1 //===- ObjCARCContract.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 late ObjC ARC optimizations. ARC stands for Automatic
11 /// Reference Counting and is a system for managing reference counts for objects
14 /// This specific file mainly deals with ``contracting'' multiple lower level
15 /// operations into singular higher level operations through pattern matching.
17 /// WARNING: This file knows about certain library functions. It recognizes them
18 /// by name, and hardwires knowledge of their semantics.
20 /// WARNING: This file knows about how certain Objective-C library functions are
21 /// used. Naive LLVM IR transformations which would otherwise be
22 /// behavior-preserving may break these assumptions.
24 //===----------------------------------------------------------------------===//
26 // TODO: ObjCARCContract could insert PHI nodes when uses aren't
27 // dominated by single calls.
29 #include "ARCRuntimeEntryPoints.h"
30 #include "DependencyAnalysis.h"
32 #include "ProvenanceAnalysis.h"
33 #include "llvm/ADT/Statistic.h"
34 #include "llvm/Analysis/EHPersonalities.h"
35 #include "llvm/IR/Dominators.h"
36 #include "llvm/IR/InlineAsm.h"
37 #include "llvm/IR/Operator.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Support/raw_ostream.h"
42 using namespace llvm::objcarc;
44 #define DEBUG_TYPE "objc-arc-contract"
46 STATISTIC(NumPeeps, "Number of calls peephole-optimized");
47 STATISTIC(NumStoreStrongs, "Number objc_storeStrong calls formed");
49 //===----------------------------------------------------------------------===//
51 //===----------------------------------------------------------------------===//
54 /// Late ARC optimizations
56 /// These change the IR in a way that makes it difficult to be analyzed by
57 /// ObjCARCOpt, so it's run late.
58 class ObjCARCContract : public FunctionPass {
62 ProvenanceAnalysis PA;
63 ARCRuntimeEntryPoints EP;
65 /// A flag indicating whether this optimization pass should run.
68 /// The inline asm string to insert between calls and RetainRV calls to make
69 /// the optimization work on targets which need it.
70 const MDString *RVInstMarker;
72 /// The set of inserted objc_storeStrong calls. If at the end of walking the
73 /// function we have found no alloca instructions, these calls can be marked
75 SmallPtrSet<CallInst *, 8> StoreStrongCalls;
77 /// Returns true if we eliminated Inst.
78 bool tryToPeepholeInstruction(
79 Function &F, Instruction *Inst, inst_iterator &Iter,
80 SmallPtrSetImpl<Instruction *> &DepInsts,
81 SmallPtrSetImpl<const BasicBlock *> &Visited,
82 bool &TailOkForStoreStrong,
83 const DenseMap<BasicBlock *, ColorVector> &BlockColors);
85 bool optimizeRetainCall(Function &F, Instruction *Retain);
88 contractAutorelease(Function &F, Instruction *Autorelease,
90 SmallPtrSetImpl<Instruction *> &DependingInstructions,
91 SmallPtrSetImpl<const BasicBlock *> &Visited);
93 void tryToContractReleaseIntoStoreStrong(
94 Instruction *Release, inst_iterator &Iter,
95 const DenseMap<BasicBlock *, ColorVector> &BlockColors);
97 void getAnalysisUsage(AnalysisUsage &AU) const override;
98 bool doInitialization(Module &M) override;
99 bool runOnFunction(Function &F) override;
103 ObjCARCContract() : FunctionPass(ID) {
104 initializeObjCARCContractPass(*PassRegistry::getPassRegistry());
109 //===----------------------------------------------------------------------===//
111 //===----------------------------------------------------------------------===//
113 /// Turn objc_retain into objc_retainAutoreleasedReturnValue if the operand is a
114 /// return value. We do this late so we do not disrupt the dataflow analysis in
116 bool ObjCARCContract::optimizeRetainCall(Function &F, Instruction *Retain) {
117 ImmutableCallSite CS(GetArgRCIdentityRoot(Retain));
118 const Instruction *Call = CS.getInstruction();
121 if (Call->getParent() != Retain->getParent())
124 // Check that the call is next to the retain.
125 BasicBlock::const_iterator I = ++Call->getIterator();
126 while (IsNoopInstruction(&*I))
131 // Turn it to an objc_retainAutoreleasedReturnValue.
