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Diffstat (limited to 'lib/Transforms/ObjCARC/ObjCARCOpts.cpp')
| -rw-r--r-- | lib/Transforms/ObjCARC/ObjCARCOpts.cpp | 4568 |
1 files changed, 4568 insertions, 0 deletions
diff --git a/lib/Transforms/ObjCARC/ObjCARCOpts.cpp b/lib/Transforms/ObjCARC/ObjCARCOpts.cpp new file mode 100644 index 0000000..411da64 --- /dev/null +++ b/lib/Transforms/ObjCARC/ObjCARCOpts.cpp @@ -0,0 +1,4568 @@ +//===- ObjCARCOpts.cpp - ObjC ARC Optimization ----------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +/// \file +/// This file defines ObjC ARC optimizations. ARC stands for Automatic +/// Reference Counting and is a system for managing reference counts for objects +/// in Objective C. +/// +/// The optimizations performed include elimination of redundant, partially +/// redundant, and inconsequential reference count operations, elimination of +/// redundant weak pointer operations, pattern-matching and replacement of +/// low-level operations into higher-level operations, and numerous minor +/// simplifications. +/// +/// This file also defines a simple ARC-aware AliasAnalysis. +/// +/// 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. +/// +//===----------------------------------------------------------------------===// + +#define DEBUG_TYPE "objc-arc" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +using namespace llvm; + +/// \brief A handy option to enable/disable all optimizations in this file. +static cl::opt<bool> EnableARCOpts("enable-objc-arc-opts", cl::init(true)); + +/// \defgroup MiscUtils Miscellaneous utilities that are not ARC specific. +/// @{ + +namespace { + /// \brief An associative container with fast insertion-order (deterministic) + /// iteration over its elements. Plus the special blot operation. + template<class KeyT, class ValueT> + class MapVector { + /// Map keys to indices in Vector. + typedef DenseMap<KeyT, size_t> MapTy; + MapTy Map; + + typedef std::vector<std::pair<KeyT, ValueT> > VectorTy; + /// Keys and values. + VectorTy Vector; + + public: + typedef typename VectorTy::iterator iterator; + typedef typename VectorTy::const_iterator const_iterator; + iterator begin() { return Vector.begin(); } + iterator end() { return Vector.end(); } + const_iterator begin() const { return Vector.begin(); } + const_iterator end() const { return Vector.end(); } + +#ifdef XDEBUG + ~MapVector() { + assert(Vector.size() >= Map.size()); // May differ due to blotting. + for (typename MapTy::const_iterator I = Map.begin(), E = Map.end(); + I != E; ++I) { + assert(I->second < Vector.size()); + assert(Vector[I->second].first == I->first); + } + for (typename VectorTy::const_iterator I = Vector.begin(), + E = Vector.end(); I != E; ++I) + assert(!I->first || + (Map.count(I->first) && + Map[I->first] == size_t(I - Vector.begin()))); + } +#endif + + ValueT &operator[](const KeyT &Arg) { + std::pair<typename MapTy::iterator, bool> Pair = + Map.insert(std::make_pair(Arg, size_t(0))); + if (Pair.second) { + size_t Num = Vector.size(); + Pair.first->second = Num; + Vector.push_back(std::make_pair(Arg, ValueT())); + return Vector[Num].second; + } + return Vector[Pair.first->second].second; + } + + std::pair<iterator, bool> + insert(const std::pair<KeyT, ValueT> &InsertPair) { + std::pair<typename MapTy::iterator, bool> Pair = + Map.insert(std::make_pair(InsertPair.first, size_t(0))); + if (Pair.second) { + size_t Num = Vector.size(); + Pair.first->second = Num; + Vector.push_back(InsertPair); + return std::make_pair(Vector.begin() + Num, true); + } + return std::make_pair(Vector.begin() + Pair.first->second, false); + } + + const_iterator find(const KeyT &Key) const { + typename MapTy::const_iterator It = Map.find(Key); + if (It == Map.end()) return Vector.end(); + return Vector.begin() + It->second; + } + + /// This is similar to erase, but instead of removing the element from the + /// vector, it just zeros out the key in the vector. This leaves iterators + /// intact, but clients must be prepared for zeroed-out keys when iterating. + void blot(const KeyT &Key) { + typename MapTy::iterator It = Map.find(Key); + if (It == Map.end()) return; + Vector[It->second].first = KeyT(); + Map.erase(It); + } + + void clear() { + Map.clear(); + Vector.clear(); + } + }; +} + +/// @} +/// +/// \defgroup ARCUtilities Utility declarations/definitions specific to ARC. +/// @{ + +#include "llvm/ADT/StringSwitch.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/Intrinsics.h" +#include "llvm/IR/Module.h" +#include "llvm/Support/CallSite.h" +#include "llvm/Transforms/Utils/Local.h" + +namespace { + /// \enum InstructionClass + /// \brief A simple classification for instructions. + enum InstructionClass { + IC_Retain, ///< objc_retain + IC_RetainRV, ///< objc_retainAutoreleasedReturnValue + IC_RetainBlock, ///< objc_retainBlock + IC_Release, ///< objc_release + IC_Autorelease, ///< objc_autorelease + IC_AutoreleaseRV, ///< objc_autoreleaseReturnValue + IC_AutoreleasepoolPush, ///< objc_autoreleasePoolPush + IC_AutoreleasepoolPop, ///< objc_autoreleasePoolPop + IC_NoopCast, ///< objc_retainedObject, etc. + IC_FusedRetainAutorelease, ///< objc_retainAutorelease + IC_FusedRetainAutoreleaseRV, ///< objc_retainAutoreleaseReturnValue + IC_LoadWeakRetained, ///< objc_loadWeakRetained (primitive) + IC_StoreWeak, ///< objc_storeWeak (primitive) + IC_InitWeak, ///< objc_initWeak (derived) + IC_LoadWeak, ///< objc_loadWeak (derived) + IC_MoveWeak, ///< objc_moveWeak (derived) + IC_CopyWeak, ///< objc_copyWeak (derived) + IC_DestroyWeak, ///< objc_destroyWeak (derived) + IC_StoreStrong, ///< objc_storeStrong (derived) + IC_CallOrUser, ///< could call objc_release and/or "use" pointers + IC_Call, ///< could call objc_release + IC_User, ///< could "use" a pointer + IC_None ///< anything else + }; + + raw_ostream &operator<<(raw_ostream &OS, const InstructionClass Class) + LLVM_ATTRIBUTE_USED; + raw_ostream &operator<<(raw_ostream &OS, const InstructionClass Class) { + switch (Class) { + case IC_Retain: + return OS << "IC_Retain"; + case IC_RetainRV: + return OS << "IC_RetainRV"; + case IC_RetainBlock: + return OS << "IC_RetainBlock"; + case IC_Release: + return OS << "IC_Release"; + case IC_Autorelease: + return OS << "IC_Autorelease"; + case IC_AutoreleaseRV: + return OS << "IC_AutoreleaseRV"; + case IC_AutoreleasepoolPush: + return OS << "IC_AutoreleasepoolPush"; + case IC_AutoreleasepoolPop: + return OS << "IC_AutoreleasepoolPop"; + case IC_NoopCast: + return OS << "IC_NoopCast"; + case IC_FusedRetainAutorelease: + return OS << "IC_FusedRetainAutorelease"; + case IC_FusedRetainAutoreleaseRV: + return OS << "IC_FusedRetainAutoreleaseRV"; + case IC_LoadWeakRetained: + return OS << "IC_LoadWeakRetained"; + case IC_StoreWeak: + return OS << "IC_StoreWeak"; + case IC_InitWeak: + return OS << "IC_InitWeak"; + case IC_LoadWeak: + return OS << "IC_LoadWeak"; + case IC_MoveWeak: + return OS << "IC_MoveWeak"; + case IC_CopyWeak: + return OS << "IC_CopyWeak"; + case IC_DestroyWeak: + return OS << "IC_DestroyWeak"; + case IC_StoreStrong: + return OS << "IC_StoreStrong"; + case IC_CallOrUser: + return OS << "IC_CallOrUser"; + case IC_Call: + return OS << "IC_Call"; + case IC_User: + return OS << "IC_User"; + case IC_None: + return OS << "IC_None"; + } + llvm_unreachable("Unknown instruction class!"); + } +} + +/// \brief Test whether the given value is possible a retainable object pointer. +static bool IsPotentialRetainableObjPtr(const Value *Op) { + // Pointers to static or stack storage are not valid retainable object pointers. + if (isa<Constant>(Op) || isa<AllocaInst>(Op)) + return false; + // Special arguments can not be a valid retainable object pointer. + if (const Argument *Arg = dyn_cast<Argument>(Op)) + if (Arg->hasByValAttr() || + Arg->hasNestAttr() || + Arg->hasStructRetAttr()) + return false; + // Only consider values with pointer types. + // + // It seemes intuitive to exclude function pointer types as well, since + // functions are never retainable object pointers, however clang occasionally + // bitcasts retainable object pointers to function-pointer type temporarily. + PointerType *Ty = dyn_cast<PointerType>(Op->getType()); + if (!Ty) + return false; + // Conservatively assume anything else is a potential retainable object pointer. + return true; +} + +/// \brief Helper for GetInstructionClass. Determines what kind of construct CS +/// is. +static InstructionClass GetCallSiteClass(ImmutableCallSite CS) { + for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); + I != E; ++I) + if (IsPotentialRetainableObjPtr(*I)) + return CS.onlyReadsMemory() ? IC_User : IC_CallOrUser; + + return CS.onlyReadsMemory() ? IC_None : IC_Call; +} + +/// \brief Determine if F is one of the special known Functions. If it isn't, +/// return IC_CallOrUser. +static InstructionClass GetFunctionClass(const Function *F) { + Function::const_arg_iterator AI = F->arg_begin(), AE = F->arg_end(); + + // No arguments. + if (AI == AE) + return StringSwitch<InstructionClass>(F->getName()) + .Case("objc_autoreleasePoolPush", IC_AutoreleasepoolPush) + .Default(IC_CallOrUser); + + // One argument. + const Argument *A0 = AI++; + if (AI == AE) + // Argument is a pointer. + if (PointerType *PTy = dyn_cast<PointerType>(A0->getType())) { + Type *ETy = PTy->getElementType(); + // Argument is i8*. + if (ETy->isIntegerTy(8)) + return StringSwitch<InstructionClass>(F->getName()) + .Case("objc_retain", IC_Retain) + .Case("objc_retainAutoreleasedReturnValue", IC_RetainRV) + .Case("objc_retainBlock", IC_RetainBlock) + .Case("objc_release", IC_Release) + .Case("objc_autorelease", IC_Autorelease) + .Case("objc_autoreleaseReturnValue", IC_AutoreleaseRV) + .Case("objc_autoreleasePoolPop", IC_AutoreleasepoolPop) + .Case("objc_retainedObject", IC_NoopCast) + .Case("objc_unretainedObject", IC_NoopCast) + .Case("objc_unretainedPointer", IC_NoopCast) + .Case("objc_retain_autorelease", IC_FusedRetainAutorelease) + .Case("objc_retainAutorelease", IC_FusedRetainAutorelease) + .Case("objc_retainAutoreleaseReturnValue",IC_FusedRetainAutoreleaseRV) + .Default(IC_CallOrUser); + + // Argument is i8** + if (PointerType *Pte = dyn_cast<PointerType>(ETy)) + if (Pte->getElementType()->isIntegerTy(8)) + return StringSwitch<InstructionClass>(F->getName()) + .Case("objc_loadWeakRetained", IC_LoadWeakRetained) + .Case("objc_loadWeak", IC_LoadWeak) + .Case("objc_destroyWeak", IC_DestroyWeak) + .Default(IC_CallOrUser); + } + + // Two arguments, first is i8**. + const Argument *A1 = AI++; + if (AI == AE) + if (PointerType *PTy = dyn_cast<PointerType>(A0->getType())) + if (PointerType *Pte = dyn_cast<PointerType>(PTy->getElementType())) + if (Pte->getElementType()->isIntegerTy(8)) + if (PointerType *PTy1 = dyn_cast<PointerType>(A1->getType())) { + Type *ETy1 = PTy1->getElementType(); + // Second argument is i8* + if (ETy1->isIntegerTy(8)) + return StringSwitch<InstructionClass>(F->getName()) + .Case("objc_storeWeak", IC_StoreWeak) + .Case("objc_initWeak", IC_InitWeak) + .Case("objc_storeStrong", IC_StoreStrong) + .Default(IC_CallOrUser); + // Second argument is i8**. + if (PointerType *Pte1 = dyn_cast<PointerType>(ETy1)) + if (Pte1->getElementType()->isIntegerTy(8)) + return StringSwitch<InstructionClass>(F->getName()) + .Case("objc_moveWeak", IC_MoveWeak) + .Case("objc_copyWeak", IC_CopyWeak) + .Default(IC_CallOrUser); + } + + // Anything else. + return IC_CallOrUser; +} + +/// \brief Determine what kind of construct V is. +static InstructionClass GetInstructionClass(const Value *V) { + if (const Instruction *I = dyn_cast<Instruction>(V)) { + // Any instruction other than bitcast and gep with a pointer operand have a + // use of an objc pointer. Bitcasts, GEPs, Selects, PHIs transfer a pointer + // to a subsequent use, rather than using it themselves, in this sense. + // As a short cut, several other opcodes are known to have no pointer + // operands of interest. And ret is never followed by a release, so it's + // not interesting to examine. + switch (I->getOpcode()) { + case Instruction::Call: { + const CallInst *CI = cast<CallInst>(I); + // Check for calls to special functions. + if (const Function *F = CI->getCalledFunction()) { + InstructionClass Class = GetFunctionClass(F); + if (Class != IC_CallOrUser) + return Class; + + // None of the intrinsic functions do objc_release. For intrinsics, the + // only question is whether or not they may be users. + switch (F->getIntrinsicID()) { + case Intrinsic::returnaddress: case Intrinsic::frameaddress: + case Intrinsic::stacksave: case Intrinsic::stackrestore: + case Intrinsic::vastart: case Intrinsic::vacopy: case Intrinsic::vaend: + case Intrinsic::objectsize: case Intrinsic::prefetch: + case Intrinsic::stackprotector: + case Intrinsic::eh_return_i32: case Intrinsic::eh_return_i64: + case Intrinsic::eh_typeid_for: case Intrinsic::eh_dwarf_cfa: + case Intrinsic::eh_sjlj_lsda: case Intrinsic::eh_sjlj_functioncontext: + case Intrinsic::init_trampoline: case Intrinsic::adjust_trampoline: + case Intrinsic::lifetime_start: case Intrinsic::lifetime_end: + case Intrinsic::invariant_start: case Intrinsic::invariant_end: + // Don't let dbg info affect our results. + case Intrinsic::dbg_declare: case Intrinsic::dbg_value: + // Short cut: Some intrinsics obviously don't use ObjC pointers. + return IC_None; + default: + break; + } + } + return GetCallSiteClass(CI); + } + case Instruction::Invoke: + return GetCallSiteClass(cast<InvokeInst>(I)); + case Instruction::BitCast: + case Instruction::GetElementPtr: + case Instruction::Select: case Instruction::PHI: + case Instruction::Ret: case Instruction::Br: + case Instruction::Switch: case Instruction::IndirectBr: + case Instruction::Alloca: case Instruction::VAArg: + case Instruction::Add: case Instruction::FAdd: + case Instruction::Sub: case Instruction::FSub: + case Instruction::Mul: case Instruction::FMul: + case Instruction::SDiv: case Instruction::UDiv: case Instruction::FDiv: + case Instruction::SRem: case Instruction::URem: case Instruction::FRem: + case Instruction::Shl: case Instruction::LShr: case Instruction::AShr: + case Instruction::And: case Instruction::Or: case Instruction::Xor: + case Instruction::SExt: case Instruction::ZExt: case Instruction::Trunc: + case Instruction::IntToPtr: case Instruction::FCmp: + case Instruction::FPTrunc: case Instruction::FPExt: + case Instruction::FPToUI: case Instruction::FPToSI: + case Instruction::UIToFP: case Instruction::SIToFP: + case Instruction::InsertElement: case Instruction::ExtractElement: + case Instruction::ShuffleVector: + case Instruction::ExtractValue: + break; + case Instruction::ICmp: + // Comparing a pointer with null, or any other constant, isn't an + // interesting use, because we don't care what the pointer points to, or + // about the values of any other dynamic reference-counted pointers. + if (IsPotentialRetainableObjPtr(I->getOperand(1))) + return IC_User; + break; + default: + // For anything else, check all the operands. + // Note that this includes both operands of a Store: while the first + // operand isn't actually being dereferenced, it is being stored to + // memory where we can no longer track who might read it and dereference + // it, so we have to consider it potentially used. + for (User::const_op_iterator OI = I->op_begin(), OE = I->op_end(); + OI != OE; ++OI) + if (IsPotentialRetainableObjPtr(*OI)) + return IC_User; + } + } + + // Otherwise, it's