| //===- ObjCARCContract.cpp - ObjC ARC Optimization ------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| /// \file |
| /// This file defines late ObjC ARC optimizations. ARC stands for Automatic |
| /// Reference Counting and is a system for managing reference counts for objects |
| /// in Objective C. |
| /// |
| /// This specific file mainly deals with ``contracting'' multiple lower level |
| /// operations into singular higher level operations through pattern matching. |
| /// |
| /// WARNING: This file knows about certain library functions. It recognizes them |
| /// by name, and hardwires knowledge of their semantics. |
| /// |
| /// WARNING: This file knows about how certain Objective-C library functions are |
| /// used. Naive LLVM IR transformations which would otherwise be |
| /// behavior-preserving may break these assumptions. |
| /// |
| //===----------------------------------------------------------------------===// |
| |
| // TODO: ObjCARCContract could insert PHI nodes when uses aren't |
| // dominated by single calls. |
| |
| #include "ARCRuntimeEntryPoints.h" |
| #include "DependencyAnalysis.h" |
| #include "ObjCARC.h" |
| #include "ProvenanceAnalysis.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/EHPersonalities.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/InlineAsm.h" |
| #include "llvm/IR/Operator.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| |
| using namespace llvm; |
| using namespace llvm::objcarc; |
| |
| #define DEBUG_TYPE "objc-arc-contract" |
| |
| STATISTIC(NumPeeps, "Number of calls peephole-optimized"); |
| STATISTIC(NumStoreStrongs, "Number objc_storeStrong calls formed"); |
| |
| //===----------------------------------------------------------------------===// |
| // Declarations |
| //===----------------------------------------------------------------------===// |
| |
| namespace { |
| /// Late ARC optimizations |
| /// |
| /// These change the IR in a way that makes it difficult to be analyzed by |
| /// ObjCARCOpt, so it's run late. |
| class ObjCARCContract : public FunctionPass { |
| bool Changed; |
| AliasAnalysis *AA; |
| DominatorTree *DT; |
| ProvenanceAnalysis PA; |
| ARCRuntimeEntryPoints EP; |
| |
| /// A flag indicating whether this optimization pass should run. |
| bool Run; |
| |
| /// The inline asm string to insert between calls and RetainRV calls to make |
| /// the optimization work on targets which need it. |
| const MDString *RVInstMarker; |
| |
| /// The set of inserted objc_storeStrong calls. If at the end of walking the |
| /// function we have found no alloca instructions, these calls can be marked |
| /// "tail". |
| SmallPtrSet<CallInst *, 8> StoreStrongCalls; |
| |
| /// Returns true if we eliminated Inst. |
| bool tryToPeepholeInstruction( |
| Function &F, Instruction *Inst, inst_iterator &Iter, |
| SmallPtrSetImpl<Instruction *> &DepInsts, |
| SmallPtrSetImpl<const BasicBlock *> &Visited, |
| bool &TailOkForStoreStrong, |
| const DenseMap<BasicBlock *, ColorVector> &BlockColors); |
| |
| bool optimizeRetainCall(Function &F, Instruction *Retain); |
| |
| bool |
| contractAutorelease(Function &F, Instruction *Autorelease, |
| ARCInstKind Class, |
| SmallPtrSetImpl<Instruction *> &DependingInstructions, |
| SmallPtrSetImpl<const BasicBlock *> &Visited); |
| |
| void tryToContractReleaseIntoStoreStrong( |
| Instruction *Release, inst_iterator &Iter, |
| const DenseMap<BasicBlock *, ColorVector> &BlockColors); |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override; |
| bool doInitialization(Module &M) override; |
| bool runOnFunction(Function &F) override; |
| |
| public: |
| static char ID; |
| ObjCARCContract() : FunctionPass(ID) { |
| initializeObjCARCContractPass(*PassRegistry::getPassRegistry()); |
| } |
| }; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Implementation |
