xref: /freebsd/contrib/llvm-project/clang/lib/CodeGen/CGCleanup.cpp (revision 2f513db72b034fd5ef7f080b11be5c711c15186a)
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 IsActive = !(Kind & InactiveCleanup);
183   bool IsLifetimeMarker = Kind & LifetimeMarker;
184   EHCleanupScope *Scope =
185     new (Buffer) EHCleanupScope(IsNormalCleanup,
186                                 IsEHCleanup,
187                                 IsActive,
188                                 Size,
189                                 BranchFixups.size(),
190                                 InnermostNormalCleanup,
191                                 InnermostEHScope);
192   if (IsNormalCleanup)
193     InnermostNormalCleanup = stable_begin();
194   if (IsEHCleanup)
195     InnermostEHScope = stable_begin();
196   if (IsLifetimeMarker)
197     Scope->setLifetimeMarker();
198 
199   return Scope->getCleanupBuffer();
200 }
201 
202 void EHScopeStack::popCleanup() {
203   assert(!empty() && "popping exception stack when not empty");
204 
205   assert(isa<EHCleanupScope>(*begin()));
206   EHCleanupScope &Cleanup = cast<EHCleanupScope>(*begin());
207   InnermostNormalCleanup = Cleanup.getEnclosingNormalCleanup();
208   InnermostEHScope = Cleanup.getEnclosingEHScope();
209   deallocate(Cleanup.getAllocatedSize());
210 
211   // Destroy the cleanup.
212   Cleanup.Destroy();
213 
214   // Check whether we can shrink the branch-fixups stack.
215   if (!BranchFixups.empty()) {
216     // If we no longer have any normal cleanups, all the fixups are
217     // complete.
218     if (!hasNormalCleanups())
219       BranchFixups.clear();
220 
221     // Otherwise we can still trim out unnecessary nulls.
222     else
223       popNullFixups();
224   }
225 }
226 
227 EHFilterScope *EHScopeStack::pushFilter(unsigned numFilters) {
228   assert(getInnermostEHScope() == stable_end());
229   char *buffer = allocate(EHFilterScope::getSizeForNumFilters(numFilters));
230   EHFilterScope *filter = new (buffer) EHFilterScope(numFilters);
231   InnermostEHScope = stable_begin();
232   return filter;
233 }
234 
235 void EHScopeStack::popFilter() {
236   assert(!empty() && "popping exception stack when not empty");
237 
238   EHFilterScope &filter = cast<EHFilterScope>(*begin());
239   deallocate(EHFilterScope::getSizeForNumFilters(filter.getNumFilters()));
240 
241   InnermostEHScope = filter.getEnclosingEHScope();
242 }
243 
244 EHCatchScope *EHScopeStack::pushCatch(unsigned numHandlers) {
245   char *buffer = allocate(EHCatchScope::getSizeForNumHandlers(numHandlers));
246   EHCatchScope *scope =
247     new (buffer) EHCatchScope(numHandlers, InnermostEHScope);
248   InnermostEHScope = stable_begin();
249   return scope;
250 }
251 
252 void EHScopeStack::pushTerminate() {
253   char *Buffer = allocate(EHTerminateScope::getSize());
254   new (Buffer) EHTerminateScope(InnermostEHScope);
255   InnermostEHScope = stable_begin();
256 }
257 
258 /// Remove any 'null' fixups on the stack.  However, we can't pop more
259 /// fixups than the fixup depth on the innermost normal cleanup, or
260 /// else fixups that we try to add to that cleanup will end up in the
261 /// wrong place.  We *could* try to shrink fixup depths, but that's
262 /// actually a lot of work for little benefit.
263 void EHScopeStack::popNullFixups() {
264   // We expect this to only be called when there's still an innermost
265   // normal cleanup;  otherwise there really shouldn't be any fixups.
266   assert(hasNormalCleanups());
267 
268   EHScopeStack::iterator it = find(InnermostNormalCleanup);
269   unsigned MinSize = cast<EHCleanupScope>(*it).getFixupDepth();
270   assert(BranchFixups.size() >= MinSize && "fixup stack out of order");
271 
272   while (BranchFixups.size() > MinSize &&
273          BranchFixups.back().Destination == nullptr)
274     BranchFixups.pop_back();
275 }
276 
277 Address CodeGenFunction::createCleanupActiveFlag() {
278   // Create a variable to decide whether the cleanup needs to be run.
279   Address active = CreateTempAllocaWithoutCast(
280       Builder.getInt1Ty(), CharUnits::One(), "cleanup.cond");
281 
282   // Initialize it to false at a site that's guaranteed to be run
283   // before each evaluation.
284   setBeforeOutermostConditional(Builder.getFalse(), active);
285 
286   // Initialize it to true at the current location.
287   Builder.CreateStore(Builder.getTrue(), active);
288 
289   return active;
290 }
291 
292 void CodeGenFunction::initFullExprCleanupWithFlag(Address ActiveFlag) {
293   // Set that as the active flag in the cleanup.
294   EHCleanupScope &cleanup = cast<EHCleanupScope>(*EHStack.begin());
295   assert(!cleanup.hasActiveFlag() && "cleanup already has active flag?");
296   cleanup.setActiveFlag(ActiveFlag);
297 
298   if (cleanup.isNormalCleanup()) cleanup.setTestFlagInNormalCleanup();
299   if (cleanup.isEHCleanup()) cleanup.setTestFlagInEHCleanup();
300 }
301 
302 void EHScopeStack::Cleanup::anchor() {}
303 
304 static void createStoreInstBefore(llvm::Value *value, Address addr,
305                                   llvm::Instruction *beforeInst) {
306   auto store = new llvm::StoreInst(value, addr.getPointer(), beforeInst);
307   store->setAlignment(addr.getAlignment().getQuantity());
308 }
309 
310 static llvm::LoadInst *createLoadInstBefore(Address addr, const Twine &name,
311                                             llvm::Instruction *beforeInst) {
312   auto load = new llvm::LoadInst(addr.getPointer(), name, beforeInst);
313   load->setAlignment(addr.getAlignment().getQuantity());
314   return load;
315 }
316 
317 /// All the branch fixups on the EH stack have propagated out past the
318 /// outermost normal cleanup; resolve them all by adding cases to the
319 /// given switch instruction.