totally inert for ARC purposes. + return IC_None; +} + +/// \brief Determine which objc runtime call instruction class V belongs to. +/// +/// This is similar to GetInstructionClass except that it only detects objc +/// runtime calls. This allows it to be faster. +/// +static InstructionClass GetBasicInstructionClass(const Value *V) { + if (const CallInst *CI = dyn_cast<CallInst>(V)) { + if (const Function *F = CI->getCalledFunction()) + return GetFunctionClass(F); + // Otherwise, be conservative. + return IC_CallOrUser; + } + + // Otherwise, be conservative. + return isa<InvokeInst>(V) ? IC_CallOrUser : IC_User; +} + +/// \brief Test if the given class is objc_retain or equivalent. +static bool IsRetain(InstructionClass Class) { + return Class == IC_Retain || + Class == IC_RetainRV; +} + +/// \brief Test if the given class is objc_autorelease or equivalent. +static bool IsAutorelease(InstructionClass Class) { + return Class == IC_Autorelease || + Class == IC_AutoreleaseRV; +} + +/// \brief Test if the given class represents instructions which return their +/// argument verbatim. +static bool IsForwarding(InstructionClass Class) { + // objc_retainBlock technically doesn't always return its argument + // verbatim, but it doesn't matter for our purposes here. + return Class == IC_Retain || + Class == IC_RetainRV || + Class == IC_Autorelease || + Class == IC_AutoreleaseRV || + Class == IC_RetainBlock || + Class == IC_NoopCast; +} + +/// \brief Test if the given class represents instructions which do nothing if +/// passed a null pointer. +static bool IsNoopOnNull(InstructionClass Class) { + return Class == IC_Retain || + Class == IC_RetainRV || + Class == IC_Release || + Class == IC_Autorelease || + Class == IC_AutoreleaseRV || + Class == IC_RetainBlock; +} + +/// \brief Test if the given class represents instructions which are always safe +/// to mark with the "tail" keyword. +static bool IsAlwaysTail(InstructionClass Class) { + // IC_RetainBlock may be given a stack argument. + return Class == IC_Retain || + Class == IC_RetainRV || + Class == IC_AutoreleaseRV; +} + +/// \brief Test if the given class represents instructions which are never safe +/// to mark with the "tail" keyword. +static bool IsNeverTail(InstructionClass Class) { + /// It is never safe to tail call objc_autorelease since by tail calling + /// objc_autorelease, we also tail call -[NSObject autorelease] which supports + /// fast autoreleasing causing our object to be potentially reclaimed from the + /// autorelease pool which violates the semantics of __autoreleasing types in + /// ARC. + return Class == IC_Autorelease; +} + +/// \brief Test if the given class represents instructions which are always safe +/// to mark with the nounwind attribute. +static bool IsNoThrow(InstructionClass Class) { + // objc_retainBlock is not nounwind because it calls user copy constructors + // which could theoretically throw. + return Class == IC_Retain || + Class == IC_RetainRV || + Class == IC_Release || + Class == IC_Autorelease || + Class == IC_AutoreleaseRV || + Class == IC_AutoreleasepoolPush || + Class == IC_AutoreleasepoolPop; +} + +/// \brief Erase the given instruction. +/// +/// Many ObjC calls return their argument verbatim, +/// so if it's such a call and the return value has users, replace them with the +/// argument value. +/// +static void EraseInstruction(Instruction *CI) { + Value *OldArg = cast<CallInst>(CI)->getArgOperand(0); + + bool Unused = CI->use_empty(); + + if (!Unused) { + // Replace the return value with the argument. + assert(IsForwarding(GetBasicInstructionClass(CI)) && + "Can't delete non-forwarding instruction with users!"); + CI->replaceAllUsesWith(OldArg); + } + + CI->eraseFromParent(); + + if (Unused) + RecursivelyDeleteTriviallyDeadInstructions(OldArg); +} + +/// \brief This is a wrapper around getUnderlyingObject which also knows how to +/// look through objc_retain and objc_autorelease calls, which we know to return +/// their argument verbatim. +static const Value *GetUnderlyingObjCPtr(const Value *V) { + for (;;) { + V = GetUnderlyingObject(V); + if (!IsForwarding(GetBasicInstructionClass(V))) + break; + V = cast<CallInst>(V)->getArgOperand(0); + } + + return V; +} + +/// \brief This is a wrapper around Value::stripPointerCasts which also knows +/// how to look through objc_retain and objc_autorelease calls, which we know to +/// return their argument verbatim. +static const Value *StripPointerCastsAndObjCCalls(const Value *V) { + for (;;) { + V = V->stripPointerCasts(); + if (!IsForwarding(GetBasicInstructionClass(V))) + break; + V = cast<CallInst>(V)->getArgOperand(0); + } + return V; +} + +/// \brief This is a wrapper around Value::stripPointerCasts which also knows +/// how to look through objc_retain and objc_autorelease calls, which we know to +/// return their argument verbatim. +static Value *StripPointerCastsAndObjCCalls(Value *V) { + for (;;) { + V = V->stripPointerCasts(); + if (!IsForwarding(GetBasicInstructionClass(V))) + break; + V = cast<CallInst>(V)->getArgOperand(0); + } + return V; +} + +/// \brief Assuming the given instruction is one of the special calls such as +/// objc_retain or objc_release, return the argument value, stripped of no-op +/// casts and forwarding calls. +static Value *GetObjCArg(Value *Inst) { + return StripPointerCastsAndObjCCalls(cast<CallInst>(Inst)->getArgOperand(0)); +} + +/// \brief Return true if this value refers to a distinct and identifiable +/// object. +/// +/// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses +/// special knowledge of ObjC conventions. +static bool IsObjCIdentifiedObject(const Value *V) { + // Assume that call results and arguments have their own "provenance". + // Constants (including GlobalVariables) and Allocas are never + // reference-counted. + if (isa<CallInst>(V) || isa<InvokeInst>(V) || + isa<Argument>(V) || isa<Constant>(V) || + isa<AllocaInst>(V)) + return true; + + if (const LoadInst *LI = dyn_cast<LoadInst>(V)) { + const Value *Pointer = + StripPointerCastsAndObjCCalls(LI->getPointerOperand()); + if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) { + // A constant pointer can't be pointing to an object on the heap. It may + // be reference-counted, but it won't be deleted. + if (GV->isConstant()) + return true; + StringRef Name = GV->getName(); + // These special variables are known to hold values which are not + // reference-counted pointers. + if (Name.startswith("\01L_OBJC_SELECTOR_REFERENCES_") || + Name.startswith("\01L_OBJC_CLASSLIST_REFERENCES_") || + Name.startswith("\01L_OBJC_CLASSLIST_SUP_REFS_$_") || + Name.startswith("\01L_OBJC_METH_VAR_NAME_") || + Name.startswith("\01l_objc_msgSend_fixup_")) + return true; + } + } + + return false; +} + +/// \brief This is similar to StripPointerCastsAndObjCCalls but it stops as soon +/// as it finds a value with multiple uses. +static const Value *FindSingleUseIdentifiedObject(const Value *Arg) { + if (Arg->hasOneUse()) { + if (const BitCastInst *BC = dyn_cast<BitCastInst>(Arg)) + return FindSingleUseIdentifiedObject(BC->getOperand(0)); + if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Arg)) + if (GEP->hasAllZeroIndices()) + return FindSingleUseIdentifiedObject(GEP->getPointerOperand()); + if (IsForwarding(GetBasicInstructionClass(Arg))) + return FindSingleUseIdentifiedObject( + cast<CallInst>(Arg)->getArgOperand(0)); + if (!IsObjCIdentifiedObject(Arg)) + return 0; + return Arg; + } + + // If we found an identifiable object but it has multiple uses, but they are + // trivial uses, we can still consider this to be a single-use value. + if (IsObjCIdentifiedObject(Arg)) { + for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end(); + UI != UE; ++UI) { + const User *U = *UI; + if (!U->use_empty() || StripPointerCastsAndObjCCalls(U) != Arg) + return 0; + } + + return Arg; + } + + return 0; +} + +/// \brief Test if the given module looks interesting to run ARC optimization +/// on. +static bool ModuleHasARC(const Module &M) { + return + M.getNamedValue("objc_retain") || + M.getNamedValue("objc_release") || + M.getNamedValue("objc_autorelease") || + M.getNamedValue("objc_retainAutoreleasedReturnValue") || + M.getNamedValue("objc_retainBlock") || + M.getNamedValue("objc_autoreleaseReturnValue") || + M.getNamedValue("objc_autoreleasePoolPush") || + M.getNamedValue("objc_loadWeakRetained") || + M.getNamedValue("objc_loadWeak") || + M.getNamedValue("objc_destroyWeak") || + M.getNamedValue("objc_storeWeak") || + M.getNamedValue("objc_initWeak") || + M.getNamedValue("objc_moveWeak") || + M.getNamedValue("objc_copyWeak") || + M.getNamedValue("objc_retainedObject") || + M.getNamedValue("objc_unretainedObject") || + M.getNamedValue("objc_unretainedPointer"); +} + +/// \brief Test whether the given pointer, which is an Objective C block +/// pointer, does not "escape". +/// +/// This differs from regular escape analysis in that a use as an +/// argument to a call is not considered an escape. +/// +static bool DoesObjCBlockEscape(const Value *BlockPtr) { + + DEBUG(dbgs() << "DoesObjCBlockEscape: Target: " << *BlockPtr << "\n"); + + // Walk the def-use chains. + SmallVector<const Value *, 4> Worklist; + Worklist.push_back(BlockPtr); + + // Ensure we do not visit any value twice. + SmallPtrSet<const Value *, 4> VisitedSet; + + do { + const Value *V = Worklist.pop_back_val(); + + DEBUG(dbgs() << "DoesObjCBlockEscape: Visiting: " << *V << "\n"); + + for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end(); + UI != UE; ++UI) { + const User *UUser = *UI; + + DEBUG(dbgs() << "DoesObjCBlockEscape: User: " << *UUser << "\n"); + + // Special - Use by a call (callee or argument) is not considered + // to be an escape. + switch (GetBasicInstructionClass(UUser)) { + case IC_StoreWeak: + case IC_InitWeak: + case IC_StoreStrong: + case IC_Autorelease: + case IC_AutoreleaseRV: { + DEBUG(dbgs() << "DoesObjCBlockEscape: User copies pointer arguments. " + "Block Escapes!\n"); + // These special functions make copies of their pointer arguments. + return true; + } + case IC_User: + case IC_None: + // Use by an instruction which copies the value is an escape if the + // result is an escape. + if (isa<BitCastInst>(UUser) || isa<GetElementPtrInst>(UUser) || + isa<PHINode>(UUser) || isa<SelectInst>(UUser)) { + + if (!VisitedSet.insert(UUser)) { + DEBUG(dbgs() << "DoesObjCBlockEscape: User copies value. Escapes " + "if result escapes. Adding to list.\n"); + Worklist.push_back(UUser); + } else { + DEBUG(dbgs() << "DoesObjCBlockEscape: Already visited node.\n"); + } + continue; + } + // Use by a load is not an escape. + if (isa<LoadInst>(UUser)) + continue; + // Use by a store is not an escape if the use is the address. + if (const StoreInst *SI = dyn_cast<StoreInst>(UUser)) + if (V != SI->getValueOperand()) + continue; + break; + default: + // Regular calls and other stuff are not considered escapes. + continue; + } + // Otherwise, conservatively assume an escape. + DEBUG(dbgs() << "DoesObjCBlockEscape: Assuming block escapes.\n"); + return true; + } + } while (!Worklist.empty()); + + // No escapes found. + DEBUG(dbgs() << "DoesObjCBlockEscape: Block does not escape.\n"); + return false; +} + +/// @} +/// +/// \defgroup ARCAA Extends alias analysis using ObjC specific knowledge. +/// @{ + +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/Passes.h" +#include "llvm/Pass.h" + +namespace { + /// \brief This is a simple alias analysis implementation that uses knowledge + /// of ARC constructs to answer queries. + /// + /// TODO: This class could be generalized to know about other ObjC-specific + /// tricks. Such as knowing that ivars in the non-fragile ABI are non-aliasing + /// even though their offsets are dynamic. + class ObjCARCAliasAnalysis : public ImmutablePass, + public AliasAnalysis { + public: + static char ID; // Class identification, replacement for typeinfo + ObjCARCAliasAnalysis() : ImmutablePass(ID) { + initializeObjCARCAliasAnalysisPass(*PassRegistry::getPassRegistry()); + } + + private: + virtual void initializePass() { + InitializeAliasAnalysis(this); + } + + /// This method is used when a pass implements an analysis interface through + /// multiple inheritance. If needed, it should override this to adjust the + /// this pointer as needed for the specified pass info. + virtual void *getAdjustedAnalysisPointer(const void *PI) { + if (PI == &AliasAnalysis::ID) + return static_cast<AliasAnalysis *>(this); + return this; + } + + virtual void getAnalysisUsage(AnalysisUsage &AU) const; + virtual AliasResult alias(const Location &LocA, const Location &LocB); + virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal); + virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); + virtual ModRefBehavior getModRefBehavior(const Function *F); + virtual ModRefResult getModRefInfo(ImmutableCallSite CS, + const Location &Loc); + virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, + ImmutableCallSite CS2); + }; +} // End of anonymous namespace + +// Register this pass... +char ObjCARCAliasAnalysis::ID = 0; +INITIALIZE_AG_PASS(ObjCARCAliasAnalysis, AliasAnalysis, "objc-arc-aa", + "ObjC-ARC-Based Alias Analysis", false, true, false) + +ImmutablePass *llvm::createObjCARCAliasAnalysisPass() { + return new ObjCARCAliasAnalysis(); +} + +void +ObjCARCAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesAll(); + AliasAnalysis::getAnalysisUsage(AU); +} + +AliasAnalysis::AliasResult +ObjCARCAliasAnalysis::alias(const Location &LocA, const Location &LocB) { + if (!EnableARCOpts) + return AliasAnalysis::alias(LocA, LocB); + + // First, strip off no-ops, including ObjC-specific no-ops, and try making a + // precise alias query. + const Value *SA = StripPointerCastsAndObjCCalls(LocA.Ptr); + const Value *SB = StripPointerCastsAndObjCCalls(LocB.Ptr); + AliasResult Result = + AliasAnalysis::alias(Location(SA, LocA.Size, LocA.TBAATag), + Location(SB, LocB.Size, LocB.TBAATag)); + if (Result != MayAlias) + return Result; + + // If that failed, climb to the underlying object, including climbing through + // ObjC-specific no-ops, and try making an imprecise alias query. + const Value *UA = GetUnderlyingObjCPtr(SA); + const Value *UB = GetUnderlyingObjCPtr(SB); + if (UA != SA || UB != SB) { + Result = AliasAnalysis::alias(Location(UA), Location(UB)); + // We can't use MustAlias or PartialAlias results here because + // GetUnderlyingObjCPtr may return an offsetted pointer value. + if (Result == NoAlias) + return NoAlias; + } + + // If that failed, fail. We don't need to chain here, since that's covered + // by the earlier precise query. + return MayAlias; +} + +bool +ObjCARCAliasAnalysis::pointsToConstantMemory(const Location &Loc, + bool OrLocal) { + if (!EnableARCOpts) + return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); + + // First, strip off no-ops, including ObjC-specific no-ops, and try making + // a precise alias query. + const Value *S = StripPointerCastsAndObjCCalls(Loc.Ptr); + if (AliasAnalysis::pointsToConstantMemory(Location(S, Loc.Size, Loc.TBAATag), + OrLocal)) + return true; + + // If that failed, climb to the underlying object, including climbing through + // ObjC-specific no-ops, and try making an imprecise alias query. + const Value *U = GetUnderlyingObjCPtr(S); + if (U != S) + return AliasAnalysis::pointsToConstantMemory(Location(U), OrLocal); + + // If that failed, fail. We don't need to chain here, since that's covered + // by the