| //===----------------------------------------------------------------------===// |
| |
| /// Turn objc_retain into objc_retainAutoreleasedReturnValue if the operand is a |
| /// return value. We do this late so we do not disrupt the dataflow analysis in |
| /// ObjCARCOpt. |
| bool ObjCARCContract::optimizeRetainCall(Function &F, Instruction *Retain) { |
| ImmutableCallSite CS(GetArgRCIdentityRoot(Retain)); |
| const Instruction *Call = CS.getInstruction(); |
| if (!Call) |
| return false; |
| if (Call->getParent() != Retain->getParent()) |
| return false; |
| |
| // Check that the call is next to the retain. |
| BasicBlock::const_iterator I = ++Call->getIterator(); |
| while (IsNoopInstruction(&*I)) |
| ++I; |
| if (&*I != Retain) |
| return false; |
| |
| // Turn it to an objc_retainAutoreleasedReturnValue. |
| Changed = true; |
| ++NumPeeps; |
| |
| LLVM_DEBUG( |
| dbgs() << "Transforming objc_retain => " |
| "objc_retainAutoreleasedReturnValue since the operand is a " |
| "return value.\nOld: " |
| << *Retain << "\n"); |
| |
| // We do not have to worry about tail calls/does not throw since |
| // retain/retainRV have the same properties. |
| Function *Decl = EP.get(ARCRuntimeEntryPointKind::RetainRV); |
| cast<CallInst>(Retain)->setCalledFunction(Decl); |
| |
| LLVM_DEBUG(dbgs() << "New: " << *Retain << "\n"); |
| return true; |
| } |
| |
| /// Merge an autorelease with a retain into a fused call. |
| bool ObjCARCContract::contractAutorelease( |
| Function &F, Instruction *Autorelease, ARCInstKind Class, |
| SmallPtrSetImpl<Instruction *> &DependingInstructions, |
| SmallPtrSetImpl<const BasicBlock *> &Visited) { |
| const Value *Arg = GetArgRCIdentityRoot(Autorelease); |
| |
| // Check that there are no instructions between the retain and the autorelease |
| // (such as an autorelease_pop) which may change the count. |
| CallInst *Retain = nullptr; |
| if (Class == ARCInstKind::AutoreleaseRV) |
| FindDependencies(RetainAutoreleaseRVDep, Arg, |
| Autorelease->getParent(), Autorelease, |
| DependingInstructions, Visited, PA); |
| else |
| FindDependencies(RetainAutoreleaseDep, Arg, |
| Autorelease->getParent(), Autorelease, |
| DependingInstructions, Visited, PA); |
| |
| Visited.clear(); |
| if (DependingInstructions.size() != 1) { |
| DependingInstructions.clear(); |
| return false; |
| } |
| |
| Retain = dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); |
| DependingInstructions.clear(); |
| |
| if (!Retain || GetBasicARCInstKind(Retain) != ARCInstKind::Retain || |
| GetArgRCIdentityRoot(Retain) != Arg) |
| return false; |
| |
| Changed = true; |
| ++NumPeeps; |
| |
| LLVM_DEBUG(dbgs() << " Fusing retain/autorelease!\n" |
| " Autorelease:" |
| << *Autorelease |
| << "\n" |
| " Retain: " |
| << *Retain << "\n"); |
| |
| Function *Decl = EP.get(Class == ARCInstKind::AutoreleaseRV |
| ? ARCRuntimeEntryPointKind::RetainAutoreleaseRV |
| : ARCRuntimeEntryPointKind::RetainAutorelease); |
| Retain->setCalledFunction(Decl); |
| |
| LLVM_DEBUG(dbgs() << " New RetainAutorelease: " << *Retain << "\n"); |
| |
| EraseInstruction(Autorelease); |
| return true; |
| } |
| |
| static StoreInst *findSafeStoreForStoreStrongContraction(LoadInst *Load, |
| Instruction *Release, |
| ProvenanceAnalysis &PA, |
| AliasAnalysis *AA) { |
| StoreInst *Store = nullptr; |
| bool SawRelease = false; |
| |
| // Get the location associated with Load. |
| MemoryLocation Loc = MemoryLocation::get(Load); |
| auto *LocPtr = Loc.Ptr->stripPointerCasts(); |
| |
| // Walk down to find the store and the release, which may be in either order. |
| for (auto I = std::next(BasicBlock::iterator(Load)), |
| E = Load->getParent()->end(); |
| I != E; ++I) { |
| // If we found the store we were looking for and saw the release, |
| // break. There is no more work to be done. |
| if (Store && SawRelease) |
| break; |
| |
| // Now we know that we have not seen either the store or the release. If I |