320 static void ResolveAllBranchFixups(CodeGenFunction &CGF,
321                                    llvm::SwitchInst *Switch,
322                                    llvm::BasicBlock *CleanupEntry) {
323   llvm::SmallPtrSet<llvm::BasicBlock*, 4> CasesAdded;
324 
325   for (unsigned I = 0, E = CGF.EHStack.getNumBranchFixups(); I != E; ++I) {
326     // Skip this fixup if its destination isn't set.
327     BranchFixup &Fixup = CGF.EHStack.getBranchFixup(I);
328     if (Fixup.Destination == nullptr) continue;
329 
330     // If there isn't an OptimisticBranchBlock, then InitialBranch is
331     // still pointing directly to its destination; forward it to the
332     // appropriate cleanup entry.  This is required in the specific
333     // case of
334     //   { std::string s; goto lbl; }
335     //   lbl:
336     // i.e. where there's an unresolved fixup inside a single cleanup
337     // entry which we're currently popping.
338     if (Fixup.OptimisticBranchBlock == nullptr) {
339       createStoreInstBefore(CGF.Builder.getInt32(Fixup.DestinationIndex),
340                             CGF.getNormalCleanupDestSlot(),
341                             Fixup.InitialBranch);
342       Fixup.InitialBranch->setSuccessor(0, CleanupEntry);
343     }
344 
345     // Don't add this case to the switch statement twice.
346     if (!CasesAdded.insert(Fixup.Destination).second)
347       continue;
348 
349     Switch->addCase(CGF.Builder.getInt32(Fixup.DestinationIndex),
350                     Fixup.Destination);
351   }
352 
353   CGF.EHStack.clearFixups();
354 }
355 
356 /// Transitions the terminator of the given exit-block of a cleanup to
357 /// be a cleanup switch.
358 static llvm::SwitchInst *TransitionToCleanupSwitch(CodeGenFunction &CGF,
359                                                    llvm::BasicBlock *Block) {
360   // If it's a branch, turn it into a switch whose default
361   // destination is its original target.
362   llvm::Instruction *Term = Block->getTerminator();
363   assert(Term && "can't transition block without terminator");
364 
365   if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
366     assert(Br->isUnconditional());
367     auto Load = createLoadInstBefore(CGF.getNormalCleanupDestSlot(),
368                                      "cleanup.dest", Term);
369     llvm::SwitchInst *Switch =
370       llvm::SwitchInst::Create(Load, Br->getSuccessor(0), 4, Block);
371     Br->eraseFromParent();
372     return Switch;
373   } else {
374     return cast<llvm::SwitchInst>(Term);
375   }
376 }
377 
378 void CodeGenFunction::ResolveBranchFixups(llvm::BasicBlock *Block) {
379   assert(Block && "resolving a null target block");
380   if (!EHStack.getNumBranchFixups()) return;
381 
382   assert(EHStack.hasNormalCleanups() &&
383          "branch fixups exist with no normal cleanups on stack");
384 
385   llvm::SmallPtrSet<llvm::BasicBlock*, 4> ModifiedOptimisticBlocks;
386   bool ResolvedAny = false;
387 
388   for (unsigned I = 0, E = EHStack.getNumBranchFixups(); I != E; ++I) {
389     // Skip this fixup if its destination doesn't match.
390     BranchFixup &Fixup = EHStack.getBranchFixup(I);
391     if (Fixup.Destination != Block) continue;
392 
393     Fixup.Destination = nullptr;
394     ResolvedAny = true;
395 
396     // If it doesn't have an optimistic branch block, LatestBranch is
397     // already pointing to the right place.
398     llvm::BasicBlock *BranchBB = Fixup.OptimisticBranchBlock;
399     if (!BranchBB)
400       continue;
401 
402     // Don't process the same optimistic branch block twice.
403     if (!ModifiedOptimisticBlocks.insert(BranchBB).second)
404       continue;
405 
406     llvm::SwitchInst *Switch = TransitionToCleanupSwitch(*this, BranchBB);
407 
408     // Add a case to the switch.
409     Switch->addCase(Builder.getInt32(Fixup.DestinationIndex), Block);
410   }
411 
412   if (ResolvedAny)
413     EHStack.popNullFixups();
414 }
415 
416 /// Pops cleanup blocks until the given savepoint is reached.
417 void CodeGenFunction::PopCleanupBlocks(
418     EHScopeStack::stable_iterator Old,
419     std::initializer_list<llvm::Value **> ValuesToReload) {
420   assert(Old.isValid());
421 
422   bool HadBranches = false;
423   while (EHStack.stable_begin() != Old) {
424     EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
425     HadBranches |= Scope.hasBranches();
426 
427     // As long as Old strictly encloses the scope's enclosing normal
428     // cleanup, we're going to emit another normal cleanup which
429     // fallthrough can propagate through.
430     bool FallThroughIsBranchThrough =
431       Old.strictlyEncloses(Scope.getEnclosingNormalCleanup());
432 
433     PopCleanupBlock(FallThroughIsBranchThrough);
434   }
435 
436   // If we didn't have any branches, the insertion point before cleanups must
437   // dominate the current insertion point and we don't need to reload any
438   // values.
439   if (!HadBranches)
440     return;
441 
442   // Spill and reload all values that the caller wants to be live at the current
443   // insertion point.
444   for (llvm::Value **ReloadedValue : ValuesToReload) {
445     auto *Inst = dyn_cast_or_null<llvm::Instruction>(*ReloadedValue);
446     if (!Inst)
447       continue;
448 
449     // Don't spill static allocas, they dominate all cleanups. These are created
450     // by binding a reference to a local variable or temporary.
451     auto *AI = dyn_cast<llvm::AllocaInst>(Inst);
452     if (AI && AI->isStaticAlloca())
453       continue;
454 
455     Address Tmp =
456         CreateDefaultAlignTempAlloca(Inst->getType(), "tmp.exprcleanup");
457 
458     // Find an insertion point after Inst and spill it to the temporary.
