1 //===- ObjCARCOpts.cpp - ObjC ARC Optimization ----------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 /// This file defines ObjC ARC optimizations. ARC stands for Automatic
11 /// Reference Counting and is a system for managing reference counts for objects
14 /// The optimizations performed include elimination of redundant, partially
15 /// redundant, and inconsequential reference count operations, elimination of
16 /// redundant weak pointer operations, and numerous minor simplifications.
18 /// WARNING: This file knows about certain library functions. It recognizes them
19 /// by name, and hardwires knowledge of their semantics.
21 /// WARNING: This file knows about how certain Objective-C library functions are
22 /// used. Naive LLVM IR transformations which would otherwise be
23 /// behavior-preserving may break these assumptions.
25 //===----------------------------------------------------------------------===//
28 #include "ARCRuntimeEntryPoints.h"
29 #include "DependencyAnalysis.h"
30 #include "ObjCARCAliasAnalysis.h"
31 #include "ProvenanceAnalysis.h"
32 #include "BlotMapVector.h"
34 #include "llvm/ADT/DenseMap.h"
35 #include "llvm/ADT/DenseSet.h"
36 #include "llvm/ADT/STLExtras.h"
37 #include "llvm/ADT/SmallPtrSet.h"
38 #include "llvm/ADT/Statistic.h"
39 #include "llvm/IR/CFG.h"
40 #include "llvm/IR/IRBuilder.h"
41 #include "llvm/IR/LLVMContext.h"
42 #include "llvm/Support/Debug.h"
43 #include "llvm/Support/raw_ostream.h"
46 using namespace llvm::objcarc;
48 #define DEBUG_TYPE "objc-arc-opts"
50 /// \defgroup ARCUtilities Utility declarations/definitions specific to ARC.
53 /// \brief This is similar to GetRCIdentityRoot but it stops as soon
54 /// as it finds a value with multiple uses.
55 static const Value *FindSingleUseIdentifiedObject(const Value *Arg) {
56 if (Arg->hasOneUse()) {
57 if (const BitCastInst *BC = dyn_cast<BitCastInst>(Arg))
58 return FindSingleUseIdentifiedObject(BC->getOperand(0));
59 if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Arg))
60 if (GEP->hasAllZeroIndices())
61 return FindSingleUseIdentifiedObject(GEP->getPointerOperand());
62 if (IsForwarding(GetBasicARCInstKind(Arg)))
63 return FindSingleUseIdentifiedObject(
64 cast<CallInst>(Arg)->getArgOperand(0));
65 if (!IsObjCIdentifiedObject(Arg))
70 // If we found an identifiable object but it has multiple uses, but they are
71 // trivial uses, we can still consider this to be a single-use value.
72 if (IsObjCIdentifiedObject(Arg)) {
73 for (const User *U : Arg->users())
74 if (!U->use_empty() || GetRCIdentityRoot(U) != Arg)
83 /// This is a wrapper around getUnderlyingObjCPtr along the lines of
84 /// GetUnderlyingObjects except that it returns early when it sees the first
86 static inline bool AreAnyUnderlyingObjectsAnAlloca(const Value *V,
87 const DataLayout &DL) {
88 SmallPtrSet<const Value *, 4> Visited;
89 SmallVector<const Value *, 4> Worklist;
90 Worklist.push_back(V);
92 const Value *P = Worklist.pop_back_val();
93 P = GetUnderlyingObjCPtr(P, DL);
95 if (isa<AllocaInst>(P))
98 if (!Visited.insert(P).second)
101 if (const SelectInst *SI = dyn_cast<const SelectInst>(P)) {
102 Worklist.push_back(SI->getTrueValue());
103 Worklist.push_back(SI->getFalseValue());
107 if (const PHINode *PN = dyn_cast<const PHINode>(P)) {
108 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
109 Worklist.push_back(PN->getIncomingValue(i));
112 } while (!Worklist.empty());
120 /// \defgroup ARCOpt ARC Optimization.
123 // TODO: On code like this:
126 // stuff_that_cannot_release()
127 // objc_autorelease(%x)
128 // stuff_that_cannot_release()
130 // stuff_that_cannot_release()
131 // objc_autorelease(%x)
133 // The second retain and autorelease can be deleted.
135 // TODO: It should be possible to delete
136 // objc_autoreleasePoolPush and objc_autoreleasePoolPop
137 // pairs if nothing is actually autoreleased between them. Also, autorelease
138 // calls followed by objc_autoreleasePoolPop calls (perhaps in ObjC++ code
139 // after inlining) can be turned into plain release calls.
141 // TODO: Critical-edge splitting. If the optimial insertion point is
142 // a critical edge, the current algorithm has to fail, because it doesn't
143 // know how to split edges. It should be possible to make the optimizer
144 // think in terms of edges, rather than blocks, and then split critical
147 // TODO: OptimizeSequences could generalized to be Interprocedural.
149 // TODO: Recognize that a bunch of other objc runtime calls have
150 // non-escaping arguments and non-releasing arguments, and may be
151 // non-autoreleasing.
153 // TODO: Sink autorelease calls as far as possible. Unfortunately we
154 // usually can't sink them past other calls, which would be the main
155 // case where it would be useful.
157 // TODO: The pointer returned from objc_loadWeakRetained is retained.
159 // TODO: Delete release+retain pairs (rare).
161 STATISTIC(NumNoops, "Number of no-op objc calls eliminated");
162 STATISTIC(NumPartialNoops, "Number of partially no-op objc calls eliminated");
163 STATISTIC(NumAutoreleases,"Number of autoreleases converted to releases");
164 STATISTIC(NumRets, "Number of return value forwarding "
165 "retain+autoreleases eliminated");
166 STATISTIC(NumRRs, "Number of retain+release paths eliminated");
167 STATISTIC(NumPeeps, "Number of calls peephole-optimized");
169 STATISTIC(NumRetainsBeforeOpt,
170 "Number of retains before optimization");
171 STATISTIC(NumReleasesBeforeOpt,
172 "Number of releases before optimization");
173 STATISTIC(NumRetainsAfterOpt,
174 "Number of retains after optimization");
175 STATISTIC(NumReleasesAfterOpt,
176 "Number of releases after optimization");
180 /// \brief Per-BasicBlock state.
182 /// The number of unique control paths from the entry which can reach this
184 unsigned TopDownPathCount;
186 /// The number of unique control paths to exits from this block.
187 unsigned BottomUpPathCount;
189 /// The top-down traversal uses this to record information known about a
190 /// pointer at the bottom of each block.
191 BlotMapVector<const Value *, TopDownPtrState> PerPtrTopDown;
193 /// The bottom-up traversal uses this to record information known about a
194 /// pointer at the top of each block.
195 BlotMapVector<const Value *, BottomUpPtrState> PerPtrBottomUp;
197 /// Effective predecessors of the current block ignoring ignorable edges and
198 /// ignored backedges.
199 SmallVector<BasicBlock *, 2> Preds;
201 /// Effective successors of the current block ignoring ignorable edges and
202 /// ignored backedges.
203 SmallVector<BasicBlock *, 2> Succs;
206 static const unsigned OverflowOccurredValue;
208 BBState() : TopDownPathCount(0), BottomUpPathCount(0) { }
210 typedef decltype(PerPtrTopDown)::iterator top_down_ptr_iterator;
211 typedef decltype(PerPtrTopDown)::const_iterator const_top_down_ptr_iterator;
213 top_down_ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); }
214 top_down_ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); }
215 const_top_down_ptr_iterator top_down_ptr_begin() const {
216 return PerPtrTopDown.begin();
218 const_top_down_ptr_iterator top_down_ptr_end() const {
219 return PerPtrTopDown.end();
222 typedef decltype(PerPtrBottomUp)::iterator bottom_up_ptr_iterator;
224 PerPtrBottomUp)::const_iterator const_bottom_up_ptr_iterator;
226 bottom_up_ptr_iterator bottom_up_ptr_begin() {
227 return PerPtrBottomUp.begin();
229 bottom_up_ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); }
230 const_bottom_up_ptr_iterator bottom_up_ptr_begin() const {
231 return PerPtrBottomUp.begin();
233 const_bottom_up_ptr_iterator bottom_up_ptr_end() const {
234 return PerPtrBottomUp.end();
237 /// Mark this block as being an entry block, which has one path from the
238 /// entry by definition.
239 void SetAsEntry() { TopDownPathCount = 1; }
241 /// Mark this block as being an exit block, which has one path to an exit by
243 void SetAsExit() { BottomUpPathCount = 1; }
245 /// Attempt to find the PtrState object describing the top down state for
246 /// pointer Arg. Return a new initialized PtrState describing the top down
247 /// state for Arg if we do not find one.
248 TopDownPtrState &getPtrTopDownState(const Value *Arg) {
249 return PerPtrTopDown[Arg];
252 /// Attempt to find the PtrState object describing the bottom up state for
253 /// pointer Arg. Return a new initialized PtrState describing the bottom up
254 /// state for Arg if we do not find one.
255 BottomUpPtrState &getPtrBottomUpState(const Value *Arg) {
256 return PerPtrBottomUp[Arg];
259 /// Attempt to find the PtrState object describing the bottom up state for
261 bottom_up_ptr_iterator findPtrBottomUpState(const Value *Arg) {
262 return PerPtrBottomUp.find(Arg);
265 void clearBottomUpPointers() {
266 PerPtrBottomUp.clear();
269 void clearTopDownPointers() {
270 PerPtrTopDown.clear();
273 void InitFromPred(const BBState &Other);
274 void InitFromSucc(const BBState &Other);
275 void MergePred(const BBState &Other);
276 void MergeSucc(const BBState &Other);
278 /// Compute the number of possible unique paths from an entry to an exit
279 /// which pass through this block. This is only valid after both the
280 /// top-down and bottom-up traversals are complete.