| // is the release, mark that we saw the release and continue. |
| Instruction *Inst = &*I; |
| if (Inst == Release) { |
| SawRelease = true; |
| continue; |
| } |
| |
| // Otherwise, we check if Inst is a "good" store. Grab the instruction class |
| // of Inst. |
| ARCInstKind Class = GetBasicARCInstKind(Inst); |
| |
| // If Inst is an unrelated retain, we don't care about it. |
| // |
| // TODO: This is one area where the optimization could be made more |
| // aggressive. |
| if (IsRetain(Class)) |
| continue; |
| |
| // If we have seen the store, but not the release... |
| if (Store) { |
| // We need to make sure that it is safe to move the release from its |
| // current position to the store. This implies proving that any |
| // instruction in between Store and the Release conservatively can not use |
| // the RCIdentityRoot of Release. If we can prove we can ignore Inst, so |
| // continue... |
| if (!CanUse(Inst, Load, PA, Class)) { |
| continue; |
| } |
| |
| // Otherwise, be conservative and return nullptr. |
| return nullptr; |
| } |
| |
| // Ok, now we know we have not seen a store yet. See if Inst can write to |
| // our load location, if it can not, just ignore the instruction. |
| if (!isModSet(AA->getModRefInfo(Inst, Loc))) |
| continue; |
| |
| Store = dyn_cast<StoreInst>(Inst); |
| |
| // If Inst can, then check if Inst is a simple store. If Inst is not a |
| // store or a store that is not simple, then we have some we do not |
| // understand writing to this memory implying we can not move the load |
| // over the write to any subsequent store that we may find. |
| if (!Store || !Store->isSimple()) |
| return nullptr; |
| |
| // Then make sure that the pointer we are storing to is Ptr. If so, we |
| // found our Store! |
| if (Store->getPointerOperand()->stripPointerCasts() == LocPtr) |
| continue; |
| |
| // Otherwise, we have an unknown store to some other ptr that clobbers |
| // Loc.Ptr. Bail! |
| return nullptr; |
| } |
| |
| // If we did not find the store or did not see the release, fail. |
| if (!Store || !SawRelease) |
| return nullptr; |
| |
| // We succeeded! |
| return Store; |
| } |
| |
| static Instruction * |
| findRetainForStoreStrongContraction(Value *New, StoreInst *Store, |
| Instruction *Release, |
| ProvenanceAnalysis &PA) { |
| // Walk up from the Store to find the retain. |
| BasicBlock::iterator I = Store->getIterator(); |
| BasicBlock::iterator Begin = Store->getParent()->begin(); |
| while (I != Begin && GetBasicARCInstKind(&*I) != ARCInstKind::Retain) { |
| Instruction *Inst = &*I; |
| |
| // It is only safe to move the retain to the store if we can prove |
| // conservatively that nothing besides the release can decrement reference |
| // counts in between the retain and the store. |
| if (CanDecrementRefCount(Inst, New, PA) && Inst != Release) |
| return nullptr; |
| --I; |
| } |
| Instruction *Retain = &*I; |
| if (GetBasicARCInstKind(Retain) != ARCInstKind::Retain) |
| return nullptr; |
| if (GetArgRCIdentityRoot(Retain) != New) |
| return nullptr; |
| return Retain; |
| } |
| |
| /// Create a call instruction with the correct funclet token. Should be used |
| /// instead of calling CallInst::Create directly. |
| static CallInst * |
| createCallInst(FunctionType *FTy, Value *Func, ArrayRef<Value *> Args, |
| const Twine &NameStr, Instruction *InsertBefore, |
| const DenseMap<BasicBlock *, ColorVector> &BlockColors) { |
| SmallVector<OperandBundleDef, 1> OpBundles; |
| if (!BlockColors.empty()) { |
| const ColorVector &CV = BlockColors.find(InsertBefore->getParent())->second; |
| assert(CV.size() == 1 && "non-unique color for block!"); |
| Instruction *EHPad = CV.front()->getFirstNonPHI(); |
| if (EHPad->isEHPad()) |
| OpBundles.emplace_back("funclet", EHPad); |
| } |
| |
| return CallInst::Create(FTy, Func, Args, OpBundles, NameStr, InsertBefore); |