136 dbgs() << "Transforming objc_retain => "
137 "objc_retainAutoreleasedReturnValue since the operand is a "
138 "return value.\nOld: "
141 // We do not have to worry about tail calls/does not throw since
142 // retain/retainRV have the same properties.
143 Constant *Decl = EP.get(ARCRuntimeEntryPointKind::RetainRV);
144 cast<CallInst>(Retain)->setCalledFunction(Decl);
146 LLVM_DEBUG(dbgs() << "New: " << *Retain << "\n");
150 /// Merge an autorelease with a retain into a fused call.
151 bool ObjCARCContract::contractAutorelease(
152 Function &F, Instruction *Autorelease, ARCInstKind Class,
153 SmallPtrSetImpl<Instruction *> &DependingInstructions,
154 SmallPtrSetImpl<const BasicBlock *> &Visited) {
155 const Value *Arg = GetArgRCIdentityRoot(Autorelease);
157 // Check that there are no instructions between the retain and the autorelease
158 // (such as an autorelease_pop) which may change the count.
159 CallInst *Retain = nullptr;
160 if (Class == ARCInstKind::AutoreleaseRV)
161 FindDependencies(RetainAutoreleaseRVDep, Arg,
162 Autorelease->getParent(), Autorelease,
163 DependingInstructions, Visited, PA);
165 FindDependencies(RetainAutoreleaseDep, Arg,
166 Autorelease->getParent(), Autorelease,
167 DependingInstructions, Visited, PA);
170 if (DependingInstructions.size() != 1) {
171 DependingInstructions.clear();
175 Retain = dyn_cast_or_null<CallInst>(*DependingInstructions.begin());
176 DependingInstructions.clear();
178 if (!Retain || GetBasicARCInstKind(Retain) != ARCInstKind::Retain ||
179 GetArgRCIdentityRoot(Retain) != Arg)
185 LLVM_DEBUG(dbgs() << " Fusing retain/autorelease!\n"
192 Constant *Decl = EP.get(Class == ARCInstKind::AutoreleaseRV
193 ? ARCRuntimeEntryPointKind::RetainAutoreleaseRV
194 : ARCRuntimeEntryPointKind::RetainAutorelease);
195 Retain->setCalledFunction(Decl);
197 LLVM_DEBUG(dbgs() << " New RetainAutorelease: " << *Retain << "\n");
199 EraseInstruction(Autorelease);
203 static StoreInst *findSafeStoreForStoreStrongContraction(LoadInst *Load,
204 Instruction *Release,
205 ProvenanceAnalysis &PA,
207 StoreInst *Store = nullptr;
208 bool SawRelease = false;
210 // Get the location associated with Load.
211 MemoryLocation Loc = MemoryLocation::get(Load);
212 auto *LocPtr = Loc.Ptr->stripPointerCasts();
214 // Walk down to find the store and the release, which may be in either order.
215 for (auto I = std::next(BasicBlock::iterator(Load)),
216 E = Load->getParent()->end();
218 // If we found the store we were looking for and saw the release,
219 // break. There is no more work to be done.
220 if (Store && SawRelease)
223 // Now we know that we have not seen either the store or the release. If I
224 // is the release, mark that we saw the release and continue.
225 Instruction *Inst = &*I;
226 if (Inst == Release) {
231 // Otherwise, we check if Inst is a "good" store. Grab the instruction class
233 ARCInstKind Class = GetBasicARCInstKind(Inst);
235 // If Inst is an unrelated retain, we don't care about it.
237 // TODO: This is one area where the optimization could be made more
242 // If we have seen the store, but not the release...
244 // We need to make sure that it is safe to move the release from its
245 // current position to the store. This implies proving that any
246 // instruction in between Store and the Release conservatively can not use
247 // the RCIdentityRoot of Release. If we can prove we can ignore Inst, so
249 if (!CanUse(Inst, Load, PA, Class)) {
253 // Otherwise, be conservative and return nullptr.
257 // Ok, now we know we have not seen a store yet. See if Inst can write to
258 // our load location, if it can not, just ignore the instruction.
259 if (!isModSet(AA->getModRefInfo(Inst, Loc)))
262 Store = dyn_cast<StoreInst>(Inst);
264 // If Inst can, then check if Inst is a simple store. If Inst is not a
265 // store or a store that is not simple, then we have some we do not
266 // understand writing to this memory implying we can not move the load
267 // over the write to any subsequent store that we may find.