459     llvm::BasicBlock::iterator InsertBefore;
460     if (auto *Invoke = dyn_cast<llvm::InvokeInst>(Inst))
461       InsertBefore = Invoke->getNormalDest()->getFirstInsertionPt();
462     else
463       InsertBefore = std::next(Inst->getIterator());
464     CGBuilderTy(CGM, &*InsertBefore).CreateStore(Inst, Tmp);
465 
466     // Reload the value at the current insertion point.
467     *ReloadedValue = Builder.CreateLoad(Tmp);
468   }
469 }
470 
471 /// Pops cleanup blocks until the given savepoint is reached, then add the
472 /// cleanups from the given savepoint in the lifetime-extended cleanups stack.
473 void CodeGenFunction::PopCleanupBlocks(
474     EHScopeStack::stable_iterator Old, size_t OldLifetimeExtendedSize,
475     std::initializer_list<llvm::Value **> ValuesToReload) {
476   PopCleanupBlocks(Old, ValuesToReload);
477 
478   // Move our deferred cleanups onto the EH stack.
479   for (size_t I = OldLifetimeExtendedSize,
480               E = LifetimeExtendedCleanupStack.size(); I != E; /**/) {
481     // Alignment should be guaranteed by the vptrs in the individual cleanups.
482     assert((I % alignof(LifetimeExtendedCleanupHeader) == 0) &&
483            "misaligned cleanup stack entry");
484 
485     LifetimeExtendedCleanupHeader &Header =
486         reinterpret_cast<LifetimeExtendedCleanupHeader&>(
487             LifetimeExtendedCleanupStack[I]);
488     I += sizeof(Header);
489 
490     EHStack.pushCopyOfCleanup(Header.getKind(),
491                               &LifetimeExtendedCleanupStack[I],
492                               Header.getSize());
493     I += Header.getSize();
494 
495     if (Header.isConditional()) {
496       Address ActiveFlag =
497           reinterpret_cast<Address &>(LifetimeExtendedCleanupStack[I]);
498       initFullExprCleanupWithFlag(ActiveFlag);
499       I += sizeof(ActiveFlag);
500     }
501   }
502   LifetimeExtendedCleanupStack.resize(OldLifetimeExtendedSize);
503 }
504 
505 static llvm::BasicBlock *CreateNormalEntry(CodeGenFunction &CGF,
506                                            EHCleanupScope &Scope) {
507   assert(Scope.isNormalCleanup());
508   llvm::BasicBlock *Entry = Scope.getNormalBlock();
509   if (!Entry) {
510     Entry = CGF.createBasicBlock("cleanup");
511     Scope.setNormalBlock(Entry);
512   }
513   return Entry;
514 }
515 
516 /// Attempts to reduce a cleanup's entry block to a fallthrough.  This
517 /// is basically llvm::MergeBlockIntoPredecessor, except
518 /// simplified/optimized for the tighter constraints on cleanup blocks.
519 ///
520 /// Returns the new block, whatever it is.
521 static llvm::BasicBlock *SimplifyCleanupEntry(CodeGenFunction &CGF,
522                                               llvm::BasicBlock *Entry) {
523   llvm::BasicBlock *Pred = Entry->getSinglePredecessor();
524   if (!Pred) return Entry;
525 
526   llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Pred->getTerminator());
527   if (!Br || Br->isConditional()) return Entry;
528   assert(Br->getSuccessor(0) == Entry);
529 
530   // If we were previously inserting at the end of the cleanup entry
531   // block, we'll need to continue inserting at the end of the
532   // predecessor.
533   bool WasInsertBlock = CGF.Builder.GetInsertBlock() == Entry;
534   assert(!WasInsertBlock || CGF.Builder.GetInsertPoint() == Entry->end());
535 
536   // Kill the branch.
537   Br->eraseFromParent();
538 
539   // Replace all uses of the entry with the predecessor, in case there
540   // are phis in the cleanup.
541   Entry->replaceAllUsesWith(Pred);
542 
543   // Merge the blocks.
544   Pred->getInstList().splice(Pred->end(), Entry->getInstList());
545 
546   // Kill the entry block.
547   Entry->eraseFromParent();
548 
549   if (WasInsertBlock)
550     CGF.Builder.SetInsertPoint(Pred);
551 
552   return Pred;
553 }
554 
555 static void EmitCleanup(CodeGenFunction &CGF,
556                         EHScopeStack::Cleanup *Fn,
557                         EHScopeStack::Cleanup::Flags flags,
558                         Address ActiveFlag) {
559   // If there's an active flag, load it and skip the cleanup if it's
560   // false.
561   llvm::BasicBlock *ContBB = nullptr;
562   if (ActiveFlag.isValid()) {
563     ContBB = CGF.createBasicBlock("cleanup.done");
564     llvm::BasicBlock *CleanupBB = CGF.createBasicBlock("cleanup.action");
565     llvm::Value *IsActive
566       = CGF.Builder.CreateLoad(ActiveFlag, "cleanup.is_active");
567     CGF.Builder.CreateCondBr(IsActive, CleanupBB, ContBB);
568     CGF.EmitBlock(CleanupBB);
569   }
570 
571   // Ask the cleanup to emit itself.
572   Fn->Emit(CGF, flags);
573   assert(CGF.HaveInsertPoint() && "cleanup ended with no insertion point?");
574 
575   // Emit the continuation block if there was an active flag.
576   if (ActiveFlag.isValid())
577     CGF.EmitBlock(ContBB);
578 }
579 
580 static void ForwardPrebranchedFallthrough(llvm::BasicBlock *Exit,
581                                           llvm::BasicBlock *From,
582                                           llvm::BasicBlock *To) {
583   // Exit is the exit block of a cleanup, so it always terminates in
584   // an unconditional branch or a switch.
