr.getAlignment().getQuantity());
    301   return load;
    302 }
    303 
    304 /// All the branch fixups on the EH stack have propagated out past the
    305 /// outermost normal cleanup; resolve them all by adding cases to the
    306 /// given switch instruction.
    307 static void ResolveAllBranchFixups(CodeGenFunction &CGF,
    308                                    llvm::SwitchInst *Switch,
    309                                    llvm::BasicBlock *CleanupEntry) {
    310   llvm::SmallPtrSet<llvm::BasicBlock*, 4> CasesAdded;
    311 
    312   for (unsigned I = 0, E = CGF.EHStack.getNumBranchFixups(); I != E; ++I) {
    313     // Skip this fixup if its destination isn't set.
    314     BranchFixup &Fixup = CGF.EHStack.getBranchFixup(I);
    315     if (Fixup.Destination == nullptr) continue;
    316 
    317     // If there isn't an OptimisticBranchBlock, then InitialBranch is
    318     // still pointing directly to its destination; forward it to the
    319     // appropriate cleanup entry.  This is required in the specific
    320     // case of
    321     //   { std::string s; goto lbl; }
    322     //   lbl:
    323     // i.e. where there's an unresolved fixup inside a single cleanup
    324     // entry which we're currently popping.
    325     if (Fixup.OptimisticBranchBlock == nullptr) {
    326       createStoreInstBefore(CGF.Builder.getInt32(Fixup.DestinationIndex),
    327                             CGF.getNormalCleanupDestSlot(),
    328                             Fixup.InitialBranch);
    329       Fixup.InitialBranch->setSuccessor(0, CleanupEntry);
    330     }
    331 
    332     // Don't add this case to the switch statement twice.
    333     if (!CasesAdded.insert(Fixup.Destination).second)
    334       continue;
    335 
    336     Switch->addCase(CGF.Builder.getInt32(Fixup.DestinationIndex),
    337                     Fixup.Destination);
    338   }
    339 
    340   CGF.EHStack.clearFixups();
    341 }
    342 
    343 /// Transitions the terminator of the given exit-block of a cleanup to
    344 /// be a cleanup switch.
    345 static llvm::SwitchInst *TransitionToCleanupSwitch(CodeGenFunction &CGF,
    346                                                    llvm::BasicBlock *Block) {
    347   // If it's a branch, turn it into a switch whose default
    348   // destination is its original target.
    349   llvm::TerminatorInst *Term = Block->getTerminator();
    350   assert(Term && "can't transition block without terminator");
    351 
    352   if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
    353     assert(Br->isUnconditional());
    354     auto Load = createLoadInstBefore(CGF.getNormalCleanupDestSlot(),
    355                                      "cleanup.dest", Term);
    356     llvm::SwitchInst *Switch =
    357       llvm::SwitchInst::Create(Load, Br->getSuccessor(0), 4, Block);
    358     Br->eraseFromParent();
    359     return Switch;
    360   } else {
    361     return cast<llvm::SwitchInst>(Term);
    362   }
    363 }
    364 
    365 void CodeGenFunction::ResolveBranchFixups(llvm::BasicBlock *Block) {
    366   assert(Block && "resolving a null target block");
    367   if (!EHStack.getNumBranchFixups()) return;
    368 
    369   assert(EHStack.hasNormalCleanups() &&
    370          "branch fixups exist with no normal cleanups on stack");
    371 
    372   llvm::SmallPtrSet<llvm::BasicBlock*, 4> ModifiedOptimisticBlocks;
    373   bool ResolvedAny = false;
    374 
    375   for (unsigned I = 0, E = EHStack.getNumBranchFixups(); I != E; ++I) {
    376     // Skip this fixup if its destination doesn't match.
    377     BranchFixup &Fixup = EHStack.getBranchFixup(I);
    378     if (Fixup.Destination != Block) continue;
    379 
    380     Fixup.Destination = nullptr;
    381     ResolvedAny = true;
    382 
    383     // If it doesn't have an optimistic branch block, LatestBranch is
    384     // already pointing to the right place.
    385     llvm::BasicBlock *BranchBB = Fixup.OptimisticBranchBlock;
    386     if (!BranchBB)
    387       continue;
    388 
    389     // Don't process the same optimistic branch block twice.
    390     if (!ModifiedOptimisticBlocks.insert(BranchBB).second)
    391       continue;
    392 
    393     llvm::SwitchInst *Switch = TransitionToCleanupSwitch(*this, BranchBB);
    394 
    395     // Add a case to the switch.
    396     Switch->addCase(Builder.getInt32(Fixup.DestinationIndex), Block);
    397   }
    398 
    399   if (ResolvedAny)
    400     EHStack.popNullFixups();
    401 }
    402 
    403 /// Pops cleanup blocks until the given savepoint is reached.
    404 void CodeGenFunction::PopCleanupBlocks(EHScopeStack::stable_iterator Old) {
    405   assert(Old.isValid());
    406 
    407   while (EHStack.stable_begin() != Old) {
    408     EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
    409 
    410     // As long as Old strictly encloses the scope's enclosing normal
    411     // cleanup, we're going to emit another normal cleanup which
    412     // fallthrough can propagate through.