268 if (!Store || !Store->isSimple())
271 // Then make sure that the pointer we are storing to is Ptr. If so, we
273 if (Store->getPointerOperand()->stripPointerCasts() == LocPtr)
276 // Otherwise, we have an unknown store to some other ptr that clobbers
281 // If we did not find the store or did not see the release, fail.
282 if (!Store || !SawRelease)
290 findRetainForStoreStrongContraction(Value *New, StoreInst *Store,
291 Instruction *Release,
292 ProvenanceAnalysis &PA) {
293 // Walk up from the Store to find the retain.
294 BasicBlock::iterator I = Store->getIterator();
295 BasicBlock::iterator Begin = Store->getParent()->begin();
296 while (I != Begin && GetBasicARCInstKind(&*I) != ARCInstKind::Retain) {
297 Instruction *Inst = &*I;
299 // It is only safe to move the retain to the store if we can prove
300 // conservatively that nothing besides the release can decrement reference
301 // counts in between the retain and the store.
302 if (CanDecrementRefCount(Inst, New, PA) && Inst != Release)
306 Instruction *Retain = &*I;
307 if (GetBasicARCInstKind(Retain) != ARCInstKind::Retain)
309 if (GetArgRCIdentityRoot(Retain) != New)
314 /// Create a call instruction with the correct funclet token. Should be used
315 /// instead of calling CallInst::Create directly.
317 createCallInst(Value *Func, ArrayRef<Value *> Args, const Twine &NameStr,
318 Instruction *InsertBefore,
319 const DenseMap<BasicBlock *, ColorVector> &BlockColors) {
320 SmallVector<OperandBundleDef, 1> OpBundles;
321 if (!BlockColors.empty()) {
322 const ColorVector &CV = BlockColors.find(InsertBefore->getParent())->second;
323 assert(CV.size() == 1 && "non-unique color for block!");
324 Instruction *EHPad = CV.front()->getFirstNonPHI();
325 if (EHPad->isEHPad())
326 OpBundles.emplace_back("funclet", EHPad);
329 return CallInst::Create(Func, Args, OpBundles, NameStr, InsertBefore);
332 /// Attempt to merge an objc_release with a store, load, and objc_retain to form
333 /// an objc_storeStrong. An objc_storeStrong:
335 /// objc_storeStrong(i8** %old_ptr, i8* new_value)
337 /// is equivalent to the following IR sequence:
339 /// ; Load old value.
340 /// %old_value = load i8** %old_ptr (1)
342 /// ; Increment the new value and then release the old value. This must occur
343 /// ; in order in case old_value releases new_value in its destructor causing
344 /// ; us to potentially have a dangling ptr.
345 /// tail call i8* @objc_retain(i8* %new_value) (2)
346 /// tail call void @objc_release(i8* %old_value) (3)
348 /// ; Store the new_value into old_ptr
349 /// store i8* %new_value, i8** %old_ptr (4)
351 /// The safety of this optimization is based around the following
354 /// 1. We are forming the store strong at the store. Thus to perform this
355 /// optimization it must be safe to move the retain, load, and release to
357 /// 2. We need to make sure that any re-orderings of (1), (2), (3), (4) are
359 void ObjCARCContract::tryToContractReleaseIntoStoreStrong(
360 Instruction *Release, inst_iterator &Iter,
361 const DenseMap<BasicBlock *, ColorVector> &BlockColors) {
362 // See if we are releasing something that we just loaded.
363 auto *Load = dyn_cast<LoadInst>(GetArgRCIdentityRoot(Release));
364 if (!Load || !Load->isSimple())
367 // For now, require everything to be in one basic block.
368 BasicBlock *BB = Release->getParent();
369 if (Load->getParent() != BB)
372 // First scan down the BB from Load, looking for a store of the RCIdentityRoot
375 findSafeStoreForStoreStrongContraction(Load, Release, PA, AA);
380 // Then find what new_value's RCIdentity Root is.
381 Value *New = GetRCIdentityRoot(Store->getValueOperand());
383 // Then walk up the BB and look for a retain on New without any intervening
384 // instructions which conservatively might decrement ref counts.