585   llvm::Instruction *Term = Exit->getTerminator();
586 
587   if (llvm::BranchInst *Br = dyn_cast<llvm::BranchInst>(Term)) {
588     assert(Br->isUnconditional() && Br->getSuccessor(0) == From);
589     Br->setSuccessor(0, To);
590   } else {
591     llvm::SwitchInst *Switch = cast<llvm::SwitchInst>(Term);
592     for (unsigned I = 0, E = Switch->getNumSuccessors(); I != E; ++I)
593       if (Switch->getSuccessor(I) == From)
594         Switch->setSuccessor(I, To);
595   }
596 }
597 
598 /// We don't need a normal entry block for the given cleanup.
599 /// Optimistic fixup branches can cause these blocks to come into
600 /// existence anyway;  if so, destroy it.
601 ///
602 /// The validity of this transformation is very much specific to the
603 /// exact ways in which we form branches to cleanup entries.
604 static void destroyOptimisticNormalEntry(CodeGenFunction &CGF,
605                                          EHCleanupScope &scope) {
606   llvm::BasicBlock *entry = scope.getNormalBlock();
607   if (!entry) return;
608 
609   // Replace all the uses with unreachable.
610   llvm::BasicBlock *unreachableBB = CGF.getUnreachableBlock();
611   for (llvm::BasicBlock::use_iterator
612          i = entry->use_begin(), e = entry->use_end(); i != e; ) {
613     llvm::Use &use = *i;
614     ++i;
615 
616     use.set(unreachableBB);
617 
618     // The only uses should be fixup switches.
619     llvm::SwitchInst *si = cast<llvm::SwitchInst>(use.getUser());
620     if (si->getNumCases() == 1 && si->getDefaultDest() == unreachableBB) {
621       // Replace the switch with a branch.
622       llvm::BranchInst::Create(si->case_begin()->getCaseSuccessor(), si);
623 
624       // The switch operand is a load from the cleanup-dest alloca.
625       llvm::LoadInst *condition = cast<llvm::LoadInst>(si->getCondition());
626 
627       // Destroy the switch.
628       si->eraseFromParent();
629 
630       // Destroy the load.
631       assert(condition->getOperand(0) == CGF.NormalCleanupDest.getPointer());
632       assert(condition->use_empty());
633       condition->eraseFromParent();
634     }
635   }
636 
637   assert(entry->use_empty());
638   delete entry;
639 }
640 
641 /// Pops a cleanup block.  If the block includes a normal cleanup, the
642 /// current insertion point is threaded through the cleanup, as are
643 /// any branch fixups on the cleanup.
644 void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
645   assert(!EHStack.empty() && "cleanup stack is empty!");
646   assert(isa<EHCleanupScope>(*EHStack.begin()) && "top not a cleanup!");
647   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
648   assert(Scope.getFixupDepth() <= EHStack.getNumBranchFixups());
649 
650   // Remember activation information.
651   bool IsActive = Scope.isActive();
652   Address NormalActiveFlag =
653     Scope.shouldTestFlagInNormalCleanup() ? Scope.getActiveFlag()
654                                           : Address::invalid();
655   Address EHActiveFlag =
656     Scope.shouldTestFlagInEHCleanup() ? Scope.getActiveFlag()
657                                       : Address::invalid();
658 
659   // Check whether we need an EH cleanup.  This is only true if we've
660   // generated a lazy EH cleanup block.
661   llvm::BasicBlock *EHEntry = Scope.getCachedEHDispatchBlock();
662   assert(Scope.hasEHBranches() == (EHEntry != nullptr));
663   bool RequiresEHCleanup = (EHEntry != nullptr);
664   EHScopeStack::stable_iterator EHParent = Scope.getEnclosingEHScope();
665 
666   // Check the three conditions which might require a normal cleanup:
667 
668   // - whether there are branch fix-ups through this cleanup
669   unsigned FixupDepth = Scope.getFixupDepth();
670   bool HasFixups = EHStack.getNumBranchFixups() != FixupDepth;
671 
672   // - whether there are branch-throughs or branch-afters
673   bool HasExistingBranches = Scope.hasBranches();
674 
675   // - whether there's a fallthrough
676   llvm::BasicBlock *FallthroughSource = Builder.GetInsertBlock();
677   bool HasFallthrough = (FallthroughSource != nullptr && IsActive);
678 
679   // Branch-through fall-throughs leave the insertion point set to the
680   // end of the last cleanup, which points to the current scope.  The
681   // rest of IR gen doesn't need to worry about this; it only happens
682   // during the execution of PopCleanupBlocks().
683   bool HasPrebranchedFallthrough =
684     (FallthroughSource && FallthroughSource->getTerminator());
685 
686   // If this is a normal cleanup, then having a prebranched
687   // fallthrough implies that the fallthrough source unconditionally
688   // jumps here.
689   assert(!Scope.isNormalCleanup() || !HasPrebranchedFallthrough ||
690          (Scope.getNormalBlock() &&
691           FallthroughSource->getTerminator()->getSuccessor(0)
692             == Scope.getNormalBlock()));
693 
694   bool RequiresNormalCleanup = false;
695   if (Scope.isNormalCleanup() &&
696       (HasFixups || HasExistingBranches || HasFallthrough)) {
697     RequiresNormalCleanup = true;
698   }
699 
700   // If we have a prebranched fallthrough into an inactive normal
701   // cleanup, rewrite it so that it leads to the appropriate place.
702   if (Scope.isNormalCleanup() && HasPrebranchedFallthrough && !IsActive) {
703     llvm::BasicBlock *prebranchDest;
704 
705     // If the prebranch is semantically branching through the next
706     // cleanup, just forward it to the next block, leaving the
707     // insertion point in the prebranched block.
708     if (FallthroughIsBranchThrough) {
709       EHScope &enclosing = *EHStack.find(Scope.getEnclosingNormalCleanup());
710       prebranchDest = CreateNormalEntry(*this, cast<EHCleanupScope>(enclosing));
711 
712     // Otherwise, we need to make a new block.  If the normal cleanup
713     // isn't being used at all, we could actually reuse the normal
714     // entry block, but this is simpler, and it avoids conflicts with
715     // dead optimistic fixup branches.
