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 #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::alignTo(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::alignTo(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 bool EHScopeStack::requiresLandingPad() const {
 161   for (stable_iterator si = getInnermostEHScope(); si != stable_end(); ) {
 162     // Skip lifetime markers.
 163     if (auto *cleanup = dyn_cast<EHCleanupScope>(&*find(si)))
 164       if (cleanup->isLifetimeMarker()) {
 165         si = cleanup->getEnclosingEHScope();
 166         continue;
 167       }
 168     return true;
 169   }
 170
 171   return false;
 172 }
 173
 174 EHScopeStack::stable_iterator
 175 EHScopeStack::getInnermostActiveNormalCleanup() const {
 176   for (stable_iterator si = getInnermostNormalCleanup(), se = stable_end();
 177          si != se; ) {
 178     EHCleanupScope &cleanup = cast<EHCleanupScope>(*find(si));
 179     if (cleanup.isActive()) return si;
 180     si = cleanup.getEnclosingNormalCleanup();
 181   }
 182   return stable_end();
 183 }
 184
 185
 186 void *EHScopeStack::pushCleanup(CleanupKind Kind, size_t Size) {
 187   char *Buffer = allocate(EHCleanupScope::getSizeForCleanupSize(Size));
 188   bool IsNormalCleanup = Kind & NormalCleanup;
 189   bool IsEHCleanup = Kind & EHCleanup;
 190   bool IsActive = !(Kind & InactiveCleanup);
 191   bool IsLifetimeMarker = Kind & LifetimeMarker;
 192   EHCleanupScope *Scope =
 193     new (Buffer) EHCleanupScope(IsNormalCleanup,
 194                                 IsEHCleanup,
 195                                 IsActive,
 196                                 Size,
 197                                 BranchFixups.size(),
 198                                 InnermostNormalCleanup,
 199                                 InnermostEHScope);
 200   if (IsNormalCleanup)
 201     InnermostNormalCleanup = stable_begin();
 202   if (IsEHCleanup)
 203     InnermostEHScope = stable_begin();
 204   if (IsLifetimeMarker)
 205     Scope->setLifetimeMarker();
 206
 207   return Scope->getCleanupBuffer();
 208 }
 209
 210 void EHScopeStack::popCleanup() {
 211   assert(!empty() && "popping exception stack when not empty");
 212
 213   assert(isa<EHCleanupScope>(*begin()));
 214   EHCleanupScope &Cleanup = cast<EHCleanupScope>(*begin());
 215   InnermostNormalCleanup = Cleanup.getEnclosingNormalCleanup();
 216   InnermostEHScope = Cleanup.getEnclosingEHScope();
 217   deallocate(Cleanup.getAllocatedSize());
 218
 219   // Destroy the cleanup.
 220   Cleanup.Destroy();
 221
 222   // Check whether we can shrink the branch-fixups stack.
 223   if (!BranchFixups.empty()) {
 224     // If we no longer have any normal cleanups, all the fixups are
 225     // complete.
 226     if (!hasNormalCleanups())
 227       BranchFixups.clear();
 228
 229     // Otherwise we can still trim out unnecessary nulls.
 230     else
 231       popNullFixups();
 232   }
 233 }
 234
 235 EHFilterScope *EHScopeStack::pushFilter(unsigned numFilters) {
 236   assert(getInnermostEHScope() == stable_end());
 237   char *buffer = allocate(EHFilterScope::getSizeForNumFilters(numFilters));
 238   EHFilterScope *filter = new (buffer) EHFilterScope(numFilters);
 239   InnermostEHScope = stable_begin();
 240   return filter;
 241 }
 242
 243 void EHScopeStack::popFilter() {
 244   assert(!empty() && "popping exception stack when not empty");
 245
 246   EHFilterScope &filter = cast<EHFilterScope>(*begin());
 247   deallocate(EHFilterScope::getSizeForNumFilters(filter.getNumFilters()));
 248
 249   InnermostEHScope = filter.getEnclosingEHScope();
 250 }
 251
 252 EHCatchScope *EHScopeStack::pushCatch(unsigned numHandlers) {
 253   char *buffer = allocate(EHCatchScope::getSizeForNumHandlers(numHandlers));
 254   EHCatchScope *scope =
 255     new (buffer) EHCatchScope(numHandlers, InnermostEHScope);
 256   InnermostEHScope = stable_begin();
 257   return scope;
 258 }
 259
 260 void EHScopeStack::pushTerminate() {
 261   char *Buffer = allocate(EHTerminateScope::getSize());
 262   new (Buffer) EHTerminateScope(InnermostEHScope);
 263   InnermostEHScope = stable_begin();
 264 }
 265
 266 /// Remove any 'null' fixups on the stack.  However, we can't pop more
 267 /// fixups than the fixup depth on the innermost normal cleanup, or
 268 /// else fixups that we try to add to that cleanup will end up in the
 269 /// wrong place.  We *could* try to shrink fixup depths, but that's
 270 /// actually a lot of work for little benefit.
 271 void EHScopeStack::popNullFixups() {
 272   // We expect this to only be called when there's still an innermost
 273   // normal cleanup;  otherwise there really shouldn't be any fixups.
 274   assert(hasNormalCleanups());
 275
 276   EHScopeStack::iterator it = find(InnermostNormalCleanup);
 277   unsigned MinSize = cast<EHCleanupScope>(*it).getFixupDepth();
 278   assert(BranchFixups.size() >= MinSize && "fixup stack out of order");
 279
 280   while (BranchFixups.size() > MinSize &&
 281          BranchFixups.back().Destination == nullptr)
 282     BranchFixups.pop_back();
 283 }
 284
 285 void CodeGenFunction::initFullExprCleanup() {
 286   // Create a variable to decide whether the cleanup needs to be run.
 287   Address active = CreateTempAlloca(Builder.getInt1Ty(), CharUnits::One(),
 288                                     "cleanup.cond");
 289
 290   // Initialize it to false at a site that's guaranteed to be run
 291   // before each evaluation.
 292   setBeforeOutermostConditional(Builder.getFalse(), active);
 293
 294   // Initialize it to true at the current location.