| } |
| |
| static CallInst * |
| createCallInst(FunctionCallee Func, ArrayRef<Value *> Args, const Twine &NameStr, |
| Instruction *InsertBefore, |
| const DenseMap<BasicBlock *, ColorVector> &BlockColors) { |
| return createCallInst(Func.getFunctionType(), Func.getCallee(), Args, NameStr, |
| InsertBefore, BlockColors); |
| } |
| |
| /// Attempt to merge an objc_release with a store, load, and objc_retain to form |
| /// an objc_storeStrong. An objc_storeStrong: |
| /// |
| /// objc_storeStrong(i8** %old_ptr, i8* new_value) |
| /// |
| /// is equivalent to the following IR sequence: |
| /// |
| /// ; Load old value. |
| /// %old_value = load i8** %old_ptr (1) |
| /// |
| /// ; Increment the new value and then release the old value. This must occur |
| /// ; in order in case old_value releases new_value in its destructor causing |
| /// ; us to potentially have a dangling ptr. |
| /// tail call i8* @objc_retain(i8* %new_value) (2) |
| /// tail call void @objc_release(i8* %old_value) (3) |
| /// |
| /// ; Store the new_value into old_ptr |
| /// store i8* %new_value, i8** %old_ptr (4) |
| /// |
| /// The safety of this optimization is based around the following |
| /// considerations: |
| /// |
| /// 1. We are forming the store strong at the store. Thus to perform this |
| /// optimization it must be safe to move the retain, load, and release to |
| /// (4). |
| /// 2. We need to make sure that any re-orderings of (1), (2), (3), (4) are |
| /// safe. |
| void ObjCARCContract::tryToContractReleaseIntoStoreStrong( |
| Instruction *Release, inst_iterator &Iter, |
| const DenseMap<BasicBlock *, ColorVector> &BlockColors) { |
| // See if we are releasing something that we just loaded. |
| auto *Load = dyn_cast<LoadInst>(GetArgRCIdentityRoot(Release)); |
| if (!Load || !Load->isSimple()) |
| return; |
| |
| // For now, require everything to be in one basic block. |
| BasicBlock *BB = Release->getParent(); |
| if (Load->getParent() != BB) |
| return; |
| |
| // First scan down the BB from Load, looking for a store of the RCIdentityRoot |
| // of Load's |
| StoreInst *Store = |
| findSafeStoreForStoreStrongContraction(Load, Release, PA, AA); |
| // If we fail, bail. |
| if (!Store) |
| return; |
| |
| // Then find what new_value's RCIdentity Root is. |
| Value *New = GetRCIdentityRoot(Store->getValueOperand()); |
| |
| // Then walk up the BB and look for a retain on New without any intervening |
| // instructions which conservatively might decrement ref counts. |
| Instruction *Retain = |
| findRetainForStoreStrongContraction(New, Store, Release, PA); |
| |
| // If we fail, bail. |
| if (!Retain) |
| return; |
| |
| Changed = true; |
| ++NumStoreStrongs; |
| |
| LLVM_DEBUG( |
| llvm::dbgs() << " Contracting retain, release into objc_storeStrong.\n" |
| << " Old:\n" |
| << " Store: " << *Store << "\n" |
| << " Release: " << *Release << "\n" |
| << " Retain: " << *Retain << "\n" |
| << " Load: " << *Load << "\n"); |
| |
| LLVMContext &C = Release->getContext(); |
| Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); |
| Type *I8XX = PointerType::getUnqual(I8X); |
| |
| Value *Args[] = { Load->getPointerOperand(), New }; |
| if (Args[0]->getType() != I8XX) |
| Args[0] = new BitCastInst(Args[0], I8XX, "", Store); |
| if (Args[1]->getType() != I8X) |
| Args[1] = new BitCastInst(Args[1], I8X, "", Store); |
| Function *Decl = EP.get(ARCRuntimeEntryPointKind::StoreStrong); |
| CallInst *StoreStrong = createCallInst(Decl, Args, "", Store, BlockColors); |
| StoreStrong->setDoesNotThrow(); |
| StoreStrong->setDebugLoc(Store->getDebugLoc()); |
| |
| // We can't set the tail flag yet, because we haven't yet determined |
| // whether there are any escaping allocas. Remember this call, so that |
| // we can set the tail flag once we know it's safe. |
| StoreStrongCalls.insert(StoreStrong); |
| |