716     } else {
717       prebranchDest = createBasicBlock("forwarded-prebranch");
718       EmitBlock(prebranchDest);
719     }
720 
721     llvm::BasicBlock *normalEntry = Scope.getNormalBlock();
722     assert(normalEntry && !normalEntry->use_empty());
723 
724     ForwardPrebranchedFallthrough(FallthroughSource,
725                                   normalEntry, prebranchDest);
726   }
727 
728   // If we don't need the cleanup at all, we're done.
729   if (!RequiresNormalCleanup && !RequiresEHCleanup) {
730     destroyOptimisticNormalEntry(*this, Scope);
731     EHStack.popCleanup(); // safe because there are no fixups
732     assert(EHStack.getNumBranchFixups() == 0 ||
733            EHStack.hasNormalCleanups());
734     return;
735   }
736 
737   // Copy the cleanup emission data out.  This uses either a stack
738   // array or malloc'd memory, depending on the size, which is
739   // behavior that SmallVector would provide, if we could use it
740   // here. Unfortunately, if you ask for a SmallVector<char>, the
741   // alignment isn't sufficient.
742   auto *CleanupSource = reinterpret_cast<char *>(Scope.getCleanupBuffer());
743   llvm::AlignedCharArray<EHScopeStack::ScopeStackAlignment, 8 * sizeof(void *)> CleanupBufferStack;
744   std::unique_ptr<char[]> CleanupBufferHeap;
745   size_t CleanupSize = Scope.getCleanupSize();
746   EHScopeStack::Cleanup *Fn;
747 
748   if (CleanupSize <= sizeof(CleanupBufferStack)) {
749     memcpy(CleanupBufferStack.buffer, CleanupSource, CleanupSize);
750     Fn = reinterpret_cast<EHScopeStack::Cleanup *>(CleanupBufferStack.buffer);
751   } else {
752     CleanupBufferHeap.reset(new char[CleanupSize]);
753     memcpy(CleanupBufferHeap.get(), CleanupSource, CleanupSize);
754     Fn = reinterpret_cast<EHScopeStack::Cleanup *>(CleanupBufferHeap.get());
755   }
756 
757   EHScopeStack::Cleanup::Flags cleanupFlags;
758   if (Scope.isNormalCleanup())
759     cleanupFlags.setIsNormalCleanupKind();
760   if (Scope.isEHCleanup())
761     cleanupFlags.setIsEHCleanupKind();
762 
763   if (!RequiresNormalCleanup) {
764     destroyOptimisticNormalEntry(*this, Scope);
765     EHStack.popCleanup();
766   } else {
767     // If we have a fallthrough and no other need for the cleanup,
768     // emit it directly.
769     if (HasFallthrough && !HasPrebranchedFallthrough &&
770         !HasFixups && !HasExistingBranches) {
771 
772       destroyOptimisticNormalEntry(*this, Scope);
773       EHStack.popCleanup();
774 
775       EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
776 
777     // Otherwise, the best approach is to thread everything through
778     // the cleanup block and then try to clean up after ourselves.
779     } else {
780       // Force the entry block to exist.
781       llvm::BasicBlock *NormalEntry = CreateNormalEntry(*this, Scope);
782 
783       // I.  Set up the fallthrough edge in.
784 
785       CGBuilderTy::InsertPoint savedInactiveFallthroughIP;
786 
787       // If there's a fallthrough, we need to store the cleanup
788       // destination index.  For fall-throughs this is always zero.
789       if (HasFallthrough) {
790         if (!HasPrebranchedFallthrough)
791           Builder.CreateStore(Builder.getInt32(0), getNormalCleanupDestSlot());
792 
793       // Otherwise, save and clear the IP if we don't have fallthrough
794       // because the cleanup is inactive.
795       } else if (FallthroughSource) {
796         assert(!IsActive && "source without fallthrough for active cleanup");
797         savedInactiveFallthroughIP = Builder.saveAndClearIP();
798       }
799 
800       // II.  Emit the entry block.  This implicitly branches to it if
801       // we have fallthrough.  All the fixups and existing branches
802       // should already be branched to it.
803       EmitBlock(NormalEntry);
804 
805       // III.  Figure out where we're going and build the cleanup
806       // epilogue.
807 
808       bool HasEnclosingCleanups =
809         (Scope.getEnclosingNormalCleanup() != EHStack.stable_end());
810 
811       // Compute the branch-through dest if we need it:
812       //   - if there are branch-throughs threaded through the scope
813       //   - if fall-through is a branch-through
814       //   - if there are fixups that will be optimistically forwarded
815       //     to the enclosing cleanup
816       llvm::BasicBlock *BranchThroughDest = nullptr;
817       if (Scope.hasBranchThroughs() ||
818           (FallthroughSource && FallthroughIsBranchThrough) ||
819           (HasFixups && HasEnclosingCleanups)) {
820         assert(HasEnclosingCleanups);
821         EHScope &S = *EHStack.find(Scope.getEnclosingNormalCleanup());
822         BranchThroughDest = CreateNormalEntry(*this, cast<EHCleanupScope>(S));
823       }
824 
825       llvm::BasicBlock *FallthroughDest = nullptr;
826       SmallVector<llvm::Instruction*, 2> InstsToAppend;
827 
828       // If there's exactly one branch-after and no other threads,
829       // we can route it without a switch.
830       if (!Scope.hasBranchThroughs() && !HasFixups && !HasFallthrough &&
831           Scope.getNumBranchAfters() == 1) {
832         assert(!BranchThroughDest || !IsActive);
833 
834         // Clean up the possibly dead store to the cleanup dest slot.