    413     bool FallThroughIsBranchThrough =
    414       Old.strictlyEncloses(Scope.getEnclosingNormalCleanup());
    415 
    416     PopCleanupBlock(FallThroughIsBranchThrough);
    417   }
    418 }
    419 
    420 /// Pops cleanup blocks until the given savepoint is reached, then add the
    421 /// cleanups from the given savepoint in the lifetime-extended cleanups stack.
    422 void
    423 CodeGenFunction::PopCleanupBlocks(EHScopeStack::stable_iterator Old,
    424                                   size_t OldLifetimeExtendedSize) {
    425   PopCleanupBlocks(Old);
    426 
    427   // Move our deferred cleanups onto the EH stack.
    428   for (size_t I = OldLifetimeExtendedSize,
    429               E = LifetimeExtendedCleanupStack.size(); I != E; /**/) {
    430     // Alignment should be guaranteed by the vptrs in the individual cleanups.
    431     assert((I % llvm::alignOf<LifetimeExtendedCleanupHeader>() == 0) &&
    432            "misaligned cleanup stack entry");
    433 
    434     LifetimeExtendedCleanupHeader &Header =
    435         reinterpret_cast<LifetimeExtendedCleanupHeader&>(
    436             LifetimeExtendedCleanupStack[I]);
    437     I += sizeof(Header);
    438 
    439     EHStack.pushCopyOfCleanup(Header.getKind(),
    440                               &LifetimeExtendedCleanupStack[I],
    441                               Header.getSize());
    442     I += Header.getSize();
    443   }
    444   LifetimeExtendedCleanupStack.resize(OldLifetimeExtendedSize);
    445 }
    446 
    447 static llvm::BasicBlock *CreateNormalEntry(CodeGenFunction &CGF,
    448                                            EHCleanupScope &Scope) {
    449   assert(Scope.isNormalCleanup());
    450   llvm::BasicBlock *Entry = Scope.getNormalBlock();
    451   if (!Entry) {
    452     Entry = CGF.createBasicBlock("cleanup");
    453     Scope.setNormalBlock(Entry);
    454   }
    455   return Entry;
    456 }
    457 
    458 /// Attempts to reduce a cleanup's entry block to a fallthrough.  This
    459 /// is basically llvm::MergeBlockIntoPredecessor, except
    460 /// simplified/optimized for the tighter constraints on cleanup blocks.
    461 ///
    462 /// Returns the new block, whatever it is.
    463 static llvm::BasicBlock *SimplifyCleanupEntry(CodeGenFunction &CGF,
    464                                               llvm::BasicBlock *Entry) {
    465   llvm::BasicBlock *Pred = Entry->getSinglePredecessor();
    466   if (!Pred) return Entry;
    467 
    468   llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Pred->getTerminator());
    469   if (!Br || Br->isConditional()) return Entry;
    470   assert(Br->getSuccessor(0) == Entry);
    471 
    472   // If we were previously inserting at the end of the cleanup entry
    473   // block, we'll need to continue inserting at the end of the
    474   // predecessor.
    475   bool WasInsertBlock = CGF.Builder.GetInsertBlock() == Entry;
    476   assert(!WasInsertBlock || CGF.Builder.GetInsertPoint() == Entry->end());
    477 
    478   // Kill the branch.
    479   Br->eraseFromParent();
    480 
    481   // Replace all uses of the entry with the predecessor, in case there
    482   // are phis in the cleanup.
    483   Entry->replaceAllUsesWith(Pred);
    484 
    485   // Merge the blocks.
    486   Pred->getInstList().splice(Pred->end(), Entry->getInstList());
    487 
    488   // Kill the entry block.
    489   Entry->eraseFromParent();
    490 
    491   if (WasInsertBlock)
    492     CGF.Builder.SetInsertPoint(Pred);
    493 
    494   return Pred;
    495 }
    496 
    497 static void EmitCleanup(CodeGenFunction &CGF,
    498                         EHScopeStack::Cleanup *Fn,
    499                         EHScopeStack::Cleanup::Flags flags,
    500                         Address ActiveFlag) {
    501   // If there's an active flag, load it and skip the cleanup if it's
    502   // false.
    503   llvm::BasicBlock *ContBB = nullptr;
    504   if (ActiveFlag.isValid()) {
    505     ContBB = CGF.createBasicBlock("cleanup.done");
    506     llvm::BasicBlock *CleanupBB = CGF.createBasicBlock("cleanup.action");
    507     llvm::Value *IsActive
    508       = CGF.Builder.CreateLoad(ActiveFlag, "cleanup.is_active");
    509     CGF.Builder.CreateCondBr(IsActive, CleanupBB, ContBB);
    510     CGF.EmitBlock(CleanupBB);
    511   }
    512 
    513   // Ask the cleanup to emit itself.
    514   Fn->Emit(CGF, flags);
    515   assert(CGF.HaveInsertPoint() && "cleanup ended with no insertion point?");
    516 
    517   // Emit the continuation block if there was an active flag.
    518   if (ActiveFlag.isValid())
    519     CGF.EmitBlock(ContBB);
    520 }
    521 
    522 static void ForwardPrebranchedFallthrough(llvm::BasicBlock *Exit,
    523                                           llvm::BasicBlock *From,
    524                                           llvm::BasicBlock *To) {
    525   // Exit is the exit block of a cleanup, so it always terminates in
    526   // an unconditional branch or a switch.