earlier precise query. + return false; +} + +AliasAnalysis::ModRefBehavior +ObjCARCAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) { + // We have nothing to do. Just chain to the next AliasAnalysis. + return AliasAnalysis::getModRefBehavior(CS); +} + +AliasAnalysis::ModRefBehavior +ObjCARCAliasAnalysis::getModRefBehavior(const Function *F) { + if (!EnableARCOpts) + return AliasAnalysis::getModRefBehavior(F); + + switch (GetFunctionClass(F)) { + case IC_NoopCast: + return DoesNotAccessMemory; + default: + break; + } + + return AliasAnalysis::getModRefBehavior(F); +} + +AliasAnalysis::ModRefResult +ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS, const Location &Loc) { + if (!EnableARCOpts) + return AliasAnalysis::getModRefInfo(CS, Loc); + + switch (GetBasicInstructionClass(CS.getInstruction())) { + case IC_Retain: + case IC_RetainRV: + case IC_Autorelease: + case IC_AutoreleaseRV: + case IC_NoopCast: + case IC_AutoreleasepoolPush: + case IC_FusedRetainAutorelease: + case IC_FusedRetainAutoreleaseRV: + // These functions don't access any memory visible to the compiler. + // Note that this doesn't include objc_retainBlock, because it updates + // pointers when it copies block data. + return NoModRef; + default: + break; + } + + return AliasAnalysis::getModRefInfo(CS, Loc); +} + +AliasAnalysis::ModRefResult +ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS1, + ImmutableCallSite CS2) { + // TODO: Theoretically we could check for dependencies between objc_* calls + // and OnlyAccessesArgumentPointees calls or other well-behaved calls. + return AliasAnalysis::getModRefInfo(CS1, CS2); +} + +/// @} +/// +/// \defgroup ARCExpansion Early ARC Optimizations. +/// @{ + +#include "llvm/Support/InstIterator.h" +#include "llvm/Transforms/ObjCARC.h" + +namespace { + /// \brief Early ARC transformations. + class ObjCARCExpand : public FunctionPass { + virtual void getAnalysisUsage(AnalysisUsage &AU) const; + virtual bool doInitialization(Module &M); + virtual bool runOnFunction(Function &F); + + /// A flag indicating whether this optimization pass should run. + bool Run; + + public: + static char ID; + ObjCARCExpand() : FunctionPass(ID) { + initializeObjCARCExpandPass(*PassRegistry::getPassRegistry()); + } + }; +} + +char ObjCARCExpand::ID = 0; +INITIALIZE_PASS(ObjCARCExpand, + "objc-arc-expand", "ObjC ARC expansion", false, false) + +Pass *llvm::createObjCARCExpandPass() { + return new ObjCARCExpand(); +} + +void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesCFG(); +} + +bool ObjCARCExpand::doInitialization(Module &M) { + Run = ModuleHasARC(M); + return false; +} + +bool ObjCARCExpand::runOnFunction(Function &F) { + if (!EnableARCOpts) + return false; + + // If nothing in the Module uses ARC, don't do anything. + if (!Run) + return false; + + bool Changed = false; + + DEBUG(dbgs() << "ObjCARCExpand: Visiting Function: " << F.getName() << "\n"); + + for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ++I) { + Instruction *Inst = &*I; + + DEBUG(dbgs() << "ObjCARCExpand: Visiting: " << *Inst << "\n"); + + switch (GetBasicInstructionClass(Inst)) { + case IC_Retain: + case IC_RetainRV: + case IC_Autorelease: + case IC_AutoreleaseRV: + case IC_FusedRetainAutorelease: + case IC_FusedRetainAutoreleaseRV: { + // These calls return their argument verbatim, as a low-level + // optimization. However, this makes high-level optimizations + // harder. Undo any uses of this optimization that the front-end + // emitted here. We'll redo them in the contract pass. + Changed = true; + Value *Value = cast<CallInst>(Inst)->getArgOperand(0); + DEBUG(dbgs() << "ObjCARCExpand: Old = " << *Inst << "\n" + " New = " << *Value << "\n"); + Inst->replaceAllUsesWith(Value); + break; + } + default: + break; + } + } + + DEBUG(dbgs() << "ObjCARCExpand: Finished List.\n\n"); + + return Changed; +} + +/// @} +/// +/// \defgroup ARCAPElim ARC Autorelease Pool Elimination. +/// @{ + +#include "llvm/ADT/STLExtras.h" +#include "llvm/IR/Constants.h" + +namespace { + /// \brief Autorelease pool elimination. + class ObjCARCAPElim : public ModulePass { + virtual void getAnalysisUsage(AnalysisUsage &AU) const; + virtual bool runOnModule(Module &M); + + static bool MayAutorelease(ImmutableCallSite CS, unsigned Depth = 0); + static bool OptimizeBB(BasicBlock *BB); + + public: + static char ID; + ObjCARCAPElim() : ModulePass(ID) { + initializeObjCARCAPElimPass(*PassRegistry::getPassRegistry()); + } + }; +} + +char ObjCARCAPElim::ID = 0; +INITIALIZE_PASS(ObjCARCAPElim, + "objc-arc-apelim", + "ObjC ARC autorelease pool elimination", + false, false) + +Pass *llvm::createObjCARCAPElimPass() { + return new ObjCARCAPElim(); +} + +void ObjCARCAPElim::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesCFG(); +} + +/// Interprocedurally determine if calls made by the given call site can +/// possibly produce autoreleases. +bool ObjCARCAPElim::MayAutorelease(ImmutableCallSite CS, unsigned Depth) { + if (const Function *Callee = CS.getCalledFunction()) { + if (Callee->isDeclaration() || Callee->mayBeOverridden()) + return true; + for (Function::const_iterator I = Callee->begin(), E = Callee->end(); + I != E; ++I) { + const BasicBlock *BB = I; + for (BasicBlock::const_iterator J = BB->begin(), F = BB->end(); + J != F; ++J) + if (ImmutableCallSite JCS = ImmutableCallSite(J)) + // This recursion depth limit is arbitrary. It's just great + // enough to cover known interesting testcases. + if (Depth < 3 && + !JCS.onlyReadsMemory() && + MayAutorelease(JCS, Depth + 1)) + return true; + } + return false; + } + + return true; +} + +bool ObjCARCAPElim::OptimizeBB(BasicBlock *BB) { + bool Changed = false; + + Instruction *Push = 0; + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { + Instruction *Inst = I++; + switch (GetBasicInstructionClass(Inst)) { + case IC_AutoreleasepoolPush: + Push = Inst; + break; + case IC_AutoreleasepoolPop: + // If this pop matches a push and nothing in between can autorelease, + // zap the pair. + if (Push && cast<CallInst>(Inst)->getArgOperand(0) == Push) { + Changed = true; + DEBUG(dbgs() << "ObjCARCAPElim::OptimizeBB: Zapping push pop " + "autorelease pair:\n" + " Pop: " << *Inst << "\n" + << " Push: " << *Push << "\n"); + Inst->eraseFromParent(); + Push->eraseFromParent(); + } + Push = 0; + break; + case IC_CallOrUser: + if (MayAutorelease(ImmutableCallSite(Inst))) + Push = 0; + break; + default: + break; + } + } + + return Changed; +} + +bool ObjCARCAPElim::runOnModule(Module &M) { + if (!EnableARCOpts) + return false; + + // If nothing in the Module uses ARC, don't do anything. + if (!ModuleHasARC(M)) + return false; + + // Find the llvm.global_ctors variable, as the first step in + // identifying the global constructors. In theory, unnecessary autorelease + // pools could occur anywhere, but in practice it's pretty rare. Global + // ctors are a place where autorelease pools get inserted automatically, + // so it's pretty common for them to be unnecessary, and it's pretty + // profitable to eliminate them. + GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors"); + if (!GV) + return false; + + assert(GV->hasDefinitiveInitializer() && + "llvm.global_ctors is uncooperative!"); + + bool Changed = false; + + // Dig the constructor functions out of GV's initializer. + ConstantArray *Init = cast<ConstantArray>(GV->getInitializer()); + for (User::op_iterator OI = Init->op_begin(), OE = Init->op_end(); + OI != OE; ++OI) { + Value *Op = *OI; + // llvm.global_ctors is an array of pairs where the second members + // are constructor functions. + Function *F = dyn_cast<Function>(cast<ConstantStruct>(Op)->getOperand(1)); + // If the user used a constructor function with the wrong signature and + // it got bitcasted or whatever, look the other way. + if (!F) + continue; + // Only look at function definitions. + if (F->isDeclaration()) + continue; + // Only look at functions with one basic block. + if (llvm::next(F->begin()) != F->end()) + continue; + // Ok, a single-block constructor function definition. Try to optimize it. + Changed |= OptimizeBB(F->begin()); + } + + return Changed; +} + +/// @} +/// +/// \defgroup ARCOpt ARC Optimization. +/// @{ + +// TODO: On code like this: +// +// objc_retain(%x) +// stuff_that_cannot_release() +// objc_autorelease(%x) +// stuff_that_cannot_release() +// objc_retain(%x) +// stuff_that_cannot_release() +// objc_autorelease(%x) +// +// The second retain and autorelease can be deleted. + +// TODO: It should be possible to delete +// objc_autoreleasePoolPush and objc_autoreleasePoolPop +// pairs if nothing is actually autoreleased between them. Also, autorelease +// calls followed by objc_autoreleasePoolPop calls (perhaps in ObjC++ code +// after inlining) can be turned into plain release calls. + +// TODO: Critical-edge splitting. If the optimial insertion point is +// a critical edge, the current algorithm has to fail, because it doesn't +// know how to split edges. It should be possible to make the optimizer +// think in terms of edges, rather than blocks, and then split critical +// edges on demand. + +// TODO: OptimizeSequences could generalized to be Interprocedural. + +// TODO: Recognize that a bunch of other objc runtime calls have +// non-escaping arguments and non-releasing arguments, and may be +// non-autoreleasing. + +// TODO: Sink autorelease calls as far as possible. Unfortunately we +// usually can't sink them past other calls, which would be the main +// case where it would be useful. + +// TODO: The pointer returned from objc_loadWeakRetained is retained. + +// TODO: Delete release+retain pairs (rare). + +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/Support/CFG.h" + +STATISTIC(NumNoops, "Number of no-op objc calls eliminated"); +STATISTIC(NumPartialNoops, "Number of partially no-op objc calls eliminated"); +STATISTIC(NumAutoreleases,"Number of autoreleases converted to releases"); +STATISTIC(NumRets, "Number of return value forwarding " + "retain+autoreleaes eliminated"); +STATISTIC(NumRRs, "Number of retain+release paths eliminated"); +STATISTIC(NumPeeps, "Number of calls peephole-optimized"); + +namespace { + /// \brief This is similar to BasicAliasAnalysis, and it uses many of the same + /// techniques, except it uses special ObjC-specific reasoning about pointer + /// relationships. + /// + /// In this context ``Provenance'' is defined as the history of an object's + /// ownership. Thus ``Provenance Analysis'' is defined by using the notion of + /// an ``independent provenance source'' of a pointer to determine whether or + /// not two pointers have the same provenance source and thus could + /// potentially be related. + class ProvenanceAnalysis { + AliasAnalysis *AA; + + typedef std::pair<const Value *, const Value *> ValuePairTy; + typedef DenseMap<ValuePairTy, bool> CachedResultsTy; + CachedResultsTy CachedResults; + + bool relatedCheck(const Value *A, const Value *B); + bool relatedSelect(const SelectInst *A, const Value *B); + bool relatedPHI(const PHINode *A, const Value *B); + + void operator=(const ProvenanceAnalysis &) LLVM_DELETED_FUNCTION; + ProvenanceAnalysis(const ProvenanceAnalysis &) LLVM_DELETED_FUNCTION; + + public: + ProvenanceAnalysis() {} + + void setAA(AliasAnalysis *aa) { AA = aa; } + + AliasAnalysis *getAA() const { return AA; } + + bool related(const Value *A, const Value *B); + + void clear() { + CachedResults.clear(); + } + }; +} + +bool ProvenanceAnalysis::relatedSelect(const SelectInst *A, const Value *B) { + // If the values are Selects with the same condition, we can do a more precise + // check: just check for relations between the values on corresponding arms. + if (const SelectInst *SB = dyn_cast<SelectInst>(B)) + if (A->getCondition() == SB->getCondition()) + return related(A->getTrueValue(), SB->getTrueValue()) || + related(A->getFalseValue(), SB->getFalseValue()); + + // Check both arms of the Select node individually. + return related(A->getTrueValue(), B) || + related(A->getFalseValue(), B); +} + +bool ProvenanceAnalysis::relatedPHI(const PHINode *A, const Value *B) { + // If the values are PHIs in the same block, we can do a more precise as well + // as efficient check: just check for relations between the values on + // corresponding edges. + if (const PHINode *PNB = dyn_cast<PHINode>(B)) + if (PNB->getParent() == A->getParent()) { + for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i) + if (related(A->getIncomingValue(i), + PNB->getIncomingValueForBlock(A->getIncomingBlock(i)))) + return true; + return false; + } + + // Check each unique source of the PHI node against B. + SmallPtrSet<const Value *, 4> UniqueSrc; + for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i) { + const Value *PV1 = A->getIncomingValue(i); + if (UniqueSrc.insert(PV1) && related(PV1, B)) + return true; + } + + // All of the arms checked out. + return false; +} + +/// Test if the value of P, or any value covered by its provenance, is ever +/// stored within the function (not counting callees). +static bool isStoredObjCPointer(const Value *P) { + SmallPtrSet<const Value *, 8> Visited; + SmallVector<const Value *, 8> Worklist; + Worklist.push_back(P); + Visited.insert(P); + do { + P = Worklist.pop_back_val(); + for (Value::const_use_iterator UI = P->use_begin(), UE = P->use_end(); + UI != UE; ++UI) { + const User *Ur = *UI; + if (isa<StoreInst>(Ur)) { + if (UI.getOperandNo() == 0) + // The pointer is stored. + return true; + // The pointed is stored through. + continue; + } + if (isa<CallInst>(Ur)) + // The pointer is passed as an argument, ignore this. + continue; + if (isa<PtrToIntInst>(P)) + // Assume the worst. + return true; + if (Visited.insert(Ur)) + Worklist.push_back(Ur); + } + } while (!Worklist.empty()); + + // Everything checked out. + return false; +} + +bool ProvenanceAnalysis::relatedCheck(const Value *A, const Value *B) { + // Skip past provenance pass-throughs. + A = GetUnderlyingObjCPtr(A); + B = GetUnderlyingObjCPtr(B); + + // Quick check. + if (A == B) + return true; + + // Ask regular AliasAnalysis, for a first approximation. + switch (AA->alias(A, B)) { + case AliasAnalysis::NoAlias: + return false; + case AliasAnalysis::MustAlias: + case AliasAnalysis::PartialAlias: + return true; + case AliasAnalysis::MayAlias: + break; + } + + bool AIsIdentified = IsObjCIdentifiedObject(A); + bool BIsIdentified = IsObjCIdentifiedObject(B); + + // An ObjC-Identified object can't alias a load if it is never locally stored. + if (AIsIdentified) { + // Check for an obvious escape. + if (isa<LoadInst>(B)) + return isStoredObjCPointer(A); + if (BIsIdentified) { + // Check for an obvious escape. + if (isa<LoadInst>(A)) + return isStoredObjCPointer(B); + // Both pointers are identified and escapes aren't an evident problem. + return false; + } + } else if (BIsIdentified) { + // Check for an obvious escape. + if (isa<LoadInst>(A)) + return isStoredObjCPointer(B); + } + + // Special handling for PHI and Select. + if (const PHINode *PN = dyn_cast<PHINode>(A)) + return relatedPHI(PN, B); + if (const PHINode *PN = dyn_cast<PHINode>(B)) + return relatedPHI(PN, A); + if (const SelectInst *S = dyn_cast<SelectInst>(A)) + return relatedSelect(S, B); + if (const SelectInst *S = dyn_cast<SelectInst>(B)) + return relatedSelect(S, A); + + // Conservative. + return true; +} + +bool ProvenanceAnalysis::related(const Value *A, const Value *B) { + // Begin by inserting a conservative value into the map. If the