clang/lib/CodeGen/CGCleanup.cpp

   1 //===--- CGCleanup.cpp - Bookkeeping and code emission for cleanups -------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file contains code dealing with the IR generation for cleanups
  10 // and related information.
  11 //
  12 // A "cleanup" is a piece of code which needs to be executed whenever
  13 // control transfers out of a particular scope.  This can be
  14 // conditionalized to occur only on exceptional control flow, only on
  15 // normal control flow, or both.
  16 //
  17 //===----------------------------------------------------------------------===//
  18
  19 #include "CGCleanup.h"
  20 #include "CodeGenFunction.h"
  21 #include "llvm/Support/SaveAndRestore.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.getAggregatePointer());
  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, nullptr, ScalarLiteral);
  42
  43     // Everything else needs an alloca.
  44     Address addr =
  45       CGF.CreateDefaultAlignTempAlloca(V->getType(), "saved-rvalue");
  46     CGF.Builder.CreateStore(V, addr);
  47     return saved_type(addr.getPointer(), nullptr, ScalarAddress);
  48   }
  49
  50   if (rv.isComplex()) {
  51     CodeGenFunction::ComplexPairTy V = rv.getComplexVal();
  52     llvm::Type *ComplexTy =
  53         llvm::StructType::get(V.first->getType(), V.second->getType());
  54     Address addr = CGF.CreateDefaultAlignTempAlloca(ComplexTy, "saved-complex");
  55     CGF.Builder.CreateStore(V.first, CGF.Builder.CreateStructGEP(addr, 0));
  56     CGF.Builder.CreateStore(V.second, CGF.Builder.CreateStructGEP(addr, 1));
  57     return saved_type(addr.getPointer(), nullptr, ComplexAddress);
  58   }
  59
  60   assert(rv.isAggregate());
  61   Address V = rv.getAggregateAddress(); // TODO: volatile?
  62   if (!DominatingLLVMValue::needsSaving(V.getPointer()))
  63     return saved_type(V.getPointer(), V.getElementType(), AggregateLiteral,
  64                       V.getAlignment().getQuantity());
  65
  66   Address addr =
  67     CGF.CreateTempAlloca(V.getType(), CGF.getPointerAlign(), "saved-rvalue");
  68   CGF.Builder.CreateStore(V.getPointer(), addr);
  69   return saved_type(addr.getPointer(), V.getElementType(), AggregateAddress,
  70                     V.getAlignment().getQuantity());
  71 }
  72
  73 /// Given a saved r-value produced by SaveRValue, perform the code
  74 /// necessary to restore it to usability at the current insertion
  75 /// point.
  76 RValue DominatingValue<RValue>::saved_type::restore(CodeGenFunction &CGF) {
  77   auto getSavingAddress = [&](llvm::Value *value) {
  78     auto *AI = cast<llvm::AllocaInst>(value);
  79     return Address(value, AI->getAllocatedType(),
  80                    CharUnits::fromQuantity(AI->getAlign().value()));
  81   };
  82   switch (K) {
  83   case ScalarLiteral:
  84     return RValue::get(Value);
  85   case ScalarAddress:
  86     return RValue::get(CGF.Builder.CreateLoad(getSavingAddress(Value)));
  87   case AggregateLiteral:
  88     return RValue::getAggregate(
  89         Address(Value, ElementType, CharUnits::fromQuantity(Align)));
  90   case AggregateAddress: {
  91     auto addr = CGF.Builder.CreateLoad(getSavingAddress(Value));
  92     return RValue::getAggregate(
  93         Address(addr, ElementType, CharUnits::fromQuantity(Align)));
  94   }
  95   case ComplexAddress: {
  96     Address address = getSavingAddress(Value);
  97     llvm::Value *real =
  98         CGF.Builder.CreateLoad(CGF.Builder.CreateStructGEP(address, 0));
  99     llvm::Value *imag =
 100         CGF.Builder.CreateLoad(CGF.Builder.CreateStructGEP(address, 1));
 101     return RValue::getComplex(real, imag);
 102   }
 103   }
 104
 105   llvm_unreachable("bad saved r-value kind");
 106 }
 107
 108 /// Push an entry of the given size onto this protected-scope stack.
 109 char *EHScopeStack::allocate(size_t Size) {
 110   Size = llvm::alignTo(Size, ScopeStackAlignment);
 111   if (!StartOfBuffer) {
 112     unsigned Capacity = 1024;
 113     while (Capacity < Size) Capacity *= 2;
 114     StartOfBuffer = new char[Capacity];
 115     StartOfData = EndOfBuffer = StartOfBuffer + Capacity;
 116   } else if (static_cast<size_t>(StartOfData - StartOfBuffer) < Size) {
 117     unsigned CurrentCapacity = EndOfBuffer - StartOfBuffer;
 118     unsigned UsedCapacity = CurrentCapacity - (StartOfData - StartOfBuffer);
 119
 120     unsigned NewCapacity = CurrentCapacity;
 121     do {
 122       NewCapacity *= 2;
 123     } while (NewCapacity < UsedCapacity + Size);
 124
 125     char *NewStartOfBuffer = new char[NewCapacity];
 126     char *NewEndOfBuffer = NewStartOfBuffer + NewCapacity;
 127     char *NewStartOfData = NewEndOfBuffer - UsedCapacity;
 128     memcpy(NewStartOfData, StartOfData, UsedCapacity);
 129     delete [] StartOfBuffer;
 130     StartOfBuffer = NewStartOfBuffer;
 131     EndOfBuffer = NewEndOfBuffer;
 132     StartOfData = NewStartOfData;
 133   }
 134
 135   assert(StartOfBuffer + Size <= StartOfData);
 136   StartOfData -= Size;
 137   return StartOfData;
 138 }
 139
 140 void EHScopeStack::deallocate(size_t Size) {
 141   StartOfData += llvm::alignTo(Size, ScopeStackAlignment);
 142 }
 143
 144 bool EHScopeStack::containsOnlyLifetimeMarkers(
 145     EHScopeStack::stable_iterator Old) const {
 146   for (EHScopeStack::iterator it = begin(); stabilize(it) != Old; it++) {
 147     EHCleanupScope *cleanup = dyn_cast<EHCleanupScope>(&*it);
 148     if (!cleanup || !cleanup->isLifetimeMarker())
 149       return false;
 150   }
 151
 152   return true;
 153 }
 154
 155 bool EHScopeStack::requiresLandingPad() const {
 156   for (stable_iterator si = getInnermostEHScope(); si != stable_end(); ) {
 157     // Skip lifetime markers.
 158     if (auto *cleanup = dyn_cast<EHCleanupScope>(&*find(si)))
 159       if (cleanup->isLifetimeMarker()) {
 160         si = cleanup->getEnclosingEHScope();
 161         continue;
 162       }
 163     return true;
 164   }
 165
 166   return false;
 167 }
 168
 169 EHScopeStack::stable_iterator
 170 EHScopeStack::getInnermostActiveNormalCleanup() const {
 171   for (stable_iterator si = getInnermostNormalCleanup(), se = stable_end();
 172          si != se; ) {
 173     EHCleanupScope &cleanup = cast<EHCleanupScope>(*find(si));
 174     if (cleanup.isActive()) return si;
 175     si = cleanup.getEnclosingNormalCleanup();
 176   }
 177   return stable_end();
 178 }
 179
 180
 181 void *EHScopeStack::pushCleanup(CleanupKind Kind, size_t Size) {
 182   char *Buffer = allocate(EHCleanupScope::getSizeForCleanupSize(Size));
 183   bool IsNormalCleanup = Kind & NormalCleanup;
 184   bool IsEHCleanup = Kind & EHCleanup;
 185   bool IsLifetimeMarker = Kind & LifetimeMarker;
 186
 187   // Per C++ [except.terminate], it is implementation-defined whether none,
 188   // some, or all cleanups are called before std::terminate. Thus, when
 189   // terminate is the current EH scope, we may skip adding any EH cleanup
 190   // scopes.