 295   Builder.CreateStore(Builder.getTrue(), active);
 296
 297   // Set that as the active flag in the cleanup.
 298   EHCleanupScope &cleanup = cast<EHCleanupScope>(*EHStack.begin());
 299   assert(!cleanup.hasActiveFlag() && "cleanup already has active flag?");
 300   cleanup.setActiveFlag(active);
 301
 302   if (cleanup.isNormalCleanup()) cleanup.setTestFlagInNormalCleanup();
 303   if (cleanup.isEHCleanup()) cleanup.setTestFlagInEHCleanup();
 304 }
 305
 306 void EHScopeStack::Cleanup::anchor() {}
 307
 308 static void createStoreInstBefore(llvm::Value *value, Address addr,
 309                                   llvm::Instruction *beforeInst) {
 310   auto store = new llvm::StoreInst(value, addr.getPointer(), beforeInst);
 311   store->setAlignment(addr.getAlignment().getQuantity());
 312 }
 313
 314 static llvm::LoadInst *createLoadInstBefore(Address addr, const Twine &name,
 315                                             llvm::Instruction *beforeInst) {
 316   auto load = new llvm::LoadInst(addr.getPointer(), name, beforeInst);
 317   load->setAlignment(addr.getAlignment().getQuantity());
 318   return load;
 319 }
 320
 321 /// All the branch fixups on the EH stack have propagated out past the
 322 /// outermost normal cleanup; resolve them all by adding cases to the
 323 /// given switch instruction.
 324 static void ResolveAllBranchFixups(CodeGenFunction &CGF,
 325                                    llvm::SwitchInst *Switch,
 326                                    llvm::BasicBlock *CleanupEntry) {
 327   llvm::SmallPtrSet<llvm::BasicBlock*, 4> CasesAdded;
 328
 329   for (unsigned I = 0, E = CGF.EHStack.getNumBranchFixups(); I != E; ++I) {
 330     // Skip this fixup if its destination isn't set.
 331     BranchFixup &Fixup = CGF.EHStack.getBranchFixup(I);
 332     if (Fixup.Destination == nullptr) continue;
 333
 334     // If there isn't an OptimisticBranchBlock, then InitialBranch is
 335     // still pointing directly to its destination; forward it to the
 336     // appropriate cleanup entry.  This is required in the specific
 337     // case of
 338     //   { std::string s; goto lbl; }
 339     //   lbl:
 340     // i.e. where there's an unresolved fixup inside a single cleanup
 341     // entry which we're currently popping.
 342     if (Fixup.OptimisticBranchBlock == nullptr) {
 343       createStoreInstBefore(CGF.Builder.getInt32(Fixup.DestinationIndex),
 344                             CGF.getNormalCleanupDestSlot(),
 345                             Fixup.InitialBranch);
 346       Fixup.InitialBranch->setSuccessor(0, CleanupEntry);
 347     }
 348
 349     // Don't add this case to the switch statement twice.
 350     if (!CasesAdded.insert(Fixup.Destination).second)
 351       continue;
 352
 353     Switch->addCase(CGF.Builder.getInt32(Fixup.DestinationIndex),
 354                     Fixup.Destination);
 355   }
 356
 357   CGF.EHStack.clearFixups();
 358 }
 359
 360 /// Transitions the terminator of the given exit-block of a cleanup to
 361 /// be a cleanup switch.
 362 static llvm::SwitchInst *TransitionToCleanupSwitch(CodeGenFunction &CGF,
 363                                                    llvm::BasicBlock *Block) {
 364   // If it's a branch, turn it into a switch whose default
 365   // destination is its original target.
 366   llvm::TerminatorInst *Term = Block->getTerminator();
 367   assert(Term && "can't transition block without terminator");
 368
 369   if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
 370     assert(Br->isUnconditional());
 371     auto Load = createLoadInstBefore(CGF.getNormalCleanupDestSlot(),
 372                                      "cleanup.dest", Term);
 373     llvm::SwitchInst *Switch =
 374       llvm::SwitchInst::Create(Load, Br->getSuccessor(0), 4, Block);
 375     Br->eraseFromParent();
 376     return Switch;
 377   } else {
 378     return cast<llvm::SwitchInst>(Term);
 379   }
 380 }
 381
 382 void CodeGenFunction::ResolveBranchFixups(llvm::BasicBlock *Block) {
 383   assert(Block && "resolving a null target block");
 384   if (!EHStack.getNumBranchFixups()) return;
 385
 386   assert(EHStack.hasNormalCleanups() &&
 387          "branch fixups exist with no normal cleanups on stack");
 388
 389   llvm::SmallPtrSet<llvm::BasicBlock*, 4> ModifiedOptimisticBlocks;
 390   bool ResolvedAny = false;
 391
 392   for (unsigned I = 0, E = EHStack.getNumBranchFixups(); I != E; ++I) {
 393     // Skip this fixup if its destination doesn't match.
 394     BranchFixup &Fixup = EHStack.getBranchFixup(I);
 395     if (Fixup.Destination != Block) continue;
 396
 397     Fixup.Destination = nullptr;
 398     ResolvedAny = true;
 399
 400     // If it doesn't have an optimistic branch block, LatestBranch is
 401     // already pointing to the right place.
 402     llvm::BasicBlock *BranchBB = Fixup.OptimisticBranchBlock;
 403     if (!BranchBB)
 404       continue;
 405
 406     // Don't process the same optimistic branch block twice.
 407     if (!ModifiedOptimisticBlocks.insert(BranchBB).second)
 408       continue;
 409
 410     llvm::SwitchInst *Switch = TransitionToCleanupSwitch(*this, BranchBB);
 411
 412     // Add a case to the switch.
 413     Switch->addCase(Builder.getInt32(Fixup.DestinationIndex), Block);
 414   }
 415
 416   if (ResolvedAny)
 417     EHStack.popNullFixups();
 418 }
 419
 420 /// Pops cleanup blocks until the given savepoint is reached.