insertion + // fails, we have the answer already. If it succeeds, leave it there until we + // compute the real answer to guard against recursive queries. + if (A > B) std::swap(A, B); + std::pair<CachedResultsTy::iterator, bool> Pair = + CachedResults.insert(std::make_pair(ValuePairTy(A, B), true)); + if (!Pair.second) + return Pair.first->second; + + bool Result = relatedCheck(A, B); + CachedResults[ValuePairTy(A, B)] = Result; + return Result; +} + +namespace { + /// \enum Sequence + /// + /// \brief A sequence of states that a pointer may go through in which an + /// objc_retain and objc_release are actually needed. + enum Sequence { + S_None, + S_Retain, ///< objc_retain(x) + S_CanRelease, ///< foo(x) -- x could possibly see a ref count decrement + S_Use, ///< any use of x + S_Stop, ///< like S_Release, but code motion is stopped + S_Release, ///< objc_release(x) + S_MovableRelease ///< objc_release(x), !clang.imprecise_release + }; +} + +static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) { + // The easy cases. + if (A == B) + return A; + if (A == S_None || B == S_None) + return S_None; + + if (A > B) std::swap(A, B); + if (TopDown) { + // Choose the side which is further along in the sequence. + if ((A == S_Retain || A == S_CanRelease) && + (B == S_CanRelease || B == S_Use)) + return B; + } else { + // Choose the side which is further along in the sequence. + if ((A == S_Use || A == S_CanRelease) && + (B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease)) + return A; + // If both sides are releases, choose the more conservative one. + if (A == S_Stop && (B == S_Release || B == S_MovableRelease)) + return A; + if (A == S_Release && B == S_MovableRelease) + return A; + } + + return S_None; +} + +namespace { + /// \brief Unidirectional information about either a + /// retain-decrement-use-release sequence or release-use-decrement-retain + /// reverese sequence. + struct RRInfo { + /// After an objc_retain, the reference count of the referenced + /// object is known to be positive. Similarly, before an objc_release, the + /// reference count of the referenced object is known to be positive. If + /// there are retain-release pairs in code regions where the retain count + /// is known to be positive, they can be eliminated, regardless of any side + /// effects between them. + /// + /// Also, a retain+release pair nested within another retain+release + /// pair all on the known same pointer value can be eliminated, regardless + /// of any intervening side effects. + /// + /// KnownSafe is true when either of these conditions is satisfied. + bool KnownSafe; + + /// True if the Calls are objc_retainBlock calls (as opposed to objc_retain + /// calls). + bool IsRetainBlock; + + /// True of the objc_release calls are all marked with the "tail" keyword. + bool IsTailCallRelease; + + /// If the Calls are objc_release calls and they all have a + /// clang.imprecise_release tag, this is the metadata tag. + MDNode *ReleaseMetadata; + + /// For a top-down sequence, the set of objc_retains or + /// objc_retainBlocks. For bottom-up, the set of objc_releases. + SmallPtrSet<Instruction *, 2> Calls; + + /// The set of optimal insert positions for moving calls in the opposite + /// sequence. + SmallPtrSet<Instruction *, 2> ReverseInsertPts; + + RRInfo() : + KnownSafe(false), IsRetainBlock(false), + IsTailCallRelease(false), + ReleaseMetadata(0) {} + + void clear(); + }; +} + +void RRInfo::clear() { + KnownSafe = false; + IsRetainBlock = false; + IsTailCallRelease = false; + ReleaseMetadata = 0; + Calls.clear(); + ReverseInsertPts.clear(); +} + +namespace { + /// \brief This class summarizes several per-pointer runtime properties which + /// are propogated through the flow graph. + class PtrState { + /// True if the reference count is known to be incremented. + bool KnownPositiveRefCount; + + /// True of we've seen an opportunity for partial RR elimination, such as + /// pushing calls into a CFG triangle or into one side of a CFG diamond. + bool Partial; + + /// The current position in the sequence. + Sequence Seq : 8; + + public: + /// Unidirectional information about the current sequence. + /// + /// TODO: Encapsulate this better. + RRInfo RRI; + + PtrState() : KnownPositiveRefCount(false), Partial(false), + Seq(S_None) {} + + void SetKnownPositiveRefCount() { + KnownPositiveRefCount = true; + } + + void ClearRefCount() { + KnownPositiveRefCount = false; + } + + bool IsKnownIncremented() const { + return KnownPositiveRefCount; + } + + void SetSeq(Sequence NewSeq) { + Seq = NewSeq; + } + + Sequence GetSeq() const { + return Seq; + } + + void ClearSequenceProgress() { + ResetSequenceProgress(S_None); + } + + void ResetSequenceProgress(Sequence NewSeq) { + Seq = NewSeq; + Partial = false; + RRI.clear(); + } + + void Merge(const PtrState &Other, bool TopDown); + }; +} + +void +PtrState::Merge(const PtrState &Other, bool TopDown) { + Seq = MergeSeqs(Seq, Other.Seq, TopDown); + KnownPositiveRefCount = KnownPositiveRefCount && Other.KnownPositiveRefCount; + + // We can't merge a plain objc_retain with an objc_retainBlock. + if (RRI.IsRetainBlock != Other.RRI.IsRetainBlock) + Seq = S_None; + + // If we're not in a sequence (anymore), drop all associated state. + if (Seq == S_None) { + Partial = false; + RRI.clear(); + } else if (Partial || Other.Partial) { + // If we're doing a merge on a path that's previously seen a partial + // merge, conservatively drop the sequence, to avoid doing partial + // RR elimination. If the branch predicates for the two merge differ, + // mixing them is unsafe. + ClearSequenceProgress(); + } else { + // Conservatively merge the ReleaseMetadata information. + if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata) + RRI.ReleaseMetadata = 0; + + RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe; + RRI.IsTailCallRelease = RRI.IsTailCallRelease && + Other.RRI.IsTailCallRelease; + RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end()); + + // Merge the insert point sets. If there are any differences, + // that makes this a partial merge. + Partial = RRI.ReverseInsertPts.size() != Other.RRI.ReverseInsertPts.size(); + for (SmallPtrSet<Instruction *, 2>::const_iterator + I = Other.RRI.ReverseInsertPts.begin(), + E = Other.RRI.ReverseInsertPts.end(); I != E; ++I) + Partial |= RRI.ReverseInsertPts.insert(*I); + } +} + +namespace { + /// \brief Per-BasicBlock state. + class BBState { + /// The number of unique control paths from the entry which can reach this + /// block. + unsigned TopDownPathCount; + + /// The number of unique control paths to exits from this block. + unsigned BottomUpPathCount; + + /// A type for PerPtrTopDown and PerPtrBottomUp. + typedef MapVector<const Value *, PtrState> MapTy; + + /// The top-down traversal uses this to record information known about a + /// pointer at the bottom of each block. + MapTy PerPtrTopDown; + + /// The bottom-up traversal uses this to record information known about a + /// pointer at the top of each block. + MapTy PerPtrBottomUp; + + /// Effective predecessors of the current block ignoring ignorable edges and + /// ignored backedges. + SmallVector<BasicBlock *, 2> Preds; + /// Effective successors of the current block ignoring ignorable edges and + /// ignored backedges. + SmallVector<BasicBlock *, 2> Succs; + + public: + BBState() : TopDownPathCount(0), BottomUpPathCount(0) {} + + typedef MapTy::iterator ptr_iterator; + typedef MapTy::const_iterator ptr_const_iterator; + + ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); } + ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); } + ptr_const_iterator top_down_ptr_begin() const { + return PerPtrTopDown.begin(); + } + ptr_const_iterator top_down_ptr_end() const { + return PerPtrTopDown.end(); + } + + ptr_iterator bottom_up_ptr_begin() { return PerPtrBottomUp.begin(); } + ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); } + ptr_const_iterator bottom_up_ptr_begin() const { + return PerPtrBottomUp.begin(); + } + ptr_const_iterator bottom_up_ptr_end() const { + return PerPtrBottomUp.end(); + } + + /// Mark this block as being an entry block, which has one path from the + /// entry by definition. + void SetAsEntry() { TopDownPathCount = 1; } + + /// Mark this block as being an exit block, which has one path to an exit by + /// definition. + void SetAsExit() { BottomUpPathCount = 1; } + + PtrState &getPtrTopDownState(const Value *Arg) { + return PerPtrTopDown[Arg]; + } + + PtrState &getPtrBottomUpState(const Value *Arg) { + return PerPtrBottomUp[Arg]; + } + + void clearBottomUpPointers() { + PerPtrBottomUp.clear(); + } + + void clearTopDownPointers() { + PerPtrTopDown.clear(); + } + + void InitFromPred(const BBState &Other); + void InitFromSucc(const BBState &Other); + void MergePred(const BBState &Other); + void MergeSucc(const BBState &Other); + + /// Return the number of possible unique paths from an entry to an exit + /// which pass through this block. This is only valid after both the + /// top-down and bottom-up traversals are complete. + unsigned GetAllPathCount() const { + assert(TopDownPathCount != 0); + assert(BottomUpPathCount != 0); + return TopDownPathCount * BottomUpPathCount; + } + + // Specialized CFG utilities. + typedef SmallVectorImpl<BasicBlock *>::const_iterator edge_iterator; + edge_iterator pred_begin() { return Preds.begin(); } + edge_iterator pred_end() { return Preds.end(); } + edge_iterator succ_begin() { return Succs.begin(); } + edge_iterator succ_end() { return Succs.end(); } + + void addSucc(BasicBlock *Succ) { Succs.push_back(Succ); } + void addPred(BasicBlock *Pred) { Preds.push_back(Pred); } + + bool isExit() const { return Succs.empty(); } + }; +} + +void BBState::InitFromPred(const BBState &Other) { + PerPtrTopDown = Other.PerPtrTopDown; + TopDownPathCount = Other.TopDownPathCount; +} + +void BBState::InitFromSucc(const BBState &Other) { + PerPtrBottomUp = Other.PerPtrBottomUp; + BottomUpPathCount = Other.BottomUpPathCount; +} + +/// The top-down traversal uses this to merge information about predecessors to +/// form the initial state for a new block. +void BBState::MergePred(const BBState &Other) { + // Other.TopDownPathCount can be 0, in which case it is either dead or a + // loop backedge. Loop backedges are special. + TopDownPathCount += Other.TopDownPathCount; + + // Check for overflow. If we have overflow, fall back to conservative + // behavior. + if (TopDownPathCount < Other.TopDownPathCount) { + clearTopDownPointers(); + return; + } + + // For each entry in the other set, if our set has an entry with the same key, + // merge the entries. Otherwise, copy the entry and merge it with an empty + // entry. + for (ptr_const_iterator MI = Other.top_down_ptr_begin(), + ME = Other.top_down_ptr_end(); MI != ME; ++MI) { + std::pair<ptr_iterator, bool> Pair = PerPtrTopDown.insert(*MI); + Pair.first->second.Merge(Pair.second ? PtrState() : MI->second, + /*TopDown=*/true); + } + + // For each entry in our set, if the other set doesn't have an entry with the + // same key, force it to merge with an empty entry. + for (ptr_iterator MI = top_down_ptr_begin(), + ME = top_down_ptr_end(); MI != ME; ++MI) + if (Other.PerPtrTopDown.find(MI->first) == Other.PerPtrTopDown.end()) + MI->second.Merge(PtrState(), /*TopDown=*/true); +} + +/// The bottom-up traversal uses this to merge information about successors to +/// form the initial state for a new block. +void BBState::MergeSucc(const BBState &Other) { + // Other.BottomUpPathCount can be 0, in which case it is either dead or a + // loop backedge. Loop backedges are special. + BottomUpPathCount += Other.BottomUpPathCount; + + // Check for overflow. If we have overflow, fall back to conservative + // behavior. + if (BottomUpPathCount < Other.BottomUpPathCount) { + clearBottomUpPointers(); + return; + } + + // For each entry in the other set, if our set has an entry with the + // same key, merge the entries. Otherwise, copy the entry and merge + // it with an empty entry. + for (ptr_const_iterator MI = Other.bottom_up_ptr_begin(), + ME = Other.bottom_up_ptr_end(); MI != ME; ++MI) { + std::pair<ptr_iterator, bool> Pair = PerPtrBottomUp.insert(*MI); + Pair.first->second.Merge(Pair.second ? PtrState() : MI->second, + /*TopDown=*/false); + } + + // For each entry in our set, if the other set doesn't have an entry + // with the same key, force it to merge with an empty entry. + for (ptr_iterator MI = bottom_up_ptr_begin(), + ME = bottom_up_ptr_end(); MI != ME; ++MI) + if (Other.PerPtrBottomUp.find(MI->first) == Other.PerPtrBottomUp.end()) + MI->second.Merge(PtrState(), /*TopDown=*/false); +} + +namespace { + /// \brief The main ARC optimization pass. + class ObjCARCOpt : public FunctionPass { + bool Changed; + ProvenanceAnalysis PA; + + /// A flag indicating whether this optimization pass should run. + bool Run; + + /// Declarations for ObjC runtime functions, for use in creating calls to + /// them. These are initialized lazily to avoid cluttering up the Module + /// with unused declarations. + + /// Declaration for ObjC runtime function + /// objc_retainAutoreleasedReturnValue. + Constant *RetainRVCallee; + /// Declaration for ObjC runtime function objc_autoreleaseReturnValue. + Constant *AutoreleaseRVCallee; + /// Declaration for ObjC runtime function objc_release. + Constant *ReleaseCallee; + /// Declaration for ObjC runtime function objc_retain. + Constant *RetainCallee; + /// Declaration for ObjC runtime function objc_retainBlock. + Constant *RetainBlockCallee; + /// Declaration for ObjC runtime function objc_autorelease. + Constant *AutoreleaseCallee; + + /// Flags which determine whether each of the interesting runtine functions + /// is in fact used in the current function. + unsigned UsedInThisFunction; + + /// The Metadata Kind for clang.imprecise_release metadata. + unsigned ImpreciseReleaseMDKind; + + /// The Metadata Kind for clang.arc.copy_on_escape metadata. + unsigned CopyOnEscapeMDKind; + + /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata. + unsigned NoObjCARCExceptionsMDKind; + + Constant *getRetainRVCallee(Module *M); + Constant *getAutoreleaseRVCallee(Module *M); + Constant *getReleaseCallee(Module *M); + Constant *getRetainCallee(Module *M); + Constant *getRetainBlockCallee(Module *M); + Constant *getAutoreleaseCallee(Module *M); + + bool IsRetainBlockOptimizable(const Instruction *Inst); + + void OptimizeRetainCall(Function &F, Instruction *Retain); + bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV); + void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV, + InstructionClass &Class); + void OptimizeIndividualCalls(Function &F); + + void CheckForCFGHazards(const BasicBlock *BB, + DenseMap<const BasicBlock *, BBState> &BBStates, + BBState &MyStates) const; + bool VisitInstructionBottomUp(Instruction *Inst, + BasicBlock *BB, + MapVector<Value *, RRInfo> &Retains, + BBState &MyStates); + bool VisitBottomUp(BasicBlock *BB, + DenseMap<const BasicBlock *, BBState> &BBStates, + MapVector<Value *, RRInfo> &Retains); + bool VisitInstructionTopDown(Instruction *Inst, + DenseMap<Value *, RRInfo> &Releases, + BBState &MyStates); + bool VisitTopDown(BasicBlock *BB, + DenseMap<const BasicBlock *, BBState> &BBStates, + DenseMap<Value *, RRInfo> &Releases); + bool Visit(Function &F, + DenseMap<const BasicBlock *, BBState> &BBStates, + MapVector<Value *, RRInfo> &Retains, + DenseMap<Value *, RRInfo> &Releases); + + void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove, + MapVector<Value *, RRInfo> &Retains, + DenseMap<Value *, RRInfo> &Releases, + SmallVectorImpl<Instruction *> &DeadInsts, + Module *M); + + bool ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState> &BBStates, + MapVector<Value *, RRInfo> &Retains, + DenseMap<Value *, RRInfo> &Releases, + Module *M, + SmallVector<Instruction *, 4> &NewRetains, + SmallVector<Instruction *, 4> &NewReleases, + SmallVector<Instruction *, 8> &DeadInsts, + RRInfo &RetainsToMove, + RRInfo &ReleasesToMove, + Value *Arg, + bool KnownSafe, + bool &AnyPairsCompletelyEliminated); + + bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates, + MapVector<Value *, RRInfo> &Retains, + DenseMap<Value *, RRInfo> &Releases, + Module *M); + + void OptimizeWeakCalls(Function &F); + + bool OptimizeSequences(Function &F); + + void OptimizeReturns(Function &F); + + virtual void getAnalysisUsage(AnalysisUsage &AU) const; + virtual bool doInitialization(Module &M); + virtual bool runOnFunction(Function &F); + virtual void releaseMemory(); + + public: + static char ID; + ObjCARCOpt() : FunctionPass(ID) { + initializeObjCARCOptPass(*PassRegistry::getPassRegistry()); + } + }; +} + +char ObjCARCOpt::ID = 0; +INITIALIZE_PASS_BEGIN(ObjCARCOpt, + "objc-arc", "ObjC ARC optimization", false, false) +INITIALIZE_PASS_DEPENDENCY(ObjCARCAliasAnalysis) +INITIALIZE_PASS_END(ObjCARCOpt, + "objc-arc", "ObjC ARC optimization", false, false) + +Pass *llvm::createObjCARCOptPass() { + return new ObjCARCOpt(); +} + +void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequired<ObjCARCAliasAnalysis>(); + AU.addRequired<AliasAnalysis>(); + // ARC optimization doesn't currently split critical edges. + AU.setPreservesCFG(); +} + +bool ObjCARCOpt::IsRetainBlockOptimizable(const Instruction *Inst) { + // Without the magic metadata tag, we have to assume this might be an + // objc_retainBlock call inserted to convert a block pointer to an id, + // in which case it really is needed. + if (!Inst->getMetadata(CopyOnEscapeMDKind)) + return false; + + // If the pointer "escapes" (not including being used in a call), + // the copy may be needed. + if (DoesObjCBlockEscape(Inst)) + return false; + + // Otherwise, it's not needed. + return true; +} + +Constant *ObjCARCOpt::getRetainRVCallee(Module *M) { + if (!RetainRVCallee) { + LLVMContext &C = M->getContext(); + Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); + Type *Params[] = { I8X }; + FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false); + AttributeSet Attribute = + AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex, + Attribute::NoUnwind); + RetainRVCallee = + M->getOrInsertFunction("objc_retainAutoreleasedReturnValue", FTy, + Attribute); + } + return RetainRVCallee; +} + +Constant *ObjCARCOpt::getAutoreleaseRVCallee(Module *M) { + if (!AutoreleaseRVCallee) { + LLVMContext &C = M->getContext(); + Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); + Type *Params[] = { I8X }; + FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false); + AttributeSet Attribute = + AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex, + Attribute::NoUnwind); + AutoreleaseRVCallee = + M->getOrInsertFunction("objc_autoreleaseReturnValue", FTy, + Attribute); + } + return AutoreleaseRVCallee; +} + +Constant *ObjCARCOpt::getReleaseCallee(Module *M) { + if (!ReleaseCallee) { + LLVMContext &C = M->getContext(); + Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) }; + AttributeSet Attribute = + AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex, + Attribute::NoUnwind); + ReleaseCallee = + M->getOrInsertFunction( + "objc_release", + FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false), + Attribute); + } + return ReleaseCallee; +} + +Constant *ObjCARCOpt::getRetainCallee(Module *M) { + if (!RetainCallee) { + LLVMContext &C = M->getContext(); + Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) }; + AttributeSet Attribute = + AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex, + Attribute::NoUnwind); + RetainCallee = + M->getOrInsertFunction( + "objc_retain", + FunctionType::get(Params[0], Params, /*isVarArg=*/false), + Attribute); + } + return RetainCallee; +} + +Constant *ObjCARCOpt::getRetainBlockCallee(Module *M) { + if (!RetainBlockCallee) { + LLVMContext &C = M->getContext(); + Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) }; + // objc_retainBlock is not nounwind because it calls user copy constructors + // which could theoretically throw. + RetainBlockCallee = + M->getOrInsertFunction( + "objc_retainBlock", + FunctionType::get(Params[0], Params, /*isVarArg=*/false), + AttributeSet()); + } + return RetainBlockCallee; +} + +Constant *ObjCARCOpt::getAutoreleaseCallee(Module *M) { + if (!AutoreleaseCallee) { + LLVMContext &C = M->getContext(); + Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) }; + AttributeSet Attribute = + AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex, + Attribute::NoUnwind); + AutoreleaseCallee = + M->getOrInsertFunction( + "objc_autorelease", + FunctionType::get(Params[0], Params, /*isVarArg=*/false), + Attribute); + } + return AutoreleaseCallee; +} + +/// Test whether the given value is possible a reference-counted pointer, +/// including tests which utilize AliasAnalysis. +static bool IsPotentialRetainableObjPtr(const Value *Op, AliasAnalysis &AA) { + // First make the rudimentary check. + if (!IsPotentialRetainableObjPtr(Op)) + return false; + + // Objects in constant memory are not reference-counted. + if (AA.pointsToConstantMemory(Op)) + return false; + + // Pointers in constant memory are not pointing to reference-counted objects. + if (const LoadInst *LI = dyn_cast<LoadInst>(Op)) + if (AA.pointsToConstantMemory(LI->getPointerOperand())) + return false; + + // Otherwise assume the worst. + return true; +} + +/// Test whether the given instruction can result in a reference count +/// modification (positive or negative) for the pointer's object. +static bool +CanAlterRefCount(const Instruction *Inst, const Value *Ptr, + ProvenanceAnalysis &PA, InstructionClass Class) { + switch (Class) { + case IC_Autorelease: + case IC_AutoreleaseRV: + case IC_User: + // These operations never directly modify a reference count. + return false; + default: break; + } + + ImmutableCallSite CS = static_cast<const Value *>(Inst); + assert(CS && "Only calls can alter reference counts!"); + + // See if AliasAnalysis can help us with the call. + AliasAnalysis::ModRefBehavior MRB = PA.getAA()->getModRefBehavior(CS); + if (AliasAnalysis::onlyReadsMemory(MRB)) + return false; + if (AliasAnalysis::onlyAccessesArgPointees(MRB)) { + for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); + I != E; ++I) { + const Value *Op = *I; + if (IsPotentialRetainableObjPtr(Op, *PA.getAA()) && PA.related(Ptr, Op)) + return true; + } + return false; + } + + // Assume the worst. + return true; +} + +/// Test whether the given instruction can "use" the given pointer's object in a +/// way that requires the reference count to be positive. +static bool +CanUse(const Instruction *Inst, const Value *Ptr, ProvenanceAnalysis &PA, + InstructionClass Class) { + // IC_Call operations (as opposed to IC_CallOrUser) never "use" objc pointers. + if (Class == IC_Call) + return false; + + // Consider various instructions which may have pointer arguments which are + // not "uses". + if (const ICmpInst *ICI = dyn_cast<ICmpInst>(Inst)) { + // Comparing a pointer with null, or any other constant, isn't really a use, + // because we don't care what the pointer points to, or about the values + // of any other dynamic reference-counted pointers. + if (!IsPotentialRetainableObjPtr(ICI->getOperand(1), *PA.getAA())) + return false; + } else if (ImmutableCallSite CS = static_cast<const Value *>(Inst)) { + // For calls, just check the arguments (and not the callee operand). + for (ImmutableCallSite::arg_iterator OI = CS.arg_begin(), + OE = CS.arg_end(); OI != OE; ++OI) { + const Value *Op = *OI; + if (IsPotentialRetainableObjPtr(Op, *PA.getAA()) && PA.related(Ptr, Op)) + return true; + } + return false; + } else if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) { + // Special-case stores, because we don't care about the stored value, just + // the store address. + const Value *Op = GetUnderlyingObjCPtr(SI->getPointerOperand()); + // If we can't tell what the underlying object was, assume there is a + // dependence. + return IsPotentialRetainableObjPtr(Op, *PA.getAA()) && PA.related(Op, Ptr); + } + + // Check each operand for a match. + for (User::const_op_iterator OI = Inst->op_begin(), OE = Inst->op_end(); + OI != OE; ++OI) { + const Value *Op = *OI; + if (IsPotentialRetainableObjPtr(Op, *PA.getAA()) && PA.related(Ptr, Op)) + return true; + } + return false; +} + +/// Test whether the given instruction can autorelease any pointer or cause an +/// autoreleasepool pop. +static bool +CanInterruptRV(InstructionClass Class) { + switch (Class) { + case IC_AutoreleasepoolPop: + case IC_CallOrUser: + case IC_Call: + case IC_Autorelease: + case IC_AutoreleaseRV: + case IC_FusedRetainAutorelease: + case IC_FusedRetainAutoreleaseRV: + return true; + default: + return false; + } +} + +namespace { + /// \enum DependenceKind + /// \brief Defines different dependence kinds among various ARC constructs. + /// + /// There are several kinds of dependence-like concepts in use here. + /// + enum DependenceKind { + NeedsPositiveRetainCount, + AutoreleasePoolBoundary, + CanChangeRetainCount, + RetainAutoreleaseDep, ///< Blocks objc_retainAutorelease. + RetainAutoreleaseRVDep, ///< Blocks objc_retainAutoreleaseReturnValue. + RetainRVDep ///< Blocks objc_retainAutoreleasedReturnValue. + }; +} + +/// Test if there can be dependencies on Inst through Arg. This function only +/// tests dependencies relevant for removing pairs of calls. +static bool +Depends(DependenceKind Flavor, Instruction *Inst, const Value *Arg, + ProvenanceAnalysis &PA) { + // If we've reached the definition of Arg, stop. + if (Inst == Arg) + return true; + + switch (Flavor) { + case NeedsPositiveRetainCount: { + InstructionClass Class = GetInstructionClass(Inst); + switch (Class) { + case IC_AutoreleasepoolPop: + case IC_AutoreleasepoolPush: + case IC_None: + return false; + default: + return CanUse(Inst, Arg, PA, Class); + } + } + + case AutoreleasePoolBoundary: { + InstructionClass Class = GetInstructionClass(Inst); + switch (Class) { + case IC_AutoreleasepoolPop: + case IC_AutoreleasepoolPush: + // These mark the end and begin of an autorelease pool scope. + return true; + default: + // Nothing else does this. + return false; + } + } + + case CanChangeRetainCount: { + InstructionClass Class = GetInstructionClass(Inst); + switch (Class) { + case IC_AutoreleasepoolPop: + // Conservatively assume this can decrement any count. + return true; + case IC_AutoreleasepoolPush: + case IC_None: + return false; + default: + return CanAlterRefCount(Inst, Arg, PA, Class); + } + } + + case RetainAutoreleaseDep: + switch (GetBasicInstructionClass(Inst)) { + case IC_AutoreleasepoolPop: + case IC_AutoreleasepoolPush: + // Don't merge an objc_autorelease with an objc_retain inside a different + // autoreleasepool scope. + return true; + case IC_Retain: + case IC_RetainRV: + // Check for a retain of the same pointer for merging. + return GetObjCArg(Inst) == Arg; + default: + // Nothing else matters for objc_retainAutorelease formation. + return false; + } + + case RetainAutoreleaseRVDep: { + InstructionClass Class = GetBasicInstructionClass(Inst); + switch (Class) { + case IC_Retain: + case IC_RetainRV: + // Check for a retain of the same pointer for merging. + return GetObjCArg(Inst) == Arg; + default: + // Anything that can autorelease interrupts + // retainAutoreleaseReturnValue formation. + return CanInterruptRV(Class); + } + } + + case RetainRVDep: + return CanInterruptRV(GetBasicInstructionClass(Inst)); + } + + llvm_unreachable("Invalid dependence flavor"); +} + +/// Walk up the CFG from StartPos (which is in StartBB) and find local and +/// non-local dependencies on Arg. +/// +/// TODO: Cache results? +static void +FindDependencies(DependenceKind Flavor, + const Value *Arg, + BasicBlock *StartBB, Instruction *StartInst, + SmallPtrSet<Instruction *, 4> &DependingInstructions, + SmallPtrSet<const BasicBlock *, 4> &Visited, + ProvenanceAnalysis &PA) { + BasicBlock::iterator StartPos = StartInst; + + SmallVector<std::pair<BasicBlock *, BasicBlock::iterator>, 4> Worklist; + Worklist.push_back(std::make_pair(StartBB, StartPos)); + do { + std::pair<BasicBlock *, BasicBlock::iterator> Pair = + Worklist.pop_back_val(); + BasicBlock *LocalStartBB = Pair.first; + BasicBlock::iterator LocalStartPos = Pair.second; + BasicBlock::iterator StartBBBegin = LocalStartBB->begin(); + for (;;) { + if (LocalStartPos == StartBBBegin) { + pred_iterator PI(LocalStartBB), PE(LocalStartBB, false); + if (PI == PE) + // If we've reached the function entry, produce a null dependence. + DependingInstructions.insert(0); + else + // Add the predecessors to the worklist. + do { + BasicBlock *PredBB = *PI; + if (Visited.insert(PredBB)) + Worklist.push_back(std::make_pair(PredBB, PredBB->end())); + } while (++PI != PE); + break; + } + + Instruction *Inst = --LocalStartPos; + if (Depends(Flavor, Inst, Arg, PA)) { + DependingInstructions.insert(Inst); + break; + } + } + } while (!Worklist.empty()); + + // Determine whether the original StartBB post-dominates all of the blocks we + // visited. If not, insert a sentinal indicating that most optimizations are + // not safe. + for (SmallPtrSet<const BasicBlock *, 4>::const_iterator I = Visited.begin(), + E = Visited.end(); I != E; ++I) { + const BasicBlock *BB = *I; + if (BB == StartBB) + continue; + const TerminatorInst *TI = cast<TerminatorInst>(&BB->back()); + for (succ_const_iterator SI(TI), SE(TI, false); SI != SE; ++SI) { + const BasicBlock *Succ = *SI; + if (Succ != StartBB && !Visited.count(Succ)) { + DependingInstructions.insert(reinterpret_cast<Instruction *>(-1)); + return; + } + } + } +} + +static bool isNullOrUndef(const Value *V) { + return isa<ConstantPointerNull>(V) || isa<UndefValue>(V); +} + +static bool isNoopInstruction(const Instruction *I) { + return isa<BitCastInst>(I) || + (isa<GetElementPtrInst>(I) && + cast<GetElementPtrInst>(I)->hasAllZeroIndices()); +} + +/// Turn objc_retain into objc_retainAutoreleasedReturnValue if the operand is a +/// return value. +void +ObjCARCOpt::OptimizeRetainCall(Function &F, Instruction *Retain) { + ImmutableCallSite CS(GetObjCArg(Retain)); + const Instruction *Call = CS.getInstruction(); + if (!Call) return; + if (Call->getParent() != Retain->getParent()) return; + + // Check that the call is next to the retain. + BasicBlock::const_iterator I = Call; + ++I; + while (isNoopInstruction(I)) ++I; + if (&*I != Retain) + return; + + // Turn it to an objc_retainAutoreleasedReturnValue.. + Changed = true; + ++NumPeeps; + + DEBUG(dbgs() << "ObjCARCOpt::OptimizeRetainCall: Transforming " + "objc_retain => objc_retainAutoreleasedReturnValue" + " since the operand is a return value.