282 /// Returns true if overflow occurred. Returns false if overflow did not
284 bool GetAllPathCountWithOverflow(unsigned &PathCount) const {
285 if (TopDownPathCount == OverflowOccurredValue ||
286 BottomUpPathCount == OverflowOccurredValue)
288 unsigned long long Product =
289 (unsigned long long)TopDownPathCount*BottomUpPathCount;
290 // Overflow occurred if any of the upper bits of Product are set or if all
291 // the lower bits of Product are all set.
292 return (Product >> 32) ||
293 ((PathCount = Product) == OverflowOccurredValue);
296 // Specialized CFG utilities.
297 typedef SmallVectorImpl<BasicBlock *>::const_iterator edge_iterator;
298 edge_iterator pred_begin() const { return Preds.begin(); }
299 edge_iterator pred_end() const { return Preds.end(); }
300 edge_iterator succ_begin() const { return Succs.begin(); }
301 edge_iterator succ_end() const { return Succs.end(); }
303 void addSucc(BasicBlock *Succ) { Succs.push_back(Succ); }
304 void addPred(BasicBlock *Pred) { Preds.push_back(Pred); }
306 bool isExit() const { return Succs.empty(); }
309 const unsigned BBState::OverflowOccurredValue = 0xffffffff;
312 void BBState::InitFromPred(const BBState &Other) {
313 PerPtrTopDown = Other.PerPtrTopDown;
314 TopDownPathCount = Other.TopDownPathCount;
317 void BBState::InitFromSucc(const BBState &Other) {
318 PerPtrBottomUp = Other.PerPtrBottomUp;
319 BottomUpPathCount = Other.BottomUpPathCount;
322 /// The top-down traversal uses this to merge information about predecessors to
323 /// form the initial state for a new block.
324 void BBState::MergePred(const BBState &Other) {
325 if (TopDownPathCount == OverflowOccurredValue)
328 // Other.TopDownPathCount can be 0, in which case it is either dead or a
329 // loop backedge. Loop backedges are special.
330 TopDownPathCount += Other.TopDownPathCount;
332 // In order to be consistent, we clear the top down pointers when by adding
333 // TopDownPathCount becomes OverflowOccurredValue even though "true" overflow
335 if (TopDownPathCount == OverflowOccurredValue) {
336 clearTopDownPointers();
340 // Check for overflow. If we have overflow, fall back to conservative
342 if (TopDownPathCount < Other.TopDownPathCount) {
343 TopDownPathCount = OverflowOccurredValue;
344 clearTopDownPointers();
348 // For each entry in the other set, if our set has an entry with the same key,
349 // merge the entries. Otherwise, copy the entry and merge it with an empty
351 for (auto MI = Other.top_down_ptr_begin(), ME = Other.top_down_ptr_end();
353 auto Pair = PerPtrTopDown.insert(*MI);
354 Pair.first->second.Merge(Pair.second ? TopDownPtrState() : MI->second,
358 // For each entry in our set, if the other set doesn't have an entry with the
359 // same key, force it to merge with an empty entry.
360 for (auto MI = top_down_ptr_begin(), ME = top_down_ptr_end(); MI != ME; ++MI)
361 if (Other.PerPtrTopDown.find(MI->first) == Other.PerPtrTopDown.end())
362 MI->second.Merge(TopDownPtrState(), /*TopDown=*/true);
365 /// The bottom-up traversal uses this to merge information about successors to
366 /// form the initial state for a new block.
367 void BBState::MergeSucc(const BBState &Other) {
368 if (BottomUpPathCount == OverflowOccurredValue)
371 // Other.BottomUpPathCount can be 0, in which case it is either dead or a
372 // loop backedge. Loop backedges are special.
373 BottomUpPathCount += Other.BottomUpPathCount;
375 // In order to be consistent, we clear the top down pointers when by adding
376 // BottomUpPathCount becomes OverflowOccurredValue even though "true" overflow
378 if (BottomUpPathCount == OverflowOccurredValue) {
379 clearBottomUpPointers();
383 // Check for overflow. If we have overflow, fall back to conservative
385 if (BottomUpPathCount < Other.BottomUpPathCount) {
386 BottomUpPathCount = OverflowOccurredValue;
387 clearBottomUpPointers();
391 // For each entry in the other set, if our set has an entry with the
392 // same key, merge the entries. Otherwise, copy the entry and merge
393 // it with an empty entry.
394 for (auto MI = Other.bottom_up_ptr_begin(), ME = Other.bottom_up_ptr_end();
396 auto Pair = PerPtrBottomUp.insert(*MI);
397 Pair.first->second.Merge(Pair.second ? BottomUpPtrState() : MI->second,
401 // For each entry in our set, if the other set doesn't have an entry
402 // with the same key, force it to merge with an empty entry.
403 for (auto MI = bottom_up_ptr_begin(), ME = bottom_up_ptr_end(); MI != ME;
405 if (Other.PerPtrBottomUp.find(MI->first) == Other.PerPtrBottomUp.end())
406 MI->second.Merge(BottomUpPtrState(), /*TopDown=*/false);
411 /// \brief The main ARC optimization pass.
412 class ObjCARCOpt : public FunctionPass {
414 ProvenanceAnalysis PA;
416 /// A cache of references to runtime entry point constants.
417 ARCRuntimeEntryPoints EP;
419 /// A cache of MDKinds that can be passed into other functions to propagate
420 /// MDKind identifiers.
421 ARCMDKindCache MDKindCache;
423 // This is used to track if a pointer is stored into an alloca.
424 DenseSet<const Value *> MultiOwnersSet;
426 /// A flag indicating whether this optimization pass should run.
429 /// Flags which determine whether each of the interesting runtine functions
430 /// is in fact used in the current function.
431 unsigned UsedInThisFunction;
433 bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV);
434 void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
436 void OptimizeIndividualCalls(Function &F);
438 void CheckForCFGHazards(const BasicBlock *BB,
439 DenseMap<const BasicBlock *, BBState> &BBStates,
440 BBState &MyStates) const;
441 bool VisitInstructionBottomUp(Instruction *Inst, BasicBlock *BB,
442 BlotMapVector<Value *, RRInfo> &Retains,
444 bool VisitBottomUp(BasicBlock *BB,
445 DenseMap<const BasicBlock *, BBState> &BBStates,
446 BlotMapVector<Value *, RRInfo> &Retains);
447 bool VisitInstructionTopDown(Instruction *Inst,
448 DenseMap<Value *, RRInfo> &Releases,
450 bool VisitTopDown(BasicBlock *BB,
451 DenseMap<const BasicBlock *, BBState> &BBStates,
452 DenseMap<Value *, RRInfo> &Releases);
453 bool Visit(Function &F, DenseMap<const BasicBlock *, BBState> &BBStates,
454 BlotMapVector<Value *, RRInfo> &Retains,
455 DenseMap<Value *, RRInfo> &Releases);
457 void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove,
458 BlotMapVector<Value *, RRInfo> &Retains,
459 DenseMap<Value *, RRInfo> &Releases,
460 SmallVectorImpl<Instruction *> &DeadInsts, Module *M);
462 bool ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState> &BBStates,
463 BlotMapVector<Value *, RRInfo> &Retains,
464 DenseMap<Value *, RRInfo> &Releases, Module *M,
465 SmallVectorImpl<Instruction *> &NewRetains,
466 SmallVectorImpl<Instruction *> &NewReleases,
467 SmallVectorImpl<Instruction *> &DeadInsts,
468 RRInfo &RetainsToMove, RRInfo &ReleasesToMove,
469 Value *Arg, bool KnownSafe,
470 bool &AnyPairsCompletelyEliminated);
472 bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates,
473 BlotMapVector<Value *, RRInfo> &Retains,
474 DenseMap<Value *, RRInfo> &Releases, Module *M);
476 void OptimizeWeakCalls(Function &F);
478 bool OptimizeSequences(Function &F);
480 void OptimizeReturns(Function &F);
483 void GatherStatistics(Function &F, bool AfterOptimization = false);
486 void getAnalysisUsage(AnalysisUsage &AU) const override;
487 bool doInitialization(Module &M) override;
488 bool runOnFunction(Function &F) override;
489 void releaseMemory() override;
493 ObjCARCOpt() : FunctionPass(ID) {
494 initializeObjCARCOptPass(*PassRegistry::getPassRegistry());
499 char ObjCARCOpt::ID = 0;
500 INITIALIZE_PASS_BEGIN(ObjCARCOpt,
501 "objc-arc", "ObjC ARC optimization", false, false)
502 INITIALIZE_PASS_DEPENDENCY(ObjCARCAliasAnalysis)
503 INITIALIZE_PASS_END(ObjCARCOpt,
504 "objc-arc", "ObjC ARC optimization", false, false)
506 Pass *llvm::createObjCARCOptPass() {
507 return new ObjCARCOpt();
510 void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const {
511 AU.addRequired<ObjCARCAliasAnalysis>();
512 AU.addRequired<AliasAnalysis>();
513 // ARC optimization doesn't currently split critical edges.
514 AU.setPreservesCFG();
517 /// Turn objc_retainAutoreleasedReturnValue into objc_retain if the operand is
518 /// not a return value. Or, if it can be paired with an
519 /// objc_autoreleaseReturnValue, delete the pair and return true.
521 ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) {
522 // Check for the argument being from an immediately preceding call or invoke.
523 const Value *Arg = GetArgRCIdentityRoot(RetainRV);
524 ImmutableCallSite CS(Arg);
525 if (const Instruction *Call = CS.getInstruction()) {
526 if (Call->getParent() == RetainRV->getParent()) {
527 BasicBlock::const_iterator I = Call;
529 while (IsNoopInstruction(I)) ++I;
532 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
533 BasicBlock *RetainRVParent = RetainRV->getParent();
534 if (II->getNormalDest() == RetainRVParent) {
535 BasicBlock::const_iterator I = RetainRVParent->begin();
536 while (IsNoopInstruction(I)) ++I;
543 // Check for being preceded by an objc_autoreleaseReturnValue on the same
544 // pointer. In this case, we can delete the pair.