 421 void CodeGenFunction::PopCleanupBlocks(EHScopeStack::stable_iterator Old) {
 422   assert(Old.isValid());
 423
 424   while (EHStack.stable_begin() != Old) {
 425     EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
 426
 427     // As long as Old strictly encloses the scope's enclosing normal
 428     // cleanup, we're going to emit another normal cleanup which
 429     // fallthrough can propagate through.
 430     bool FallThroughIsBranchThrough =
 431       Old.strictlyEncloses(Scope.getEnclosingNormalCleanup());
 432
 433     PopCleanupBlock(FallThroughIsBranchThrough);
 434   }
 435 }
 436
 437 /// Pops cleanup blocks until the given savepoint is reached, then add the
 438 /// cleanups from the given savepoint in the lifetime-extended cleanups stack.
 439 void
 440 CodeGenFunction::PopCleanupBlocks(EHScopeStack::stable_iterator Old,
 441                                   size_t OldLifetimeExtendedSize) {
 442   PopCleanupBlocks(Old);
 443
 444   // Move our deferred cleanups onto the EH stack.
 445   for (size_t I = OldLifetimeExtendedSize,
 446               E = LifetimeExtendedCleanupStack.size(); I != E; /**/) {
 447     // Alignment should be guaranteed by the vptrs in the individual cleanups.
 448     assert((I % alignof(LifetimeExtendedCleanupHeader) == 0) &&
 449            "misaligned cleanup stack entry");
 450
 451     LifetimeExtendedCleanupHeader &Header =
 452         reinterpret_cast<LifetimeExtendedCleanupHeader&>(
 453             LifetimeExtendedCleanupStack[I]);
 454     I += sizeof(Header);
 455
 456     EHStack.pushCopyOfCleanup(Header.getKind(),
 457                               &LifetimeExtendedCleanupStack[I],
 458                               Header.getSize());
 459     I += Header.getSize();
 460   }
 461   LifetimeExtendedCleanupStack.resize(OldLifetimeExtendedSize);
 462 }
 463
 464 static llvm::BasicBlock *CreateNormalEntry(CodeGenFunction &CGF,
 465                                            EHCleanupScope &Scope) {
 466   assert(Scope.isNormalCleanup());
 467   llvm::BasicBlock *Entry = Scope.getNormalBlock();
 468   if (!Entry) {
 469     Entry = CGF.createBasicBlock("cleanup");
 470     Scope.setNormalBlock(Entry);
 471   }
 472   return Entry;
 473 }
 474
 475 /// Attempts to reduce a cleanup's entry block to a fallthrough.  This
 476 /// is basically llvm::MergeBlockIntoPredecessor, except
 477 /// simplified/optimized for the tighter constraints on cleanup blocks.
 478 ///
 479 /// Returns the new block, whatever it is.
 480 static llvm::BasicBlock *SimplifyCleanupEntry(CodeGenFunction &CGF,
 481                                               llvm::BasicBlock *Entry) {
 482   llvm::BasicBlock *Pred = Entry->getSinglePredecessor();
 483   if (!Pred) return Entry;
 484
 485   llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Pred->getTerminator());
 486   if (!Br || Br->isConditional()) return Entry;
 487   assert(Br->getSuccessor(0) == Entry);
 488
 489   // If we were previously inserting at the end of the cleanup entry
 490   // block, we'll need to continue inserting at the end of the
 491   // predecessor.
 492   bool WasInsertBlock = CGF.Builder.GetInsertBlock() == Entry;
 493   assert(!WasInsertBlock || CGF.Builder.GetInsertPoint() == Entry->end());
 494
 495   // Kill the branch.
 496   Br->eraseFromParent();
 497
 498   // Replace all uses of the entry with the predecessor, in case there
 499   // are phis in the cleanup.
 500   Entry->replaceAllUsesWith(Pred);
 501
 502   // Merge the blocks.
 503   Pred->getInstList().splice(Pred->end(), Entry->getInstList());
 504
 505   // Kill the entry block.
 506   Entry->eraseFromParent();
 507
 508   if (WasInsertBlock)
 509     CGF.Builder.SetInsertPoint(Pred);
 510
 511   return Pred;
 512 }
 513
 514 static void EmitCleanup(CodeGenFunction &CGF,
 515                         EHScopeStack::Cleanup *Fn,
 516                         EHScopeStack::Cleanup::Flags flags,
 517                         Address ActiveFlag) {
 518   // If there's an active flag, load it and skip the cleanup if it's
 519   // false.
 520   llvm::BasicBlock *ContBB = nullptr;
 521   if (ActiveFlag.isValid()) {
 522     ContBB = CGF.createBasicBlock("cleanup.done");
 523     llvm::BasicBlock *CleanupBB = CGF.createBasicBlock("cleanup.action");
 524     llvm::Value *IsActive
 525       = CGF.Builder.CreateLoad(ActiveFlag, "cleanup.is_active");
 526     CGF.Builder.CreateCondBr(IsActive, CleanupBB, ContBB);
 527     CGF.EmitBlock(CleanupBB);
 528   }
 529
 530   // Ask the cleanup to emit itself.
 531   Fn->Emit(CGF, flags);
 532   assert(CGF.HaveInsertPoint() && "cleanup ended with no insertion point?");
 533
 534   // Emit the continuation block if there was an active flag.
 535   if (ActiveFlag.isValid())
 536     CGF.EmitBlock(ContBB);
 537 }
 538
 539 static void ForwardPrebranchedFallthrough(llvm::BasicBlock *Exit,
 540                                           llvm::BasicBlock *From,
 541                                           llvm::BasicBlock *To) {
 542   // Exit is the exit block of a cleanup, so it always terminates in
 543   // an unconditional branch or a switch.
 544   llvm::TerminatorInst *Term = Exit->getTerminator();
 545
 546   if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
 547     assert(Br->isUnconditional() && Br->getSuccessor(0) == From);
 548     Br->setSuccessor(0, To);
 549   } else {
 550     llvm::SwitchInst *Switch = cast<llvm::SwitchInst>(Term);
 551     for (unsigned I = 0, E = Switch->getNumSuccessors(); I != E; ++I)
 552       if (Switch->getSuccessor(I) == From)
 553         Switch->setSuccessor(I, To);
 554   }
 555 }
 556
 557 /// We don't need a normal entry block for the given cleanup.
