contrib/llvm/tools/clang/lib/CodeGen/CGCleanup.cpp

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