545 BasicBlock::iterator I = RetainRV, Begin = RetainRV->getParent()->begin();
547 do --I; while (I != Begin && IsNoopInstruction(I));
548 if (GetBasicARCInstKind(I) == ARCInstKind::AutoreleaseRV &&
549 GetArgRCIdentityRoot(I) == Arg) {
553 DEBUG(dbgs() << "Erasing autoreleaseRV,retainRV pair: " << *I << "\n"
554 << "Erasing " << *RetainRV << "\n");
557 EraseInstruction(RetainRV);
562 // Turn it to a plain objc_retain.
566 DEBUG(dbgs() << "Transforming objc_retainAutoreleasedReturnValue => "
567 "objc_retain since the operand is not a return value.\n"
568 "Old = " << *RetainRV << "\n");
570 Constant *NewDecl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
571 cast<CallInst>(RetainRV)->setCalledFunction(NewDecl);
573 DEBUG(dbgs() << "New = " << *RetainRV << "\n");
578 /// Turn objc_autoreleaseReturnValue into objc_autorelease if the result is not
579 /// used as a return value.
580 void ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F,
581 Instruction *AutoreleaseRV,
582 ARCInstKind &Class) {
583 // Check for a return of the pointer value.
584 const Value *Ptr = GetArgRCIdentityRoot(AutoreleaseRV);
585 SmallVector<const Value *, 2> Users;
586 Users.push_back(Ptr);
588 Ptr = Users.pop_back_val();
589 for (const User *U : Ptr->users()) {
590 if (isa<ReturnInst>(U) || GetBasicARCInstKind(U) == ARCInstKind::RetainRV)
592 if (isa<BitCastInst>(U))
595 } while (!Users.empty());
600 DEBUG(dbgs() << "Transforming objc_autoreleaseReturnValue => "
601 "objc_autorelease since its operand is not used as a return "
603 "Old = " << *AutoreleaseRV << "\n");
605 CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV);
606 Constant *NewDecl = EP.get(ARCRuntimeEntryPoints::EPT_Autorelease);
607 AutoreleaseRVCI->setCalledFunction(NewDecl);
608 AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
609 Class = ARCInstKind::Autorelease;
611 DEBUG(dbgs() << "New: " << *AutoreleaseRV << "\n");
615 /// Visit each call, one at a time, and make simplifications without doing any
616 /// additional analysis.
617 void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
618 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeIndividualCalls ==\n");
619 // Reset all the flags in preparation for recomputing them.
620 UsedInThisFunction = 0;
622 // Visit all objc_* calls in F.
623 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
624 Instruction *Inst = &*I++;
626 ARCInstKind Class = GetBasicARCInstKind(Inst);
628 DEBUG(dbgs() << "Visiting: Class: " << Class << "; " << *Inst << "\n");
633 // Delete no-op casts. These function calls have special semantics, but
634 // the semantics are entirely implemented via lowering in the front-end,
635 // so by the time they reach the optimizer, they are just no-op calls
636 // which return their argument.
638 // There are gray areas here, as the ability to cast reference-counted
639 // pointers to raw void* and back allows code to break ARC assumptions,
640 // however these are currently considered to be unimportant.
641 case ARCInstKind::NoopCast:
644 DEBUG(dbgs() << "Erasing no-op cast: " << *Inst << "\n");
645 EraseInstruction(Inst);
648 // If the pointer-to-weak-pointer is null, it's undefined behavior.
649 case ARCInstKind::StoreWeak:
650 case ARCInstKind::LoadWeak:
651 case ARCInstKind::LoadWeakRetained:
652 case ARCInstKind::InitWeak:
653 case ARCInstKind::DestroyWeak: {
654 CallInst *CI = cast<CallInst>(Inst);
655 if (IsNullOrUndef(CI->getArgOperand(0))) {
657 Type *Ty = CI->getArgOperand(0)->getType();
658 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
659 Constant::getNullValue(Ty),
661 llvm::Value *NewValue = UndefValue::get(CI->getType());
662 DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
663 "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
664 CI->replaceAllUsesWith(NewValue);
665 CI->eraseFromParent();
670 case ARCInstKind::CopyWeak:
671 case ARCInstKind::MoveWeak: {
672 CallInst *CI = cast<CallInst>(Inst);
673 if (IsNullOrUndef(CI->getArgOperand(0)) ||
674 IsNullOrUndef(CI->getArgOperand(1))) {
676 Type *Ty = CI->getArgOperand(0)->getType();
677 new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
678 Constant::getNullValue(Ty),
681 llvm::Value *NewValue = UndefValue::get(CI->getType());
682 DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
683 "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
685 CI->replaceAllUsesWith(NewValue);
686 CI->eraseFromParent();
691 case ARCInstKind::RetainRV:
692 if (OptimizeRetainRVCall(F, Inst))
695 case ARCInstKind::AutoreleaseRV:
696 OptimizeAutoreleaseRVCall(F, Inst, Class);
700 // objc_autorelease(x) -> objc_release(x) if x is otherwise unused.
701 if (IsAutorelease(Class) && Inst->use_empty()) {
702 CallInst *Call = cast<CallInst>(Inst);
703 const Value *Arg = Call->getArgOperand(0);
704 Arg = FindSingleUseIdentifiedObject(Arg);
709 // Create the declaration lazily.
710 LLVMContext &C = Inst->getContext();
712 Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Release);
713 CallInst *NewCall = CallInst::Create(Decl, Call->getArgOperand(0), "",
715 NewCall->setMetadata(MDKindCache.ImpreciseReleaseMDKind,
716 MDNode::get(C, None));
718 DEBUG(dbgs() << "Replacing autorelease{,RV}(x) with objc_release(x) "
719 "since x is otherwise unused.\nOld: " << *Call << "\nNew: "
720 << *NewCall << "\n");
722 EraseInstruction(Call);
724 Class = ARCInstKind::Release;
728 // For functions which can never be passed stack arguments, add
730 if (IsAlwaysTail(Class)) {
732 DEBUG(dbgs() << "Adding tail keyword to function since it can never be "
733 "passed stack args: " << *Inst << "\n");
734 cast<CallInst>(Inst)->setTailCall();
737 // Ensure that functions that can never have a "tail" keyword due to the
738 // semantics of ARC truly do not do so.
739 if (IsNeverTail(Class)) {
741 DEBUG(dbgs() << "Removing tail keyword from function: " << *Inst <<
743 cast<CallInst>(Inst)->setTailCall(false);
746 // Set nounwind as needed.
747 if (IsNoThrow(Class)) {
749 DEBUG(dbgs() << "Found no throw class. Setting nounwind on: " << *Inst
751 cast<CallInst>(Inst)->setDoesNotThrow();
754 if (!IsNoopOnNull(Class)) {
755 UsedInThisFunction |= 1 << unsigned(Class);
759 const Value *Arg = GetArgRCIdentityRoot(Inst);
761 // ARC calls with null are no-ops. Delete them.
762 if (IsNullOrUndef(Arg)) {
765 DEBUG(dbgs() << "ARC calls with null are no-ops. Erasing: " << *Inst
767 EraseInstruction(Inst);
771 // Keep track of which of retain, release, autorelease, and retain_block
772 // are actually present in this function.
773 UsedInThisFunction |= 1 << unsigned(Class);
775 // If Arg is a PHI, and one or more incoming values to the
776 // PHI are null, and the call is control-equivalent to the PHI, and there
777 // are no relevant side effects between the PHI and the call, the call
778 // could be pushed up to just those paths with non-null incoming values.
779 // For now, don't bother splitting critical edges for this.
780 SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist;
781 Worklist.push_back(std::make_pair(Inst, Arg));
783 std::pair<Instruction *, const Value *> Pair = Worklist.pop_back_val();
787 const PHINode *PN = dyn_cast<PHINode>(Arg);
790 // Determine if the PHI has any null operands, or any incoming
792 bool HasNull = false;
793 bool HasCriticalEdges = false;
794 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
796 GetRCIdentityRoot(PN->getIncomingValue(i));
797 if (IsNullOrUndef(Incoming))
799 else if (cast<TerminatorInst>(PN->getIncomingBlock(i)->back())
800 .getNumSuccessors() != 1) {
801 HasCriticalEdges = true;
805 // If we have null operands and no critical edges, optimize.
806 if (!HasCriticalEdges && HasNull) {
807 SmallPtrSet<Instruction *, 4> DependingInstructions;
808 SmallPtrSet<const BasicBlock *, 4> Visited;
810 // Check that there is nothing that cares about the reference
811 // count between the call and the phi.
813 case ARCInstKind::Retain:
814 case ARCInstKind::RetainBlock:
815 // These can always be moved up.
817 case ARCInstKind::Release:
818 // These can't be moved across things that care about the retain
820 FindDependencies(NeedsPositiveRetainCount, Arg,
821 Inst->getParent(), Inst,
822 DependingInstructions, Visited, PA);
824 case ARCInstKind::Autorelease:
825 // These can't be moved across autorelease pool scope boundaries.
826 FindDependencies(AutoreleasePoolBoundary, Arg,
827 Inst->getParent(), Inst,
828 DependingInstructions, Visited, PA);
830 case ARCInstKind::RetainRV:
831 case ARCInstKind::AutoreleaseRV:
832 // Don't move these; the RV optimization depends on the autoreleaseRV
833 // being tail called, and the retainRV being immediately after a call
834 // (which might still happen if we get lucky with codegen layout, but
835 // it's not worth taking the chance).
838 llvm_unreachable("Invalid dependence flavor");
841 if (DependingInstructions.size() == 1 &&
842 *DependingInstructions.begin() == PN) {
845 // Clone the call into each predecessor that has a non-null value.