835         llvm::Instruction *NormalCleanupDestSlot =
836             cast<llvm::Instruction>(getNormalCleanupDestSlot().getPointer());
837         if (NormalCleanupDestSlot->hasOneUse()) {
838           NormalCleanupDestSlot->user_back()->eraseFromParent();
839           NormalCleanupDestSlot->eraseFromParent();
840           NormalCleanupDest = Address::invalid();
841         }
842 
843         llvm::BasicBlock *BranchAfter = Scope.getBranchAfterBlock(0);
844         InstsToAppend.push_back(llvm::BranchInst::Create(BranchAfter));
845 
846       // Build a switch-out if we need it:
847       //   - if there are branch-afters threaded through the scope
848       //   - if fall-through is a branch-after
849       //   - if there are fixups that have nowhere left to go and
850       //     so must be immediately resolved
851       } else if (Scope.getNumBranchAfters() ||
852                  (HasFallthrough && !FallthroughIsBranchThrough) ||
853                  (HasFixups && !HasEnclosingCleanups)) {
854 
855         llvm::BasicBlock *Default =
856           (BranchThroughDest ? BranchThroughDest : getUnreachableBlock());
857 
858         // TODO: base this on the number of branch-afters and fixups
859         const unsigned SwitchCapacity = 10;
860 
861         llvm::LoadInst *Load =
862           createLoadInstBefore(getNormalCleanupDestSlot(), "cleanup.dest",
863                                nullptr);
864         llvm::SwitchInst *Switch =
865           llvm::SwitchInst::Create(Load, Default, SwitchCapacity);
866 
867         InstsToAppend.push_back(Load);
868         InstsToAppend.push_back(Switch);
869 
870         // Branch-after fallthrough.
871         if (FallthroughSource && !FallthroughIsBranchThrough) {
872           FallthroughDest = createBasicBlock("cleanup.cont");
873           if (HasFallthrough)
874             Switch->addCase(Builder.getInt32(0), FallthroughDest);
875         }
876 
877         for (unsigned I = 0, E = Scope.getNumBranchAfters(); I != E; ++I) {
878           Switch->addCase(Scope.getBranchAfterIndex(I),
879                           Scope.getBranchAfterBlock(I));
880         }
881 
882         // If there aren't any enclosing cleanups, we can resolve all
883         // the fixups now.
884         if (HasFixups && !HasEnclosingCleanups)
885           ResolveAllBranchFixups(*this, Switch, NormalEntry);
886       } else {
887         // We should always have a branch-through destination in this case.
888         assert(BranchThroughDest);
889         InstsToAppend.push_back(llvm::BranchInst::Create(BranchThroughDest));
890       }
891 
892       // IV.  Pop the cleanup and emit it.
893       EHStack.popCleanup();
894       assert(EHStack.hasNormalCleanups() == HasEnclosingCleanups);
895 
896       EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
897 
898       // Append the prepared cleanup prologue from above.
899       llvm::BasicBlock *NormalExit = Builder.GetInsertBlock();
900       for (unsigned I = 0, E = InstsToAppend.size(); I != E; ++I)
901         NormalExit->getInstList().push_back(InstsToAppend[I]);
902 
903       // Optimistically hope that any fixups will continue falling through.
904       for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
905            I < E; ++I) {
906         BranchFixup &Fixup = EHStack.getBranchFixup(I);
907         if (!Fixup.Destination) continue;
908         if (!Fixup.OptimisticBranchBlock) {
909           createStoreInstBefore(Builder.getInt32(Fixup.DestinationIndex),
910                                 getNormalCleanupDestSlot(),
911                                 Fixup.InitialBranch);
912           Fixup.InitialBranch->setSuccessor(0, NormalEntry);
913         }
914         Fixup.OptimisticBranchBlock = NormalExit;
915       }
916 
917       // V.  Set up the fallthrough edge out.
918 
919       // Case 1: a fallthrough source exists but doesn't branch to the
920       // cleanup because the cleanup is inactive.
921       if (!HasFallthrough && FallthroughSource) {
922         // Prebranched fallthrough was forwarded earlier.
923         // Non-prebranched fallthrough doesn't need to be forwarded.
924         // Either way, all we need to do is restore the IP we cleared before.
925         assert(!IsActive);
926         Builder.restoreIP(savedInactiveFallthroughIP);
927 
928       // Case 2: a fallthrough source exists and should branch to the
929       // cleanup, but we're not supposed to branch through to the next
930       // cleanup.
931       } else if (HasFallthrough && FallthroughDest) {
932         assert(!FallthroughIsBranchThrough);
933         EmitBlock(FallthroughDest);
934 
935       // Case 3: a fallthrough source exists and should branch to the
936       // cleanup and then through to the next.
937       } else if (HasFallthrough) {
938         // Everything is already set up for this.
939 
940       // Case 4: no fallthrough source exists.
941       } else {
942         Builder.ClearInsertionPoint();
943       }
944 
945       // VI.  Assorted cleaning.
946 
947       // Check whether we can merge NormalEntry into a single predecessor.
948       // This might invalidate (non-IR) pointers to NormalEntry.
949       llvm::BasicBlock *NewNormalEntry =
950         SimplifyCleanupEntry(*this, NormalEntry);
951 
952       // If it did invalidate those pointers, and NormalEntry was the same
953       // as NormalExit, go back and patch up the fixups.
954       if (NewNormalEntry != NormalEntry && NormalEntry == NormalExit)
955         for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
956                I < E; ++I)
957           EHStack.getBranchFixup(I).OptimisticBranchBlock = NewNormalEntry;
958     }
959   }
960 
961   assert(EHStack.hasNormalCleanups() || EHStack.getNumBranchFixups() == 0);
962 
963   // Emit the EH cleanup if required.
964   if (RequiresEHCleanup) {
965     CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
966 
967     EmitBlock(EHEntry);
968 
969     llvm::BasicBlock *NextAction = getEHDispatchBlock(EHParent);
970 
971     // Push a terminate scope or cleanupendpad scope around the potentially
972     // throwing cleanups. For funclet EH personalities, the cleanupendpad models
973     // program termination when cleanups throw.
974     bool PushedTerminate = false;
975     SaveAndRestore<llvm::Instruction *> RestoreCurrentFuncletPad(
976         CurrentFuncletPad);
977     llvm::CleanupPadInst *CPI = nullptr;
978 
979     const EHPersonality &Personality = EHPersonality::get(*this);
980     if (Personality.usesFuncletPads()) {
981       llvm::Value *ParentPad = CurrentFuncletPad;
982       if (!ParentPad)
983         ParentPad = llvm::ConstantTokenNone::get(CGM.getLLVMContext());
984       CurrentFuncletPad = CPI = Builder.CreateCleanupPad(ParentPad);
985     }
986 
987     // Non-MSVC personalities need to terminate when an EH cleanup throws.