| LLVM_DEBUG(llvm::dbgs() << " New Store Strong: " << *StoreStrong |
| << "\n"); |
| |
| if (&*Iter == Retain) ++Iter; |
| if (&*Iter == Store) ++Iter; |
| Store->eraseFromParent(); |
| Release->eraseFromParent(); |
| EraseInstruction(Retain); |
| if (Load->use_empty()) |
| Load->eraseFromParent(); |
| } |
| |
| bool ObjCARCContract::tryToPeepholeInstruction( |
| Function &F, Instruction *Inst, inst_iterator &Iter, |
| SmallPtrSetImpl<Instruction *> &DependingInsts, |
| SmallPtrSetImpl<const BasicBlock *> &Visited, |
| bool &TailOkForStoreStrongs, |
| const DenseMap<BasicBlock *, ColorVector> &BlockColors) { |
| // Only these library routines return their argument. In particular, |
| // objc_retainBlock does not necessarily return its argument. |
| ARCInstKind Class = GetBasicARCInstKind(Inst); |
| switch (Class) { |
| case ARCInstKind::FusedRetainAutorelease: |
| case ARCInstKind::FusedRetainAutoreleaseRV: |
| return false; |
| case ARCInstKind::Autorelease: |
| case ARCInstKind::AutoreleaseRV: |
| return contractAutorelease(F, Inst, Class, DependingInsts, Visited); |
| case ARCInstKind::Retain: |
| // Attempt to convert retains to retainrvs if they are next to function |
| // calls. |
| if (!optimizeRetainCall(F, Inst)) |
| return false; |
| // If we succeed in our optimization, fall through. |
| LLVM_FALLTHROUGH; |
| case ARCInstKind::RetainRV: |
| case ARCInstKind::ClaimRV: { |
| // If we're compiling for a target which needs a special inline-asm |
| // marker to do the return value optimization, insert it now. |
| if (!RVInstMarker) |
| return false; |
| BasicBlock::iterator BBI = Inst->getIterator(); |
| BasicBlock *InstParent = Inst->getParent(); |
| |
| // Step up to see if the call immediately precedes the RV call. |
| // If it's an invoke, we have to cross a block boundary. And we have |
| // to carefully dodge no-op instructions. |
| do { |
| if (BBI == InstParent->begin()) { |
| BasicBlock *Pred = InstParent->getSinglePredecessor(); |
| if (!Pred) |
| goto decline_rv_optimization; |
| BBI = Pred->getTerminator()->getIterator(); |
| break; |
| } |
| --BBI; |
| } while (IsNoopInstruction(&*BBI)); |
| |
| if (&*BBI == GetArgRCIdentityRoot(Inst)) { |
| LLVM_DEBUG(dbgs() << "Adding inline asm marker for the return value " |
| "optimization.\n"); |
| Changed = true; |
| InlineAsm *IA = InlineAsm::get( |
| FunctionType::get(Type::getVoidTy(Inst->getContext()), |
| /*isVarArg=*/false), |
| RVInstMarker->getString(), |
| /*Constraints=*/"", /*hasSideEffects=*/true); |
| |
| createCallInst(IA, None, "", Inst, BlockColors); |
| } |
| decline_rv_optimization: |
| return false; |
| } |
| case ARCInstKind::InitWeak: { |
| // objc_initWeak(p, null) => *p = null |
| CallInst *CI = cast<CallInst>(Inst); |
| if (IsNullOrUndef(CI->getArgOperand(1))) { |
| Value *Null = |
| ConstantPointerNull::get(cast<PointerType>(CI->getType())); |
| Changed = true; |
| new StoreInst(Null, CI->getArgOperand(0), CI); |
| |
| LLVM_DEBUG(dbgs() << "OBJCARCContract: Old = " << *CI << "\n" |
| << " New = " << *Null << "\n"); |
| |
| CI->replaceAllUsesWith(Null); |
| CI->eraseFromParent(); |
| } |
| return true; |
| } |
| case ARCInstKind::Release: |
| // Try to form an objc store strong from our release. If we fail, there is |
| // nothing further to do below, so continue. |
| tryToContractReleaseIntoStoreStrong(Inst, Iter, BlockColors); |
| return true; |
| case ARCInstKind::User: |
| // Be conservative if the function has any alloca instructions. |
| // Technically we only care about escaping alloca instructions, |
| // but this is sufficient to handle some interesting cases. |
| if (isa<AllocaInst>(Inst)) |
| TailOkForStoreStrongs = false; |
| return true; |
| case ARCInstKind::IntrinsicUser: |
| // Remove calls to @llvm.objc.clang.arc.use(...). |
| Inst->eraseFromParent(); |
| return true; |
| default: |
| return true; |
| } |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Top Level Driver |