846 CallInst *CInst = cast<CallInst>(Inst);
847 Type *ParamTy = CInst->getArgOperand(0)->getType();
848 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
850 GetRCIdentityRoot(PN->getIncomingValue(i));
851 if (!IsNullOrUndef(Incoming)) {
852 CallInst *Clone = cast<CallInst>(CInst->clone());
853 Value *Op = PN->getIncomingValue(i);
854 Instruction *InsertPos = &PN->getIncomingBlock(i)->back();
855 if (Op->getType() != ParamTy)
856 Op = new BitCastInst(Op, ParamTy, "", InsertPos);
857 Clone->setArgOperand(0, Op);
858 Clone->insertBefore(InsertPos);
860 DEBUG(dbgs() << "Cloning "
862 "And inserting clone at " << *InsertPos << "\n");
863 Worklist.push_back(std::make_pair(Clone, Incoming));
866 // Erase the original call.
867 DEBUG(dbgs() << "Erasing: " << *CInst << "\n");
868 EraseInstruction(CInst);
872 } while (!Worklist.empty());
876 /// If we have a top down pointer in the S_Use state, make sure that there are
877 /// no CFG hazards by checking the states of various bottom up pointers.
878 static void CheckForUseCFGHazard(const Sequence SuccSSeq,
879 const bool SuccSRRIKnownSafe,
881 bool &SomeSuccHasSame,
882 bool &AllSuccsHaveSame,
883 bool &NotAllSeqEqualButKnownSafe,
884 bool &ShouldContinue) {
887 if (!S.IsKnownSafe() && !SuccSRRIKnownSafe) {
888 S.ClearSequenceProgress();
891 S.SetCFGHazardAfflicted(true);
892 ShouldContinue = true;
896 SomeSuccHasSame = true;
900 case S_MovableRelease:
901 if (!S.IsKnownSafe() && !SuccSRRIKnownSafe)
902 AllSuccsHaveSame = false;
904 NotAllSeqEqualButKnownSafe = true;
907 llvm_unreachable("bottom-up pointer in retain state!");
909 llvm_unreachable("This should have been handled earlier.");
913 /// If we have a Top Down pointer in the S_CanRelease state, make sure that
914 /// there are no CFG hazards by checking the states of various bottom up
916 static void CheckForCanReleaseCFGHazard(const Sequence SuccSSeq,
917 const bool SuccSRRIKnownSafe,
919 bool &SomeSuccHasSame,
920 bool &AllSuccsHaveSame,
921 bool &NotAllSeqEqualButKnownSafe) {
924 SomeSuccHasSame = true;
928 case S_MovableRelease:
930 if (!S.IsKnownSafe() && !SuccSRRIKnownSafe)
931 AllSuccsHaveSame = false;
933 NotAllSeqEqualButKnownSafe = true;
936 llvm_unreachable("bottom-up pointer in retain state!");
938 llvm_unreachable("This should have been handled earlier.");
942 /// Check for critical edges, loop boundaries, irreducible control flow, or
943 /// other CFG structures where moving code across the edge would result in it
944 /// being executed more.
946 ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
947 DenseMap<const BasicBlock *, BBState> &BBStates,
948 BBState &MyStates) const {
949 // If any top-down local-use or possible-dec has a succ which is earlier in
950 // the sequence, forget it.
951 for (auto I = MyStates.top_down_ptr_begin(), E = MyStates.top_down_ptr_end();
953 TopDownPtrState &S = I->second;
954 const Sequence Seq = I->second.GetSeq();
956 // We only care about S_Retain, S_CanRelease, and S_Use.
960 // Make sure that if extra top down states are added in the future that this
961 // code is updated to handle it.
962 assert((Seq == S_Retain || Seq == S_CanRelease || Seq == S_Use) &&
963 "Unknown top down sequence state.");
965 const Value *Arg = I->first;
966 const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
967 bool SomeSuccHasSame = false;
968 bool AllSuccsHaveSame = true;
969 bool NotAllSeqEqualButKnownSafe = false;
971 succ_const_iterator SI(TI), SE(TI, false);
973 for (; SI != SE; ++SI) {
974 // If VisitBottomUp has pointer information for this successor, take
975 // what we know about it.
976 const DenseMap<const BasicBlock *, BBState>::iterator BBI =
978 assert(BBI != BBStates.end());
979 const BottomUpPtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
980 const Sequence SuccSSeq = SuccS.GetSeq();
982 // If bottom up, the pointer is in an S_None state, clear the sequence
983 // progress since the sequence in the bottom up state finished
984 // suggesting a mismatch in between retains/releases. This is true for
985 // all three cases that we are handling here: S_Retain, S_Use, and
987 if (SuccSSeq == S_None) {
988 S.ClearSequenceProgress();
992 // If we have S_Use or S_CanRelease, perform our check for cfg hazard
994 const bool SuccSRRIKnownSafe = SuccS.IsKnownSafe();
996 // *NOTE* We do not use Seq from above here since we are allowing for
997 // S.GetSeq() to change while we are visiting basic blocks.
1000 bool ShouldContinue = false;
1001 CheckForUseCFGHazard(SuccSSeq, SuccSRRIKnownSafe, S, SomeSuccHasSame,
1002 AllSuccsHaveSame, NotAllSeqEqualButKnownSafe,
1008 case S_CanRelease: {
1009 CheckForCanReleaseCFGHazard(SuccSSeq, SuccSRRIKnownSafe, S,
1010 SomeSuccHasSame, AllSuccsHaveSame,
1011 NotAllSeqEqualButKnownSafe);
1018 case S_MovableRelease:
1023 // If the state at the other end of any of the successor edges
1024 // matches the current state, require all edges to match. This
1025 // guards against loops in the middle of a sequence.
1026 if (SomeSuccHasSame && !AllSuccsHaveSame) {
1027 S.ClearSequenceProgress();
1028 } else if (NotAllSeqEqualButKnownSafe) {
1029 // If we would have cleared the state foregoing the fact that we are known
1030 // safe, stop code motion. This is because whether or not it is safe to
1031 // remove RR pairs via KnownSafe is an orthogonal concept to whether we
1032 // are allowed to perform code motion.
1033 S.SetCFGHazardAfflicted(true);
1038 bool ObjCARCOpt::VisitInstructionBottomUp(
1039 Instruction *Inst, BasicBlock *BB, BlotMapVector<Value *, RRInfo> &Retains,
1040 BBState &MyStates) {
1041 bool NestingDetected = false;
1042 ARCInstKind Class = GetARCInstKind(Inst);
1043 const Value *Arg = nullptr;
1045 DEBUG(dbgs() << "Class: " << Class << "\n");
1048 case ARCInstKind::Release: {
1049 Arg = GetArgRCIdentityRoot(Inst);
1051 BottomUpPtrState &S = MyStates.getPtrBottomUpState(Arg);
1052 NestingDetected |= S.InitBottomUp(MDKindCache, Inst);
1055 case ARCInstKind::RetainBlock:
1056 // In OptimizeIndividualCalls, we have strength reduced all optimizable
1057 // objc_retainBlocks to objc_retains. Thus at this point any
1058 // objc_retainBlocks that we see are not optimizable.
1060 case ARCInstKind::Retain:
1061 case ARCInstKind::RetainRV: {
1062 Arg = GetArgRCIdentityRoot(Inst);
1063 BottomUpPtrState &S = MyStates.getPtrBottomUpState(Arg);
1064 if (S.MatchWithRetain()) {
1065 // Don't do retain+release tracking for ARCInstKind::RetainRV, because
1066 // it's better to let it remain as the first instruction after a call.
1067 if (Class != ARCInstKind::RetainRV)
1068 Retains[Inst] = S.GetRRInfo();
1069 S.ClearSequenceProgress();
1071 // A retain moving bottom up can be a use.
1074 case ARCInstKind::AutoreleasepoolPop:
1075 // Conservatively, clear MyStates for all known pointers.
1076 MyStates.clearBottomUpPointers();
1077 return NestingDetected;
1078 case ARCInstKind::AutoreleasepoolPush:
1079 case ARCInstKind::None:
1080 // These are irrelevant.
1081 return NestingDetected;
1082 case ARCInstKind::User:
1083 // If we have a store into an alloca of a pointer we are tracking, the
1084 // pointer has multiple owners implying that we must be more conservative.
1086 // This comes up in the context of a pointer being ``KnownSafe''. In the
1087 // presence of a block being initialized, the frontend will emit the
1088 // objc_retain on the original pointer and the release on the pointer loaded
1089 // from the alloca. The optimizer will through the provenance analysis
1090 // realize that the two are related, but since we only require KnownSafe in
1091 // one direction, will match the inner retain on the original pointer with
1092 // the guard release on the original pointer. This is fixed by ensuring that
1093 // in the presence of allocas we only unconditionally remove pointers if
1094 // both our retain and our release are KnownSafe.
1095 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
1096 const DataLayout &DL = BB->getModule()->getDataLayout();
1097 if (AreAnyUnderlyingObjectsAnAlloca(SI->getPointerOperand(), DL)) {
1098 auto I = MyStates.findPtrBottomUpState(
1099 GetRCIdentityRoot(SI->getValueOperand()));
1100 if (I != MyStates.bottom_up_ptr_end())
1101 MultiOwnersSet.insert(I->first);
1109 // Consider any other possible effects of this instruction on each
1110 // pointer being tracked.
1111 for (auto MI = MyStates.bottom_up_ptr_begin(),
1112 ME = MyStates.bottom_up_ptr_end();
1114 const Value *Ptr = MI->first;
1116 continue; // Handled above.
1117 BottomUpPtrState &S = MI->second;
1119 if (S.HandlePotentialAlterRefCount(Inst, Ptr, PA, Class))
1122 S.HandlePotentialUse(BB, Inst, Ptr, PA, Class);
1125 return NestingDetected;
1128 bool ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
1129 DenseMap<const BasicBlock *, BBState> &BBStates,
1130 BlotMapVector<Value *, RRInfo> &Retains) {
1132 DEBUG(dbgs() << "\n== ObjCARCOpt::VisitBottomUp ==\n");
1134 bool NestingDetected = false;
1135 BBState &MyStates = BBStates[BB];
1137 // Merge the states from each successor to compute the initial state
1138 // for the current block.