 558 /// Optimistic fixup branches can cause these blocks to come into
 559 /// existence anyway;  if so, destroy it.
 560 ///
 561 /// The validity of this transformation is very much specific to the
 562 /// exact ways in which we form branches to cleanup entries.
 563 static void destroyOptimisticNormalEntry(CodeGenFunction &CGF,
 564                                          EHCleanupScope &scope) {
 565   llvm::BasicBlock *entry = scope.getNormalBlock();
 566   if (!entry) return;
 567
 568   // Replace all the uses with unreachable.
 569   llvm::BasicBlock *unreachableBB = CGF.getUnreachableBlock();
 570   for (llvm::BasicBlock::use_iterator
 571          i = entry->use_begin(), e = entry->use_end(); i != e; ) {
 572     llvm::Use &use = *i;
 573     ++i;
 574
 575     use.set(unreachableBB);
 576
 577     // The only uses should be fixup switches.
 578     llvm::SwitchInst *si = cast<llvm::SwitchInst>(use.getUser());
 579     if (si->getNumCases() == 1 && si->getDefaultDest() == unreachableBB) {
 580       // Replace the switch with a branch.
 581       llvm::BranchInst::Create(si->case_begin().getCaseSuccessor(), si);
 582
 583       // The switch operand is a load from the cleanup-dest alloca.
 584       llvm::LoadInst *condition = cast<llvm::LoadInst>(si->getCondition());
 585
 586       // Destroy the switch.
 587       si->eraseFromParent();
 588
 589       // Destroy the load.
 590       assert(condition->getOperand(0) == CGF.NormalCleanupDest);
 591       assert(condition->use_empty());
 592       condition->eraseFromParent();
 593     }
 594   }
 595
 596   assert(entry->use_empty());
 597   delete entry;
 598 }
 599
 600 /// Pops a cleanup block.  If the block includes a normal cleanup, the
 601 /// current insertion point is threaded through the cleanup, as are
 602 /// any branch fixups on the cleanup.
 603 void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
 604   assert(!EHStack.empty() && "cleanup stack is empty!");
 605   assert(isa<EHCleanupScope>(*EHStack.begin()) && "top not a cleanup!");
 606   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
 607   assert(Scope.getFixupDepth() <= EHStack.getNumBranchFixups());
 608
 609   // Remember activation information.
 610   bool IsActive = Scope.isActive();
 611   Address NormalActiveFlag =
 612     Scope.shouldTestFlagInNormalCleanup() ? Scope.getActiveFlag()
 613                                           : Address::invalid();
 614   Address EHActiveFlag =
 615     Scope.shouldTestFlagInEHCleanup() ? Scope.getActiveFlag()
 616                                       : Address::invalid();
 617
 618   // Check whether we need an EH cleanup.  This is only true if we've
 619   // generated a lazy EH cleanup block.
 620   llvm::BasicBlock *EHEntry = Scope.getCachedEHDispatchBlock();
 621   assert(Scope.hasEHBranches() == (EHEntry != nullptr));
 622   bool RequiresEHCleanup = (EHEntry != nullptr);
 623   EHScopeStack::stable_iterator EHParent = Scope.getEnclosingEHScope();
 624
 625   // Check the three conditions which might require a normal cleanup:
 626
 627   // - whether there are branch fix-ups through this cleanup
 628   unsigned FixupDepth = Scope.getFixupDepth();
 629   bool HasFixups = EHStack.getNumBranchFixups() != FixupDepth;
 630
 631   // - whether there are branch-throughs or branch-afters
 632   bool HasExistingBranches = Scope.hasBranches();
 633
 634   // - whether there's a fallthrough
 635   llvm::BasicBlock *FallthroughSource = Builder.GetInsertBlock();
 636   bool HasFallthrough = (FallthroughSource != nullptr && IsActive);
 637
 638   // Branch-through fall-throughs leave the insertion point set to the
 639   // end of the last cleanup, which points to the current scope.  The
 640   // rest of IR gen doesn't need to worry about this; it only happens
 641   // during the execution of PopCleanupBlocks().
 642   bool HasPrebranchedFallthrough =
 643     (FallthroughSource && FallthroughSource->getTerminator());
 644
 645   // If this is a normal cleanup, then having a prebranched
 646   // fallthrough implies that the fallthrough source unconditionally
 647   // jumps here.
 648   assert(!Scope.isNormalCleanup() || !HasPrebranchedFallthrough ||
 649          (Scope.getNormalBlock() &&
 650           FallthroughSource->getTerminator()->getSuccessor(0)
 651             == Scope.getNormalBlock()));
 652
 653   bool RequiresNormalCleanup = false;
 654   if (Scope.isNormalCleanup() &&
 655       (HasFixups || HasExistingBranches || HasFallthrough)) {
 656     RequiresNormalCleanup = true;
 657   }
 658
 659   // If we have a prebranched fallthrough into an inactive normal
 660   // cleanup, rewrite it so that it leads to the appropriate place.
 661   if (Scope.isNormalCleanup() && HasPrebranchedFallthrough && !IsActive) {
 662     llvm::BasicBlock *prebranchDest;
 663
 664     // If the prebranch is semantically branching through the next
 665     // cleanup, just forward it to the next block, leaving the
 666     // insertion point in the prebranched block.
 667     if (FallthroughIsBranchThrough) {
 668       EHScope &enclosing = *EHStack.find(Scope.getEnclosingNormalCleanup());
 669       prebranchDest = CreateNormalEntry(*this, cast<EHCleanupScope>(enclosing));
 670
 671     // Otherwise, we need to make a new block.  If the normal cleanup
 672     // isn't being used at all, we could actually reuse the normal
 673     // entry block, but this is simpler, and it avoids conflicts with
 674     // dead optimistic fixup branches.