 191   if (InnermostEHScope != stable_end() &&
 192       find(InnermostEHScope)->getKind() == EHScope::Terminate)
 193     IsEHCleanup = false;
 194
 195   EHCleanupScope *Scope =
 196     new (Buffer) EHCleanupScope(IsNormalCleanup,
 197                                 IsEHCleanup,
 198                                 Size,
 199                                 BranchFixups.size(),
 200                                 InnermostNormalCleanup,
 201                                 InnermostEHScope);
 202   if (IsNormalCleanup)
 203     InnermostNormalCleanup = stable_begin();
 204   if (IsEHCleanup)
 205     InnermostEHScope = stable_begin();
 206   if (IsLifetimeMarker)
 207     Scope->setLifetimeMarker();
 208
 209   // With Windows -EHa, Invoke llvm.seh.scope.begin() for EHCleanup
 210   if (CGF->getLangOpts().EHAsynch && IsEHCleanup && !IsLifetimeMarker &&
 211       CGF->getTarget().getCXXABI().isMicrosoft())
 212     CGF->EmitSehCppScopeBegin();
 213
 214   return Scope->getCleanupBuffer();
 215 }
 216
 217 void EHScopeStack::popCleanup() {
 218   assert(!empty() && "popping exception stack when not empty");
 219
 220   assert(isa<EHCleanupScope>(*begin()));
 221   EHCleanupScope &Cleanup = cast<EHCleanupScope>(*begin());
 222   InnermostNormalCleanup = Cleanup.getEnclosingNormalCleanup();
 223   InnermostEHScope = Cleanup.getEnclosingEHScope();
 224   deallocate(Cleanup.getAllocatedSize());
 225
 226   // Destroy the cleanup.
 227   Cleanup.Destroy();
 228
 229   // Check whether we can shrink the branch-fixups stack.
 230   if (!BranchFixups.empty()) {
 231     // If we no longer have any normal cleanups, all the fixups are
 232     // complete.
 233     if (!hasNormalCleanups())
 234       BranchFixups.clear();
 235
 236     // Otherwise we can still trim out unnecessary nulls.
 237     else
 238       popNullFixups();
 239   }
 240 }
 241
 242 EHFilterScope *EHScopeStack::pushFilter(unsigned numFilters) {
 243   assert(getInnermostEHScope() == stable_end());
 244   char *buffer = allocate(EHFilterScope::getSizeForNumFilters(numFilters));
 245   EHFilterScope *filter = new (buffer) EHFilterScope(numFilters);
 246   InnermostEHScope = stable_begin();
 247   return filter;
 248 }
 249
 250 void EHScopeStack::popFilter() {
 251   assert(!empty() && "popping exception stack when not empty");
 252
 253   EHFilterScope &filter = cast<EHFilterScope>(*begin());
 254   deallocate(EHFilterScope::getSizeForNumFilters(filter.getNumFilters()));
 255
 256   InnermostEHScope = filter.getEnclosingEHScope();
 257 }
 258
 259 EHCatchScope *EHScopeStack::pushCatch(unsigned numHandlers) {
 260   char *buffer = allocate(EHCatchScope::getSizeForNumHandlers(numHandlers));
 261   EHCatchScope *scope =
 262     new (buffer) EHCatchScope(numHandlers, InnermostEHScope);
 263   InnermostEHScope = stable_begin();
 264   return scope;
 265 }
 266
 267 void EHScopeStack::pushTerminate() {
 268   char *Buffer = allocate(EHTerminateScope::getSize());
 269   new (Buffer) EHTerminateScope(InnermostEHScope);
 270   InnermostEHScope = stable_begin();
 271 }
 272
 273 /// Remove any 'null' fixups on the stack.  However, we can't pop more
 274 /// fixups than the fixup depth on the innermost normal cleanup, or
 275 /// else fixups that we try to add to that cleanup will end up in the
 276 /// wrong place.  We *could* try to shrink fixup depths, but that's
 277 /// actually a lot of work for little benefit.
 278 void EHScopeStack::popNullFixups() {
 279   // We expect this to only be called when there's still an innermost
 280   // normal cleanup;  otherwise there really shouldn't be any fixups.
 281   assert(hasNormalCleanups());
 282
 283   EHScopeStack::iterator it = find(InnermostNormalCleanup);
 284   unsigned MinSize = cast<EHCleanupScope>(*it).getFixupDepth();
 285   assert(BranchFixups.size() >= MinSize && "fixup stack out of order");
 286
 287   while (BranchFixups.size() > MinSize &&
 288          BranchFixups.back().Destination == nullptr)
 289     BranchFixups.pop_back();
 290 }
 291
 292 Address CodeGenFunction::createCleanupActiveFlag() {
 293   // Create a variable to decide whether the cleanup needs to be run.
 294   Address active = CreateTempAllocaWithoutCast(
 295       Builder.getInt1Ty(), CharUnits::One(), "cleanup.cond");
 296
 297   // Initialize it to false at a site that's guaranteed to be run
 298   // before each evaluation.
 299   setBeforeOutermostConditional(Builder.getFalse(), active);
 300
 301   // Initialize it to true at the current location.
 302   Builder.CreateStore(Builder.getTrue(), active);
 303
 304   return active;
 305 }
 306
 307 void CodeGenFunction::initFullExprCleanupWithFlag(Address ActiveFlag) {
 308   // Set that as the active flag in the cleanup.
 309   EHCleanupScope &cleanup = cast<EHCleanupScope>(*EHStack.begin());
 310   assert(!cleanup.hasActiveFlag() && "cleanup already has active flag?");
 311   cleanup.setActiveFlag(ActiveFlag);
 312
 313   if (cleanup.isNormalCleanup()) cleanup.setTestFlagInNormalCleanup();
 314   if (cleanup.isEHCleanup()) cleanup.setTestFlagInEHCleanup();
 315 }
 316
 317 void EHScopeStack::Cleanup::anchor() {}
 318
 319 static void createStoreInstBefore(llvm::Value *value, Address addr,
 320                                   llvm::Instruction *beforeInst) {
 321   auto store = new llvm::StoreInst(value, addr.getPointer(), beforeInst);
 322   store->setAlignment(addr.getAlignment().getAsAlign());
 323 }
 324
 325 static llvm::LoadInst *createLoadInstBefore(Address addr, const Twine &name,
 326                                             llvm::Instruction *beforeInst) {
 327   return new llvm::LoadInst(addr.getElementType(), addr.getPointer(), name,
 328                             false, addr.getAlignment().getAsAlign(),
 329                             beforeInst);
 330 }
 331
 332 /// All the branch fixups on the EH stack have propagated out past the
 333 /// outermost normal cleanup; resolve them all by adding cases to the
 334 /// given switch instruction.
 335 static void ResolveAllBranchFixups(CodeGenFunction &CGF,
 336                                    llvm::SwitchInst *Switch,
 337                                    llvm::BasicBlock *CleanupEntry) {
 338   llvm::SmallPtrSet<llvm::BasicBlock*, 4> CasesAdded;
 339
 340   for (unsigned I = 0, E = CGF.EHStack.getNumBranchFixups(); I != E; ++I) {
 341     // Skip this fixup if its destination isn't set.
 342     BranchFixup &Fixup = CGF.EHStack.getBranchFixup(I);
 343     if (Fixup.Destination == nullptr) continue;
 344
 345     // If there isn't an OptimisticBranchBlock, then InitialBranch is
 346     // still pointing directly to its destination; forward it to the
 347     // appropriate cleanup entry.  This is required in the specific
 348     // case of
 349     //   { std::string s; goto lbl; }
 350     //   lbl:
 351     // i.e. where there's an unresolved fixup inside a single cleanup
 352     // entry which we're currently popping.