1139 BBState::edge_iterator SI(MyStates.succ_begin()),
1140 SE(MyStates.succ_end());
1142 const BasicBlock *Succ = *SI;
1143 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Succ);
1144 assert(I != BBStates.end());
1145 MyStates.InitFromSucc(I->second);
1147 for (; SI != SE; ++SI) {
1149 I = BBStates.find(Succ);
1150 assert(I != BBStates.end());
1151 MyStates.MergeSucc(I->second);
1155 // Visit all the instructions, bottom-up.
1156 for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) {
1157 Instruction *Inst = std::prev(I);
1159 // Invoke instructions are visited as part of their successors (below).
1160 if (isa<InvokeInst>(Inst))
1163 DEBUG(dbgs() << "Visiting " << *Inst << "\n");
1165 NestingDetected |= VisitInstructionBottomUp(Inst, BB, Retains, MyStates);
1168 // If there's a predecessor with an invoke, visit the invoke as if it were
1169 // part of this block, since we can't insert code after an invoke in its own
1170 // block, and we don't want to split critical edges.
1171 for (BBState::edge_iterator PI(MyStates.pred_begin()),
1172 PE(MyStates.pred_end()); PI != PE; ++PI) {
1173 BasicBlock *Pred = *PI;
1174 if (InvokeInst *II = dyn_cast<InvokeInst>(&Pred->back()))
1175 NestingDetected |= VisitInstructionBottomUp(II, BB, Retains, MyStates);
1178 return NestingDetected;
1182 ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst,
1183 DenseMap<Value *, RRInfo> &Releases,
1184 BBState &MyStates) {
1185 bool NestingDetected = false;
1186 ARCInstKind Class = GetARCInstKind(Inst);
1187 const Value *Arg = nullptr;
1190 case ARCInstKind::RetainBlock:
1191 // In OptimizeIndividualCalls, we have strength reduced all optimizable
1192 // objc_retainBlocks to objc_retains. Thus at this point any
1193 // objc_retainBlocks that we see are not optimizable. We need to break since
1194 // a retain can be a potential use.
1196 case ARCInstKind::Retain:
1197 case ARCInstKind::RetainRV: {
1198 Arg = GetArgRCIdentityRoot(Inst);
1199 TopDownPtrState &S = MyStates.getPtrTopDownState(Arg);
1200 NestingDetected |= S.InitTopDown(Class, Inst);
1201 // A retain can be a potential use; procede to the generic checking
1205 case ARCInstKind::Release: {
1206 Arg = GetArgRCIdentityRoot(Inst);
1207 TopDownPtrState &S = MyStates.getPtrTopDownState(Arg);
1208 // Try to form a tentative pair in between this release instruction and the
1209 // top down pointers that we are tracking.
1210 if (S.MatchWithRelease(MDKindCache, Inst)) {
1211 // If we succeed, copy S's RRInfo into the Release -> {Retain Set
1212 // Map}. Then we clear S.
1213 Releases[Inst] = S.GetRRInfo();
1214 S.ClearSequenceProgress();
1218 case ARCInstKind::AutoreleasepoolPop:
1219 // Conservatively, clear MyStates for all known pointers.
1220 MyStates.clearTopDownPointers();
1222 case ARCInstKind::AutoreleasepoolPush:
1223 case ARCInstKind::None:
1224 // These can not be uses of
1230 // Consider any other possible effects of this instruction on each
1231 // pointer being tracked.
1232 for (auto MI = MyStates.top_down_ptr_begin(),
1233 ME = MyStates.top_down_ptr_end();
1235 const Value *Ptr = MI->first;
1237 continue; // Handled above.
1238 TopDownPtrState &S = MI->second;
1239 if (S.HandlePotentialAlterRefCount(Inst, Ptr, PA, Class))
1242 S.HandlePotentialUse(Inst, Ptr, PA, Class);
1245 return NestingDetected;
1249 ObjCARCOpt::VisitTopDown(BasicBlock *BB,
1250 DenseMap<const BasicBlock *, BBState> &BBStates,
1251 DenseMap<Value *, RRInfo> &Releases) {
1252 DEBUG(dbgs() << "\n== ObjCARCOpt::VisitTopDown ==\n");
1253 bool NestingDetected = false;
1254 BBState &MyStates = BBStates[BB];
1256 // Merge the states from each predecessor to compute the initial state
1257 // for the current block.
1258 BBState::edge_iterator PI(MyStates.pred_begin()),
1259 PE(MyStates.pred_end());
1261 const BasicBlock *Pred = *PI;
1262 DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Pred);
1263 assert(I != BBStates.end());
1264 MyStates.InitFromPred(I->second);
1266 for (; PI != PE; ++PI) {
1268 I = BBStates.find(Pred);
1269 assert(I != BBStates.end());
1270 MyStates.MergePred(I->second);
1274 // Visit all the instructions, top-down.
1275 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1276 Instruction *Inst = I;
1278 DEBUG(dbgs() << "Visiting " << *Inst << "\n");
1280 NestingDetected |= VisitInstructionTopDown(Inst, Releases, MyStates);
1283 CheckForCFGHazards(BB, BBStates, MyStates);
1284 return NestingDetected;
1288 ComputePostOrders(Function &F,
1289 SmallVectorImpl<BasicBlock *> &PostOrder,
1290 SmallVectorImpl<BasicBlock *> &ReverseCFGPostOrder,
1291 unsigned NoObjCARCExceptionsMDKind,
1292 DenseMap<const BasicBlock *, BBState> &BBStates) {
1293 /// The visited set, for doing DFS walks.
1294 SmallPtrSet<BasicBlock *, 16> Visited;
1296 // Do DFS, computing the PostOrder.
1297 SmallPtrSet<BasicBlock *, 16> OnStack;
1298 SmallVector<std::pair<BasicBlock *, succ_iterator>, 16> SuccStack;
1300 // Functions always have exactly one entry block, and we don't have
1301 // any other block that we treat like an entry block.
1302 BasicBlock *EntryBB = &F.getEntryBlock();
1303 BBState &MyStates = BBStates[EntryBB];
1304 MyStates.SetAsEntry();
1305 TerminatorInst *EntryTI = cast<TerminatorInst>(&EntryBB->back());
1306 SuccStack.push_back(std::make_pair(EntryBB, succ_iterator(EntryTI)));
1307 Visited.insert(EntryBB);
1308 OnStack.insert(EntryBB);
1311 BasicBlock *CurrBB = SuccStack.back().first;
1312 TerminatorInst *TI = cast<TerminatorInst>(&CurrBB->back());
1313 succ_iterator SE(TI, false);
1315 while (SuccStack.back().second != SE) {
1316 BasicBlock *SuccBB = *SuccStack.back().second++;
1317 if (Visited.insert(SuccBB).second) {
1318 TerminatorInst *TI = cast<TerminatorInst>(&SuccBB->back());
1319 SuccStack.push_back(std::make_pair(SuccBB, succ_iterator(TI)));
1320 BBStates[CurrBB].addSucc(SuccBB);
1321 BBState &SuccStates = BBStates[SuccBB];
1322 SuccStates.addPred(CurrBB);
1323 OnStack.insert(SuccBB);
1327 if (!OnStack.count(SuccBB)) {
1328 BBStates[CurrBB].addSucc(SuccBB);
1329 BBStates[SuccBB].addPred(CurrBB);
1332 OnStack.erase(CurrBB);
1333 PostOrder.push_back(CurrBB);
1334 SuccStack.pop_back();
1335 } while (!SuccStack.empty());
1339 // Do reverse-CFG DFS, computing the reverse-CFG PostOrder.
1340 // Functions may have many exits, and there also blocks which we treat
1341 // as exits due to ignored edges.
1342 SmallVector<std::pair<BasicBlock *, BBState::edge_iterator>, 16> PredStack;
1343 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
1344 BasicBlock *ExitBB = I;
1345 BBState &MyStates = BBStates[ExitBB];
1346 if (!MyStates.isExit())
1349 MyStates.SetAsExit();
1351 PredStack.push_back(std::make_pair(ExitBB, MyStates.pred_begin()));
1352 Visited.insert(ExitBB);
1353 while (!PredStack.empty()) {
1354 reverse_dfs_next_succ:
1355 BBState::edge_iterator PE = BBStates[PredStack.back().first].pred_end();
1356 while (PredStack.back().second != PE) {
1357 BasicBlock *BB = *PredStack.back().second++;
1358 if (Visited.insert(BB).second) {
1359 PredStack.push_back(std::make_pair(BB, BBStates[BB].pred_begin()));
1360 goto reverse_dfs_next_succ;
1363 ReverseCFGPostOrder.push_back(PredStack.pop_back_val().first);
1368 // Visit the function both top-down and bottom-up.
1369 bool ObjCARCOpt::Visit(Function &F,
1370 DenseMap<const BasicBlock *, BBState> &BBStates,
1371 BlotMapVector<Value *, RRInfo> &Retains,
1372 DenseMap<Value *, RRInfo> &Releases) {
1374 // Use reverse-postorder traversals, because we magically know that loops
1375 // will be well behaved, i.e. they won't repeatedly call retain on a single
1376 // pointer without doing a release. We can't use the ReversePostOrderTraversal
1377 // class here because we want the reverse-CFG postorder to consider each
1378 // function exit point, and we want to ignore selected cycle edges.
1379 SmallVector<BasicBlock *, 16> PostOrder;
1380 SmallVector<BasicBlock *, 16> ReverseCFGPostOrder;
1381 ComputePostOrders(F, PostOrder, ReverseCFGPostOrder,
1382 MDKindCache.NoObjCARCExceptionsMDKind, BBStates);
1384 // Use reverse-postorder on the reverse CFG for bottom-up.
1385 bool BottomUpNestingDetected = false;
1386 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
1387 ReverseCFGPostOrder.rbegin(), E = ReverseCFGPostOrder.rend();
1389 BottomUpNestingDetected |= VisitBottomUp(*I, BBStates, Retains);
1391 // Use reverse-postorder for top-down.