 675     } else {
 676       prebranchDest = createBasicBlock("forwarded-prebranch");
 677       EmitBlock(prebranchDest);
 678     }
 679
 680     llvm::BasicBlock *normalEntry = Scope.getNormalBlock();
 681     assert(normalEntry && !normalEntry->use_empty());
 682
 683     ForwardPrebranchedFallthrough(FallthroughSource,
 684                                   normalEntry, prebranchDest);
 685   }
 686
 687   // If we don't need the cleanup at all, we're done.
 688   if (!RequiresNormalCleanup && !RequiresEHCleanup) {
 689     destroyOptimisticNormalEntry(*this, Scope);
 690     EHStack.popCleanup(); // safe because there are no fixups
 691     assert(EHStack.getNumBranchFixups() == 0 ||
 692            EHStack.hasNormalCleanups());
 693     return;
 694   }
 695
 696   // Copy the cleanup emission data out.  This uses either a stack
 697   // array or malloc'd memory, depending on the size, which is
 698   // behavior that SmallVector would provide, if we could use it
 699   // here. Unfortunately, if you ask for a SmallVector<char>, the
 700   // alignment isn't sufficient.
 701   auto *CleanupSource = reinterpret_cast<char *>(Scope.getCleanupBuffer());
 702   llvm::AlignedCharArray<EHScopeStack::ScopeStackAlignment, 8 * sizeof(void *)> CleanupBufferStack;
 703   std::unique_ptr<char[]> CleanupBufferHeap;
 704   size_t CleanupSize = Scope.getCleanupSize();
 705   EHScopeStack::Cleanup *Fn;
 706
 707   if (CleanupSize <= sizeof(CleanupBufferStack)) {
 708     memcpy(CleanupBufferStack.buffer, CleanupSource, CleanupSize);
 709     Fn = reinterpret_cast<EHScopeStack::Cleanup *>(CleanupBufferStack.buffer);
 710   } else {
 711     CleanupBufferHeap.reset(new char[CleanupSize]);
 712     memcpy(CleanupBufferHeap.get(), CleanupSource, CleanupSize);
 713     Fn = reinterpret_cast<EHScopeStack::Cleanup *>(CleanupBufferHeap.get());
 714   }
 715
 716   EHScopeStack::Cleanup::Flags cleanupFlags;
 717   if (Scope.isNormalCleanup())
 718     cleanupFlags.setIsNormalCleanupKind();
 719   if (Scope.isEHCleanup())
 720     cleanupFlags.setIsEHCleanupKind();
 721
 722   if (!RequiresNormalCleanup) {
 723     destroyOptimisticNormalEntry(*this, Scope);
 724     EHStack.popCleanup();
 725   } else {
 726     // If we have a fallthrough and no other need for the cleanup,
 727     // emit it directly.
 728     if (HasFallthrough && !HasPrebranchedFallthrough &&
 729         !HasFixups && !HasExistingBranches) {
 730
 731       destroyOptimisticNormalEntry(*this, Scope);
 732       EHStack.popCleanup();
 733
 734       EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
 735
 736     // Otherwise, the best approach is to thread everything through
 737     // the cleanup block and then try to clean up after ourselves.
 738     } else {
 739       // Force the entry block to exist.
 740       llvm::BasicBlock *NormalEntry = CreateNormalEntry(*this, Scope);
 741
 742       // I.  Set up the fallthrough edge in.
 743
 744       CGBuilderTy::InsertPoint savedInactiveFallthroughIP;
 745
 746       // If there's a fallthrough, we need to store the cleanup
 747       // destination index.  For fall-throughs this is always zero.
 748       if (HasFallthrough) {
 749         if (!HasPrebranchedFallthrough)
 750           Builder.CreateStore(Builder.getInt32(0), getNormalCleanupDestSlot());
 751
 752       // Otherwise, save and clear the IP if we don't have fallthrough
 753       // because the cleanup is inactive.
 754       } else if (FallthroughSource) {
 755         assert(!IsActive && "source without fallthrough for active cleanup");
 756         savedInactiveFallthroughIP = Builder.saveAndClearIP();
 757       }
 758
 759       // II.  Emit the entry block.  This implicitly branches to it if
 760       // we have fallthrough.  All the fixups and existing branches
 761       // should already be branched to it.
 762       EmitBlock(NormalEntry);
 763
 764       // III.  Figure out where we're going and build the cleanup
 765       // epilogue.
 766
 767       bool HasEnclosingCleanups =
 768         (Scope.getEnclosingNormalCleanup() != EHStack.stable_end());
 769
 770       // Compute the branch-through dest if we need it:
 771       //   - if there are branch-throughs threaded through the scope
 772       //   - if fall-through is a branch-through
 773       //   - if there are fixups that will be optimistically forwarded
 774       //     to the enclosing cleanup
 775       llvm::BasicBlock *BranchThroughDest = nullptr;
 776       if (Scope.hasBranchThroughs() ||
 777           (FallthroughSource && FallthroughIsBranchThrough) ||
 778           (HasFixups && HasEnclosingCleanups)) {
 779         assert(HasEnclosingCleanups);
 780         EHScope &S = *EHStack.find(Scope.getEnclosingNormalCleanup());
 781         BranchThroughDest = CreateNormalEntry(*this, cast<EHCleanupScope>(S));
 782       }
 783
 784       llvm::BasicBlock *FallthroughDest = nullptr;
 785       SmallVector<llvm::Instruction*, 2> InstsToAppend;
 786
 787       // If there's exactly one branch-after and no other threads,
 788       // we can route it without a switch.
 789       if (!Scope.hasBranchThroughs() && !HasFixups && !HasFallthrough &&
 790           Scope.getNumBranchAfters() == 1) {
 791         assert(!BranchThroughDest || !IsActive);
 792
 793         // Clean up the possibly dead store to the cleanup dest slot.