 353     if (Fixup.OptimisticBranchBlock == nullptr) {
 354       createStoreInstBefore(CGF.Builder.getInt32(Fixup.DestinationIndex),
 355                             CGF.getNormalCleanupDestSlot(),
 356                             Fixup.InitialBranch);
 357       Fixup.InitialBranch->setSuccessor(0, CleanupEntry);
 358     }
 359
 360     // Don't add this case to the switch statement twice.
 361     if (!CasesAdded.insert(Fixup.Destination).second)
 362       continue;
 363
 364     Switch->addCase(CGF.Builder.getInt32(Fixup.DestinationIndex),
 365                     Fixup.Destination);
 366   }
 367
 368   CGF.EHStack.clearFixups();
 369 }
 370
 371 /// Transitions the terminator of the given exit-block of a cleanup to
 372 /// be a cleanup switch.
 373 static llvm::SwitchInst *TransitionToCleanupSwitch(CodeGenFunction &CGF,
 374                                                    llvm::BasicBlock *Block) {
 375   // If it's a branch, turn it into a switch whose default
 376   // destination is its original target.
 377   llvm::Instruction *Term = Block->getTerminator();
 378   assert(Term && "can't transition block without terminator");
 379
 380   if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
 381     assert(Br->isUnconditional());
 382     auto Load = createLoadInstBefore(CGF.getNormalCleanupDestSlot(),
 383                                      "cleanup.dest", Term);
 384     llvm::SwitchInst *Switch =
 385       llvm::SwitchInst::Create(Load, Br->getSuccessor(0), 4, Block);
 386     Br->eraseFromParent();
 387     return Switch;
 388   } else {
 389     return cast<llvm::SwitchInst>(Term);
 390   }
 391 }
 392
 393 void CodeGenFunction::ResolveBranchFixups(llvm::BasicBlock *Block) {
 394   assert(Block && "resolving a null target block");
 395   if (!EHStack.getNumBranchFixups()) return;
 396
 397   assert(EHStack.hasNormalCleanups() &&
 398          "branch fixups exist with no normal cleanups on stack");
 399
 400   llvm::SmallPtrSet<llvm::BasicBlock*, 4> ModifiedOptimisticBlocks;
 401   bool ResolvedAny = false;
 402
 403   for (unsigned I = 0, E = EHStack.getNumBranchFixups(); I != E; ++I) {
 404     // Skip this fixup if its destination doesn't match.
 405     BranchFixup &Fixup = EHStack.getBranchFixup(I);
 406     if (Fixup.Destination != Block) continue;
 407
 408     Fixup.Destination = nullptr;
 409     ResolvedAny = true;
 410
 411     // If it doesn't have an optimistic branch block, LatestBranch is
 412     // already pointing to the right place.
 413     llvm::BasicBlock *BranchBB = Fixup.OptimisticBranchBlock;
 414     if (!BranchBB)
 415       continue;
 416
 417     // Don't process the same optimistic branch block twice.
 418     if (!ModifiedOptimisticBlocks.insert(BranchBB).second)
 419       continue;
 420
 421     llvm::SwitchInst *Switch = TransitionToCleanupSwitch(*this, BranchBB);
 422
 423     // Add a case to the switch.
 424     Switch->addCase(Builder.getInt32(Fixup.DestinationIndex), Block);
 425   }
 426
 427   if (ResolvedAny)
 428     EHStack.popNullFixups();
 429 }
 430
 431 /// Pops cleanup blocks until the given savepoint is reached.
 432 void CodeGenFunction::PopCleanupBlocks(
 433     EHScopeStack::stable_iterator Old,
 434     std::initializer_list<llvm::Value **> ValuesToReload) {
 435   assert(Old.isValid());
 436
 437   bool HadBranches = false;
 438   while (EHStack.stable_begin() != Old) {
 439     EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
 440     HadBranches |= Scope.hasBranches();
 441
 442     // As long as Old strictly encloses the scope's enclosing normal
 443     // cleanup, we're going to emit another normal cleanup which
 444     // fallthrough can propagate through.
 445     bool FallThroughIsBranchThrough =
 446       Old.strictlyEncloses(Scope.getEnclosingNormalCleanup());
 447
 448     PopCleanupBlock(FallThroughIsBranchThrough);
 449   }
 450
 451   // If we didn't have any branches, the insertion point before cleanups must
 452   // dominate the current insertion point and we don't need to reload any
 453   // values.
 454   if (!HadBranches)
 455     return;
 456
 457   // Spill and reload all values that the caller wants to be live at the current
 458   // insertion point.
 459   for (llvm::Value **ReloadedValue : ValuesToReload) {
 460     auto *Inst = dyn_cast_or_null<llvm::Instruction>(*ReloadedValue);
 461     if (!Inst)
 462       continue;
 463
 464     // Don't spill static allocas, they dominate all cleanups. These are created
 465     // by binding a reference to a local variable or temporary.
 466     auto *AI = dyn_cast<llvm::AllocaInst>(Inst);
 467     if (AI && AI->isStaticAlloca())
 468       continue;
 469
 470     Address Tmp =
 471         CreateDefaultAlignTempAlloca(Inst->getType(), "tmp.exprcleanup");
 472
 473     // Find an insertion point after Inst and spill it to the temporary.
 474     llvm::BasicBlock::iterator InsertBefore;
 475     if (auto *Invoke = dyn_cast<llvm::InvokeInst>(Inst))
 476       InsertBefore = Invoke->getNormalDest()->getFirstInsertionPt();
 477     else
 478       InsertBefore = std::next(Inst->getIterator());
 479     CGBuilderTy(CGM, &*InsertBefore).CreateStore(Inst, Tmp);
 480
 481     // Reload the value at the current insertion point.
 482     *ReloadedValue = Builder.CreateLoad(Tmp);
 483   }
 484 }
 485
 486 /// Pops cleanup blocks until the given savepoint is reached, then add the
 487 /// cleanups from the given savepoint in the lifetime-extended cleanups stack.
 488 void CodeGenFunction::PopCleanupBlocks(
 489     EHScopeStack::stable_iterator Old, size_t OldLifetimeExtendedSize,
 490     std::initializer_list<llvm::Value **> ValuesToReload) {
 491   PopCleanupBlocks(Old, ValuesToReload);
 492
 493   // Move our deferred cleanups onto the EH stack.
 494   for (size_t I = OldLifetimeExtendedSize,
 495               E = LifetimeExtendedCleanupStack.size(); I != E; /**/) {
 496     // Alignment should be guaranteed by the vptrs in the individual cleanups.
 497     assert((I % alignof(LifetimeExtendedCleanupHeader) == 0) &&
 498            "misaligned cleanup stack entry");
 499
 500     LifetimeExtendedCleanupHeader &Header =
 501         reinterpret_cast<LifetimeExtendedCleanupHeader&>(
 502             LifetimeExtendedCleanupStack[I]);
 503     I += sizeof(Header);
 504
 505     EHStack.pushCopyOfCleanup(Header.getKind(),
 506                               &LifetimeExtendedCleanupStack[I],
 507                               Header.getSize());
 508     I += Header.getSize();
 509
 510     if (Header.isConditional()) {
 511       Address ActiveFlag =
 512           reinterpret_cast<Address &>(LifetimeExtendedCleanupStack[I]);
 513       initFullExprCleanupWithFlag(ActiveFlag);
 514       I += sizeof(ActiveFlag);
 515     }
 516   }
 517   LifetimeExtendedCleanupStack.resize(OldLifetimeExtendedSize);
 518 }
 519
 520 static llvm::BasicBlock *CreateNormalEntry(CodeGenFunction &CGF,
 521                                            EHCleanupScope &Scope) {
 522   assert(Scope.isNormalCleanup());
 523   llvm::BasicBlock *Entry = Scope.getNormalBlock();
 524   if (!Entry) {
 525     Entry = CGF.createBasicBlock("cleanup");
 526     Scope.setNormalBlock(Entry);
 527   }
 528   return Entry;
 529 }
 530
 531 /// Attempts to reduce a cleanup's entry block to a fallthrough.  This
 532 /// is basically llvm::MergeBlockIntoPredecessor, except
 533 /// simplified/optimized for the tighter constraints on cleanup blocks.
