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