    527   llvm::TerminatorInst *Term = Exit->getTerminator();
    528 
    529   if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
    530     assert(Br->isUnconditional() && Br->getSuccessor(0) == From);
    531     Br->setSuccessor(0, To);
    532   } else {
    533     llvm::SwitchInst *Switch = cast<llvm::SwitchInst>(Term);
    534     for (unsigned I = 0, E = Switch->getNumSuccessors(); I != E; ++I)
    535       if (Switch->getSuccessor(I) == From)
    536         Switch->setSuccessor(I, To);
    537   }
    538 }
    539 
    540 /// We don't need a normal entry block for the given cleanup.
    541 /// Optimistic fixup branches can cause these blocks to come into
    542 /// existence anyway;  if so, destroy it.
    543 ///
    544 /// The validity of this transformation is very much specific to the
    545 /// exact ways in which we form branches to cleanup entries.
    546 static void destroyOptimisticNormalEntry(CodeGenFunction &CGF,
    547                                          EHCleanupScope &scope) {
    548   llvm::BasicBlock *entry = scope.getNormalBlock();
    549   if (!entry) return;
    550 
    551   // Replace all the uses with unreachable.
    552   llvm::BasicBlock *unreachableBB = CGF.getUnreachableBlock();
    553   for (llvm::BasicBlock::use_iterator
    554          i = entry->use_begin(), e = entry->use_end(); i != e; ) {
    555     llvm::Use &use = *i;
    556     ++i;
    557 
    558     use.set(unreachableBB);
    559 
    560     // The only uses should be fixup switches.
    561     llvm::SwitchInst *si = cast<llvm::SwitchInst>(use.getUser());
    562     if (si->getNumCases() == 1 && si->getDefaultDest() == unreachableBB) {
    563       // Replace the switch with a branch.
    564       llvm::BranchInst::Create(si->case_begin().getCaseSuccessor(), si);
    565 
    566       // The switch operand is a load from the cleanup-dest alloca.
    567       llvm::LoadInst *condition = cast<llvm::LoadInst>(si->getCondition());
    568 
    569       // Destroy the switch.
    570       si->eraseFromParent();
    571 
    572       // Destroy the load.
    573       assert(condition->getOperand(0) == CGF.NormalCleanupDest);
    574       assert(condition->use_empty());
    575       condition->eraseFromParent();
    576     }
    577   }
    578 
    579   assert(entry->use_empty());
    580   delete entry;
    581 }
    582 
    583 /// Pops a cleanup block.  If the block includes a normal cleanup, the
    584 /// current insertion point is threaded through the cleanup, as are
    585 /// any branch fixups on the cleanup.
    586 void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
    587   assert(!EHStack.empty() && "cleanup stack is empty!");
    588   assert(isa<EHCleanupScope>(*EHStack.begin()) && "top not a cleanup!");
    589   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
    590   assert(Scope.getFixupDepth() <= EHStack.getNumBranchFixups());
    591 
    592   // Remember activation information.
    593   bool IsActive = Scope.isActive();
    594   Address NormalActiveFlag =
    595     Scope.shouldTestFlagInNormalCleanup() ? Scope.getActiveFlag()
    596                                           : Address::invalid();
    597   Address EHActiveFlag =
    598     Scope.shouldTestFlagInEHCleanup() ? Scope.getActiveFlag()
    599                                       : Address::invalid();
    600 
    601   // Check whether we need an EH cleanup.  This is only true if we've
    602   // generated a lazy EH cleanup block.
    603   llvm::BasicBlock *EHEntry = Scope.getCachedEHDispatchBlock();
    604   assert(Scope.hasEHBranches() == (EHEntry != nullptr));
    605   bool RequiresEHCleanup = (EHEntry != nullptr);
    606   EHScopeStack::stable_iterator EHParent = Scope.getEnclosingEHScope();
    607 
    608   // Check the three conditions which might require a normal cleanup:
    609 
    610   // - whether there are branch fix-ups through this cleanup
    611   unsigned FixupDepth = Scope.getFixupDepth();
    612   bool HasFixups = EHStack.getNumBranchFixups() != FixupDepth;
    613 
    614   // - whether there are branch-throughs or branch-afters
    615   bool HasExistingBranches = Scope.hasBranches();
    616 
    617   // - whether there's a fallthrough
    618   llvm::BasicBlock *FallthroughSource = Builder.GetInsertBlock();
    619   bool HasFallthrough = (FallthroughSource != nullptr && IsActive);
    620 
    621   // Branch-through fall-throughs leave the insertion point set to the
    622   // end of the last cleanup, which points to the current scope.  The
    623   // rest of IR gen doesn't need to worry about this; it only happens
    624   // during the execution of PopCleanupBlocks().
    625   bool HasPrebranchedFallthrough =
    626     (FallthroughSource && FallthroughSource->getTerminator());
    627 
    628   // If this is a normal cleanup, then having a prebranched
    629   // fallthrough implies that the fallthrough source unconditionally
    630   // jumps here.