385 Instruction *Retain =
386 findRetainForStoreStrongContraction(New, Store, Release, PA);
396 llvm::dbgs() << " Contracting retain, release into objc_storeStrong.\n"
398 << " Store: " << *Store << "\n"
399 << " Release: " << *Release << "\n"
400 << " Retain: " << *Retain << "\n"
401 << " Load: " << *Load << "\n");
403 LLVMContext &C = Release->getContext();
404 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
405 Type *I8XX = PointerType::getUnqual(I8X);
407 Value *Args[] = { Load->getPointerOperand(), New };
408 if (Args[0]->getType() != I8XX)
409 Args[0] = new BitCastInst(Args[0], I8XX, "", Store);
410 if (Args[1]->getType() != I8X)
411 Args[1] = new BitCastInst(Args[1], I8X, "", Store);
412 Constant *Decl = EP.get(ARCRuntimeEntryPointKind::StoreStrong);
413 CallInst *StoreStrong = createCallInst(Decl, Args, "", Store, BlockColors);
414 StoreStrong->setDoesNotThrow();
415 StoreStrong->setDebugLoc(Store->getDebugLoc());
417 // We can't set the tail flag yet, because we haven't yet determined
418 // whether there are any escaping allocas. Remember this call, so that
419 // we can set the tail flag once we know it's safe.
420 StoreStrongCalls.insert(StoreStrong);
422 LLVM_DEBUG(llvm::dbgs() << " New Store Strong: " << *StoreStrong
425 if (&*Iter == Retain) ++Iter;
426 if (&*Iter == Store) ++Iter;
427 Store->eraseFromParent();
428 Release->eraseFromParent();
429 EraseInstruction(Retain);
430 if (Load->use_empty())
431 Load->eraseFromParent();
434 bool ObjCARCContract::tryToPeepholeInstruction(
435 Function &F, Instruction *Inst, inst_iterator &Iter,
436 SmallPtrSetImpl<Instruction *> &DependingInsts,
437 SmallPtrSetImpl<const BasicBlock *> &Visited,
438 bool &TailOkForStoreStrongs,
439 const DenseMap<BasicBlock *, ColorVector> &BlockColors) {
440 // Only these library routines return their argument. In particular,
441 // objc_retainBlock does not necessarily return its argument.
442 ARCInstKind Class = GetBasicARCInstKind(Inst);
444 case ARCInstKind::FusedRetainAutorelease:
445 case ARCInstKind::FusedRetainAutoreleaseRV:
447 case ARCInstKind::Autorelease:
448 case ARCInstKind::AutoreleaseRV:
449 return contractAutorelease(F, Inst, Class, DependingInsts, Visited);
450 case ARCInstKind::Retain:
451 // Attempt to convert retains to retainrvs if they are next to function
453 if (!optimizeRetainCall(F, Inst))
455 // If we succeed in our optimization, fall through.
457 case ARCInstKind::RetainRV:
458 case ARCInstKind::ClaimRV: {
459 // If we're compiling for a target which needs a special inline-asm
460 // marker to do the return value optimization, insert it now.
463 BasicBlock::iterator BBI = Inst->getIterator();
464 BasicBlock *InstParent = Inst->getParent();
466 // Step up to see if the call immediately precedes the RV call.
467 // If it's an invoke, we have to cross a block boundary. And we have
468 // to carefully dodge no-op instructions.
470 if (BBI == InstParent->begin()) {
471 BasicBlock *Pred = InstParent->getSinglePredecessor();
473 goto decline_rv_optimization;
474 BBI = Pred->getTerminator()->getIterator();
478 } while (IsNoopInstruction(&*BBI));
480 if (&*BBI == GetArgRCIdentityRoot(Inst)) {
481 LLVM_DEBUG(dbgs() << "Adding inline asm marker for the return value "
484 InlineAsm *IA = InlineAsm::get(
485 FunctionType::get(Type::getVoidTy(Inst->getContext()),
487 RVInstMarker->getString(),
488 /*Constraints=*/"", /*hasSideEffects=*/true);
490 createCallInst(IA, None, "", Inst, BlockColors);
492 decline_rv_optimization:
495 case ARCInstKind::InitWeak: {
496 // objc_initWeak(p, null) => *p = null
497 CallInst *CI = cast<CallInst>(Inst);
498 if (IsNullOrUndef(CI->getArgOperand(1))) {
500 ConstantPointerNull::get(cast<PointerType>(CI->getType()));
502 new StoreInst(Null, CI->getArgOperand(0), CI);
504 LLVM_DEBUG(dbgs() << "OBJCARCContract: Old = " << *CI << "\n"
505 << " New = " << *Null << "\n");
507 CI->replaceAllUsesWith(Null);
508 CI->eraseFromParent();
512 case ARCInstKind::Release:
513 // Try to form an objc store strong from our release. If we fail, there is
514 // nothing further to do below, so continue.