 534 ///
 535 /// Returns the new block, whatever it is.
 536 static llvm::BasicBlock *SimplifyCleanupEntry(CodeGenFunction &CGF,
 537                                               llvm::BasicBlock *Entry) {
 538   llvm::BasicBlock *Pred = Entry->getSinglePredecessor();
 539   if (!Pred) return Entry;
 540
 541   llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Pred->getTerminator());
 542   if (!Br || Br->isConditional()) return Entry;
 543   assert(Br->getSuccessor(0) == Entry);
 544
 545   // If we were previously inserting at the end of the cleanup entry
 546   // block, we'll need to continue inserting at the end of the
 547   // predecessor.
 548   bool WasInsertBlock = CGF.Builder.GetInsertBlock() == Entry;
 549   assert(!WasInsertBlock || CGF.Builder.GetInsertPoint() == Entry->end());
 550
 551   // Kill the branch.
 552   Br->eraseFromParent();
 553
 554   // Replace all uses of the entry with the predecessor, in case there
 555   // are phis in the cleanup.
 556   Entry->replaceAllUsesWith(Pred);
 557
 558   // Merge the blocks.
 559   Pred->getInstList().splice(Pred->end(), Entry->getInstList());
 560
 561   // Kill the entry block.
 562   Entry->eraseFromParent();
 563
 564   if (WasInsertBlock)
 565     CGF.Builder.SetInsertPoint(Pred);
 566
 567   return Pred;
 568 }
 569
 570 static void EmitCleanup(CodeGenFunction &CGF,
 571                         EHScopeStack::Cleanup *Fn,
 572                         EHScopeStack::Cleanup::Flags flags,
 573                         Address ActiveFlag) {
 574   // If there's an active flag, load it and skip the cleanup if it's
 575   // false.
 576   llvm::BasicBlock *ContBB = nullptr;
 577   if (ActiveFlag.isValid()) {
 578     ContBB = CGF.createBasicBlock("cleanup.done");
 579     llvm::BasicBlock *CleanupBB = CGF.createBasicBlock("cleanup.action");
 580     llvm::Value *IsActive
 581       = CGF.Builder.CreateLoad(ActiveFlag, "cleanup.is_active");
 582     CGF.Builder.CreateCondBr(IsActive, CleanupBB, ContBB);
 583     CGF.EmitBlock(CleanupBB);
 584   }
 585
 586   // Ask the cleanup to emit itself.
 587   Fn->Emit(CGF, flags);
 588   assert(CGF.HaveInsertPoint() && "cleanup ended with no insertion point?");
 589
 590   // Emit the continuation block if there was an active flag.
 591   if (ActiveFlag.isValid())
 592     CGF.EmitBlock(ContBB);
 593 }
 594
 595 static void ForwardPrebranchedFallthrough(llvm::BasicBlock *Exit,
 596                                           llvm::BasicBlock *From,
 597                                           llvm::BasicBlock *To) {
 598   // Exit is the exit block of a cleanup, so it always terminates in
 599   // an unconditional branch or a switch.
 600   llvm::Instruction *Term = Exit->getTerminator();
 601
 602   if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
 603     assert(Br->isUnconditional() && Br->getSuccessor(0) == From);
 604     Br->setSuccessor(0, To);
 605   } else {
 606     llvm::SwitchInst *Switch = cast<llvm::SwitchInst>(Term);
 607     for (unsigned I = 0, E = Switch->getNumSuccessors(); I != E; ++I)
 608       if (Switch->getSuccessor(I) == From)
 609         Switch->setSuccessor(I, To);
 610   }
 611 }
 612
 613 /// We don't need a normal entry block for the given cleanup.
 614 /// Optimistic fixup branches can cause these blocks to come into
 615 /// existence anyway;  if so, destroy it.
 616 ///
 617 /// The validity of this transformation is very much specific to the
 618 /// exact ways in which we form branches to cleanup entries.
 619 static void destroyOptimisticNormalEntry(CodeGenFunction &CGF,
 620                                          EHCleanupScope &scope) {
 621   llvm::BasicBlock *entry = scope.getNormalBlock();
 622   if (!entry) return;
 623
 624   // Replace all the uses with unreachable.
 625   llvm::BasicBlock *unreachableBB = CGF.getUnreachableBlock();
 626   for (llvm::BasicBlock::use_iterator
 627          i = entry->use_begin(), e = entry->use_end(); i != e; ) {
 628     llvm::Use &use = *i;
 629     ++i;
 630
 631     use.set(unreachableBB);
 632
 633     // The only uses should be fixup switches.
 634     llvm::SwitchInst *si = cast<llvm::SwitchInst>(use.getUser());
 635     if (si->getNumCases() == 1 && si->getDefaultDest() == unreachableBB) {
 636       // Replace the switch with a branch.
 637       llvm::BranchInst::Create(si->case_begin()->getCaseSuccessor(), si);
 638
 639       // The switch operand is a load from the cleanup-dest alloca.
 640       llvm::LoadInst *condition = cast<llvm::LoadInst>(si->getCondition());
 641
 642       // Destroy the switch.
 643       si->eraseFromParent();
 644
 645       // Destroy the load.
 646       assert(condition->getOperand(0) == CGF.NormalCleanupDest.getPointer());
 647       assert(condition->use_empty());
 648       condition->eraseFromParent();
 649     }
 650   }
 651
 652   assert(entry->use_empty());
 653   delete entry;
 654 }
 655
 656 /// Pops a cleanup block.  If the block includes a normal cleanup, the
 657 /// current insertion point is threaded through the cleanup, as are
 658 /// any branch fixups on the cleanup.
 659 void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
 660   assert(!EHStack.empty() && "cleanup stack is empty!");
 661   assert(isa<EHCleanupScope>(*EHStack.begin()) && "top not a cleanup!");
 662   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
 663   assert(Scope.getFixupDepth() <= EHStack.getNumBranchFixups());
 664
 665   // Remember activation information.
 666   bool IsActive = Scope.isActive();
 667   Address NormalActiveFlag =
 668     Scope.shouldTestFlagInNormalCleanup() ? Scope.getActiveFlag()
 669                                           : Address::invalid();
 670   Address EHActiveFlag =
 671     Scope.shouldTestFlagInEHCleanup() ? Scope.getActiveFlag()
 672                                       : Address::invalid();
 673
 674   // Check whether we need an EH cleanup.  This is only true if we've
 675   // generated a lazy EH cleanup block.
 676   llvm::BasicBlock *EHEntry = Scope.getCachedEHDispatchBlock();
 677   assert(Scope.hasEHBranches() == (EHEntry != nullptr));
 678   bool RequiresEHCleanup = (EHEntry != nullptr);
 679   EHScopeStack::stable_iterator EHParent = Scope.getEnclosingEHScope();
 680
 681   // Check the three conditions which might require a normal cleanup:
 682
 683   // - whether there are branch fix-ups through this cleanup
 684   unsigned FixupDepth = Scope.getFixupDepth();
 685   bool HasFixups = EHStack.getNumBranchFixups() != FixupDepth;
 686
 687   // - whether there are branch-throughs or branch-afters
 688   bool HasExistingBranches = Scope.hasBranches();
 689
 690   // - whether there's a fallthrough
 691   llvm::BasicBlock *FallthroughSource = Builder.GetInsertBlock();
 692   bool HasFallthrough = (FallthroughSource != nullptr && IsActive);
 693
 694   // Branch-through fall-throughs leave the insertion point set to the
 695   // end of the last cleanup, which points to the current scope.  The
 696   // rest of IR gen doesn't need to worry about this; it only happens
 697   // during the execution of PopCleanupBlocks().