| //===----------------------------------------------------------------------===// |
| |
| bool ObjCARCContract::runOnFunction(Function &F) { |
| if (!EnableARCOpts) |
| return false; |
| |
| // If nothing in the Module uses ARC, don't do anything. |
| if (!Run) |
| return false; |
| |
| Changed = false; |
| AA = &getAnalysis<AAResultsWrapperPass>().getAAResults(); |
| DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); |
| |
| PA.setAA(&getAnalysis<AAResultsWrapperPass>().getAAResults()); |
| |
| DenseMap<BasicBlock *, ColorVector> BlockColors; |
| if (F.hasPersonalityFn() && |
| isScopedEHPersonality(classifyEHPersonality(F.getPersonalityFn()))) |
| BlockColors = colorEHFunclets(F); |
| |
| LLVM_DEBUG(llvm::dbgs() << "**** ObjCARC Contract ****\n"); |
| |
| // Track whether it's ok to mark objc_storeStrong calls with the "tail" |
| // keyword. Be conservative if the function has variadic arguments. |
| // It seems that functions which "return twice" are also unsafe for the |
| // "tail" argument, because they are setjmp, which could need to |
| // return to an earlier stack state. |
| bool TailOkForStoreStrongs = |
| !F.isVarArg() && !F.callsFunctionThatReturnsTwice(); |
| |
| // For ObjC library calls which return their argument, replace uses of the |
| // argument with uses of the call return value, if it dominates the use. This |
| // reduces register pressure. |
| SmallPtrSet<Instruction *, 4> DependingInstructions; |
| SmallPtrSet<const BasicBlock *, 4> Visited; |
| for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E;) { |
| Instruction *Inst = &*I++; |
| |
| LLVM_DEBUG(dbgs() << "Visiting: " << *Inst << "\n"); |
| |
| // First try to peephole Inst. If there is nothing further we can do in |
| // terms of undoing objc-arc-expand, process the next inst. |
| if (tryToPeepholeInstruction(F, Inst, I, DependingInstructions, Visited, |
| TailOkForStoreStrongs, BlockColors)) |
| continue; |
| |
| // Otherwise, try to undo objc-arc-expand. |
| |
| // Don't use GetArgRCIdentityRoot because we don't want to look through bitcasts |
| // and such; to do the replacement, the argument must have type i8*. |
| |
| // Function for replacing uses of Arg dominated by Inst. |
| auto ReplaceArgUses = [Inst, this](Value *Arg) { |
| // If we're compiling bugpointed code, don't get in trouble. |
| if (!isa<Instruction>(Arg) && !isa<Argument>(Arg)) |
| return; |
| |
| // Look through the uses of the pointer. |
| for (Value::use_iterator UI = Arg->use_begin(), UE = Arg->use_end(); |
| UI != UE; ) { |
| // Increment UI now, because we may unlink its element. |
| Use &U = *UI++; |
| unsigned OperandNo = U.getOperandNo(); |
| |
| // If the call's return value dominates a use of the call's argument |
| // value, rewrite the use to use the return value. We check for |
| // reachability here because an unreachable call is considered to |
| // trivially dominate itself, which would lead us to rewriting its |
| // argument in terms of its return value, which would lead to |
| // infinite loops in GetArgRCIdentityRoot. |
| if (!DT->isReachableFromEntry(U) || !DT->dominates(Inst, U)) |
| continue; |
| |
| Changed = true; |
| Instruction *Replacement = Inst; |
| Type *UseTy = U.get()->getType(); |
| if (PHINode *PHI = dyn_cast<PHINode>(U.getUser())) { |
| // For PHI nodes, insert the bitcast in the predecessor block. |
| unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo); |
| BasicBlock *IncomingBB = PHI->getIncomingBlock(ValNo); |
| if (Replacement->getType() != UseTy) { |
| // A catchswitch is both a pad and a terminator, meaning a basic |
| // block with a catchswitch has no insertion point. Keep going up |
| // the dominator tree until we find a non-catchswitch. |
| BasicBlock *InsertBB = IncomingBB; |
| while (isa<CatchSwitchInst>(InsertBB->getFirstNonPHI())) { |