 794         llvm::Instruction *NormalCleanupDestSlot =
 795             cast<llvm::Instruction>(getNormalCleanupDestSlot().getPointer());
 796         if (NormalCleanupDestSlot->hasOneUse()) {
 797           NormalCleanupDestSlot->user_back()->eraseFromParent();
 798           NormalCleanupDestSlot->eraseFromParent();
 799           NormalCleanupDest = nullptr;
 800         }
 801
 802         llvm::BasicBlock *BranchAfter = Scope.getBranchAfterBlock(0);
 803         InstsToAppend.push_back(llvm::BranchInst::Create(BranchAfter));
 804
 805       // Build a switch-out if we need it:
 806       //   - if there are branch-afters threaded through the scope
 807       //   - if fall-through is a branch-after
 808       //   - if there are fixups that have nowhere left to go and
 809       //     so must be immediately resolved
 810       } else if (Scope.getNumBranchAfters() ||
 811                  (HasFallthrough && !FallthroughIsBranchThrough) ||
 812                  (HasFixups && !HasEnclosingCleanups)) {
 813
 814         llvm::BasicBlock *Default =
 815           (BranchThroughDest ? BranchThroughDest : getUnreachableBlock());
 816
 817         // TODO: base this on the number of branch-afters and fixups
 818         const unsigned SwitchCapacity = 10;
 819
 820         llvm::LoadInst *Load =
 821           createLoadInstBefore(getNormalCleanupDestSlot(), "cleanup.dest",
 822                                nullptr);
 823         llvm::SwitchInst *Switch =
 824           llvm::SwitchInst::Create(Load, Default, SwitchCapacity);
 825
 826         InstsToAppend.push_back(Load);
 827         InstsToAppend.push_back(Switch);
 828
 829         // Branch-after fallthrough.
 830         if (FallthroughSource && !FallthroughIsBranchThrough) {
 831           FallthroughDest = createBasicBlock("cleanup.cont");
 832           if (HasFallthrough)
 833             Switch->addCase(Builder.getInt32(0), FallthroughDest);
 834         }
 835
 836         for (unsigned I = 0, E = Scope.getNumBranchAfters(); I != E; ++I) {
 837           Switch->addCase(Scope.getBranchAfterIndex(I),
 838                           Scope.getBranchAfterBlock(I));
 839         }
 840
 841         // If there aren't any enclosing cleanups, we can resolve all
 842         // the fixups now.
 843         if (HasFixups && !HasEnclosingCleanups)
 844           ResolveAllBranchFixups(*this, Switch, NormalEntry);
 845       } else {
 846         // We should always have a branch-through destination in this case.
 847         assert(BranchThroughDest);
 848         InstsToAppend.push_back(llvm::BranchInst::Create(BranchThroughDest));
 849       }
 850
 851       // IV.  Pop the cleanup and emit it.
 852       EHStack.popCleanup();
 853       assert(EHStack.hasNormalCleanups() == HasEnclosingCleanups);
 854
 855       EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
 856
 857       // Append the prepared cleanup prologue from above.
 858       llvm::BasicBlock *NormalExit = Builder.GetInsertBlock();
 859       for (unsigned I = 0, E = InstsToAppend.size(); I != E; ++I)
 860         NormalExit->getInstList().push_back(InstsToAppend[I]);
 861
 862       // Optimistically hope that any fixups will continue falling through.
 863       for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
 864            I < E; ++I) {
 865         BranchFixup &Fixup = EHStack.getBranchFixup(I);
 866         if (!Fixup.Destination) continue;
 867         if (!Fixup.OptimisticBranchBlock) {
 868           createStoreInstBefore(Builder.getInt32(Fixup.DestinationIndex),
 869                                 getNormalCleanupDestSlot(),
 870                                 Fixup.InitialBranch);
 871           Fixup.InitialBranch->setSuccessor(0, NormalEntry);
 872         }
 873         Fixup.OptimisticBranchBlock = NormalExit;
 874       }
 875
 876       // V.  Set up the fallthrough edge out.
 877
 878       // Case 1: a fallthrough source exists but doesn't branch to the
 879       // cleanup because the cleanup is inactive.
 880       if (!HasFallthrough && FallthroughSource) {
 881         // Prebranched fallthrough was forwarded earlier.
 882         // Non-prebranched fallthrough doesn't need to be forwarded.
 883         // Either way, all we need to do is restore the IP we cleared before.
 884         assert(!IsActive);
 885         Builder.restoreIP(savedInactiveFallthroughIP);
 886
 887       // Case 2: a fallthrough source exists and should branch to the
 888       // cleanup, but we're not supposed to branch through to the next
 889       // cleanup.
 890       } else if (HasFallthrough && FallthroughDest) {
 891         assert(!FallthroughIsBranchThrough);
 892         EmitBlock(FallthroughDest);
 893
 894       // Case 3: a fallthrough source exists and should branch to the
 895       // cleanup and then through to the next.
 896       } else if (HasFallthrough) {
 897         // Everything is already set up for this.
 898
 899       // Case 4: no fallthrough source exists.
 900       } else {
 901         Builder.ClearInsertionPoint();
 902       }
 903
 904       // VI.  Assorted cleaning.
 905
 906       // Check whether we can merge NormalEntry into a single predecessor.
 907       // This might invalidate (non-IR) pointers to NormalEntry.
 908       llvm::BasicBlock *NewNormalEntry =
 909         SimplifyCleanupEntry(*this, NormalEntry);
 910
 911       // If it did invalidate those pointers, and NormalEntry was the same
 912       // as NormalExit, go back and patch up the fixups.
 913       if (NewNormalEntry != NormalEntry && NormalEntry == NormalExit)
 914         for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
 915                I < E; ++I)
 916           EHStack.getBranchFixup(I).OptimisticBranchBlock = NewNormalEntry;
 917     }
 918   }
 919
 920   assert(EHStack.hasNormalCleanups() || EHStack.getNumBranchFixups() == 0);
 921
 922   // Emit the EH cleanup if required.
 923   if (RequiresEHCleanup) {
 924     CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
 925
 926     EmitBlock(EHEntry);
 927
 928     llvm::BasicBlock *NextAction = getEHDispatchBlock(EHParent);
 929
 930     // Push a terminate scope or cleanupendpad scope around the potentially
 931     // throwing cleanups. For funclet EH personalities, the cleanupendpad models
 932     // program termination when cleanups throw.