515 tryToContractReleaseIntoStoreStrong(Inst, Iter, BlockColors);
517 case ARCInstKind::User:
518 // Be conservative if the function has any alloca instructions.
519 // Technically we only care about escaping alloca instructions,
520 // but this is sufficient to handle some interesting cases.
521 if (isa<AllocaInst>(Inst))
522 TailOkForStoreStrongs = false;
524 case ARCInstKind::IntrinsicUser:
525 // Remove calls to @clang.arc.use(...).
526 Inst->eraseFromParent();
533 //===----------------------------------------------------------------------===//
535 //===----------------------------------------------------------------------===//
537 bool ObjCARCContract::runOnFunction(Function &F) {
541 // If nothing in the Module uses ARC, don't do anything.
546 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
547 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
549 PA.setAA(&getAnalysis<AAResultsWrapperPass>().getAAResults());
551 DenseMap<BasicBlock *, ColorVector> BlockColors;
552 if (F.hasPersonalityFn() &&
553 isScopedEHPersonality(classifyEHPersonality(F.getPersonalityFn())))
554 BlockColors = colorEHFunclets(F);
556 LLVM_DEBUG(llvm::dbgs() << "**** ObjCARC Contract ****\n");
558 // Track whether it's ok to mark objc_storeStrong calls with the "tail"
559 // keyword. Be conservative if the function has variadic arguments.
560 // It seems that functions which "return twice" are also unsafe for the
561 // "tail" argument, because they are setjmp, which could need to
562 // return to an earlier stack state.
563 bool TailOkForStoreStrongs =
564 !F.isVarArg() && !F.callsFunctionThatReturnsTwice();
566 // For ObjC library calls which return their argument, replace uses of the
567 // argument with uses of the call return value, if it dominates the use. This
568 // reduces register pressure.
569 SmallPtrSet<Instruction *, 4> DependingInstructions;
570 SmallPtrSet<const BasicBlock *, 4> Visited;
571 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E;) {
572 Instruction *Inst = &*I++;
574 LLVM_DEBUG(dbgs() << "Visiting: " << *Inst << "\n");
576 // First try to peephole Inst. If there is nothing further we can do in
577 // terms of undoing objc-arc-expand, process the next inst.
578 if (tryToPeepholeInstruction(F, Inst, I, DependingInstructions, Visited,
579 TailOkForStoreStrongs, BlockColors))
582 // Otherwise, try to undo objc-arc-expand.
584 // Don't use GetArgRCIdentityRoot because we don't want to look through bitcasts
585 // and such; to do the replacement, the argument must have type i8*.
587 // Function for replacing uses of Arg dominated by Inst.
588 auto ReplaceArgUses = [Inst, this](Value *Arg) {
589 // If we're compiling bugpointed code, don't get in trouble.
590 if (!isa<Instruction>(Arg) && !isa<Argument>(Arg))
593 // Look through the uses of the pointer.
594 for (Value::use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
596 // Increment UI now, because we may unlink its element.
598 unsigned OperandNo = U.getOperandNo();
600 // If the call's return value dominates a use of the call's argument
601 // value, rewrite the use to use the return value. We check for
602 // reachability here because an unreachable call is considered to
603 // trivially dominate itself, which would lead us to rewriting its
604 // argument in terms of its return value, which would lead to
605 // infinite loops in GetArgRCIdentityRoot.
606 if (!DT->isReachableFromEntry(U) || !DT->dominates(Inst, U))
610 Instruction *Replacement = Inst;
611 Type *UseTy = U.get()->getType();
612 if (PHINode *PHI = dyn_cast<PHINode>(U.getUser())) {
613 // For PHI nodes, insert the bitcast in the predecessor block.
614 unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
615 BasicBlock *IncomingBB = PHI->getIncomingBlock(ValNo);
616 if (Replacement->getType() != UseTy) {
617 // A catchswitch is both a pad and a terminator, meaning a basic
618 // block with a catchswitch has no insertion point. Keep going up
619 // the dominator tree until we find a non-catchswitch.
