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