\n" + " Old: " + << *Retain << "\n"); + + cast<CallInst>(Retain)->setCalledFunction(getRetainRVCallee(F.getParent())); + + DEBUG(dbgs() << " New: " + << *Retain << "\n"); +} + +/// Turn objc_retainAutoreleasedReturnValue into objc_retain if the operand is +/// not a return value. Or, if it can be paired with an +/// objc_autoreleaseReturnValue, delete the pair and return true. +bool +ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) { + // Check for the argument being from an immediately preceding call or invoke. + const Value *Arg = GetObjCArg(RetainRV); + ImmutableCallSite CS(Arg); + if (const Instruction *Call = CS.getInstruction()) { + if (Call->getParent() == RetainRV->getParent()) { + BasicBlock::const_iterator I = Call; + ++I; + while (isNoopInstruction(I)) ++I; + if (&*I == RetainRV) + return false; + } else if (const InvokeInst *II = dyn_cast<InvokeInst>(Call)) { + BasicBlock *RetainRVParent = RetainRV->getParent(); + if (II->getNormalDest() == RetainRVParent) { + BasicBlock::const_iterator I = RetainRVParent->begin(); + while (isNoopInstruction(I)) ++I; + if (&*I == RetainRV) + return false; + } + } + } + + // Check for being preceded by an objc_autoreleaseReturnValue on the same + // pointer. In this case, we can delete the pair. + BasicBlock::iterator I = RetainRV, Begin = RetainRV->getParent()->begin(); + if (I != Begin) { + do --I; while (I != Begin && isNoopInstruction(I)); + if (GetBasicInstructionClass(I) == IC_AutoreleaseRV && + GetObjCArg(I) == Arg) { + Changed = true; + ++NumPeeps; + + DEBUG(dbgs() << "ObjCARCOpt::OptimizeRetainRVCall: Erasing " << *I << "\n" + << " Erasing " << *RetainRV + << "\n"); + + EraseInstruction(I); + EraseInstruction(RetainRV); + return true; + } + } + + // Turn it to a plain objc_retain. + Changed = true; + ++NumPeeps; + + DEBUG(dbgs() << "ObjCARCOpt::OptimizeRetainRVCall: Transforming " + "objc_retainAutoreleasedReturnValue => " + "objc_retain since the operand is not a return value.\n" + " Old: " + << *RetainRV << "\n"); + + cast<CallInst>(RetainRV)->setCalledFunction(getRetainCallee(F.getParent())); + + DEBUG(dbgs() << " New: " + << *RetainRV << "\n"); + + return false; +} + +/// Turn objc_autoreleaseReturnValue into objc_autorelease if the result is not +/// used as a return value. +void +ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV, + InstructionClass &Class) { + // Check for a return of the pointer value. + const Value *Ptr = GetObjCArg(AutoreleaseRV); + SmallVector<const Value *, 2> Users; + Users.push_back(Ptr); + do { + Ptr = Users.pop_back_val(); + for (Value::const_use_iterator UI = Ptr->use_begin(), UE = Ptr->use_end(); + UI != UE; ++UI) { + const User *I = *UI; + if (isa<ReturnInst>(I) || GetBasicInstructionClass(I) == IC_RetainRV) + return; + if (isa<BitCastInst>(I)) + Users.push_back(I); + } + } while (!Users.empty()); + + Changed = true; + ++NumPeeps; + + DEBUG(dbgs() << "ObjCARCOpt::OptimizeAutoreleaseRVCall: Transforming " + "objc_autoreleaseReturnValue => " + "objc_autorelease since its operand is not used as a return " + "value.\n" + " Old: " + << *AutoreleaseRV << "\n"); + + CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV); + AutoreleaseRVCI-> + setCalledFunction(getAutoreleaseCallee(F.getParent())); + AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease. + Class = IC_Autorelease; + + DEBUG(dbgs() << " New: " + << *AutoreleaseRV << "\n"); + +} + +/// Visit each call, one at a time, and make simplifications without doing any +/// additional analysis. +void ObjCARCOpt::OptimizeIndividualCalls(Function &F) { + // Reset all the flags in preparation for recomputing them. + UsedInThisFunction = 0; + + // Visit all objc_* calls in F. + for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) { + Instruction *Inst = &*I++; + + InstructionClass Class = GetBasicInstructionClass(Inst); + + DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Visiting: Class: " + << Class << "; " << *Inst << "\n"); + + switch (Class) { + default: break; + + // Delete no-op casts. These function calls have special semantics, but + // the semantics are entirely implemented via lowering in the front-end, + // so by the time they reach the optimizer, they are just no-op calls + // which return their argument. + // + // There are gray areas here, as the ability to cast reference-counted + // pointers to raw void* and back allows code to break ARC assumptions, + // however these are currently considered to be unimportant. + case IC_NoopCast: + Changed = true; + ++NumNoops; + DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Erasing no-op cast:" + " " << *Inst << "\n"); + EraseInstruction(Inst); + continue; + + // If the pointer-to-weak-pointer is null, it's undefined behavior. + case IC_StoreWeak: + case IC_LoadWeak: + case IC_LoadWeakRetained: + case IC_InitWeak: + case IC_DestroyWeak: { + CallInst *CI = cast<CallInst>(Inst); + if (isNullOrUndef(CI->getArgOperand(0))) { + Changed = true; + Type *Ty = CI->getArgOperand(0)->getType(); + new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()), + Constant::getNullValue(Ty), + CI); + llvm::Value *NewValue = UndefValue::get(CI->getType()); + DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: A null " + "pointer-to-weak-pointer is undefined behavior.\n" + " Old = " << *CI << + "\n New = " << + *NewValue << "\n"); + CI->replaceAllUsesWith(NewValue); + CI->eraseFromParent(); + continue; + } + break; + } + case IC_CopyWeak: + case IC_MoveWeak: { + CallInst *CI = cast<CallInst>(Inst); + if (isNullOrUndef(CI->getArgOperand(0)) || + isNullOrUndef(CI->getArgOperand(1))) { + Changed = true; + Type *Ty = CI->getArgOperand(0)->getType(); + new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()), + Constant::getNullValue(Ty), + CI); + + llvm::Value *NewValue = UndefValue::get(CI->getType()); + DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: A null " + "pointer-to-weak-pointer is undefined behavior.\n" + " Old = " << *CI << + "\n New = " << + *NewValue << "\n"); + + CI->replaceAllUsesWith(NewValue); + CI->eraseFromParent(); + continue; + } + break; + } + case IC_Retain: + OptimizeRetainCall(F, Inst); + break; + case IC_RetainRV: + if (OptimizeRetainRVCall(F, Inst)) + continue; + break; + case IC_AutoreleaseRV: + OptimizeAutoreleaseRVCall(F, Inst, Class); + break; + } + + // objc_autorelease(x) -> objc_release(x) if x is otherwise unused. + if (IsAutorelease(Class) && Inst->use_empty()) { + CallInst *Call = cast<CallInst>(Inst); + const Value *Arg = Call->getArgOperand(0); + Arg = FindSingleUseIdentifiedObject(Arg); + if (Arg) { + Changed = true; + ++NumAutoreleases; + + // Create the declaration lazily. + LLVMContext &C = Inst->getContext(); + CallInst *NewCall = + CallInst::Create(getReleaseCallee(F.getParent()), + Call->getArgOperand(0), "", Call); + NewCall->setMetadata(ImpreciseReleaseMDKind, + MDNode::get(C, ArrayRef<Value *>())); + + DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Replacing " + "objc_autorelease(x) with objc_release(x) since x is " + "otherwise unused.\n" + " Old: " << *Call << + "\n New: " << + *NewCall << "\n"); + + EraseInstruction(Call); + Inst = NewCall; + Class = IC_Release; + } + } + + // For functions which can never be passed stack arguments, add + // a tail keyword. + if (IsAlwaysTail(Class)) { + Changed = true; + DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Adding tail keyword" + " to function since it can never be passed stack args: " << *Inst << + "\n"); + cast<CallInst>(Inst)->setTailCall(); + } + + // Ensure that functions that can never have a "tail" keyword due to the + // semantics of ARC truly do not do so. + if (IsNeverTail(Class)) { + Changed = true; + DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Removing tail " + "keyword from function: " << *Inst << + "\n"); + cast<CallInst>(Inst)->setTailCall(false); + } + + // Set nounwind as needed. + if (IsNoThrow(Class)) { + Changed = true; + DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Found no throw" + " class. Setting nounwind on: " << *Inst << "\n"); + cast<CallInst>(Inst)->setDoesNotThrow(); + } + + if (!IsNoopOnNull(Class)) { + UsedInThisFunction |= 1 << Class; + continue; + } + + const Value *Arg = GetObjCArg(Inst); + + // ARC calls with null are no-ops. Delete them. + if (isNullOrUndef(Arg)) { + Changed = true; + ++NumNoops; + DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: ARC calls with " + " null are no-ops. Erasing: " << *Inst << "\n"); + EraseInstruction(Inst); + continue; + } + + // Keep track of which of retain, release, autorelease, and retain_block + // are actually present in this function. + UsedInThisFunction |= 1 << Class; + + // If Arg is a PHI, and one or more incoming values to the + // PHI are null, and the call is control-equivalent to the PHI, and there + // are no relevant side effects between the PHI and the call, the call + // could be pushed up to just those paths with non-null incoming values. + // For now, don't bother splitting critical edges for this. + SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist; + Worklist.push_back(std::make_pair(Inst, Arg)); + do { + std::pair<Instruction *, const Value *> Pair = Worklist.pop_back_val(); + Inst = Pair.first; + Arg = Pair.second; + + const PHINode *PN = dyn_cast<PHINode>(Arg); + if (!PN) continue; + + // Determine if the PHI has any null operands, or any incoming + // critical edges. + bool HasNull = false; + bool HasCriticalEdges = false; + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + Value *Incoming = + StripPointerCastsAndObjCCalls(PN->getIncomingValue(i)); + if (isNullOrUndef(Incoming)) + HasNull = true; + else if (cast<TerminatorInst>(PN->getIncomingBlock(i)->back()) + .getNumSuccessors() != 1) { + HasCriticalEdges = true; + break; + } + } + // If we have null operands and no critical edges, optimize. + if (!HasCriticalEdges && HasNull) { + SmallPtrSet<Instruction *, 4> DependingInstructions; + SmallPtrSet<const BasicBlock *, 4> Visited; + + // Check that there is nothing that cares about the reference + // count between the call and the phi. + switch (Class) { + case IC_Retain: + case IC_RetainBlock: + // These can always be moved up. + break; + case IC_Release: + // These can't be moved across things that care about the retain + // count. + FindDependencies(NeedsPositiveRetainCount, Arg, + Inst->getParent(), Inst, + DependingInstructions, Visited, PA); + break; + case IC_Autorelease: + // These can't be moved across autorelease pool scope boundaries. + FindDependencies(AutoreleasePoolBoundary, Arg, + Inst->getParent(), Inst, + DependingInstructions, Visited, PA); + break; + case IC_RetainRV: + case IC_AutoreleaseRV: + // Don't move these; the RV optimization depends on the autoreleaseRV + // being tail called, and the retainRV being immediately after a call + // (which might still happen if we get lucky with codegen layout, but + // it's not worth taking the chance). + continue; + default: + llvm_unreachable("Invalid dependence flavor"); + } + + if (DependingInstructions.size() == 1 && + *DependingInstructions.begin() == PN) { + Changed = true; + ++NumPartialNoops; + // Clone the call into each predecessor that has a non-null value. + CallInst *CInst = cast<CallInst>(Inst); + Type *ParamTy = CInst->getArgOperand(0)->getType(); + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + Value *Incoming = + StripPointerCastsAndObjCCalls(PN->getIncomingValue(i)); + if (!isNullOrUndef(Incoming)) { + CallInst *Clone = cast<CallInst>(CInst->clone()); + Value *Op = PN->getIncomingValue(i); + Instruction *InsertPos = &PN->getIncomingBlock(i)->back(); + if (Op->getType() != ParamTy) + Op = new BitCastInst(Op, ParamTy, "", InsertPos); + Clone->setArgOperand(0, Op); + Clone->insertBefore(InsertPos); + + DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Cloning " + << *CInst << "\n" + " And inserting " + "clone at " << *InsertPos << "\n"); + Worklist.push_back(std::make_pair(Clone, Incoming)); + } + } + // Erase the original call. + DEBUG(dbgs() << "Erasing: " << *CInst << "\n"); + EraseInstruction(CInst); + continue; + } + } + } while (!Worklist.empty()); + } + DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Finished List.\n"); +} + +/// Check for critical edges, loop boundaries, irreducible control flow, or +/// other CFG structures where moving code across the edge would result in it +/// being executed more. +void +ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB, + DenseMap<const BasicBlock *, BBState> &BBStates, + BBState &MyStates) const { + // If any top-down local-use or possible-dec has a succ which is earlier in + // the sequence, forget it. + for (BBState::ptr_iterator I = MyStates.top_down_ptr_begin(), + E = MyStates.top_down_ptr_end(); I != E; ++I) + switch (I->second.GetSeq()) { + default: break; + case S_Use: { + const Value *Arg = I->first; + const TerminatorInst *TI = cast<TerminatorInst>(&BB->back()); + bool SomeSuccHasSame = false; + bool AllSuccsHaveSame = true; + PtrState &S = I->second; + succ_const_iterator SI(TI), SE(TI, false); + + for (; SI != SE; ++SI) { + Sequence SuccSSeq = S_None; + bool SuccSRRIKnownSafe = false; + // If VisitBottomUp has pointer information for this successor, take + // what we know about it. + DenseMap<const BasicBlock *, BBState>::iterator BBI = + BBStates.find(*SI); + assert(BBI != BBStates.end()); + const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg); + SuccSSeq = SuccS.GetSeq(); + SuccSRRIKnownSafe = SuccS.RRI.KnownSafe; + switch (SuccSSeq) { + case S_None: + case S_CanRelease: { + if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) { + S.ClearSequenceProgress(); + break; + } + continue; + } + case S_Use: + SomeSuccHasSame = true; + break; + case S_Stop: + case S_Release: + case S_MovableRelease: + if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) + AllSuccsHaveSame = false; + break; + case S_Retain: + llvm_unreachable("bottom-up pointer in retain state!"); + } + } + // If the state at the other end of any of the successor edges + // matches the current state, require all edges to match. This + // guards against loops in the middle of a sequence. + if (SomeSuccHasSame && !AllSuccsHaveSame) + S.ClearSequenceProgress(); + break; + } + case S_CanRelease: { + const Value *Arg = I->first; + const TerminatorInst *TI = cast<TerminatorInst>(&BB->back()); + bool SomeSuccHasSame = false; + bool AllSuccsHaveSame = true; + PtrState &S = I->second; + succ_const_iterator SI(TI), SE(TI, false); + + for (; SI != SE; ++SI) { + Sequence SuccSSeq = S_None; + bool SuccSRRIKnownSafe = false; + // If VisitBottomUp has pointer information for this successor, take + // what we know about it. + DenseMap<const BasicBlock *, BBState>::iterator BBI = + BBStates.find(*SI); + assert(BBI != BBStates.end()); + const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg); + SuccSSeq = SuccS.GetSeq(); + SuccSRRIKnownSafe = SuccS.RRI.KnownSafe; + switch (SuccSSeq) { + case S_None: { + if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) { + S.ClearSequenceProgress(); + break; + } + continue; + } + case S_CanRelease: + SomeSuccHasSame = true; + break; + case S_Stop: + case S_Release: + case S_MovableRelease: + case S_Use: + if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) + AllSuccsHaveSame = false; + break; + case S_Retain: + llvm_unreachable("bottom-up pointer in retain state!"); + } + } + // If the state at the other end of any of the successor edges + // matches the current state, require all edges to match. This + // guards against loops in the middle of a sequence. + if (SomeSuccHasSame && !AllSuccsHaveSame) + S.ClearSequenceProgress(); + break; + } + } +} + +bool +ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst, + BasicBlock *BB, + MapVector<Value *, RRInfo> &Retains, + BBState &MyStates) { + bool