1392 bool TopDownNestingDetected = false;
1393 for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
1394 PostOrder.rbegin(), E = PostOrder.rend();
1396 TopDownNestingDetected |= VisitTopDown(*I, BBStates, Releases);
1398 return TopDownNestingDetected && BottomUpNestingDetected;
1401 /// Move the calls in RetainsToMove and ReleasesToMove.
1402 void ObjCARCOpt::MoveCalls(Value *Arg, RRInfo &RetainsToMove,
1403 RRInfo &ReleasesToMove,
1404 BlotMapVector<Value *, RRInfo> &Retains,
1405 DenseMap<Value *, RRInfo> &Releases,
1406 SmallVectorImpl<Instruction *> &DeadInsts,
1408 Type *ArgTy = Arg->getType();
1409 Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext()));
1411 DEBUG(dbgs() << "== ObjCARCOpt::MoveCalls ==\n");
1413 // Insert the new retain and release calls.
1414 for (Instruction *InsertPt : ReleasesToMove.ReverseInsertPts) {
1415 Value *MyArg = ArgTy == ParamTy ? Arg :
1416 new BitCastInst(Arg, ParamTy, "", InsertPt);
1417 Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
1418 CallInst *Call = CallInst::Create(Decl, MyArg, "", InsertPt);
1419 Call->setDoesNotThrow();
1420 Call->setTailCall();
1422 DEBUG(dbgs() << "Inserting new Retain: " << *Call << "\n"
1423 "At insertion point: " << *InsertPt << "\n");
1425 for (Instruction *InsertPt : RetainsToMove.ReverseInsertPts) {
1426 Value *MyArg = ArgTy == ParamTy ? Arg :
1427 new BitCastInst(Arg, ParamTy, "", InsertPt);
1428 Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Release);
1429 CallInst *Call = CallInst::Create(Decl, MyArg, "", InsertPt);
1430 // Attach a clang.imprecise_release metadata tag, if appropriate.
1431 if (MDNode *M = ReleasesToMove.ReleaseMetadata)
1432 Call->setMetadata(MDKindCache.ImpreciseReleaseMDKind, M);
1433 Call->setDoesNotThrow();
1434 if (ReleasesToMove.IsTailCallRelease)
1435 Call->setTailCall();
1437 DEBUG(dbgs() << "Inserting new Release: " << *Call << "\n"
1438 "At insertion point: " << *InsertPt << "\n");
1441 // Delete the original retain and release calls.
1442 for (Instruction *OrigRetain : RetainsToMove.Calls) {
1443 Retains.blot(OrigRetain);
1444 DeadInsts.push_back(OrigRetain);
1445 DEBUG(dbgs() << "Deleting retain: " << *OrigRetain << "\n");
1447 for (Instruction *OrigRelease : ReleasesToMove.Calls) {
1448 Releases.erase(OrigRelease);
1449 DeadInsts.push_back(OrigRelease);
1450 DEBUG(dbgs() << "Deleting release: " << *OrigRelease << "\n");
1455 bool ObjCARCOpt::ConnectTDBUTraversals(
1456 DenseMap<const BasicBlock *, BBState> &BBStates,
1457 BlotMapVector<Value *, RRInfo> &Retains,
1458 DenseMap<Value *, RRInfo> &Releases, Module *M,
1459 SmallVectorImpl<Instruction *> &NewRetains,
1460 SmallVectorImpl<Instruction *> &NewReleases,
1461 SmallVectorImpl<Instruction *> &DeadInsts, RRInfo &RetainsToMove,
1462 RRInfo &ReleasesToMove, Value *Arg, bool KnownSafe,
1463 bool &AnyPairsCompletelyEliminated) {
1464 // If a pair happens in a region where it is known that the reference count
1465 // is already incremented, we can similarly ignore possible decrements unless
1466 // we are dealing with a retainable object with multiple provenance sources.
1467 bool KnownSafeTD = true, KnownSafeBU = true;
1468 bool MultipleOwners = false;
1469 bool CFGHazardAfflicted = false;
1471 // Connect the dots between the top-down-collected RetainsToMove and
1472 // bottom-up-collected ReleasesToMove to form sets of related calls.
1473 // This is an iterative process so that we connect multiple releases
1474 // to multiple retains if needed.
1475 unsigned OldDelta = 0;
1476 unsigned NewDelta = 0;
1477 unsigned OldCount = 0;
1478 unsigned NewCount = 0;
1479 bool FirstRelease = true;
1481 for (SmallVectorImpl<Instruction *>::const_iterator
1482 NI = NewRetains.begin(), NE = NewRetains.end(); NI != NE; ++NI) {
1483 Instruction *NewRetain = *NI;
1484 auto It = Retains.find(NewRetain);
1485 assert(It != Retains.end());
1486 const RRInfo &NewRetainRRI = It->second;
1487 KnownSafeTD &= NewRetainRRI.KnownSafe;
1489 MultipleOwners || MultiOwnersSet.count(GetArgRCIdentityRoot(NewRetain));
1490 for (Instruction *NewRetainRelease : NewRetainRRI.Calls) {
1491 auto Jt = Releases.find(NewRetainRelease);
1492 if (Jt == Releases.end())
1494 const RRInfo &NewRetainReleaseRRI = Jt->second;
1496 // If the release does not have a reference to the retain as well,
1497 // something happened which is unaccounted for. Do not do anything.
1499 // This can happen if we catch an additive overflow during path count
1501 if (!NewRetainReleaseRRI.Calls.count(NewRetain))
1504 if (ReleasesToMove.Calls.insert(NewRetainRelease).second) {
1506 // If we overflow when we compute the path count, don't remove/move
1508 const BBState &NRRBBState = BBStates[NewRetainRelease->getParent()];
1509 unsigned PathCount = BBState::OverflowOccurredValue;
1510 if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
1512 assert(PathCount != BBState::OverflowOccurredValue &&
1513 "PathCount at this point can not be "
1514 "OverflowOccurredValue.");
1515 OldDelta -= PathCount;
1517 // Merge the ReleaseMetadata and IsTailCallRelease values.
1519 ReleasesToMove.ReleaseMetadata =
1520 NewRetainReleaseRRI.ReleaseMetadata;
1521 ReleasesToMove.IsTailCallRelease =
1522 NewRetainReleaseRRI.IsTailCallRelease;
1523 FirstRelease = false;
1525 if (ReleasesToMove.ReleaseMetadata !=
1526 NewRetainReleaseRRI.ReleaseMetadata)
1527 ReleasesToMove.ReleaseMetadata = nullptr;
1528 if (ReleasesToMove.IsTailCallRelease !=
1529 NewRetainReleaseRRI.IsTailCallRelease)
1530 ReleasesToMove.IsTailCallRelease = false;
1533 // Collect the optimal insertion points.
1535 for (Instruction *RIP : NewRetainReleaseRRI.ReverseInsertPts) {
1536 if (ReleasesToMove.ReverseInsertPts.insert(RIP).second) {
1537 // If we overflow when we compute the path count, don't
1538 // remove/move anything.
1539 const BBState &RIPBBState = BBStates[RIP->getParent()];
1540 PathCount = BBState::OverflowOccurredValue;
1541 if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
1543 assert(PathCount != BBState::OverflowOccurredValue &&
1544 "PathCount at this point can not be "
1545 "OverflowOccurredValue.");
1546 NewDelta -= PathCount;
1549 NewReleases.push_back(NewRetainRelease);
1554 if (NewReleases.empty()) break;
1556 // Back the other way.
1557 for (SmallVectorImpl<Instruction *>::const_iterator
1558 NI = NewReleases.begin(), NE = NewReleases.end(); NI != NE; ++NI) {
1559 Instruction *NewRelease = *NI;
1560 auto It = Releases.find(NewRelease);
1561 assert(It != Releases.end());
1562 const RRInfo &NewReleaseRRI = It->second;
1563 KnownSafeBU &= NewReleaseRRI.KnownSafe;
1564 CFGHazardAfflicted |= NewReleaseRRI.CFGHazardAfflicted;
1565 for (Instruction *NewReleaseRetain : NewReleaseRRI.Calls) {
1566 auto Jt = Retains.find(NewReleaseRetain);
1567 if (Jt == Retains.end())
1569 const RRInfo &NewReleaseRetainRRI = Jt->second;
1571 // If the retain does not have a reference to the release as well,
1572 // something happened which is unaccounted for. Do not do anything.
1574 // This can happen if we catch an additive overflow during path count
1576 if (!NewReleaseRetainRRI.Calls.count(NewRelease))
1579 if (RetainsToMove.Calls.insert(NewReleaseRetain).second) {
1580 // If we overflow when we compute the path count, don't remove/move
1582 const BBState &NRRBBState = BBStates[NewReleaseRetain->getParent()];
1583 unsigned PathCount = BBState::OverflowOccurredValue;
1584 if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
1586 assert(PathCount != BBState::OverflowOccurredValue &&
1587 "PathCount at this point can not be "
1588 "OverflowOccurredValue.");
1589 OldDelta += PathCount;
1590 OldCount += PathCount;
1592 // Collect the optimal insertion points.
1594 for (Instruction *RIP : NewReleaseRetainRRI.ReverseInsertPts) {
1595 if (RetainsToMove.ReverseInsertPts.insert(RIP).second) {
1596 // If we overflow when we compute the path count, don't
1597 // remove/move anything.
1598 const BBState &RIPBBState = BBStates[RIP->getParent()];
1600 PathCount = BBState::OverflowOccurredValue;
1601 if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
1603 assert(PathCount != BBState::OverflowOccurredValue &&
1604 "PathCount at this point can not be "
1605 "OverflowOccurredValue.");
1606 NewDelta += PathCount;
1607 NewCount += PathCount;
1610 NewRetains.push_back(NewReleaseRetain);
1614 NewReleases.clear();
1615 if (NewRetains.empty()) break;
1618 // If the pointer is known incremented in 1 direction and we do not have
1619 // MultipleOwners, we can safely remove the retain/releases. Otherwise we need
1620 // to be known safe in both directions.