 698   bool HasPrebranchedFallthrough =
 699     (FallthroughSource && FallthroughSource->getTerminator());
 700
 701   // If this is a normal cleanup, then having a prebranched
 702   // fallthrough implies that the fallthrough source unconditionally
 703   // jumps here.
 704   assert(!Scope.isNormalCleanup() || !HasPrebranchedFallthrough ||
 705          (Scope.getNormalBlock() &&
 706           FallthroughSource->getTerminator()->getSuccessor(0)
 707             == Scope.getNormalBlock()));
 708
 709   bool RequiresNormalCleanup = false;
 710   if (Scope.isNormalCleanup() &&
 711       (HasFixups || HasExistingBranches || HasFallthrough)) {
 712     RequiresNormalCleanup = true;
 713   }
 714
 715   // If we have a prebranched fallthrough into an inactive normal
 716   // cleanup, rewrite it so that it leads to the appropriate place.
 717   if (Scope.isNormalCleanup() && HasPrebranchedFallthrough && !IsActive) {
 718     llvm::BasicBlock *prebranchDest;
 719
 720     // If the prebranch is semantically branching through the next
 721     // cleanup, just forward it to the next block, leaving the
 722     // insertion point in the prebranched block.
 723     if (FallthroughIsBranchThrough) {
 724       EHScope &enclosing = *EHStack.find(Scope.getEnclosingNormalCleanup());
 725       prebranchDest = CreateNormalEntry(*this, cast<EHCleanupScope>(enclosing));
 726
 727     // Otherwise, we need to make a new block.  If the normal cleanup
 728     // isn't being used at all, we could actually reuse the normal
 729     // entry block, but this is simpler, and it avoids conflicts with
 730     // dead optimistic fixup branches.
 731     } else {
 732       prebranchDest = createBasicBlock("forwarded-prebranch");
 733       EmitBlock(prebranchDest);
 734     }
 735
 736     llvm::BasicBlock *normalEntry = Scope.getNormalBlock();
 737     assert(normalEntry && !normalEntry->use_empty());
 738
 739     ForwardPrebranchedFallthrough(FallthroughSource,
 740                                   normalEntry, prebranchDest);
 741   }
 742
 743   // If we don't need the cleanup at all, we're done.
 744   if (!RequiresNormalCleanup && !RequiresEHCleanup) {
 745     destroyOptimisticNormalEntry(*this, Scope);
 746     EHStack.popCleanup(); // safe because there are no fixups
 747     assert(EHStack.getNumBranchFixups() == 0 ||
 748            EHStack.hasNormalCleanups());
 749     return;
 750   }
 751
 752   // Copy the cleanup emission data out.  This uses either a stack
 753   // array or malloc'd memory, depending on the size, which is
 754   // behavior that SmallVector would provide, if we could use it
 755   // here. Unfortunately, if you ask for a SmallVector<char>, the
 756   // alignment isn't sufficient.
 757   auto *CleanupSource = reinterpret_cast<char *>(Scope.getCleanupBuffer());
 758   alignas(EHScopeStack::ScopeStackAlignment) char
 759       CleanupBufferStack[8 * sizeof(void *)];
 760   std::unique_ptr<char[]> CleanupBufferHeap;
 761   size_t CleanupSize = Scope.getCleanupSize();
 762   EHScopeStack::Cleanup *Fn;
 763
 764   if (CleanupSize <= sizeof(CleanupBufferStack)) {
 765     memcpy(CleanupBufferStack, CleanupSource, CleanupSize);
 766     Fn = reinterpret_cast<EHScopeStack::Cleanup *>(CleanupBufferStack);
 767   } else {
 768     CleanupBufferHeap.reset(new char[CleanupSize]);
 769     memcpy(CleanupBufferHeap.get(), CleanupSource, CleanupSize);
 770     Fn = reinterpret_cast<EHScopeStack::Cleanup *>(CleanupBufferHeap.get());
 771   }
 772
 773   EHScopeStack::Cleanup::Flags cleanupFlags;
 774   if (Scope.isNormalCleanup())
 775     cleanupFlags.setIsNormalCleanupKind();
 776   if (Scope.isEHCleanup())
 777     cleanupFlags.setIsEHCleanupKind();
 778
 779   // Under -EHa, invoke seh.scope.end() to mark scope end before dtor
 780   bool IsEHa = getLangOpts().EHAsynch && !Scope.isLifetimeMarker();
 781   const EHPersonality &Personality = EHPersonality::get(*this);
 782   if (!RequiresNormalCleanup) {
 783     // Mark CPP scope end for passed-by-value Arg temp
 784     //   per Windows ABI which is "normally" Cleanup in callee
 785     if (IsEHa && getInvokeDest()) {
 786       if (Personality.isMSVCXXPersonality())
 787         EmitSehCppScopeEnd();
 788     }
 789     destroyOptimisticNormalEntry(*this, Scope);
 790     EHStack.popCleanup();
 791   } else {
 792     // If we have a fallthrough and no other need for the cleanup,
 793     // emit it directly.
 794     if (HasFallthrough && !HasPrebranchedFallthrough && !HasFixups &&
 795         !HasExistingBranches) {
 796
 797       // mark SEH scope end for fall-through flow
 798       if (IsEHa && getInvokeDest()) {
 799         if (Personality.isMSVCXXPersonality())
 800           EmitSehCppScopeEnd();
 801         else
 802           EmitSehTryScopeEnd();
 803       }
 804
 805       destroyOptimisticNormalEntry(*this, Scope);
 806       EHStack.popCleanup();
 807
 808       EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
 809
 810     // Otherwise, the best approach is to thread everything through
 811     // the cleanup block and then try to clean up after ourselves.
 812     } else {
 813       // Force the entry block to exist.
 814       llvm::BasicBlock *NormalEntry = CreateNormalEntry(*this, Scope);
 815
 816       // I.  Set up the fallthrough edge in.
 817
 818       CGBuilderTy::InsertPoint savedInactiveFallthroughIP;
 819
 820       // If there's a fallthrough, we need to store the cleanup
 821       // destination index.  For fall-throughs this is always zero.
 822       if (HasFallthrough) {
 823         if (!HasPrebranchedFallthrough)
 824           Builder.CreateStore(Builder.getInt32(0), getNormalCleanupDestSlot());
 825
 826       // Otherwise, save and clear the IP if we don't have fallthrough
 827       // because the cleanup is inactive.
 828       } else if (FallthroughSource) {
 829         assert(!IsActive && "source without fallthrough for active cleanup");
 830         savedInactiveFallthroughIP = Builder.saveAndClearIP();
 831       }
 832
 833       // II.  Emit the entry block.  This implicitly branches to it if
 834       // we have fallthrough.  All the fixups and existing branches
 835       // should already be branched to it.
 836       EmitBlock(NormalEntry);
 837
 838       // intercept normal cleanup to mark SEH scope end
 839       if (IsEHa) {
 840         if (Personality.isMSVCXXPersonality())
 841           EmitSehCppScopeEnd();
 842         else
 843           EmitSehTryScopeEnd();
 844       }
 845
 846       // III.  Figure out where we're going and build the cleanup
 847       // epilogue.