| InsertBB = DT->getNode(InsertBB)->getIDom()->getBlock(); |
| } |
| |
| assert(DT->dominates(Inst, &InsertBB->back()) && |
| "Invalid insertion point for bitcast"); |
| Replacement = |
| new BitCastInst(Replacement, UseTy, "", &InsertBB->back()); |
| } |
| |
| // While we're here, rewrite all edges for this PHI, rather |
| // than just one use at a time, to minimize the number of |
| // bitcasts we emit. |
| for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) |
| if (PHI->getIncomingBlock(i) == IncomingBB) { |
| // Keep the UI iterator valid. |
| if (UI != UE && |
| &PHI->getOperandUse( |
| PHINode::getOperandNumForIncomingValue(i)) == &*UI) |
| ++UI; |
| PHI->setIncomingValue(i, Replacement); |
| } |
| } else { |
| if (Replacement->getType() != UseTy) |
| Replacement = new BitCastInst(Replacement, UseTy, "", |
| cast<Instruction>(U.getUser())); |
| U.set(Replacement); |
| } |
| } |
| }; |
| |
| |
| Value *Arg = cast<CallInst>(Inst)->getArgOperand(0); |
| Value *OrigArg = Arg; |
| |
| // TODO: Change this to a do-while. |
| for (;;) { |
| ReplaceArgUses(Arg); |
| |
| // If Arg is a no-op casted pointer, strip one level of casts and iterate. |
| if (const BitCastInst *BI = dyn_cast<BitCastInst>(Arg)) |
| Arg = BI->getOperand(0); |
| else if (isa<GEPOperator>(Arg) && |
| cast<GEPOperator>(Arg)->hasAllZeroIndices()) |
| Arg = cast<GEPOperator>(Arg)->getPointerOperand(); |
| else if (isa<GlobalAlias>(Arg) && |
| !cast<GlobalAlias>(Arg)->isInterposable()) |
| Arg = cast<GlobalAlias>(Arg)->getAliasee(); |
| else { |
| // If Arg is a PHI node, get PHIs that are equivalent to it and replace |
| // their uses. |
| if (PHINode *PN = dyn_cast<PHINode>(Arg)) { |
| SmallVector<Value *, 1> PHIList; |
| getEquivalentPHIs(*PN, PHIList); |
| for (Value *PHI : PHIList) |
| ReplaceArgUses(PHI); |
| } |
| break; |
| } |
| } |
| |
| // Replace bitcast users of Arg that are dominated by Inst. |
| SmallVector<BitCastInst *, 2> BitCastUsers; |
| |
| // Add all bitcast users of the function argument first. |
| for (User *U : OrigArg->users()) |
| if (auto *BC = dyn_cast<BitCastInst>(U)) |
| BitCastUsers.push_back(BC); |
| |
| // Replace the bitcasts with the call return. Iterate until list is empty. |
| while (!BitCastUsers.empty()) { |
| auto *BC = BitCastUsers.pop_back_val(); |
| for (User *U : BC->users()) |
| if (auto *B = dyn_cast<BitCastInst>(U)) |
| BitCastUsers.push_back(B); |
| |
| ReplaceArgUses(BC); |
| } |
| } |
| |
| // If this function has no escaping allocas or suspicious vararg usage, |
| // objc_storeStrong calls can be marked with the "tail" keyword. |
| if (TailOkForStoreStrongs) |
| for (CallInst *CI : StoreStrongCalls) |
| CI->setTailCall(); |
| StoreStrongCalls.clear(); |
| |
| return Changed; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Misc Pass Manager |
| //===----------------------------------------------------------------------===// |
| |
| char ObjCARCContract::ID = 0; |
| INITIALIZE_PASS_BEGIN(ObjCARCContract, "objc-arc-contract", |
| "ObjC ARC contraction", false, false) |
| INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) |
| INITIALIZE_PASS_END(ObjCARCContract, "objc-arc-contract", |
| "ObjC ARC contraction", false, false) |
| |
| void ObjCARCContract::getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<AAResultsWrapperPass>(); |
| AU.addRequired<DominatorTreeWrapperPass>(); |
| AU.setPreservesCFG(); |
| } |
| |
| Pass *llvm::createObjCARCContractPass() { return new ObjCARCContract(); } |
| |
| bool ObjCARCContract::doInitialization(Module &M) { |
| // If nothing in the Module uses ARC, don't do anything. |
| Run = ModuleHasARC(M); |
| if (!Run) |
| return false; |
| |
| EP.init(&M); |
| |
| // Initialize RVInstMarker. |
| const char *MarkerKey = "clang.arc.retainAutoreleasedReturnValueMarker"; |
| RVInstMarker = dyn_cast_or_null<MDString>(M.getModuleFlag(MarkerKey)); |
| |
| return false; |
| } |