 933     bool PushedTerminate = false;
 934     SaveAndRestore<llvm::Instruction *> RestoreCurrentFuncletPad(
 935         CurrentFuncletPad);
 936     llvm::CleanupPadInst *CPI = nullptr;
 937     if (!EHPersonality::get(*this).usesFuncletPads()) {
 938       EHStack.pushTerminate();
 939       PushedTerminate = true;
 940     } else {
 941       llvm::Value *ParentPad = CurrentFuncletPad;
 942       if (!ParentPad)
 943         ParentPad = llvm::ConstantTokenNone::get(CGM.getLLVMContext());
 944       CurrentFuncletPad = CPI = Builder.CreateCleanupPad(ParentPad);
 945     }
 946
 947     // We only actually emit the cleanup code if the cleanup is either
 948     // active or was used before it was deactivated.
 949     if (EHActiveFlag.isValid() || IsActive) {
 950       cleanupFlags.setIsForEHCleanup();
 951       EmitCleanup(*this, Fn, cleanupFlags, EHActiveFlag);
 952     }
 953
 954     if (CPI)
 955       Builder.CreateCleanupRet(CPI, NextAction);
 956     else
 957       Builder.CreateBr(NextAction);
 958
 959     // Leave the terminate scope.
 960     if (PushedTerminate)
 961       EHStack.popTerminate();
 962
 963     Builder.restoreIP(SavedIP);
 964
 965     SimplifyCleanupEntry(*this, EHEntry);
 966   }
 967 }
 968
 969 /// isObviouslyBranchWithoutCleanups - Return true if a branch to the
 970 /// specified destination obviously has no cleanups to run.  'false' is always
 971 /// a conservatively correct answer for this method.
 972 bool CodeGenFunction::isObviouslyBranchWithoutCleanups(JumpDest Dest) const {
 973   assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
 974          && "stale jump destination");
 975
 976   // Calculate the innermost active normal cleanup.
 977   EHScopeStack::stable_iterator TopCleanup =
 978     EHStack.getInnermostActiveNormalCleanup();
 979
 980   // If we're not in an active normal cleanup scope, or if the
 981   // destination scope is within the innermost active normal cleanup
 982   // scope, we don't need to worry about fixups.
 983   if (TopCleanup == EHStack.stable_end() ||
 984       TopCleanup.encloses(Dest.getScopeDepth())) // works for invalid
 985     return true;
 986
 987   // Otherwise, we might need some cleanups.
 988   return false;
 989 }
 990
 991
 992 /// Terminate the current block by emitting a branch which might leave
 993 /// the current cleanup-protected scope.  The target scope may not yet
 994 /// be known, in which case this will require a fixup.
 995 ///
 996 /// As a side-effect, this method clears the insertion point.
 997 void CodeGenFunction::EmitBranchThroughCleanup(JumpDest Dest) {
 998   assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
 999          && "stale jump destination");
1000
1001   if (!HaveInsertPoint())
1002     return;
1003
1004   // Create the branch.
1005   llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock());
1006
1007   // Calculate the innermost active normal cleanup.
1008   EHScopeStack::stable_iterator
1009     TopCleanup = EHStack.getInnermostActiveNormalCleanup();
1010
1011   // If we're not in an active normal cleanup scope, or if the
1012   // destination scope is within the innermost active normal cleanup
1013   // scope, we don't need to worry about fixups.
1014   if (TopCleanup == EHStack.stable_end() ||
1015       TopCleanup.encloses(Dest.getScopeDepth())) { // works for invalid
1016     Builder.ClearInsertionPoint();
1017     return;
1018   }
1019
1020   // If we can't resolve the destination cleanup scope, just add this
1021   // to the current cleanup scope as a branch fixup.
1022   if (!Dest.getScopeDepth().isValid()) {
1023     BranchFixup &Fixup = EHStack.addBranchFixup();
1024     Fixup.Destination = Dest.getBlock();
1025     Fixup.DestinationIndex = Dest.getDestIndex();
1026     Fixup.InitialBranch = BI;
1027     Fixup.OptimisticBranchBlock = nullptr;
1028
1029     Builder.ClearInsertionPoint();
1030     return;
1031   }
1032
1033   // Otherwise, thread through all the normal cleanups in scope.
1034
1035   // Store the index at the start.
1036   llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex());
1037   createStoreInstBefore(Index, getNormalCleanupDestSlot(), BI);
1038
1039   // Adjust BI to point to the first cleanup block.
1040   {
1041     EHCleanupScope &Scope =
1042       cast<EHCleanupScope>(*EHStack.find(TopCleanup));
1043     BI->setSuccessor(0, CreateNormalEntry(*this, Scope));
1044   }
1045
1046   // Add this destination to all the scopes involved.
1047   EHScopeStack::stable_iterator I = TopCleanup;
1048   EHScopeStack::stable_iterator E = Dest.getScopeDepth();
1049   if (E.strictlyEncloses(I)) {
1050     while (true) {
1051       EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(I));
1052       assert(Scope.isNormalCleanup());
1053       I = Scope.getEnclosingNormalCleanup();
1054
1055       // If this is the last cleanup we're propagating through, tell it
1056       // that there's a resolved jump moving through it.
1057       if (!E.strictlyEncloses(I)) {
1058         Scope.addBranchAfter(Index, Dest.getBlock());
1059         break;
1060       }
1061
1062       // Otherwise, tell the scope that there's a jump propoagating
1063       // through it.  If this isn't new information, all the rest of
1064       // the work has been done before.
1065       if (!Scope.addBranchThrough(Dest.getBlock()))
1066         break;
1067     }
1068   }
1069
1070   Builder.ClearInsertionPoint();
1071 }
1072
1073 static bool IsUsedAsNormalCleanup(EHScopeStack &EHStack,
1074                                   EHScopeStack::stable_iterator C) {
1075   // If we needed a normal block for any reason, that counts.
1076   if (cast<EHCleanupScope>(*EHStack.find(C)).getNormalBlock())
1077     return true;
1078
1079   // Check whether any enclosed cleanups were needed.