    631   assert(!Scope.isNormalCleanup() || !HasPrebranchedFallthrough ||
    632          (Scope.getNormalBlock() &&
    633           FallthroughSource->getTerminator()->getSuccessor(0)
    634             == Scope.getNormalBlock()));
    635 
    636   bool RequiresNormalCleanup = false;
    637   if (Scope.isNormalCleanup() &&
    638       (HasFixups || HasExistingBranches || HasFallthrough)) {
    639     RequiresNormalCleanup = true;
    640   }
    641 
    642   // If we have a prebranched fallthrough into an inactive normal
    643   // cleanup, rewrite it so that it leads to the appropriate place.
    644   if (Scope.isNormalCleanup() && HasPrebranchedFallthrough && !IsActive) {
    645     llvm::BasicBlock *prebranchDest;
    646 
    647     // If the prebranch is semantically branching through the next
    648     // cleanup, just forward it to the next block, leaving the
    649     // insertion point in the prebranched block.
    650     if (FallthroughIsBranchThrough) {
    651       EHScope &enclosing = *EHStack.find(Scope.getEnclosingNormalCleanup());
    652       prebranchDest = CreateNormalEntry(*this, cast<EHCleanupScope>(enclosing));
    653 
    654     // Otherwise, we need to make a new block.  If the normal cleanup
    655     // isn't being used at all, we could actually reuse the normal
    656     // entry block, but this is simpler, and it avoids conflicts with
    657     // dead optimistic fixup branches.
    658     } else {
    659       prebranchDest = createBasicBlock("forwarded-prebranch");
    660       EmitBlock(prebranchDest);
    661     }
    662 
    663     llvm::BasicBlock *normalEntry = Scope.getNormalBlock();
    664     assert(normalEntry && !normalEntry->use_empty());
    665 
    666     ForwardPrebranchedFallthrough(FallthroughSource,
    667                                   normalEntry, prebranchDest);
    668   }
    669 
    670   // If we don't need the cleanup at all, we're done.
    671   if (!RequiresNormalCleanup && !RequiresEHCleanup) {
    672     destroyOptimisticNormalEntry(*this, Scope);
    673     EHStack.popCleanup(); // safe because there are no fixups
    674     assert(EHStack.getNumBranchFixups() == 0 ||
    675            EHStack.hasNormalCleanups());
    676     return;
    677   }
    678 
    679   // Copy the cleanup emission data out.  Note that SmallVector
    680   // guarantees maximal alignment for its buffer regardless of its
    681   // type parameter.
    682   auto *CleanupSource = reinterpret_cast<char *>(Scope.getCleanupBuffer());
    683   SmallVector<char, 8 * sizeof(void *)> CleanupBuffer(
    684       CleanupSource, CleanupSource + Scope.getCleanupSize());
    685   auto *Fn = reinterpret_cast<EHScopeStack::Cleanup *>(CleanupBuffer.data());
    686 
    687   EHScopeStack::Cleanup::Flags cleanupFlags;
    688   if (Scope.isNormalCleanup())
    689     cleanupFlags.setIsNormalCleanupKind();
    690   if (Scope.isEHCleanup())
    691     cleanupFlags.setIsEHCleanupKind();
    692 
    693   if (!RequiresNormalCleanup) {
    694     destroyOptimisticNormalEntry(*this, Scope);
    695     EHStack.popCleanup();
    696   } else {
    697     // If we have a fallthrough and no other need for the cleanup,
    698     // emit it directly.
    699     if (HasFallthrough && !HasPrebranchedFallthrough &&
    700         !HasFixups && !HasExistingBranches) {
    701 
    702       destroyOptimisticNormalEntry(*this, Scope);
    703       EHStack.popCleanup();
    704 
    705       EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
    706 
    707     // Otherwise, the best approach is to thread everything through
    708     // the cleanup block and then try to clean up after ourselves.
    709     } else {
    710       // Force the entry block to exist.
    711       llvm::BasicBlock *NormalEntry = CreateNormalEntry(*this, Scope);
    712 
    713       // I.  Set up the fallthrough edge in.
    714 
    715       CGBuilderTy::InsertPoint savedInactiveFallthroughIP;
    716 
    717       // If there's a fallthrough, we need to store the cleanup
    718       // destination index.  For fall-throughs this is always zero.
    719       if (HasFallthrough) {
    720         if (!HasPrebranchedFallthrough)
    721           Builder.CreateStore(Builder.getInt32(0), getNormalCleanupDestSlot());
    722 
    723       // Otherwise, save and clear the IP if we don't have fallthrough
    724       // because the cleanup is inactive.
    725       } else if (FallthroughSource) {
    726         assert(!IsActive && "source without fallthrough for active cleanup");
    727         savedInactiveFallthroughIP = Builder.saveAndClearIP();
    728       }
    729 
    730       // II.  Emit the entry block.  This implicitly branches to it if
    731       // we have fallthrough.  All the fixups and existing branches
    732       // should already be branched to it.
    733       EmitBlock(NormalEntry);
    734 
    735       // III.  Figure out where we're going and build the cleanup
    736       // epilogue.