988     if (!Personality.isMSVCPersonality()) {
989       EHStack.pushTerminate();
990       PushedTerminate = true;
991     }
992 
993     // We only actually emit the cleanup code if the cleanup is either
994     // active or was used before it was deactivated.
995     if (EHActiveFlag.isValid() || IsActive) {
996       cleanupFlags.setIsForEHCleanup();
997       EmitCleanup(*this, Fn, cleanupFlags, EHActiveFlag);
998     }
999 
1000     if (CPI)
1001       Builder.CreateCleanupRet(CPI, NextAction);
1002     else
1003       Builder.CreateBr(NextAction);
1004 
1005     // Leave the terminate scope.
1006     if (PushedTerminate)
1007       EHStack.popTerminate();
1008 
1009     Builder.restoreIP(SavedIP);
1010 
1011     SimplifyCleanupEntry(*this, EHEntry);
1012   }
1013 }
1014 
1015 /// isObviouslyBranchWithoutCleanups - Return true if a branch to the
1016 /// specified destination obviously has no cleanups to run.  'false' is always
1017 /// a conservatively correct answer for this method.
1018 bool CodeGenFunction::isObviouslyBranchWithoutCleanups(JumpDest Dest) const {
1019   assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
1020          && "stale jump destination");
1021 
1022   // Calculate the innermost active normal cleanup.
1023   EHScopeStack::stable_iterator TopCleanup =
1024     EHStack.getInnermostActiveNormalCleanup();
1025 
1026   // If we're not in an active normal cleanup scope, or if the
1027   // destination scope is within the innermost active normal cleanup
1028   // scope, we don't need to worry about fixups.
1029   if (TopCleanup == EHStack.stable_end() ||
1030       TopCleanup.encloses(Dest.getScopeDepth())) // works for invalid
1031     return true;
1032 
1033   // Otherwise, we might need some cleanups.
1034   return false;
1035 }
1036 
1037 
1038 /// Terminate the current block by emitting a branch which might leave
1039 /// the current cleanup-protected scope.  The target scope may not yet
1040 /// be known, in which case this will require a fixup.
1041 ///
1042 /// As a side-effect, this method clears the insertion point.
1043 void CodeGenFunction::EmitBranchThroughCleanup(JumpDest Dest) {
1044   assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
1045          && "stale jump destination");
1046 
1047   if (!HaveInsertPoint())
1048     return;
1049 
1050   // Create the branch.
1051   llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock());
1052 
1053   // Calculate the innermost active normal cleanup.
1054   EHScopeStack::stable_iterator
1055     TopCleanup = EHStack.getInnermostActiveNormalCleanup();
1056 
1057   // If we're not in an active normal cleanup scope, or if the
1058   // destination scope is within the innermost active normal cleanup
1059   // scope, we don't need to worry about fixups.
1060   if (TopCleanup == EHStack.stable_end() ||
1061       TopCleanup.encloses(Dest.getScopeDepth())) { // works for invalid
1062     Builder.ClearInsertionPoint();
1063     return;
1064   }
1065 
1066   // If we can't resolve the destination cleanup scope, just add this
1067   // to the current cleanup scope as a branch fixup.
1068   if (!Dest.getScopeDepth().isValid()) {
1069     BranchFixup &Fixup = EHStack.addBranchFixup();
1070     Fixup.Destination = Dest.getBlock();
1071     Fixup.DestinationIndex = Dest.getDestIndex();
1072     Fixup.InitialBranch = BI;
1073     Fixup.OptimisticBranchBlock = nullptr;
1074 
1075     Builder.ClearInsertionPoint();
1076     return;
1077   }
1078 
1079   // Otherwise, thread through all the normal cleanups in scope.
1080 
1081   // Store the index at the start.
1082   llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex());
1083   createStoreInstBefore(Index, getNormalCleanupDestSlot(), BI);
1084 
1085   // Adjust BI to point to the first cleanup block.
1086   {
1087     EHCleanupScope &Scope =
1088       cast<EHCleanupScope>(*EHStack.find(TopCleanup));
1089     BI->setSuccessor(0, CreateNormalEntry(*this, Scope));
1090   }
1091 
1092   // Add this destination to all the scopes involved.
1093   EHScopeStack::stable_iterator I = TopCleanup;
1094   EHScopeStack::stable_iterator E = Dest.getScopeDepth();
1095   if (E.strictlyEncloses(I)) {
1096     while (true) {
1097       EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(I));
1098       assert(Scope.isNormalCleanup());
1099       I = Scope.getEnclosingNormalCleanup();
1100 
1101       // If this is the last cleanup we're propagating through, tell it
1102       // that there's a resolved jump moving through it.
1103       if (!E.strictlyEncloses(I)) {
1104         Scope.addBranchAfter(Index, Dest.getBlock());
1105         break;
1106       }
1107 
1108       // Otherwise, tell the scope that there's a jump propagating
1109       // through it.  If this isn't new information, all the rest of
1110       // the work has been done before.
1111       if (!Scope.addBranchThrough(Dest.getBlock()))
1112         break;
1113     }
1114   }
1115 
1116   Builder.ClearInsertionPoint();
1117 }
1118 
1119 static bool IsUsedAsNormalCleanup(EHScopeStack &EHStack,
1120                                   EHScopeStack::stable_iterator C) {
1121   // If we needed a normal block for any reason, that counts.
1122   if (cast<EHCleanupScope>(*EHStack.find(C)).getNormalBlock())
1123     return true;
1124 
1125   // Check whether any enclosed cleanups were needed.