1080   for (EHScopeStack::stable_iterator
1081          I = EHStack.getInnermostNormalCleanup();
1082          I != C; ) {
1083     assert(C.strictlyEncloses(I));
1084     EHCleanupScope &S = cast<EHCleanupScope>(*EHStack.find(I));
1085     if (S.getNormalBlock()) return true;
1086     I = S.getEnclosingNormalCleanup();
1087   }
1088
1089   return false;
1090 }
1091
1092 static bool IsUsedAsEHCleanup(EHScopeStack &EHStack,
1093                               EHScopeStack::stable_iterator cleanup) {
1094   // If we needed an EH block for any reason, that counts.
1095   if (EHStack.find(cleanup)->hasEHBranches())
1096     return true;
1097
1098   // Check whether any enclosed cleanups were needed.
1099   for (EHScopeStack::stable_iterator
1100          i = EHStack.getInnermostEHScope(); i != cleanup; ) {
1101     assert(cleanup.strictlyEncloses(i));
1102
1103     EHScope &scope = *EHStack.find(i);
1104     if (scope.hasEHBranches())
1105       return true;
1106
1107     i = scope.getEnclosingEHScope();
1108   }
1109
1110   return false;
1111 }
1112
1113 enum ForActivation_t {
1114   ForActivation,
1115   ForDeactivation
1116 };
1117
1118 /// The given cleanup block is changing activation state.  Configure a
1119 /// cleanup variable if necessary.
1120 ///
1121 /// It would be good if we had some way of determining if there were
1122 /// extra uses *after* the change-over point.
1123 static void SetupCleanupBlockActivation(CodeGenFunction &CGF,
1124                                         EHScopeStack::stable_iterator C,
1125                                         ForActivation_t kind,
1126                                         llvm::Instruction *dominatingIP) {
1127   EHCleanupScope &Scope = cast<EHCleanupScope>(*CGF.EHStack.find(C));
1128
1129   // We always need the flag if we're activating the cleanup in a
1130   // conditional context, because we have to assume that the current
1131   // location doesn't necessarily dominate the cleanup's code.
1132   bool isActivatedInConditional =
1133     (kind == ForActivation && CGF.isInConditionalBranch());
1134
1135   bool needFlag = false;
1136
1137   // Calculate whether the cleanup was used:
1138
1139   //   - as a normal cleanup
1140   if (Scope.isNormalCleanup() &&
1141       (isActivatedInConditional || IsUsedAsNormalCleanup(CGF.EHStack, C))) {
1142     Scope.setTestFlagInNormalCleanup();
1143     needFlag = true;
1144   }
1145
1146   //  - as an EH cleanup
1147   if (Scope.isEHCleanup() &&
1148       (isActivatedInConditional || IsUsedAsEHCleanup(CGF.EHStack, C))) {
1149     Scope.setTestFlagInEHCleanup();
1150     needFlag = true;
1151   }
1152
1153   // If it hasn't yet been used as either, we're done.
1154   if (!needFlag) return;
1155
1156   Address var = Scope.getActiveFlag();
1157   if (!var.isValid()) {
1158     var = CGF.CreateTempAlloca(CGF.Builder.getInt1Ty(), CharUnits::One(),
1159                                "cleanup.isactive");
1160     Scope.setActiveFlag(var);
1161
1162     assert(dominatingIP && "no existing variable and no dominating IP!");
1163
1164     // Initialize to true or false depending on whether it was
1165     // active up to this point.
1166     llvm::Constant *value = CGF.Builder.getInt1(kind == ForDeactivation);
1167
1168     // If we're in a conditional block, ignore the dominating IP and
1169     // use the outermost conditional branch.
1170     if (CGF.isInConditionalBranch()) {
1171       CGF.setBeforeOutermostConditional(value, var);
1172     } else {
1173       createStoreInstBefore(value, var, dominatingIP);
1174     }
1175   }
1176
1177   CGF.Builder.CreateStore(CGF.Builder.getInt1(kind == ForActivation), var);
1178 }
1179
1180 /// Activate a cleanup that was created in an inactivated state.
1181 void CodeGenFunction::ActivateCleanupBlock(EHScopeStack::stable_iterator C,
1182                                            llvm::Instruction *dominatingIP) {
1183   assert(C != EHStack.stable_end() && "activating bottom of stack?");
1184   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
1185   assert(!Scope.isActive() && "double activation");
1186
1187   SetupCleanupBlockActivation(*this, C, ForActivation, dominatingIP);
1188
1189   Scope.setActive(true);
1190 }
1191
1192 /// Deactive a cleanup that was created in an active state.
1193 void CodeGenFunction::DeactivateCleanupBlock(EHScopeStack::stable_iterator C,
1194                                              llvm::Instruction *dominatingIP) {
1195   assert(C != EHStack.stable_end() && "deactivating bottom of stack?");
1196   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
1197   assert(Scope.isActive() && "double deactivation");
1198
1199   // If it's the top of the stack, just pop it.
1200   if (C == EHStack.stable_begin()) {
1201     // If it's a normal cleanup, we need to pretend that the
1202     // fallthrough is unreachable.
1203     CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
1204     PopCleanupBlock();
1205     Builder.restoreIP(SavedIP);
1206     return;
1207   }
1208
1209   // Otherwise, follow the general case.
1210   SetupCleanupBlockActivation(*this, C, ForDeactivation, dominatingIP);
1211
1212   Scope.setActive(false);
1213 }
1214
1215 Address CodeGenFunction::getNormalCleanupDestSlot() {
1216   if (!NormalCleanupDest)
1217     NormalCleanupDest =
1218       CreateTempAlloca(Builder.getInt32Ty(), "cleanup.dest.slot");
1219   return Address(NormalCleanupDest, CharUnits::fromQuantity(4));
1220 }
1221
1222 /// Emits all the code to cause the given temporary to be cleaned up.
1223 void CodeGenFunction::EmitCXXTemporary(const CXXTemporary *Temporary,
1224                                        QualType TempType,
1225                                        Address Ptr) {
1226   pushDestroy(NormalAndEHCleanup, Ptr, TempType, destroyCXXObject,
1227               /*useEHCleanup*/ true);
1228 }