    737 
    738       bool HasEnclosingCleanups =
    739         (Scope.getEnclosingNormalCleanup() != EHStack.stable_end());
    740 
    741       // Compute the branch-through dest if we need it:
    742       //   - if there are branch-throughs threaded through the scope
    743       //   - if fall-through is a branch-through
    744       //   - if there are fixups that will be optimistically forwarded
    745       //     to the enclosing cleanup
    746       llvm::BasicBlock *BranchThroughDest = nullptr;
    747       if (Scope.hasBranchThroughs() ||
    748           (FallthroughSource && FallthroughIsBranchThrough) ||
    749           (HasFixups && HasEnclosingCleanups)) {
    750         assert(HasEnclosingCleanups);
    751         EHScope &S = *EHStack.find(Scope.getEnclosingNormalCleanup());
    752         BranchThroughDest = CreateNormalEntry(*this, cast<EHCleanupScope>(S));
    753       }
    754 
    755       llvm::BasicBlock *FallthroughDest = nullptr;
    756       SmallVector<llvm::Instruction*, 2> InstsToAppend;
    757 
    758       // If there's exactly one branch-after and no other threads,
    759       // we can route it without a switch.
    760       if (!Scope.hasBranchThroughs() && !HasFixups && !HasFallthrough &&
    761           Scope.getNumBranchAfters() == 1) {
    762         assert(!BranchThroughDest || !IsActive);
    763 
    764         // Clean up the possibly dead store to the cleanup dest slot.
    765         llvm::Instruction *NormalCleanupDestSlot =
    766             cast<llvm::Instruction>(getNormalCleanupDestSlot().getPointer());
    767         if (NormalCleanupDestSlot->hasOneUse()) {
    768           NormalCleanupDestSlot->user_back()->eraseFromParent();
    769           NormalCleanupDestSlot->eraseFromParent();
    770           NormalCleanupDest = nullptr;
    771         }
    772 
    773         llvm::BasicBlock *BranchAfter = Scope.getBranchAfterBlock(0);
    774         InstsToAppend.push_back(llvm::BranchInst::Create(BranchAfter));
    775 
    776       // Build a switch-out if we need it:
    777       //   - if there are branch-afters threaded through the scope
    778       //   - if fall-through is a branch-after
    779       //   - if there are fixups that have nowhere left to go and
    780       //     so must be immediately resolved
    781       } else if (Scope.getNumBranchAfters() ||
    782                  (HasFallthrough && !FallthroughIsBranchThrough) ||
    783                  (HasFixups && !HasEnclosingCleanups)) {
    784 
    785         llvm::BasicBlock *Default =
    786           (BranchThroughDest ? BranchThroughDest : getUnreachableBlock());
    787 
    788         // TODO: base this on the number of branch-afters and fixups
    789         const unsigned SwitchCapacity = 10;
    790 
    791         llvm::LoadInst *Load =
    792           createLoadInstBefore(getNormalCleanupDestSlot(), "cleanup.dest",
    793                                nullptr);
    794         llvm::SwitchInst *Switch =
    795           llvm::SwitchInst::Create(Load, Default, SwitchCapacity);
    796 
    797         InstsToAppend.push_back(Load);
    798         InstsToAppend.push_back(Switch);
    799 
    800         // Branch-after fallthrough.
    801         if (FallthroughSource && !FallthroughIsBranchThrough) {
    802           FallthroughDest = createBasicBlock("cleanup.cont");
    803           if (HasFallthrough)
    804             Switch->addCase(Builder.getInt32(0), FallthroughDest);
    805         }
    806 
    807         for (unsigned I = 0, E = Scope.getNumBranchAfters(); I != E; ++I) {
    808           Switch->addCase(Scope.getBranchAfterIndex(I),
    809                           Scope.getBranchAfterBlock(I));
    810         }
    811 
    812         // If there aren't any enclosing cleanups, we can resolve all
    813         // the fixups now.
    814         if (HasFixups && !HasEnclosingCleanups)
    815           ResolveAllBranchFixups(*this, Switch, NormalEntry);
    816       } else {
    817         // We should always have a branch-through destination in this case.
    818         assert(BranchThroughDest);
    819         InstsToAppend.push_back(llvm::BranchInst::Create(BranchThroughDest));
    820       }
    821 
    822       // IV.  Pop the cleanup and emit it.
    823       EHStack.popCleanup();
    824       assert(EHStack.hasNormalCleanups() == HasEnclosingCleanups);
    825 
    826       EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
    827 
    828       // Append the prepared cleanup prologue from above.
    829       llvm::BasicBlock *NormalExit = Builder.GetInsertBlock();
    830       for (unsigned I = 0, E = InstsToAppend.size(); I != E; ++I)
    831         NormalExit->getInstList().push_back(InstsToAppend[I]);
    832 
    833       // Optimistically hope that any fixups will continue falling through.
    834       for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
    835            I < E; ++I) {
    836         BranchFixup &Fixup = EHStack.getBranchFixup(I);
    837         if (!Fixup.Destination) continue;
    838         if (!Fixup.OptimisticBranchBlock) {
    839           createStoreInstBefore(Builder.getInt32(Fixup.DestinationIndex),
    840                                 getNormalCleanupDestSlot(),
    841                                 Fixup.InitialBranch);
    842           Fixup.InitialBranch->setSuccessor(0, NormalEntry);
    843         }
    844         Fixup.OptimisticBranchBlock = NormalExit;
    845       }
    846 
    847       // V.  Set up the fallthrough edge out.