NestingDetected = false; + InstructionClass Class = GetInstructionClass(Inst); + const Value *Arg = 0; + + switch (Class) { + case IC_Release: { + Arg = GetObjCArg(Inst); + + PtrState &S = MyStates.getPtrBottomUpState(Arg); + + // If we see two releases in a row on the same pointer. If so, make + // a note, and we'll cicle back to revisit it after we've + // hopefully eliminated the second release, which may allow us to + // eliminate the first release too. + // Theoretically we could implement removal of nested retain+release + // pairs by making PtrState hold a stack of states, but this is + // simple and avoids adding overhead for the non-nested case. + if (S.GetSeq() == S_Release || S.GetSeq() == S_MovableRelease) { + DEBUG(dbgs() << "ObjCARCOpt::VisitInstructionBottomUp: Found nested " + "releases (i.e. a release pair)\n"); + NestingDetected = true; + } + + MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind); + S.ResetSequenceProgress(ReleaseMetadata ? S_MovableRelease : S_Release); + S.RRI.ReleaseMetadata = ReleaseMetadata; + S.RRI.KnownSafe = S.IsKnownIncremented(); + S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall(); + S.RRI.Calls.insert(Inst); + + S.SetKnownPositiveRefCount(); + break; + } + case IC_RetainBlock: + // An objc_retainBlock call with just a use may need to be kept, + // because it may be copying a block from the stack to the heap. + if (!IsRetainBlockOptimizable(Inst)) + break; + // FALLTHROUGH + case IC_Retain: + case IC_RetainRV: { + Arg = GetObjCArg(Inst); + + PtrState &S = MyStates.getPtrBottomUpState(Arg); + S.SetKnownPositiveRefCount(); + + switch (S.GetSeq()) { + case S_Stop: + case S_Release: + case S_MovableRelease: + case S_Use: + S.RRI.ReverseInsertPts.clear(); + // FALL THROUGH + case S_CanRelease: + // Don't do retain+release tracking for IC_RetainRV, because it's + // better to let it remain as the first instruction after a call. + if (Class != IC_RetainRV) { + S.RRI.IsRetainBlock = Class == IC_RetainBlock; + Retains[Inst] = S.RRI; + } + S.ClearSequenceProgress(); + break; + case S_None: + break; + case S_Retain: + llvm_unreachable("bottom-up pointer in retain state!"); + } + return NestingDetected; + } + case IC_AutoreleasepoolPop: + // Conservatively, clear MyStates for all known pointers. + MyStates.clearBottomUpPointers(); + return NestingDetected; + case IC_AutoreleasepoolPush: + case IC_None: + // These are irrelevant. + return NestingDetected; + default: + break; + } + + // Consider any other possible effects of this instruction on each + // pointer being tracked. + for (BBState::ptr_iterator MI = MyStates.bottom_up_ptr_begin(), + ME = MyStates.bottom_up_ptr_end(); MI != ME; ++MI) { + const Value *Ptr = MI->first; + if (Ptr == Arg) + continue; // Handled above. + PtrState &S = MI->second; + Sequence Seq = S.GetSeq(); + + // Check for possible releases. + if (CanAlterRefCount(Inst, Ptr, PA, Class)) { + S.ClearRefCount(); + switch (Seq) { + case S_Use: + S.SetSeq(S_CanRelease); + continue; + case S_CanRelease: + case S_Release: + case S_MovableRelease: + case S_Stop: + case S_None: + break; + case S_Retain: + llvm_unreachable("bottom-up pointer in retain state!"); + } + } + + // Check for possible direct uses. + switch (Seq) { + case S_Release: + case S_MovableRelease: + if (CanUse(Inst, Ptr, PA, Class)) { + assert(S.RRI.ReverseInsertPts.empty()); + // If this is an invoke instruction, we're scanning it as part of + // one of its successor blocks, since we can't insert code after it + // in its own block, and we don't want to split critical edges. + if (isa<InvokeInst>(Inst)) + S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt()); + else + S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst))); + S.SetSeq(S_Use); + } else if (Seq == S_Release && + (Class == IC_User || Class == IC_CallOrUser)) { + // Non-movable releases depend on any possible objc pointer use. + S.SetSeq(S_Stop); + assert(S.RRI.ReverseInsertPts.empty()); + // As above; handle invoke specially. + if (isa<InvokeInst>(Inst)) + S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt()); + else + S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst))); + } + break; + case S_Stop: + if (CanUse(Inst, Ptr, PA, Class)) + S.SetSeq(S_Use); + break; + case S_CanRelease: + case S_Use: + case S_None: + break; + case S_Retain: + llvm_unreachable("bottom-up pointer in retain state!"); + } + } + + return NestingDetected; +} + +bool +ObjCARCOpt::VisitBottomUp(BasicBlock *BB, + DenseMap<const BasicBlock *, BBState> &BBStates, + MapVector<Value *, RRInfo> &Retains) { + bool NestingDetected = false; + BBState &MyStates = BBStates[BB]; + + // Merge the states from each successor to compute the initial state + // for the current block. + BBState::edge_iterator SI(MyStates.succ_begin()), + SE(MyStates.succ_end()); + if (SI != SE) { + const BasicBlock *Succ = *SI; + DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Succ); + assert(I != BBStates.end()); + MyStates.InitFromSucc(I->second); + ++SI; + for (; SI != SE; ++SI) { + Succ = *SI; + I = BBStates.find(Succ); + assert(I != BBStates.end()); + MyStates.MergeSucc(I->second); + } + } + + // Visit all the instructions, bottom-up. + for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) { + Instruction *Inst = llvm::prior(I); + + // Invoke instructions are visited as part of their successors (below). + if (isa<InvokeInst>(Inst)) + continue; + + DEBUG(dbgs() << "ObjCARCOpt::VisitButtonUp: Visiting " << *Inst << "\n"); + + NestingDetected |= VisitInstructionBottomUp(Inst, BB, Retains, MyStates); + } + + // If there's a predecessor with an invoke, visit the invoke as if it were + // part of this block, since we can't insert code after an invoke in its own + // block, and we don't want to split critical edges. + for (BBState::edge_iterator PI(MyStates.pred_begin()), + PE(MyStates.pred_end()); PI != PE; ++PI) { + BasicBlock *Pred = *PI; + if (InvokeInst *II = dyn_cast<InvokeInst>(&Pred->back())) + NestingDetected |= VisitInstructionBottomUp(II, BB, Retains, MyStates); + } + + return NestingDetected; +} + +bool +ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst, + DenseMap<Value *, RRInfo> &Releases, + BBState &MyStates) { + bool NestingDetected = false; + InstructionClass Class = GetInstructionClass(Inst); + const Value *Arg = 0; + + switch (Class) { + case IC_RetainBlock: + // An objc_retainBlock call with just a use may need to be kept, + // because it may be copying a block from the stack to the heap. + if (!IsRetainBlockOptimizable(Inst)) + break; + // FALLTHROUGH + case IC_Retain: + case IC_RetainRV: { + Arg = GetObjCArg(Inst); + + PtrState &S = MyStates.getPtrTopDownState(Arg); + + // Don't do retain+release tracking for IC_RetainRV, because it's + // better to let it remain as the first instruction after a call. + if (Class != IC_RetainRV) { + // If we see two retains in a row on the same pointer. If so, make + // a note, and we'll cicle back to revisit it after we've + // hopefully eliminated the second retain, which may allow us to + // eliminate the first retain too. + // Theoretically we could implement removal of nested retain+release + // pairs by making PtrState hold a stack of states, but this is + // simple and avoids adding overhead for the non-nested case. + if (S.GetSeq() == S_Retain) + NestingDetected = true; + + S.ResetSequenceProgress(S_Retain); + S.RRI.IsRetainBlock = Class == IC_RetainBlock; + S.RRI.KnownSafe = S.IsKnownIncremented(); + S.RRI.Calls.insert(Inst); + } + + S.SetKnownPositiveRefCount(); + + // A retain can be a potential use; procede to the generic checking + // code below. + break; + } + case IC_Release: { + Arg = GetObjCArg(Inst); + + PtrState &S = MyStates.getPtrTopDownState(Arg); + S.ClearRefCount(); + + switch (S.GetSeq()) { + case S_Retain: + case S_CanRelease: + S.RRI.ReverseInsertPts.clear(); + // FALL THROUGH + case S_Use: + S.RRI.ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind); + S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall(); + Releases[Inst] = S.RRI; + S.ClearSequenceProgress(); + break; + case S_None: + break; + case S_Stop: + case S_Release: + case S_MovableRelease: + llvm_unreachable("top-down pointer in release state!"); + } + break; + } + case IC_AutoreleasepoolPop: + // Conservatively, clear MyStates for all known pointers. + MyStates.clearTopDownPointers(); + return NestingDetected; + case IC_AutoreleasepoolPush: + case IC_None: + // These are irrelevant. + return NestingDetected; + default: + break; + } + + // Consider any other possible effects of this instruction on each + // pointer being tracked. + for (BBState::ptr_iterator MI = MyStates.top_down_ptr_begin(), + ME = MyStates.top_down_ptr_end(); MI != ME; ++MI) { + const Value *Ptr = MI->first; + if (Ptr == Arg) + continue; // Handled above. + PtrState &S = MI->second; + Sequence Seq = S.GetSeq(); + + // Check for possible releases. + if (CanAlterRefCount(Inst, Ptr, PA, Class)) { + S.ClearRefCount(); + switch (Seq) { + case S_Retain: + S.SetSeq(S_CanRelease); + assert(S.RRI.ReverseInsertPts.empty()); + S.RRI.ReverseInsertPts.insert(Inst); + + // One call can't cause a transition from S_Retain to S_CanRelease + // and S_CanRelease to S_Use. If we've made the first transition, + // we're done. + continue; + case S_Use: + case S_CanRelease: + case S_None: + break; + case S_Stop: + case S_Release: + case S_MovableRelease: + llvm_unreachable("top-down pointer in release state!"); + } + } + + // Check for possible direct uses. + switch (Seq) { + case S_CanRelease: + if (CanUse(Inst, Ptr, PA, Class)) + S.SetSeq(S_Use); + break; + case S_Retain: + case S_Use: + case S_None: + break; + case S_Stop: + case S_Release: + case S_MovableRelease: + llvm_unreachable("top-down pointer in release state!"); + } + } + + return NestingDetected; +} + +bool +ObjCARCOpt::VisitTopDown(BasicBlock *BB, + DenseMap<const BasicBlock *, BBState> &BBStates, + DenseMap<Value *, RRInfo> &Releases) { + bool NestingDetected = false; + BBState &MyStates = BBStates[BB]; + + // Merge the states from each predecessor to compute the initial state + // for the current block. + BBState::edge_iterator PI(MyStates.pred_begin()), + PE(MyStates.pred_end()); + if (PI != PE) { + const BasicBlock *Pred = *PI; + DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Pred); + assert(I != BBStates.end()); + MyStates.InitFromPred(I->second); + ++PI; + for (; PI != PE; ++PI) { + Pred = *PI; + I = BBStates.find(Pred); + assert(I != BBStates.end()); + MyStates.MergePred(I->second); + } + } + + // Visit all the instructions, top-down. + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { + Instruction *Inst = I; + + DEBUG(dbgs() << "ObjCARCOpt::VisitTopDown: Visiting " << *Inst << "\n"); + + NestingDetected |= VisitInstructionTopDown(Inst, Releases, MyStates); + } + + CheckForCFGHazards(BB, BBStates, MyStates); + return NestingDetected; +} + +static void +ComputePostOrders(Function &F, + SmallVectorImpl<BasicBlock *> &PostOrder, + SmallVectorImpl<BasicBlock *> &ReverseCFGPostOrder, + unsigned NoObjCARCExceptionsMDKind, + DenseMap<const BasicBlock *, BBState> &BBStates) { + /// The visited set, for doing DFS walks. + SmallPtrSet<BasicBlock *, 16> Visited; + + // Do DFS, computing the PostOrder. + SmallPtrSet<BasicBlock *, 16> OnStack; + SmallVector<std::pair<BasicBlock *, succ_iterator>, 16> SuccStack; + + // Functions always have exactly one entry block, and we don't have + // any other block that we treat like an entry block. + BasicBlock *EntryBB = &F.getEntryBlock(); + BBState &MyStates = BBStates[EntryBB]; + MyStates.SetAsEntry(); + TerminatorInst *EntryTI = cast<TerminatorInst>(&EntryBB->back()); + SuccStack.push_back(std::make_pair(EntryBB, succ_iterator(EntryTI))); + Visited.insert(EntryBB); + OnStack.insert(EntryBB); + do { + dfs_next_succ: + BasicBlock *CurrBB = SuccStack.back().first; + TerminatorInst *TI = cast<TerminatorInst>(&CurrBB->back()); + succ_iterator SE(TI, false); + + while (SuccStack.back().second != SE) { + BasicBlock *SuccBB = *SuccStack.back().second++; + if (Visited.insert(SuccBB)) { + TerminatorInst *TI = cast<TerminatorInst>(&SuccBB->back()); + SuccStack.push_back(std::make_pair(SuccBB, succ_iterator(TI))); + BBStates[CurrBB].addSucc(SuccBB); + BBState &SuccStates = BBStates[SuccBB]; + SuccStates.addPred(CurrBB); + OnStack.insert(SuccBB); + goto dfs_next_succ; + } + + if (!OnStack.count(SuccBB)) { + BBStates[CurrBB].addSucc(SuccBB); + BBStates[SuccBB].addPred(CurrBB); + } + } + OnStack.erase(CurrBB); + PostOrder.push_back(CurrBB); + SuccStack.pop_back(); + } while (!SuccStack.empty()); + + Visited.clear(); + + // Do reverse-CFG DFS, computing the reverse-CFG PostOrder. + // Functions may have many exits, and there also blocks which we treat + // as exits due to ignored edges. + SmallVector<std::pair<BasicBlock *, BBState::edge_iterator>, 16> PredStack; + for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) { + BasicBlock *ExitBB = I; + BBState &MyStates = BBStates[ExitBB]; + if (!MyStates.isExit()) + continue; + + MyStates.SetAsExit(); + + PredStack.push_back(std::make_pair(ExitBB, MyStates.pred_begin())); + Visited.insert(ExitBB); + while (!PredStack.empty()) { + reverse_dfs_next_succ: + BBState::edge_iterator PE = BBStates[PredStack.back().first].pred_end(); + while (PredStack.back().second != PE) { + BasicBlock *BB = *PredStack.back().second++; + if (Visited.insert(BB)) { + PredStack.push_back(std::make_pair(BB, BBStates[BB].pred_begin())); + goto reverse_dfs_next_succ; + } + } + ReverseCFGPostOrder.push_back(PredStack.pop_back_val().first); + } + } +} + +// Visit the function both top-down and bottom-up. +bool +ObjCARCOpt::Visit(Function &F, + DenseMap<const BasicBlock *, BBState> &BBStates, + MapVector<Value *, RRInfo> &Retains, + DenseMap<Value *, RRInfo> &Releases) { + + // Use reverse-postorder traversals, because we magically know that loops + // will be well behaved, i.e. they won't repeatedly call retain on a single + // pointer without doing a release. We can't use the ReversePostOrderTraversal + // class here because we want the reverse-CFG postorder to consider each + // function exit point, and we want to ignore selected cycle edges. + SmallVector<BasicBlock *, 16> PostOrder; + SmallVector<BasicBlock *, 16> ReverseCFGPostOrder; + ComputePostOrders(F, PostOrder, ReverseCFGPostOrder, + NoObjCARCExceptionsMDKind, + BBStates); + + // Use reverse-postorder on the reverse CFG for bottom-up. + bool BottomUpNestingDetected = false; + for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I = + ReverseCFGPostOrder.rbegin(), E = ReverseCFGPostOrder.rend(); + I != E; ++I) + BottomUpNestingDetected |= VisitBottomUp(*I, BBStates, Retains); + + // Use reverse-postorder for top-down. + bool TopDownNestingDetected = false; + for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I = + PostOrder.rbegin(), E = PostOrder.rend(); + I != E; ++I) + TopDownNestingDetected |= VisitTopDown(*I, BBStates, Releases); + + return TopDownNestingDetected && BottomUpNestingDetected; +} + +/// Move the calls in RetainsToMove and ReleasesToMove. +void ObjCARCOpt::MoveCalls(Value *Arg, + RRInfo &RetainsToMove, + RRInfo &ReleasesToMove, + MapVector<Value *, RRInfo> &Retains, + DenseMap<Value *, RRInfo> &Releases, + SmallVectorImpl<Instruction *> &DeadInsts, + Module *M) { + Type *ArgTy = Arg->getType(); + Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext())); + + // Insert the new retain