620 BasicBlock *InsertBB = IncomingBB;
621 while (isa<CatchSwitchInst>(InsertBB->getFirstNonPHI())) {
622 InsertBB = DT->getNode(InsertBB)->getIDom()->getBlock();
625 assert(DT->dominates(Inst, &InsertBB->back()) &&
626 "Invalid insertion point for bitcast");
628 new BitCastInst(Replacement, UseTy, "", &InsertBB->back());
631 // While we're here, rewrite all edges for this PHI, rather
632 // than just one use at a time, to minimize the number of
634 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
635 if (PHI->getIncomingBlock(i) == IncomingBB) {
636 // Keep the UI iterator valid.
639 PHINode::getOperandNumForIncomingValue(i)) == &*UI)
641 PHI->setIncomingValue(i, Replacement);
644 if (Replacement->getType() != UseTy)
645 Replacement = new BitCastInst(Replacement, UseTy, "",
646 cast<Instruction>(U.getUser()));
653 Value *Arg = cast<CallInst>(Inst)->getArgOperand(0);
654 Value *OrigArg = Arg;
656 // TODO: Change this to a do-while.
660 // If Arg is a no-op casted pointer, strip one level of casts and iterate.
661 if (const BitCastInst *BI = dyn_cast<BitCastInst>(Arg))
662 Arg = BI->getOperand(0);
663 else if (isa<GEPOperator>(Arg) &&
664 cast<GEPOperator>(Arg)->hasAllZeroIndices())
665 Arg = cast<GEPOperator>(Arg)->getPointerOperand();
666 else if (isa<GlobalAlias>(Arg) &&
667 !cast<GlobalAlias>(Arg)->isInterposable())
668 Arg = cast<GlobalAlias>(Arg)->getAliasee();
670 // If Arg is a PHI node, get PHIs that are equivalent to it and replace
672 if (PHINode *PN = dyn_cast<PHINode>(Arg)) {
673 SmallVector<Value *, 1> PHIList;
674 getEquivalentPHIs(*PN, PHIList);
675 for (Value *PHI : PHIList)
682 // Replace bitcast users of Arg that are dominated by Inst.
683 SmallVector<BitCastInst *, 2> BitCastUsers;
685 // Add all bitcast users of the function argument first.
686 for (User *U : OrigArg->users())
687 if (auto *BC = dyn_cast<BitCastInst>(U))
688 BitCastUsers.push_back(BC);
690 // Replace the bitcasts with the call return. Iterate until list is empty.
691 while (!BitCastUsers.empty()) {
692 auto *BC = BitCastUsers.pop_back_val();
693 for (User *U : BC->users())
694 if (auto *B = dyn_cast<BitCastInst>(U))
695 BitCastUsers.push_back(B);
701 // If this function has no escaping allocas or suspicious vararg usage,
702 // objc_storeStrong calls can be marked with the "tail" keyword.
703 if (TailOkForStoreStrongs)
704 for (CallInst *CI : StoreStrongCalls)
706 StoreStrongCalls.clear();
711 //===----------------------------------------------------------------------===//
713 //===----------------------------------------------------------------------===//
715 char ObjCARCContract::ID = 0;
716 INITIALIZE_PASS_BEGIN(ObjCARCContract, "objc-arc-contract",
717 "ObjC ARC contraction", false, false)
718 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
719 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
720 INITIALIZE_PASS_END(ObjCARCContract, "objc-arc-contract",
721 "ObjC ARC contraction", false, false)
723 void ObjCARCContract::getAnalysisUsage(AnalysisUsage &AU) const {
724 AU.addRequired<AAResultsWrapperPass>();
725 AU.addRequired<DominatorTreeWrapperPass>();
726 AU.setPreservesCFG();
729 Pass *llvm::createObjCARCContractPass() { return new ObjCARCContract(); }
731 bool ObjCARCContract::doInitialization(Module &M) {
732 // If nothing in the Module uses ARC, don't do anything.
733 Run = ModuleHasARC(M);
739 // Initialize RVInstMarker.
740 RVInstMarker = nullptr;
741 if (NamedMDNode *NMD =
742 M.getNamedMetadata("clang.arc.retainAutoreleasedReturnValueMarker"))
743 if (NMD->getNumOperands() == 1) {
744 const MDNode *N = NMD->getOperand(0);
745 if (N->getNumOperands() == 1)
746 if (const MDString *S = dyn_cast<MDString>(N->getOperand(0)))