    848 
    849       // Case 1: a fallthrough source exists but doesn't branch to the
    850       // cleanup because the cleanup is inactive.
    851       if (!HasFallthrough && FallthroughSource) {
    852         // Prebranched fallthrough was forwarded earlier.
    853         // Non-prebranched fallthrough doesn't need to be forwarded.
    854         // Either way, all we need to do is restore the IP we cleared before.
    855         assert(!IsActive);
    856         Builder.restoreIP(savedInactiveFallthroughIP);
    857 
    858       // Case 2: a fallthrough source exists and should branch to the
    859       // cleanup, but we're not supposed to branch through to the next
    860       // cleanup.
    861       } else if (HasFallthrough && FallthroughDest) {
    862         assert(!FallthroughIsBranchThrough);
    863         EmitBlock(FallthroughDest);
    864 
    865       // Case 3: a fallthrough source exists and should branch to the
    866       // cleanup and then through to the next.
    867       } else if (HasFallthrough) {
    868         // Everything is already set up for this.
    869 
    870       // Case 4: no fallthrough source exists.
    871       } else {
    872         Builder.ClearInsertionPoint();
    873       }
    874 
    875       // VI.  Assorted cleaning.
    876 
    877       // Check whether we can merge NormalEntry into a single predecessor.
    878       // This might invalidate (non-IR) pointers to NormalEntry.
    879       llvm::BasicBlock *NewNormalEntry =
    880         SimplifyCleanupEntry(*this, NormalEntry);
    881 
    882       // If it did invalidate those pointers, and NormalEntry was the same
    883       // as NormalExit, go back and patch up the fixups.
    884       if (NewNormalEntry != NormalEntry && NormalEntry == NormalExit)
    885         for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
    886                I < E; ++I)
    887           EHStack.getBranchFixup(I).OptimisticBranchBlock = NewNormalEntry;
    888     }
    889   }
    890 
    891   assert(EHStack.hasNormalCleanups() || EHStack.getNumBranchFixups() == 0);
    892 
    893   // Emit the EH cleanup if required.
    894   if (RequiresEHCleanup) {
    895     CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
    896 
    897     EmitBlock(EHEntry);
    898 
    899     llvm::BasicBlock *NextAction = getEHDispatchBlock(EHParent);
    900 
    901     // Push a terminate scope or cleanupendpad scope around the potentially
    902     // throwing cleanups. For funclet EH personalities, the cleanupendpad models
    903     // program termination when cleanups throw.
    904     bool PushedTerminate = false;
    905     SaveAndRestore<llvm::Instruction *> RestoreCurrentFuncletPad(
    906         CurrentFuncletPad);
    907     llvm::CleanupPadInst *CPI = nullptr;
    908     if (!EHPersonality::get(*this).usesFuncletPads()) {
    909       EHStack.pushTerminate();
    910       PushedTerminate = true;
    911     } else {
    912       llvm::Value *ParentPad = CurrentFuncletPad;
    913       if (!ParentPad)
    914         ParentPad = llvm::ConstantTokenNone::get(CGM.getLLVMContext());
    915       CurrentFuncletPad = CPI = Builder.CreateCleanupPad(ParentPad);
    916     }
    917 
    918     // We only actually emit the cleanup code if the cleanup is either
    919     // active or was used before it was deactivated.
    920     if (EHActiveFlag.isValid() || IsActive) {
    921       cleanupFlags.setIsForEHCleanup();
    922       EmitCleanup(*this, Fn, cleanupFlags, EHActiveFlag);
    923     }
    924 
    925     if (CPI)
    926       Builder.CreateCleanupRet(CPI, NextAction);
    927     else
    928       Builder.CreateBr(NextAction);
    929 
    930     // Leave the terminate scope.
    931     if (PushedTerminate)
    932       EHStack.popTerminate();
    933 
    934     Builder.restoreIP(SavedIP);
    935 
    936     SimplifyCleanupEntry(*this, EHEntry);
    937   }
    938 }
    939 
    940 /// isObviouslyBranchWithoutCleanups - Return true if a branch to the
    941 /// specified destination obviously has no cleanups to run.  'false' is always
    942 /// a conservatively correct answer for this method.
    943 bool CodeGenFunction::isObviouslyBranchWithoutCleanups(JumpDest Dest) const {
    944   assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
    945          && "stale jump destination");
    946 
    947   // Calculate the innermost active normal cleanup.
    948   EHScopeStack::stable_iterator TopCleanup =
    949     EHStack.getInnermostActiveNormalCleanup();
    950 
    951   // If we're not in an active normal cleanup scope, or if the
    952   // destination scope is within the innermost active normal cleanup
    953   // scope, we don't need to worry about fixups.
    954   if (TopCleanup == EHStack.stable_end() ||
    955       TopCleanup.encloses(Dest.getScopeDepth())) // works for invalid
    956     return true;
    957 
    958   // Otherwise, we might need some cleanups.