1621 bool UnconditionallySafe = (KnownSafeTD && KnownSafeBU) ||
1622 ((KnownSafeTD || KnownSafeBU) && !MultipleOwners);
1623 if (UnconditionallySafe) {
1624 RetainsToMove.ReverseInsertPts.clear();
1625 ReleasesToMove.ReverseInsertPts.clear();
1628 // Determine whether the new insertion points we computed preserve the
1629 // balance of retain and release calls through the program.
1630 // TODO: If the fully aggressive solution isn't valid, try to find a
1631 // less aggressive solution which is.
1635 // At this point, we are not going to remove any RR pairs, but we still are
1636 // able to move RR pairs. If one of our pointers is afflicted with
1637 // CFGHazards, we cannot perform such code motion so exit early.
1638 const bool WillPerformCodeMotion = RetainsToMove.ReverseInsertPts.size() ||
1639 ReleasesToMove.ReverseInsertPts.size();
1640 if (CFGHazardAfflicted && WillPerformCodeMotion)
1644 // Determine whether the original call points are balanced in the retain and
1645 // release calls through the program. If not, conservatively don't touch
1647 // TODO: It's theoretically possible to do code motion in this case, as
1648 // long as the existing imbalances are maintained.
1653 assert(OldCount != 0 && "Unreachable code?");
1654 NumRRs += OldCount - NewCount;
1655 // Set to true if we completely removed any RR pairs.
1656 AnyPairsCompletelyEliminated = NewCount == 0;
1658 // We can move calls!
1662 /// Identify pairings between the retains and releases, and delete and/or move
1664 bool ObjCARCOpt::PerformCodePlacement(
1665 DenseMap<const BasicBlock *, BBState> &BBStates,
1666 BlotMapVector<Value *, RRInfo> &Retains,
1667 DenseMap<Value *, RRInfo> &Releases, Module *M) {
1668 DEBUG(dbgs() << "\n== ObjCARCOpt::PerformCodePlacement ==\n");
1670 bool AnyPairsCompletelyEliminated = false;
1671 RRInfo RetainsToMove;
1672 RRInfo ReleasesToMove;
1673 SmallVector<Instruction *, 4> NewRetains;
1674 SmallVector<Instruction *, 4> NewReleases;
1675 SmallVector<Instruction *, 8> DeadInsts;
1677 // Visit each retain.
1678 for (BlotMapVector<Value *, RRInfo>::const_iterator I = Retains.begin(),
1681 Value *V = I->first;
1682 if (!V) continue; // blotted
1684 Instruction *Retain = cast<Instruction>(V);
1686 DEBUG(dbgs() << "Visiting: " << *Retain << "\n");
1688 Value *Arg = GetArgRCIdentityRoot(Retain);
1690 // If the object being released is in static or stack storage, we know it's
1691 // not being managed by ObjC reference counting, so we can delete pairs
1692 // regardless of what possible decrements or uses lie between them.
1693 bool KnownSafe = isa<Constant>(Arg) || isa<AllocaInst>(Arg);
1695 // A constant pointer can't be pointing to an object on the heap. It may
1696 // be reference-counted, but it won't be deleted.
1697 if (const LoadInst *LI = dyn_cast<LoadInst>(Arg))
1698 if (const GlobalVariable *GV =
1699 dyn_cast<GlobalVariable>(
1700 GetRCIdentityRoot(LI->getPointerOperand())))
1701 if (GV->isConstant())
1704 // Connect the dots between the top-down-collected RetainsToMove and
1705 // bottom-up-collected ReleasesToMove to form sets of related calls.
1706 NewRetains.push_back(Retain);
1707 bool PerformMoveCalls =
1708 ConnectTDBUTraversals(BBStates, Retains, Releases, M, NewRetains,
1709 NewReleases, DeadInsts, RetainsToMove,
1710 ReleasesToMove, Arg, KnownSafe,
1711 AnyPairsCompletelyEliminated);
1713 if (PerformMoveCalls) {
1714 // Ok, everything checks out and we're all set. Let's move/delete some
1716 MoveCalls(Arg, RetainsToMove, ReleasesToMove,
1717 Retains, Releases, DeadInsts, M);
1720 // Clean up state for next retain.
1721 NewReleases.clear();
1723 RetainsToMove.clear();
1724 ReleasesToMove.clear();
1727 // Now that we're done moving everything, we can delete the newly dead
1728 // instructions, as we no longer need them as insert points.
1729 while (!DeadInsts.empty())
1730 EraseInstruction(DeadInsts.pop_back_val());
1732 return AnyPairsCompletelyEliminated;
1735 /// Weak pointer optimizations.
1736 void ObjCARCOpt::OptimizeWeakCalls(Function &F) {
1737 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeWeakCalls ==\n");
1739 // First, do memdep-style RLE and S2L optimizations. We can't use memdep
1740 // itself because it uses AliasAnalysis and we need to do provenance
1742 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
1743 Instruction *Inst = &*I++;
1745 DEBUG(dbgs() << "Visiting: " << *Inst << "\n");
1747 ARCInstKind Class = GetBasicARCInstKind(Inst);
1748 if (Class != ARCInstKind::LoadWeak &&
1749 Class != ARCInstKind::LoadWeakRetained)
1752 // Delete objc_loadWeak calls with no users.
1753 if (Class == ARCInstKind::LoadWeak && Inst->use_empty()) {
1754 Inst->eraseFromParent();
1758 // TODO: For now, just look for an earlier available version of this value
1759 // within the same block. Theoretically, we could do memdep-style non-local
1760 // analysis too, but that would want caching. A better approach would be to
1761 // use the technique that EarlyCSE uses.
1762 inst_iterator Current = std::prev(I);
1763 BasicBlock *CurrentBB = Current.getBasicBlockIterator();
1764 for (BasicBlock::iterator B = CurrentBB->begin(),
1765 J = Current.getInstructionIterator();
1767 Instruction *EarlierInst = &*std::prev(J);
1768 ARCInstKind EarlierClass = GetARCInstKind(EarlierInst);
1769 switch (EarlierClass) {
1770 case ARCInstKind::LoadWeak:
1771 case ARCInstKind::LoadWeakRetained: {
1772 // If this is loading from the same pointer, replace this load's value
1774 CallInst *Call = cast<CallInst>(Inst);
1775 CallInst *EarlierCall = cast<CallInst>(EarlierInst);
1776 Value *Arg = Call->getArgOperand(0);
1777 Value *EarlierArg = EarlierCall->getArgOperand(0);
1778 switch (PA.getAA()->alias(Arg, EarlierArg)) {
1779 case AliasAnalysis::MustAlias:
1781 // If the load has a builtin retain, insert a plain retain for it.
1782 if (Class == ARCInstKind::LoadWeakRetained) {
1783 Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
1784 CallInst *CI = CallInst::Create(Decl, EarlierCall, "", Call);
1787 // Zap the fully redundant load.
1788 Call->replaceAllUsesWith(EarlierCall);
1789 Call->eraseFromParent();
1791 case AliasAnalysis::MayAlias:
1792 case AliasAnalysis::PartialAlias:
1794 case AliasAnalysis::NoAlias:
1799 case ARCInstKind::StoreWeak:
1800 case ARCInstKind::InitWeak: {
1801 // If this is storing to the same pointer and has the same size etc.
1802 // replace this load's value with the stored value.
1803 CallInst *Call = cast<CallInst>(Inst);
1804 CallInst *EarlierCall = cast<CallInst>(EarlierInst);
1805 Value *Arg = Call->getArgOperand(0);
1806 Value *EarlierArg = EarlierCall->getArgOperand(0);
1807 switch (PA.getAA()->alias(Arg, EarlierArg)) {
1808 case AliasAnalysis::MustAlias:
1810 // If the load has a builtin retain, insert a plain retain for it.
1811 if (Class == ARCInstKind::LoadWeakRetained) {
1812 Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
1813 CallInst *CI = CallInst::Create(Decl, EarlierCall, "", Call);
1816 // Zap the fully redundant load.
1817 Call->replaceAllUsesWith(EarlierCall->getArgOperand(1));
1818 Call->eraseFromParent();
1820 case AliasAnalysis::MayAlias:
1821 case AliasAnalysis::PartialAlias:
1823 case AliasAnalysis::NoAlias:
1828 case ARCInstKind::MoveWeak:
1829 case ARCInstKind::CopyWeak:
1830 // TOOD: Grab the copied value.
1832 case ARCInstKind::AutoreleasepoolPush:
1833 case ARCInstKind::None:
1834 case ARCInstKind::IntrinsicUser:
1835 case ARCInstKind::User:
1836 // Weak pointers are only modified through the weak entry points
1837 // (and arbitrary calls, which could call the weak entry points).
1840 // Anything else could modify the weak pointer.
1847 // Then, for each destroyWeak with an alloca operand, check to see if
1848 // the alloca and all its users can be zapped.
1849 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
1850 Instruction *Inst = &*I++;
1851 ARCInstKind Class = GetBasicARCInstKind(Inst);
1852 if (Class != ARCInstKind::DestroyWeak)
1855 CallInst *Call = cast<CallInst>(Inst);
1856 Value *Arg = Call->getArgOperand(0);
1857 if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) {
1858 for (User *U : Alloca->users()) {
1859 const Instruction *UserInst = cast<Instruction>(U);
1860 switch (GetBasicARCInstKind(UserInst)) {
1861 case ARCInstKind::InitWeak:
1862 case ARCInstKind::StoreWeak:
1863 case ARCInstKind::DestroyWeak:
1870 for (auto UI = Alloca->user_begin(), UE = Alloca->user_end(); UI != UE;) {
1871 CallInst *UserInst = cast<CallInst>(*UI++);
1872 switch (GetBasicARCInstKind(UserInst)) {
1873 case ARCInstKind::InitWeak:
1874 case ARCInstKind::StoreWeak:
1875 // These functions return their second argument.