1126   for (EHScopeStack::stable_iterator
1127          I = EHStack.getInnermostNormalCleanup();
1128          I != C; ) {
1129     assert(C.strictlyEncloses(I));
1130     EHCleanupScope &S = cast<EHCleanupScope>(*EHStack.find(I));
1131     if (S.getNormalBlock()) return true;
1132     I = S.getEnclosingNormalCleanup();
1133   }
1134 
1135   return false;
1136 }
1137 
1138 static bool IsUsedAsEHCleanup(EHScopeStack &EHStack,
1139                               EHScopeStack::stable_iterator cleanup) {
1140   // If we needed an EH block for any reason, that counts.
1141   if (EHStack.find(cleanup)->hasEHBranches())
1142     return true;
1143 
1144   // Check whether any enclosed cleanups were needed.
1145   for (EHScopeStack::stable_iterator
1146          i = EHStack.getInnermostEHScope(); i != cleanup; ) {
1147     assert(cleanup.strictlyEncloses(i));
1148 
1149     EHScope &scope = *EHStack.find(i);
1150     if (scope.hasEHBranches())
1151       return true;
1152 
1153     i = scope.getEnclosingEHScope();
1154   }
1155 
1156   return false;
1157 }
1158 
1159 enum ForActivation_t {
1160   ForActivation,
1161   ForDeactivation
1162 };
1163 
1164 /// The given cleanup block is changing activation state.  Configure a
1165 /// cleanup variable if necessary.
1166 ///
1167 /// It would be good if we had some way of determining if there were
1168 /// extra uses *after* the change-over point.
1169 static void SetupCleanupBlockActivation(CodeGenFunction &CGF,
1170                                         EHScopeStack::stable_iterator C,
1171                                         ForActivation_t kind,
1172                                         llvm::Instruction *dominatingIP) {
1173   EHCleanupScope &Scope = cast<EHCleanupScope>(*CGF.EHStack.find(C));
1174 
1175   // We always need the flag if we're activating the cleanup in a
1176   // conditional context, because we have to assume that the current
1177   // location doesn't necessarily dominate the cleanup's code.
1178   bool isActivatedInConditional =
1179     (kind == ForActivation && CGF.isInConditionalBranch());
1180 
1181   bool needFlag = false;
1182 
1183   // Calculate whether the cleanup was used:
1184 
1185   //   - as a normal cleanup
1186   if (Scope.isNormalCleanup() &&
1187       (isActivatedInConditional || IsUsedAsNormalCleanup(CGF.EHStack, C))) {
1188     Scope.setTestFlagInNormalCleanup();
1189     needFlag = true;
1190   }
1191 
1192   //  - as an EH cleanup
1193   if (Scope.isEHCleanup() &&
1194       (isActivatedInConditional || IsUsedAsEHCleanup(CGF.EHStack, C))) {
1195     Scope.setTestFlagInEHCleanup();
1196     needFlag = true;
1197   }
1198 
1199   // If it hasn't yet been used as either, we're done.
1200   if (!needFlag) return;
1201 
1202   Address var = Scope.getActiveFlag();
1203   if (!var.isValid()) {
1204     var = CGF.CreateTempAlloca(CGF.Builder.getInt1Ty(), CharUnits::One(),
1205                                "cleanup.isactive");
1206     Scope.setActiveFlag(var);
1207 
1208     assert(dominatingIP && "no existing variable and no dominating IP!");
1209 
1210     // Initialize to true or false depending on whether it was
1211     // active up to this point.
1212     llvm::Constant *value = CGF.Builder.getInt1(kind == ForDeactivation);
1213 
1214     // If we're in a conditional block, ignore the dominating IP and
1215     // use the outermost conditional branch.
1216     if (CGF.isInConditionalBranch()) {
1217       CGF.setBeforeOutermostConditional(value, var);
1218     } else {
1219       createStoreInstBefore(value, var, dominatingIP);
1220     }
1221   }
1222 
1223   CGF.Builder.CreateStore(CGF.Builder.getInt1(kind == ForActivation), var);
1224 }
1225 
1226 /// Activate a cleanup that was created in an inactivated state.
1227 void CodeGenFunction::ActivateCleanupBlock(EHScopeStack::stable_iterator C,
1228                                            llvm::Instruction *dominatingIP) {
1229   assert(C != EHStack.stable_end() && "activating bottom of stack?");
1230   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
1231   assert(!Scope.isActive() && "double activation");
1232 
1233   SetupCleanupBlockActivation(*this, C, ForActivation, dominatingIP);
1234 
1235   Scope.setActive(true);
1236 }
1237 
1238 /// Deactive a cleanup that was created in an active state.
1239 void CodeGenFunction::DeactivateCleanupBlock(EHScopeStack::stable_iterator C,
1240                                              llvm::Instruction *dominatingIP) {
1241   assert(C != EHStack.stable_end() && "deactivating bottom of stack?");
1242   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(C));
1243   assert(Scope.isActive() && "double deactivation");
1244 
1245   // If it's the top of the stack, just pop it, but do so only if it belongs
1246   // to the current RunCleanupsScope.
1247   if (C == EHStack.stable_begin() &&
1248       CurrentCleanupScopeDepth.strictlyEncloses(C)) {
1249     // If it's a normal cleanup, we need to pretend that the
1250     // fallthrough is unreachable.
1251     CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
1252     PopCleanupBlock();
1253     Builder.restoreIP(SavedIP);
1254     return;
1255   }
1256 
1257   // Otherwise, follow the general case.
1258   SetupCleanupBlockActivation(*this, C, ForDeactivation, dominatingIP);
1259 
1260   Scope.setActive(false);
1261 }
1262 
1263 Address CodeGenFunction::getNormalCleanupDestSlot() {
1264   if (!NormalCleanupDest.isValid())
1265     NormalCleanupDest =
1266       CreateDefaultAlignTempAlloca(Builder.getInt32Ty(), "cleanup.dest.slot");
1267   return NormalCleanupDest;
1268 }
1269 
1270 /// Emits all the code to cause the given temporary to be cleaned up.
1271 void CodeGenFunction::EmitCXXTemporary(const CXXTemporary *Temporary,
1272                                        QualType TempType,
1273                                        Address Ptr) {
1274   pushDestroy(NormalAndEHCleanup, Ptr, TempType, destroyCXXObject,
1275               /*useEHCleanup*/ true);
1276 }
1277