 848
 849       bool HasEnclosingCleanups =
 850         (Scope.getEnclosingNormalCleanup() != EHStack.stable_end());
 851
 852       // Compute the branch-through dest if we need it:
 853       //   - if there are branch-throughs threaded through the scope
 854       //   - if fall-through is a branch-through
 855       //   - if there are fixups that will be optimistically forwarded
 856       //     to the enclosing cleanup
 857       llvm::BasicBlock *BranchThroughDest = nullptr;
 858       if (Scope.hasBranchThroughs() ||
 859           (FallthroughSource && FallthroughIsBranchThrough) ||
 860           (HasFixups && HasEnclosingCleanups)) {
 861         assert(HasEnclosingCleanups);
 862         EHScope &S = *EHStack.find(Scope.getEnclosingNormalCleanup());
 863         BranchThroughDest = CreateNormalEntry(*this, cast<EHCleanupScope>(S));
 864       }
 865
 866       llvm::BasicBlock *FallthroughDest = nullptr;
 867       SmallVector<llvm::Instruction*, 2> InstsToAppend;
 868
 869       // If there's exactly one branch-after and no other threads,
 870       // we can route it without a switch.
 871       if (!Scope.hasBranchThroughs() && !HasFixups && !HasFallthrough &&
 872           Scope.getNumBranchAfters() == 1) {
 873         assert(!BranchThroughDest || !IsActive);
 874
 875         // Clean up the possibly dead store to the cleanup dest slot.
 876         llvm::Instruction *NormalCleanupDestSlot =
 877             cast<llvm::Instruction>(getNormalCleanupDestSlot().getPointer());
 878         if (NormalCleanupDestSlot->hasOneUse()) {
 879           NormalCleanupDestSlot->user_back()->eraseFromParent();
 880           NormalCleanupDestSlot->eraseFromParent();
 881           NormalCleanupDest = Address::invalid();
 882         }
 883
 884         llvm::BasicBlock *BranchAfter = Scope.getBranchAfterBlock(0);
 885         InstsToAppend.push_back(llvm::BranchInst::Create(BranchAfter));
 886
 887       // Build a switch-out if we need it:
 888       //   - if there are branch-afters threaded through the scope
 889       //   - if fall-through is a branch-after
 890       //   - if there are fixups that have nowhere left to go and
 891       //     so must be immediately resolved
 892       } else if (Scope.getNumBranchAfters() ||
 893                  (HasFallthrough && !FallthroughIsBranchThrough) ||
 894                  (HasFixups && !HasEnclosingCleanups)) {
 895
 896         llvm::BasicBlock *Default =
 897           (BranchThroughDest ? BranchThroughDest : getUnreachableBlock());
 898
 899         // TODO: base this on the number of branch-afters and fixups
 900         const unsigned SwitchCapacity = 10;
 901
 902         // pass the abnormal exit flag to Fn (SEH cleanup)
 903         cleanupFlags.setHasExitSwitch();
 904
 905         llvm::LoadInst *Load =
 906           createLoadInstBefore(getNormalCleanupDestSlot(), "cleanup.dest",
 907                                nullptr);
 908         llvm::SwitchInst *Switch =
 909           llvm::SwitchInst::Create(Load, Default, SwitchCapacity);
 910
 911         InstsToAppend.push_back(Load);
 912         InstsToAppend.push_back(Switch);
 913
 914         // Branch-after fallthrough.
 915         if (FallthroughSource && !FallthroughIsBranchThrough) {
 916           FallthroughDest = createBasicBlock("cleanup.cont");
 917           if (HasFallthrough)
 918             Switch->addCase(Builder.getInt32(0), FallthroughDest);
 919         }
 920
 921         for (unsigned I = 0, E = Scope.getNumBranchAfters(); I != E; ++I) {
 922           Switch->addCase(Scope.getBranchAfterIndex(I),
 923                           Scope.getBranchAfterBlock(I));
 924         }
 925
 926         // If there aren't any enclosing cleanups, we can resolve all
 927         // the fixups now.
 928         if (HasFixups && !HasEnclosingCleanups)
 929           ResolveAllBranchFixups(*this, Switch, NormalEntry);
 930       } else {
 931         // We should always have a branch-through destination in this case.
 932         assert(BranchThroughDest);
 933         InstsToAppend.push_back(llvm::BranchInst::Create(BranchThroughDest));
 934       }
 935
 936       // IV.  Pop the cleanup and emit it.
 937       EHStack.popCleanup();
 938       assert(EHStack.hasNormalCleanups() == HasEnclosingCleanups);
 939
 940       EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
 941
 942       // Append the prepared cleanup prologue from above.
 943       llvm::BasicBlock *NormalExit = Builder.GetInsertBlock();
 944       for (unsigned I = 0, E = InstsToAppend.size(); I != E; ++I)
 945         NormalExit->getInstList().push_back(InstsToAppend[I]);
 946
 947       // Optimistically hope that any fixups will continue falling through.
 948       for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
 949            I < E; ++I) {
 950         BranchFixup &Fixup = EHStack.getBranchFixup(I);
 951         if (!Fixup.Destination) continue;
 952         if (!Fixup.OptimisticBranchBlock) {
 953           createStoreInstBefore(Builder.getInt32(Fixup.DestinationIndex),
 954                                 getNormalCleanupDestSlot(),
 955                                 Fixup.InitialBranch);
 956           Fixup.InitialBranch->setSuccessor(0, NormalEntry);
 957         }
 958         Fixup.OptimisticBranchBlock = NormalExit;
 959       }
 960
 961       // V.  Set up the fallthrough edge out.
 962
 963       // Case 1: a fallthrough source exists but doesn't branch to the
 964       // cleanup because the cleanup is inactive.
 965       if (!HasFallthrough && FallthroughSource) {
 966         // Prebranched fallthrough was forwarded earlier.
 967         // Non-prebranched fallthrough doesn't need to be forwarded.
 968         // Either way, all we need to do is restore the IP we cleared before.
 969         assert(!IsActive);
 970         Builder.restoreIP(savedInactiveFallthroughIP);
 971
 972       // Case 2: a fallthrough source exists and should branch to the
 973       // cleanup, but we're not supposed to branch through to the next
 974       // cleanup.
 975       } else if (HasFallthrough && FallthroughDest) {
 976         assert(!FallthroughIsBranchThrough);
 977         EmitBlock(FallthroughDest);
 978
 979       // Case 3: a fallthrough source exists and should branch to the
 980       // cleanup and then through to the next.
 981       } else if (HasFallthrough) {
 982         // Everything is already set up for this.
 983
 984       // Case 4: no fallthrough source exists.
 985       } else {
 986         Builder.ClearInsertionPoint();
 987       }
 988
 989       // VI.  Assorted cleaning.
 990
 991       // Check whether we can merge NormalEntry into a single predecessor.
 992       // This might invalidate (non-IR) pointers to NormalEntry.
 993       llvm::BasicBlock *NewNormalEntry =
 994         SimplifyCleanupEntry(*this, NormalEntry);
 995
 996       // If it did invalidate those pointers, and NormalEntry was the same
 997       // as NormalExit, go back and patch up the fixups.
 998       if (NewNormalEntry != NormalEntry && NormalEntry == NormalExit)
 999         for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
1000                I < E; ++I)
1001           EHStack.getBranchFixup(I).OptimisticBranchBlock = NewNormalEntry;
1002     }
1003   }
1004
1005   assert(EHStack.hasNormalCleanups() || EHStack.getNumBranchFixups() == 0);
1006
1007   // Emit the EH cleanup if required.
1008   if (RequiresEHCleanup) {
1009     CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
1010
1011     EmitBlock(EHEntry);
1012
1013     llvm::BasicBlock *NextAction = getEHDispatchBlock(EHParent);
1014
1015     // Push a terminate scope or cleanupendpad scope around the potentially
1016     // throwing cleanups. For funclet EH personalities, the cleanupendpad models
1017     // program termination when cleanups throw.