    959   return false;
    960 }
    961 
    962 
    963 /// Terminate the current block by emitting a branch which might leave
    964 /// the current cleanup-protected scope.  The target scope may not yet
    965 /// be known, in which case this will require a fixup.
    966 ///
    967 /// As a side-effect, this method clears the insertion point.
    968 void CodeGenFunction::EmitBranchThroughCleanup(JumpDest Dest) {
    969   assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
    970          && "stale jump destination");
    971 
    972   if (!HaveInsertPoint())
    973     return;
    974 
    975   // Create the branch.
    976   llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock());
    977 
    978   // Calculate the innermost active normal cleanup.
    979   EHScopeStack::stable_iterator
    980     TopCleanup = EHStack.getInnermostActiveNormalCleanup();
    981 
    982   // If we're not in an active normal cleanup scope, or if the
    983   // destination scope is within the innermost active normal cleanup
    984   // scope, we don't need to worry about fixups.
    985   if (TopCleanup == EHStack.stable_end() ||
    986       TopCleanup.encloses(Dest.getScopeDepth())) { // works for invalid
    987     Builder.ClearInsertionPoint();
    988     return;
    989   }
    990 
    991   // If we can't resolve the destination cleanup scope, just add this
    992   // to the current cleanup scope as a branch fixup.
    993   if (!Dest.getScopeDepth().isValid()) {
    994     BranchFixup &Fixup = EHStack.addBranchFixup();
    995     Fixup.Destination = Dest.getBlock();
    996     Fixup.DestinationIndex = Dest.getDestIndex();
    997     Fixup.InitialBranch = BI;
    998     Fixup.OptimisticBranchBlock = nullptr;
    999 
   1000     Builder.ClearInsertionPoint();
   1001     return;
   1002   }
   1003 
   1004   // Otherwise, thread through all the normal cleanups in scope.
   1005 
   1006   // Store the index at the start.
   1007   llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex());
   1008   createStoreInstBefore(Index, getNormalCleanupDestSlot(), BI);
   1009 
   1010   // Adjust BI to point to the first cleanup block.
   1011   {
   1012     EHCleanupScope &Scope =
   1013       cast<EHCleanupScope>(*EHStack.find(TopCleanup));
   1014     BI->setSuccessor(0, CreateNormalEntry(*this, Scope));
   1015   }
   1016 
   1017   // Add this destination to all the scopes involved.
   1018   EHScopeStack::stable_iterator I = TopCleanup;
   1019   EHScopeStack::stable_iterator E = Dest.getScopeDepth();
   1020   if (E.strictlyEncloses(I)) {
   1021     while (true) {
   1022       EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(I));
   1023       assert(Scope.isNormalCleanup());
   1024       I = Scope.getEnclosingNormalCleanup();
   1025 
   1026       // If this is the last cleanup we're propagating through, tell it
   1027       // that there's a resolved jump moving through it.
   1028       if (!E.strictlyEncloses(I)) {
   1029         Scope.addBranchAfter(Index, Dest.getBlock());
   1030         break;
   1031       }
   1032 
   1033       // Otherwise, tell the scope that there's a jump propoagating
   1034       // through it.  If this isn't new information, all the rest of
   1035       // the work has been done before.
   1036       if (!Scope.addBranchThrough(Dest.getBlock()))
   1037         break;
   1038     }
   1039   }
   1040 
   1041   Builder.ClearInsertionPoint();
   1042 }
   1043 
   1044 static bool IsUsedAsNormalCleanup(EHScopeStack &EHStack,
   1045                                   EHScopeStack::stable_iterator C) {
   1046   // If we needed a normal block for any reason, that counts.
   1047   if (cast<EHCleanupScope>(*EHStack.find(C)).getNormalBlock())
   1048     return true;
   1049 
   1050   // Check whether any enclosed cleanups were needed.
   1051   for (EHScopeStack::stable_iterator
   1052          I = EHStack.getInnermostNormalCleanup();
   1053          I != C; ) {
   1054     assert(C.strictlyEncloses(I));
   1055     EHCleanupScope &S = cast<EHCleanupScope>(*EHStack.find(I));
   1056     if (S.getNormalBlock()) return true;
   1057     I = S.getEnclosingNormalCleanup();
   1058   }
   1059 
   1060   return false;
   1061 }
   1062 
   1063 static bool IsUsedAsEHCleanup(EHScopeStack &EHStack,
   1064                               EHScopeStack::stable_iterator cleanup) {
   1065   // If we needed an EH block for any reason, that counts.
   1066   if (EHStack.find(cleanup)->hasEHBranches())
   1067     return true;
   1068 
   1069   // Check whether any enclosed cleanups were needed.
   1070   for (EHScopeStack::stable_iterator
   1071          i = EHStack.getInnermostEHScope(); i != cleanup; ) {
   1072     assert(cleanup.strictlyEncloses(i));
   1073 
   1074     EHScope &scope = *EHStack.find(i);
   1075     if (scope.hasEHBranches())
   1076       return true;
   1077 
   1078     i = scope.getEnclosingEHScope();
   1079   }
   1080 
   1081   return false;
   1082 }
   1083 
   1084 enum ForActivation_t {
   1085   ForActivation,
   1086   ForDeactivation
   1087 };
   1088 
   1089 /// The given cleanup block is changing activation state.  Configure a
   1090 /// cleanup variable if necessary.