1876 UserInst->replaceAllUsesWith(UserInst->getArgOperand(1));
1878 case ARCInstKind::DestroyWeak:
1882 llvm_unreachable("alloca really is used!");
1884 UserInst->eraseFromParent();
1886 Alloca->eraseFromParent();
1892 /// Identify program paths which execute sequences of retains and releases which
1893 /// can be eliminated.
1894 bool ObjCARCOpt::OptimizeSequences(Function &F) {
1895 // Releases, Retains - These are used to store the results of the main flow
1896 // analysis. These use Value* as the key instead of Instruction* so that the
1897 // map stays valid when we get around to rewriting code and calls get
1898 // replaced by arguments.
1899 DenseMap<Value *, RRInfo> Releases;
1900 BlotMapVector<Value *, RRInfo> Retains;
1902 // This is used during the traversal of the function to track the
1903 // states for each identified object at each block.
1904 DenseMap<const BasicBlock *, BBState> BBStates;
1906 // Analyze the CFG of the function, and all instructions.
1907 bool NestingDetected = Visit(F, BBStates, Retains, Releases);
1910 bool AnyPairsCompletelyEliminated = PerformCodePlacement(BBStates, Retains,
1915 MultiOwnersSet.clear();
1917 return AnyPairsCompletelyEliminated && NestingDetected;
1920 /// Check if there is a dependent call earlier that does not have anything in
1921 /// between the Retain and the call that can affect the reference count of their
1922 /// shared pointer argument. Note that Retain need not be in BB.
1924 HasSafePathToPredecessorCall(const Value *Arg, Instruction *Retain,
1925 SmallPtrSetImpl<Instruction *> &DepInsts,
1926 SmallPtrSetImpl<const BasicBlock *> &Visited,
1927 ProvenanceAnalysis &PA) {
1928 FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain,
1929 DepInsts, Visited, PA);
1930 if (DepInsts.size() != 1)
1933 auto *Call = dyn_cast_or_null<CallInst>(*DepInsts.begin());
1935 // Check that the pointer is the return value of the call.
1936 if (!Call || Arg != Call)
1939 // Check that the call is a regular call.
1940 ARCInstKind Class = GetBasicARCInstKind(Call);
1941 if (Class != ARCInstKind::CallOrUser && Class != ARCInstKind::Call)
1947 /// Find a dependent retain that precedes the given autorelease for which there
1948 /// is nothing in between the two instructions that can affect the ref count of
1951 FindPredecessorRetainWithSafePath(const Value *Arg, BasicBlock *BB,
1952 Instruction *Autorelease,
1953 SmallPtrSetImpl<Instruction *> &DepInsts,
1954 SmallPtrSetImpl<const BasicBlock *> &Visited,
1955 ProvenanceAnalysis &PA) {
1956 FindDependencies(CanChangeRetainCount, Arg,
1957 BB, Autorelease, DepInsts, Visited, PA);
1958 if (DepInsts.size() != 1)
1961 auto *Retain = dyn_cast_or_null<CallInst>(*DepInsts.begin());
1963 // Check that we found a retain with the same argument.
1964 if (!Retain || !IsRetain(GetBasicARCInstKind(Retain)) ||
1965 GetArgRCIdentityRoot(Retain) != Arg) {
1972 /// Look for an ``autorelease'' instruction dependent on Arg such that there are
1973 /// no instructions dependent on Arg that need a positive ref count in between
1974 /// the autorelease and the ret.
1976 FindPredecessorAutoreleaseWithSafePath(const Value *Arg, BasicBlock *BB,
1978 SmallPtrSetImpl<Instruction *> &DepInsts,
1979 SmallPtrSetImpl<const BasicBlock *> &V,
1980 ProvenanceAnalysis &PA) {
1981 FindDependencies(NeedsPositiveRetainCount, Arg,
1982 BB, Ret, DepInsts, V, PA);
1983 if (DepInsts.size() != 1)
1986 auto *Autorelease = dyn_cast_or_null<CallInst>(*DepInsts.begin());
1989 ARCInstKind AutoreleaseClass = GetBasicARCInstKind(Autorelease);
1990 if (!IsAutorelease(AutoreleaseClass))
1992 if (GetArgRCIdentityRoot(Autorelease) != Arg)
1998 /// Look for this pattern:
2000 /// %call = call i8* @something(...)
2001 /// %2 = call i8* @objc_retain(i8* %call)
2002 /// %3 = call i8* @objc_autorelease(i8* %2)
2005 /// And delete the retain and autorelease.
2006 void ObjCARCOpt::OptimizeReturns(Function &F) {
2007 if (!F.getReturnType()->isPointerTy())
2010 DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeReturns ==\n");
2012 SmallPtrSet<Instruction *, 4> DependingInstructions;
2013 SmallPtrSet<const BasicBlock *, 4> Visited;
2014 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
2015 BasicBlock *BB = FI;
2016 ReturnInst *Ret = dyn_cast<ReturnInst>(&BB->back());
2018 DEBUG(dbgs() << "Visiting: " << *Ret << "\n");
2023 const Value *Arg = GetRCIdentityRoot(Ret->getOperand(0));
2025 // Look for an ``autorelease'' instruction that is a predecessor of Ret and
2026 // dependent on Arg such that there are no instructions dependent on Arg
2027 // that need a positive ref count in between the autorelease and Ret.
2028 CallInst *Autorelease =
2029 FindPredecessorAutoreleaseWithSafePath(Arg, BB, Ret,
2030 DependingInstructions, Visited,
2032 DependingInstructions.clear();
2039 FindPredecessorRetainWithSafePath(Arg, BB, Autorelease,
2040 DependingInstructions, Visited, PA);
2041 DependingInstructions.clear();
2047 // Check that there is nothing that can affect the reference count
2048 // between the retain and the call. Note that Retain need not be in BB.
2049 bool HasSafePathToCall = HasSafePathToPredecessorCall(Arg, Retain,
2050 DependingInstructions,
2052 DependingInstructions.clear();
2055 if (!HasSafePathToCall)
2058 // If so, we can zap the retain and autorelease.
2061 DEBUG(dbgs() << "Erasing: " << *Retain << "\nErasing: "
2062 << *Autorelease << "\n");
2063 EraseInstruction(Retain);
2064 EraseInstruction(Autorelease);
2070 ObjCARCOpt::GatherStatistics(Function &F, bool AfterOptimization) {
2071 llvm::Statistic &NumRetains =
2072 AfterOptimization? NumRetainsAfterOpt : NumRetainsBeforeOpt;
2073 llvm::Statistic &NumReleases =
2074 AfterOptimization? NumReleasesAfterOpt : NumReleasesBeforeOpt;
2076 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
2077 Instruction *Inst = &*I++;
2078 switch (GetBasicARCInstKind(Inst)) {
2081 case ARCInstKind::Retain:
2084 case ARCInstKind::Release:
2092 bool ObjCARCOpt::doInitialization(Module &M) {
2096 // If nothing in the Module uses ARC, don't do anything.
2097 Run = ModuleHasARC(M);
2101 // Identify the imprecise release metadata kind.
2102 MDKindCache.ImpreciseReleaseMDKind =
2103 M.getContext().getMDKindID("clang.imprecise_release");
2104 MDKindCache.CopyOnEscapeMDKind =
2105 M.getContext().getMDKindID("clang.arc.copy_on_escape");
2106 MDKindCache.NoObjCARCExceptionsMDKind =
2107 M.getContext().getMDKindID("clang.arc.no_objc_arc_exceptions");
2109 // Intuitively, objc_retain and others are nocapture, however in practice
2110 // they are not, because they return their argument value. And objc_release
2111 // calls finalizers which can have arbitrary side effects.
2113 // Initialize our runtime entry point cache.
2119 bool ObjCARCOpt::runOnFunction(Function &F) {
2123 // If nothing in the Module uses ARC, don't do anything.
2129 DEBUG(dbgs() << "<<< ObjCARCOpt: Visiting Function: " << F.getName() << " >>>"
2132 PA.setAA(&getAnalysis<AliasAnalysis>());
2135 if (AreStatisticsEnabled()) {
2136 GatherStatistics(F, false);
2140 // This pass performs several distinct transformations. As a compile-time aid
2141 // when compiling code that isn't ObjC, skip these if the relevant ObjC
2142 // library functions aren't declared.
2144 // Preliminary optimizations. This also computes UsedInThisFunction.
2145 OptimizeIndividualCalls(F);
2147 // Optimizations for weak pointers.
2148 if (UsedInThisFunction & ((1 << unsigned(ARCInstKind::LoadWeak)) |
2149 (1 << unsigned(ARCInstKind::LoadWeakRetained)) |
2150 (1 << unsigned(ARCInstKind::StoreWeak)) |
2151 (1 << unsigned(ARCInstKind::InitWeak)) |
2152 (1 << unsigned(ARCInstKind::CopyWeak)) |
2153 (1 << unsigned(ARCInstKind::MoveWeak)) |
2154 (1 << unsigned(ARCInstKind::DestroyWeak))))
2155 OptimizeWeakCalls(F);
2157 // Optimizations for retain+release pairs.
2158 if (UsedInThisFunction & ((1 << unsigned(ARCInstKind::Retain)) |
2159 (1 << unsigned(ARCInstKind::RetainRV)) |
2160 (1 << unsigned(ARCInstKind::RetainBlock))))
2161 if (UsedInThisFunction & (1 << unsigned(ARCInstKind::Release)))
2162 // Run OptimizeSequences until it either stops making changes or
2163 // no retain+release pair nesting is detected.
2164 while (OptimizeSequences(F)) {}
2166 // Optimizations if objc_autorelease is used.
2167 if (UsedInThisFunction & ((1 << unsigned(ARCInstKind::Autorelease)) |
2168 (1 << unsigned(ARCInstKind::AutoreleaseRV))))
2171 // Gather statistics after optimization.
2173 if (AreStatisticsEnabled()) {
2174 GatherStatistics(F, true);
2178 DEBUG(dbgs() << "\n");
2183 void ObjCARCOpt::releaseMemory() {