1018     bool PushedTerminate = false;
1019     SaveAndRestore<llvm::Instruction *> RestoreCurrentFuncletPad(
1020         CurrentFuncletPad);
1021     llvm::CleanupPadInst *CPI = nullptr;
1022
1023     const EHPersonality &Personality = EHPersonality::get(*this);
1024     if (Personality.usesFuncletPads()) {
1025       llvm::Value *ParentPad = CurrentFuncletPad;
1026       if (!ParentPad)
1027         ParentPad = llvm::ConstantTokenNone::get(CGM.getLLVMContext());
1028       CurrentFuncletPad = CPI = Builder.CreateCleanupPad(ParentPad);
1029     }
1030
1031     // Non-MSVC personalities need to terminate when an EH cleanup throws.
1032     if (!Personality.isMSVCPersonality()) {
1033       EHStack.pushTerminate();
1034       PushedTerminate = true;
1035     }
1036
1037     // We only actually emit the cleanup code if the cleanup is either
1038     // active or was used before it was deactivated.
1039     if (EHActiveFlag.isValid() || IsActive) {
1040       cleanupFlags.setIsForEHCleanup();
1041       EmitCleanup(*this, Fn, cleanupFlags, EHActiveFlag);
1042     }
1043
1044     if (CPI)
1045       Builder.CreateCleanupRet(CPI, NextAction);
1046     else
1047       Builder.CreateBr(NextAction);
1048
1049     // Leave the terminate scope.
1050     if (PushedTerminate)
1051       EHStack.popTerminate();
1052
1053     Builder.restoreIP(SavedIP);
1054
1055     SimplifyCleanupEntry(*this, EHEntry);
1056   }
1057 }
1058
1059 /// isObviouslyBranchWithoutCleanups - Return true if a branch to the
1060 /// specified destination obviously has no cleanups to run.  'false' is always
1061 /// a conservatively correct answer for this method.
1062 bool CodeGenFunction::isObviouslyBranchWithoutCleanups(JumpDest Dest) const {
1063   assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
1064          && "stale jump destination");
1065
1066   // Calculate the innermost active normal cleanup.
1067   EHScopeStack::stable_iterator TopCleanup =
1068     EHStack.getInnermostActiveNormalCleanup();
1069
1070   // If we're not in an active normal cleanup scope, or if the
1071   // destination scope is within the innermost active normal cleanup
1072   // scope, we don't need to worry about fixups.
1073   if (TopCleanup == EHStack.stable_end() ||
1074       TopCleanup.encloses(Dest.getScopeDepth())) // works for invalid
1075     return true;
1076
1077   // Otherwise, we might need some cleanups.
1078   return false;
1079 }
1080
1081
1082 /// Terminate the current block by emitting a branch which might leave
1083 /// the current cleanup-protected scope.  The target scope may not yet
1084 /// be known, in which case this will require a fixup.
1085 ///
1086 /// As a side-effect, this method clears the insertion point.
1087 void CodeGenFunction::EmitBranchThroughCleanup(JumpDest Dest) {
1088   assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
1089          && "stale jump destination");
1090
1091   if (!HaveInsertPoint())
1092     return;
1093
1094   // Create the branch.
1095   llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock());
1096
1097   // Calculate the innermost active normal cleanup.
1098   EHScopeStack::stable_iterator
1099     TopCleanup = EHStack.getInnermostActiveNormalCleanup();
1100
1101   // If we're not in an active normal cleanup scope, or if the
1102   // destination scope is within the innermost active normal cleanup
1103   // scope, we don't need to worry about fixups.
1104   if (TopCleanup == EHStack.stable_end() ||
1105       TopCleanup.encloses(Dest.getScopeDepth())) { // works for invalid
1106     Builder.ClearInsertionPoint();
1107     return;
1108   }
1109
1110   // If we can't resolve the destination cleanup scope, just add this
1111   // to the current cleanup scope as a branch fixup.
1112   if (!Dest.getScopeDepth().isValid()) {
1113     BranchFixup &Fixup = EHStack.addBranchFixup();
1114     Fixup.Destination = Dest.getBlock();
1115     Fixup.DestinationIndex = Dest.getDestIndex();
1116     Fixup.InitialBranch = BI;
1117     Fixup.OptimisticBranchBlock = nullptr;
1118
1119     Builder.ClearInsertionPoint();
1120     return;
1121   }
1122
1123   // Otherwise, thread through all the normal cleanups in scope.
1124
1125   // Store the index at the start.
1126   llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex());
1127   createStoreInstBefore(Index, getNormalCleanupDestSlot(), BI);
1128
1129   // Adjust BI to point to the first cleanup block.
1130   {
1131     EHCleanupScope &Scope =
1132       cast<EHCleanupScope>(*EHStack.find(TopCleanup));
1133     BI->setSuccessor(0, CreateNormalEntry(*this, Scope));
1134   }
1135
1136   // Add this destination to all the scopes involved.
1137   EHScopeStack::stable_iterator I = TopCleanup;
1138   EHScopeStack::stable_iterator E = Dest.getScopeDepth();
1139   if (E.strictlyEncloses(I)) {
1140     while (true) {
1141       EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(I));
1142       assert(Scope.isNormalCleanup());
1143       I = Scope.getEnclosingNormalCleanup();
1144
1145       // If this is the last cleanup we're propagating through, tell it
1146       // that there's a resolved jump moving through it.
1147       if (!E.strictlyEncloses(I)) {
1148         Scope.addBranchAfter(Index, Dest.getBlock());
1149         break;
1150       }
1151
1152       // Otherwise, tell the scope that there's a jump propagating
1153       // through it.  If this isn't new information, all the rest of
1154       // the work has been done before.
1155       if (!Scope.addBranchThrough(Dest.getBlock()))
1156         break;
1157     }
1158   }
1159
1160   Builder.ClearInsertionPoint();
1161 }
1162
1163 static bool IsUsedAsNormalCleanup(EHScopeStack &EHStack,
1164                                   EHScopeStack::stable_iterator C) {
1165   // If we needed a normal block for any reason, that counts.
1166   if (cast<EHCleanupScope>(*EHStack.find(C)).getNormalBlock())
1167     return true;
1168
1169   // Check whether any enclosed cleanups were needed.
1170   for (EHScopeStack::stable_iterator
1171          I = EHStack.getInnermostNormalCleanup();
1172          I != C; ) {
1173     assert(C.strictlyEncloses(I));
1174     EHCleanupScope &S = cast<EHCleanupScope>(*EHStack.find(I));
1175     if (S.getNormalBlock()) return true;
1176     I = S.getEnclosingNormalCleanup();
1177   }
1178
1179   return false;
1180 }
1181
1182 static bool IsUsedAsEHCleanup(EHScopeStack &EHStack,
1183                               EHScopeStack::stable_iterator cleanup) {
1184   // If we needed an EH block for any reason, that counts.
1185   if (EHStack.find(cleanup)->hasEHBranches())
1186     return true;
1187
1188   // Check whether any enclosed cleanups were needed.
1189   for (EHScopeStack::stable_iterator
1190          i = EHStack.getInnermostEHScope(); i != cleanup; ) {
1191     assert(cleanup.strictlyEncloses(i));
1192
1193     EHScope &scope = *EHStack.find(i);
1194     if (scope.hasEHBranches())
1195       return true;
1196
1197     i = scope.getEnclosingEHScope();
1198   }
1199
1200   return false;
1201 }
1202
1203 enum ForActivation_t {
1204   ForActivation,
1205   ForDeactivation
1206 };
1207
1208 /// The given cleanup block is changing activation state.  Configure a
1209 /// cleanup variable if necessary.
1210 ///
1211 /// It would be good if we had some way of determining if there were
1212 /// extra uses *after* the change-over point.
1213 static void SetupCleanupBlockActivation(CodeGenFunction &CGF,
1214                                         EHScopeStack::stable_iterator C,
1215                                         ForActivation_t kind,
1216                                         llvm::Instruction *dominatingIP) {
1217   EHCleanupScope &Scope = cast<EHCleanupScope>(*CGF.EHStack.find(C));
1218
1219   // We always need the flag if we're activating the cleanup in a
1220   // conditional context, because we have to assume that the current
1221   // location doesn't necessarily dominate the cleanup's code.