   1091 ///
   1092 /// It would be good if we had some way of determining if there were
   1093 /// extra uses *after* the change-over point.
   1094 static void SetupCleanupBlockActivation(CodeGenFunction &CGF,
   1095                                         EHScopeStack::stable_iterator C,
   1096                                         ForActivation_t kind,
   1097                                         llvm::Instruction *dominatingIP) {
   1098   EHCleanupScope &Scope = cast<EHCleanupScope>(*CGF.EHStack.find(C));
   1099 
   1100   // We always need the flag if we're activating the cleanup in a
   1101   // conditional context, because we have to assume that the current
   1102   // location doesn't necessarily dominate the cleanup's code.
   1103   bool isActivatedInConditional =
   1104     (kind == ForActivation && CGF.isInConditionalBranch());
   1105 
   1106   bool needFlag = false;
   1107 
   1108   // Calculate whether the cleanup was used:
   1109 
   1110   //   - as a normal cleanup
   1111   if (Scope.isNormalCleanup() &&
   1112       (isActivatedInConditional || IsUsedAsNormalCleanup(CGF.EHStack, C))) {
   1113     Scope.setTestFlagInNormalCleanup();
   1114     needFlag = true;
   1115   }
   1116 
   1117   //  - as an EH cleanup
   1118   if (Scope.isEHCleanup() &&
   1119       (isActivatedInConditional || IsUsedAsEHCleanup(CGF.EHStack, C))) {
   1120     Scope.setTestFlagInEHCleanup();
   1121     needFlag = true;
   1122   }
   1123 
   1124   // If it hasn't yet been used as either, we're done.
   1125   if (!needFlag) return;
   1126 
   1127   Address var = Scope.getActiveFlag();
   1128   if (!var.isValid()) {
   1129     var = CGF.CreateTempAlloca(CGF.Builder.getInt1Ty(), CharUnits::One(),
   1130                                "cleanup.isactive");
   1131     Scope.setActiveFlag(var);
   1132 
   1133     assert(dominatingIP && "no existing variable and no dominating IP!");
   1134 
   1135     // Initialize to true or false depending on whether it was
   1136     // active up to this point.
   1137     llvm::Constant *value = CGF.Builder.getInt1(kind == ForDeactivation);
   1138 
   1139     // If we're in a conditional block, ignore the dominating IP and
   1140     // use the outermost conditional branch.
   1141     if (CGF.isInConditionalBranch()) {
   1142       CGF.setBeforeOutermostConditional(value, var);
   1143     } else {
   1144       createStoreInstBefore(value, var, dominatingIP);
   1145     }
   1146   }
   1147 
   1148   CGF.Builder.CreateStore(CGF.Builder.getInt1(kind == ForActivation), var);
   1149 }
   1150 
   1151 /// Activate a cleanup that was created in an inactivated state.
   1152 void CodeGenFunction::ActivateCleanupBlock(EHScopeStack::stable_iterator C,
   1153                                            llvm::Instruction *dominatingIP) {
   1154   assert(C != EHStack.stable_end() && "activating bottom of stack?");
   1155   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
   1156   assert(!Scope.isActive() && "double activation");
   1157 
   1158   SetupCleanupBlockActivation(*this, C, ForActivation, dominatingIP);
   1159 
   1160   Scope.setActive(true);
   1161 }
   1162 
   1163 /// Deactive a cleanup that was created in an active state.
   1164 void CodeGenFunction::DeactivateCleanupBlock(EHScopeStack::stable_iterator C,
   1165                                              llvm::Instruction *dominatingIP) {
   1166   assert(C != EHStack.stable_end() && "deactivating bottom of stack?");
   1167   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
   1168   assert(Scope.isActive() && "double deactivation");
   1169 
   1170   // If it's the top of the stack, just pop it.
   1171   if (C == EHStack.stable_begin()) {
   1172     // If it's a normal cleanup, we need to pretend that the
   1173     // fallthrough is unreachable.
   1174     CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
   1175     PopCleanupBlock();
   1176     Builder.restoreIP(SavedIP);
   1177     return;
   1178   }
   1179 
   1180   // Otherwise, follow the general case.
   1181   SetupCleanupBlockActivation(*this, C, ForDeactivation, dominatingIP);
   1182 
   1183   Scope.setActive(false);
   1184 }
   1185 
   1186 Address CodeGenFunction::getNormalCleanupDestSlot() {
   1187   if (!NormalCleanupDest)
   1188     NormalCleanupDest =
   1189       CreateTempAlloca(Builder.getInt32Ty(), "cleanup.dest.slot");
   1190   return Address(NormalCleanupDest, CharUnits::fromQuantity(4));
   1191 }
   1192 
   1193 /// Emits all the code to cause the given temporary to be cleaned up.
   1194 void CodeGenFunction::EmitCXXTemporary(const CXXTemporary *Temporary,
   1195                                        QualType TempType,
   1196                                        Address Ptr) {
   1197   pushDestroy(NormalAndEHCleanup, Ptr, TempType, destroyCXXObject,
   1198               /*useEHCleanup*/ true);
   1199 }
   1200