1222   bool isActivatedInConditional =
1223     (kind == ForActivation && CGF.isInConditionalBranch());
1224
1225   bool needFlag = false;
1226
1227   // Calculate whether the cleanup was used:
1228
1229   //   - as a normal cleanup
1230   if (Scope.isNormalCleanup() &&
1231       (isActivatedInConditional || IsUsedAsNormalCleanup(CGF.EHStack, C))) {
1232     Scope.setTestFlagInNormalCleanup();
1233     needFlag = true;
1234   }
1235
1236   //  - as an EH cleanup
1237   if (Scope.isEHCleanup() &&
1238       (isActivatedInConditional || IsUsedAsEHCleanup(CGF.EHStack, C))) {
1239     Scope.setTestFlagInEHCleanup();
1240     needFlag = true;
1241   }
1242
1243   // If it hasn't yet been used as either, we're done.
1244   if (!needFlag) return;
1245
1246   Address var = Scope.getActiveFlag();
1247   if (!var.isValid()) {
1248     var = CGF.CreateTempAlloca(CGF.Builder.getInt1Ty(), CharUnits::One(),
1249                                "cleanup.isactive");
1250     Scope.setActiveFlag(var);
1251
1252     assert(dominatingIP && "no existing variable and no dominating IP!");
1253
1254     // Initialize to true or false depending on whether it was
1255     // active up to this point.
1256     llvm::Constant *value = CGF.Builder.getInt1(kind == ForDeactivation);
1257
1258     // If we're in a conditional block, ignore the dominating IP and
1259     // use the outermost conditional branch.
1260     if (CGF.isInConditionalBranch()) {
1261       CGF.setBeforeOutermostConditional(value, var);
1262     } else {
1263       createStoreInstBefore(value, var, dominatingIP);
1264     }
1265   }
1266
1267   CGF.Builder.CreateStore(CGF.Builder.getInt1(kind == ForActivation), var);
1268 }
1269
1270 /// Activate a cleanup that was created in an inactivated state.
1271 void CodeGenFunction::ActivateCleanupBlock(EHScopeStack::stable_iterator C,
1272                                            llvm::Instruction *dominatingIP) {
1273   assert(C != EHStack.stable_end() && "activating bottom of stack?");
1274   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
1275   assert(!Scope.isActive() && "double activation");
1276
1277   SetupCleanupBlockActivation(*this, C, ForActivation, dominatingIP);
1278
1279   Scope.setActive(true);
1280 }
1281
1282 /// Deactive a cleanup that was created in an active state.
1283 void CodeGenFunction::DeactivateCleanupBlock(EHScopeStack::stable_iterator C,
1284                                              llvm::Instruction *dominatingIP) {
1285   assert(C != EHStack.stable_end() && "deactivating bottom of stack?");
1286   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
1287   assert(Scope.isActive() && "double deactivation");
1288
1289   // If it's the top of the stack, just pop it, but do so only if it belongs
1290   // to the current RunCleanupsScope.
1291   if (C == EHStack.stable_begin() &&
1292       CurrentCleanupScopeDepth.strictlyEncloses(C)) {
1293     // Per comment below, checking EHAsynch is not really necessary
1294     // it's there to assure zero-impact w/o EHAsynch option
1295     if (!Scope.isNormalCleanup() && getLangOpts().EHAsynch) {
1296       PopCleanupBlock();
1297     } else {
1298       // If it's a normal cleanup, we need to pretend that the
1299       // fallthrough is unreachable.
1300       CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
1301       PopCleanupBlock();
1302       Builder.restoreIP(SavedIP);
1303     }
1304     return;
1305   }
1306
1307   // Otherwise, follow the general case.
1308   SetupCleanupBlockActivation(*this, C, ForDeactivation, dominatingIP);
1309
1310   Scope.setActive(false);
1311 }
1312
1313 Address CodeGenFunction::getNormalCleanupDestSlot() {
1314   if (!NormalCleanupDest.isValid())
1315     NormalCleanupDest =
1316       CreateDefaultAlignTempAlloca(Builder.getInt32Ty(), "cleanup.dest.slot");
1317   return NormalCleanupDest;
1318 }
1319
1320 /// Emits all the code to cause the given temporary to be cleaned up.
1321 void CodeGenFunction::EmitCXXTemporary(const CXXTemporary *Temporary,
1322                                        QualType TempType,
1323                                        Address Ptr) {
1324   pushDestroy(NormalAndEHCleanup, Ptr, TempType, destroyCXXObject,
1325               /*useEHCleanup*/ true);
1326 }
1327
1328 // Need to set "funclet" in OperandBundle properly for noThrow
1329 //       intrinsic (see CGCall.cpp)
1330 static void EmitSehScope(CodeGenFunction &CGF,
1331                          llvm::FunctionCallee &SehCppScope) {
1332   llvm::BasicBlock *InvokeDest = CGF.getInvokeDest();
1333   assert(CGF.Builder.GetInsertBlock() && InvokeDest);
1334   llvm::BasicBlock *Cont = CGF.createBasicBlock("invoke.cont");
1335   SmallVector<llvm::OperandBundleDef, 1> BundleList =
1336       CGF.getBundlesForFunclet(SehCppScope.getCallee());
1337   if (CGF.CurrentFuncletPad)
1338     BundleList.emplace_back("funclet", CGF.CurrentFuncletPad);
1339   CGF.Builder.CreateInvoke(SehCppScope, Cont, InvokeDest, None, BundleList);
1340   CGF.EmitBlock(Cont);
1341 }
1342
1343 // Invoke a llvm.seh.scope.begin at the beginning of a CPP scope for -EHa
1344 void CodeGenFunction::EmitSehCppScopeBegin() {
1345   assert(getLangOpts().EHAsynch);
1346   llvm::FunctionType *FTy =
1347       llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
1348   llvm::FunctionCallee SehCppScope =
1349       CGM.CreateRuntimeFunction(FTy, "llvm.seh.scope.begin");
1350   EmitSehScope(*this, SehCppScope);
1351 }
1352
1353 // Invoke a llvm.seh.scope.end at the end of a CPP scope for -EHa
1354 //   llvm.seh.scope.end is emitted before popCleanup, so it's "invoked"
1355 void CodeGenFunction::EmitSehCppScopeEnd() {
1356   assert(getLangOpts().EHAsynch);
1357   llvm::FunctionType *FTy =
1358       llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
1359   llvm::FunctionCallee SehCppScope =
1360       CGM.CreateRuntimeFunction(FTy, "llvm.seh.scope.end");
1361   EmitSehScope(*this, SehCppScope);
1362 }
1363
1364 // Invoke a llvm.seh.try.begin at the beginning of a SEH scope for -EHa
1365 void CodeGenFunction::EmitSehTryScopeBegin() {
1366   assert(getLangOpts().EHAsynch);
1367   llvm::FunctionType *FTy =
1368       llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
1369   llvm::FunctionCallee SehCppScope =
1370       CGM.CreateRuntimeFunction(FTy, "llvm.seh.try.begin");
1371   EmitSehScope(*this, SehCppScope);
1372 }
1373
1374 // Invoke a llvm.seh.try.end at the end of a SEH scope for -EHa
1375 void CodeGenFunction::EmitSehTryScopeEnd() {
1376   assert(getLangOpts().EHAsynch);
1377   llvm::FunctionType *FTy =
1378       llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
1379   llvm::FunctionCallee SehCppScope =
1380       CGM.CreateRuntimeFunction(FTy, "llvm.seh.try.end");
1381   EmitSehScope(*this, SehCppScope);
1382 }