and release calls. + for (SmallPtrSet<Instruction *, 2>::const_iterator + PI = ReleasesToMove.ReverseInsertPts.begin(), + PE = ReleasesToMove.ReverseInsertPts.end(); PI != PE; ++PI) { + Instruction *InsertPt = *PI; + Value *MyArg = ArgTy == ParamTy ? Arg : + new BitCastInst(Arg, ParamTy, "", InsertPt); + CallInst *Call = + CallInst::Create(RetainsToMove.IsRetainBlock ? + getRetainBlockCallee(M) : getRetainCallee(M), + MyArg, "", InsertPt); + Call->setDoesNotThrow(); + if (RetainsToMove.IsRetainBlock) + Call->setMetadata(CopyOnEscapeMDKind, + MDNode::get(M->getContext(), ArrayRef<Value *>())); + else + Call->setTailCall(); + + DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Inserting new Release: " << *Call + << "\n" + " At insertion point: " << *InsertPt + << "\n"); + } + for (SmallPtrSet<Instruction *, 2>::const_iterator + PI = RetainsToMove.ReverseInsertPts.begin(), + PE = RetainsToMove.ReverseInsertPts.end(); PI != PE; ++PI) { + Instruction *InsertPt = *PI; + Value *MyArg = ArgTy == ParamTy ? Arg : + new BitCastInst(Arg, ParamTy, "", InsertPt); + CallInst *Call = CallInst::Create(getReleaseCallee(M), MyArg, + "", InsertPt); + // Attach a clang.imprecise_release metadata tag, if appropriate. + if (MDNode *M = ReleasesToMove.ReleaseMetadata) + Call->setMetadata(ImpreciseReleaseMDKind, M); + Call->setDoesNotThrow(); + if (ReleasesToMove.IsTailCallRelease) + Call->setTailCall(); + + DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Inserting new Retain: " << *Call + << "\n" + " At insertion point: " << *InsertPt + << "\n"); + } + + // Delete the original retain and release calls. + for (SmallPtrSet<Instruction *, 2>::const_iterator + AI = RetainsToMove.Calls.begin(), + AE = RetainsToMove.Calls.end(); AI != AE; ++AI) { + Instruction *OrigRetain = *AI; + Retains.blot(OrigRetain); + DeadInsts.push_back(OrigRetain); + DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Deleting retain: " << *OrigRetain << + "\n"); + } + for (SmallPtrSet<Instruction *, 2>::const_iterator + AI = ReleasesToMove.Calls.begin(), + AE = ReleasesToMove.Calls.end(); AI != AE; ++AI) { + Instruction *OrigRelease = *AI; + Releases.erase(OrigRelease); + DeadInsts.push_back(OrigRelease); + DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Deleting release: " << *OrigRelease + << "\n"); + } +} + +bool +ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState> + &BBStates, + MapVector<Value *, RRInfo> &Retains, + DenseMap<Value *, RRInfo> &Releases, + Module *M, + SmallVector<Instruction *, 4> &NewRetains, + SmallVector<Instruction *, 4> &NewReleases, + SmallVector<Instruction *, 8> &DeadInsts, + RRInfo &RetainsToMove, + RRInfo &ReleasesToMove, + Value *Arg, + bool KnownSafe, + bool &AnyPairsCompletelyEliminated) { + // If a pair happens in a region where it is known that the reference count + // is already incremented, we can similarly ignore possible decrements. + bool KnownSafeTD = true, KnownSafeBU = true; + + // Connect the dots between the top-down-collected RetainsToMove and + // bottom-up-collected ReleasesToMove to form sets of related calls. + // This is an iterative process so that we connect multiple releases + // to multiple retains if needed. + unsigned OldDelta = 0; + unsigned NewDelta = 0; + unsigned OldCount = 0; + unsigned NewCount = 0; + bool FirstRelease = true; + bool FirstRetain = true; + for (;;) { + for (SmallVectorImpl<Instruction *>::const_iterator + NI = NewRetains.begin(), NE = NewRetains.end(); NI != NE; ++NI) { + Instruction *NewRetain = *NI; + MapVector<Value *, RRInfo>::const_iterator It = Retains.find(NewRetain); + assert(It != Retains.end()); + const RRInfo &NewRetainRRI = It->second; + KnownSafeTD &= NewRetainRRI.KnownSafe; + for (SmallPtrSet<Instruction *, 2>::const_iterator + LI = NewRetainRRI.Calls.begin(), + LE = NewRetainRRI.Calls.end(); LI != LE; ++LI) { + Instruction *NewRetainRelease = *LI; + DenseMap<Value *, RRInfo>::const_iterator Jt = + Releases.find(NewRetainRelease); + if (Jt == Releases.end()) + return false; + const RRInfo &NewRetainReleaseRRI = Jt->second; + assert(NewRetainReleaseRRI.Calls.count(NewRetain)); + if (ReleasesToMove.Calls.insert(NewRetainRelease)) { + OldDelta -= + BBStates[NewRetainRelease->getParent()].GetAllPathCount(); + + // Merge the ReleaseMetadata and IsTailCallRelease values. + if (FirstRelease) { + ReleasesToMove.ReleaseMetadata = + NewRetainReleaseRRI.ReleaseMetadata; + ReleasesToMove.IsTailCallRelease = + NewRetainReleaseRRI.IsTailCallRelease; + FirstRelease = false; + } else { + if (ReleasesToMove.ReleaseMetadata != + NewRetainReleaseRRI.ReleaseMetadata) + ReleasesToMove.ReleaseMetadata = 0; + if (ReleasesToMove.IsTailCallRelease != + NewRetainReleaseRRI.IsTailCallRelease) + ReleasesToMove.IsTailCallRelease = false; + } + + // Collect the optimal insertion points. + if (!KnownSafe) + for (SmallPtrSet<Instruction *, 2>::const_iterator + RI = NewRetainReleaseRRI.ReverseInsertPts.begin(), + RE = NewRetainReleaseRRI.ReverseInsertPts.end(); + RI != RE; ++RI) { + Instruction *RIP = *RI; + if (ReleasesToMove.ReverseInsertPts.insert(RIP)) + NewDelta -= BBStates[RIP->getParent()].GetAllPathCount(); + } + NewReleases.push_back(NewRetainRelease); + } + } + } + NewRetains.clear(); + if (NewReleases.empty()) break; + + // Back the other way. + for (SmallVectorImpl<Instruction *>::const_iterator + NI = NewReleases.begin(), NE = NewReleases.end(); NI != NE; ++NI) { + Instruction *NewRelease = *NI; + DenseMap<Value *, RRInfo>::const_iterator It = + Releases.find(NewRelease); + assert(It != Releases.end()); + const RRInfo &NewReleaseRRI = It->second; + KnownSafeBU &= NewReleaseRRI.KnownSafe; + for (SmallPtrSet<Instruction *, 2>::const_iterator + LI = NewReleaseRRI.Calls.begin(), + LE = NewReleaseRRI.Calls.end(); LI != LE; ++LI) { + Instruction *NewReleaseRetain = *LI; + MapVector<Value *, RRInfo>::const_iterator Jt = + Retains.find(NewReleaseRetain); + if (Jt == Retains.end()) + return false; + const RRInfo &NewReleaseRetainRRI = Jt->second; + assert(NewReleaseRetainRRI.Calls.count(NewRelease)); + if (RetainsToMove.Calls.insert(NewReleaseRetain)) { + unsigned PathCount = + BBStates[NewReleaseRetain->getParent()].GetAllPathCount(); + OldDelta += PathCount; + OldCount += PathCount; + + // Merge the IsRetainBlock values. + if (FirstRetain) { + RetainsToMove.IsRetainBlock = NewReleaseRetainRRI.IsRetainBlock; + FirstRetain = false; + } else if (ReleasesToMove.IsRetainBlock != + NewReleaseRetainRRI.IsRetainBlock) + // It's not possible to merge the sequences if one uses + // objc_retain and the other uses objc_retainBlock. + return false; + + // Collect the optimal insertion points. + if (!KnownSafe) + for (SmallPtrSet<Instruction *, 2>::const_iterator + RI = NewReleaseRetainRRI.ReverseInsertPts.begin(), + RE = NewReleaseRetainRRI.ReverseInsertPts.end(); + RI != RE; ++RI) { + Instruction *RIP = *RI; + if (RetainsToMove.ReverseInsertPts.insert(RIP)) { + PathCount = BBStates[RIP->getParent()].GetAllPathCount(); + NewDelta += PathCount; + NewCount += PathCount; + } + } + NewRetains.push_back(NewReleaseRetain); + } + } + } + NewReleases.clear(); + if (NewRetains.empty()) break; + } + + // If the pointer is known incremented or nested, we can safely delete the + // pair regardless of what's between them. + if (KnownSafeTD || KnownSafeBU) { + RetainsToMove.ReverseInsertPts.clear(); + ReleasesToMove.ReverseInsertPts.clear(); + NewCount = 0; + } else { + // Determine whether the new insertion points we computed preserve the + // balance of retain and release calls through the program. + // TODO: If the fully aggressive solution isn't valid, try to find a + // less aggressive solution which is. + if (NewDelta != 0) + return false; + } + + // Determine whether the original call points are balanced in the retain and + // release calls through the program. If not, conservatively don't touch + // them. + // TODO: It's theoretically possible to do code motion in this case, as + // long as the existing imbalances are maintained. + if (OldDelta != 0) + return false; + + Changed = true; + assert(OldCount != 0 && "Unreachable code?"); + NumRRs += OldCount - NewCount; + // Set to true if we completely removed any RR pairs. + AnyPairsCompletelyEliminated = NewCount == 0; + + // We can move calls! + return true; +} + +/// Identify pairings between the retains and releases, and delete and/or move +/// them. +bool +ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState> + &BBStates, + MapVector<Value *, RRInfo> &Retains, + DenseMap<Value *, RRInfo> &Releases, + Module *M) { + bool AnyPairsCompletelyEliminated = false; + RRInfo RetainsToMove; + RRInfo ReleasesToMove; + SmallVector<Instruction *, 4> NewRetains; + SmallVector<Instruction *, 4> NewReleases; + SmallVector<Instruction *, 8> DeadInsts; + + // Visit each retain. + for (MapVector<Value *, RRInfo>::const_iterator I = Retains.begin(), + E = Retains.end(); I != E; ++I) { + Value *V = I->first; + if (!V) continue; // blotted + + Instruction *Retain = cast<Instruction>(V); + + DEBUG(dbgs() << "ObjCARCOpt::PerformCodePlacement: Visiting: " << *Retain + << "\n"); + + Value *Arg = GetObjCArg(Retain); + + // If the object being released is in static or stack storage, we know it's + // not being managed by ObjC reference counting, so we can delete pairs + // regardless of what possible decrements or uses lie between them. + bool KnownSafe = isa<Constant>(Arg) || isa<AllocaInst>(Arg); + + // A constant pointer can't be pointing to an object on the heap. It may + // be reference-counted, but it won't be deleted. + if (const LoadInst *LI = dyn_cast<LoadInst>(Arg)) + if (const GlobalVariable *GV = + dyn_cast<GlobalVariable>( + StripPointerCastsAndObjCCalls(LI->getPointerOperand()))) + if (GV->isConstant()) + KnownSafe = true; + + // Connect the dots between the top-down-collected RetainsToMove and + // bottom-up-collected ReleasesToMove to form sets of related calls. + NewRetains.push_back(Retain); + bool PerformMoveCalls = + ConnectTDBUTraversals(BBStates, Retains, Releases, M, NewRetains, + NewReleases, DeadInsts, RetainsToMove, + ReleasesToMove, Arg, KnownSafe, + AnyPairsCompletelyEliminated); + + if (PerformMoveCalls) { + // Ok, everything checks out and we're all set. Let's move/delete some + // code! + MoveCalls(Arg, RetainsToMove, ReleasesToMove, + Retains, Releases, DeadInsts, M); + } + + // Clean up state for next retain. + NewReleases.clear(); + NewRetains.clear(); + RetainsToMove.clear(); + ReleasesToMove.clear(); + } + + // Now that we're done moving everything, we can delete the newly dead + // instructions, as we no longer need them as insert points. + while (!DeadInsts.empty()) + EraseInstruction(DeadInsts.pop_back_val()); + + return AnyPairsCompletelyEliminated; +} + +/// Weak pointer optimizations. +void ObjCARCOpt::OptimizeWeakCalls(Function &F) { + // First, do memdep-style RLE and S2L optimizations. We can't use memdep + // itself because it uses AliasAnalysis and we need to do provenance + // queries instead. + for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) { + Instruction *Inst = &*I++; + + DEBUG(dbgs() << "ObjCARCOpt::OptimizeWeakCalls: Visiting: " << *Inst << + "\n"); + + InstructionClass Class = GetBasicInstructionClass(Inst); + if (Class != IC_LoadWeak && Class != IC_LoadWeakRetained) + continue; + + // Delete objc_loadWeak calls with no users. + if (Class == IC_LoadWeak && Inst->use_empty()) { + Inst->eraseFromParent(); + continue; + } + + // TODO: For now, just look for an earlier available version of this value + // within the same block. Theoretically, we could do memdep-style non-local + // analysis too, but that would want caching. A better approach would be to + // use the technique that EarlyCSE uses. + inst_iterator Current = llvm::prior(I); + BasicBlock *CurrentBB = Current.getBasicBlockIterator(); + for (BasicBlock::iterator B = CurrentBB->begin(), + J = Current.getInstructionIterator(); + J != B; --J) { + Instruction *EarlierInst = &*llvm::prior(J); + InstructionClass EarlierClass = GetInstructionClass(EarlierInst); + switch (EarlierClass) { + case IC_LoadWeak: + case IC_LoadWeakRetained: { + // If this is loading from the same pointer, replace this load's value + // with that one. + CallInst *Call = cast<CallInst>(Inst); + CallInst *EarlierCall = cast<CallInst>(EarlierInst); + Value *Arg = Call->getArgOperand(0); + Value *EarlierArg = EarlierCall->getArgOperand(0); + switch (PA.getAA()->alias(Arg, EarlierArg)) { + case AliasAnalysis::MustAlias: + Changed = true; + // If the load has a builtin retain, insert a plain retain for it. + if (Class == IC_LoadWeakRetained) { + CallInst *CI = + CallInst::Create(getRetainCallee(F.getParent()), EarlierCall, + "", Call); + CI->setTailCall(); + } + // Zap the fully redundant load. + Call->replaceAllUsesWith(EarlierCall); + Call->eraseFromParent(); + goto clobbered; + case AliasAnalysis::MayAlias: + case AliasAnalysis::PartialAlias: + goto clobbered; + case AliasAnalysis::NoAlias: + break; + } + break; + } + case IC_StoreWeak: + case IC_InitWeak: { + // If this is storing to the same pointer and has the same size etc. + // replace this load's value with the stored value. + CallInst *Call = cast<CallInst>(Inst); + CallInst *EarlierCall = cast<CallInst>(EarlierInst); + Value *Arg = Call->getArgOperand(0); + Value *EarlierArg = EarlierCall->getArgOperand(0); + switch (PA.getAA()->alias(Arg, EarlierArg)) { + case AliasAnalysis::MustAlias: + Changed = true; + // If the load has a builtin retain, insert a plain retain for it. + if (Class == IC_LoadWeakRetained) { + CallInst *CI = + CallInst::Create(getRetainCallee(F.getParent()), EarlierCall, + "", Call); + CI->setTailCall(); + } + // Zap the fully redundant load. + Call->replaceAllUsesWith(EarlierCall->getArgOperand(1)); + Call->eraseFromParent(); + goto clobbered; + case AliasAnalysis::MayAlias: + case AliasAnalysis::PartialAlias: + goto clobbered; + case AliasAnalysis::NoAlias: + break; + } + break; + } + case IC_MoveWeak: + case IC_CopyWeak: + // TOOD: Grab the copied value. + goto clobbered; + case IC_AutoreleasepoolPush: + case IC_None: + case IC_User: + // Weak pointers are only modified through the weak entry points + // (and arbitrary calls, which could call the weak entry points). + break; + default: + // Anything else could modify the weak pointer. + goto clobbered; + } + } + clobbered:; + } + + // Then, for each destroyWeak with an alloca operand, check to see if + // the alloca and all its users can be zapped. + for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) { + Instruction *Inst = &*I++; + InstructionClass Class = GetBasicInstructionClass(Inst); + if (Class != IC_DestroyWeak) + continue; + + CallInst *Call = cast<CallInst>(Inst); + Value *Arg = Call->getArgOperand(0); + if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) { + for (Value::use_iterator UI = Alloca->use_begin(), + UE = Alloca->use_end(); UI != UE; ++UI) { + const Instruction *UserInst = cast<Instruction>(*UI); + switch (GetBasicInstructionClass(UserInst)) { + case IC_InitWeak: + case IC_StoreWeak: + case IC_DestroyWeak: + continue; + default: + goto done; + } + } + Changed = true; + for (Value::use_iterator UI = Alloca->use_begin(), + UE = Alloca->use_end(); UI != UE; ) { + CallInst *UserInst = cast<CallInst>(*UI++); + switch (GetBasicInstructionClass(UserInst)) { + case IC_InitWeak: + case IC_StoreWeak: + // These functions return their second argument. + UserInst->replaceAllUsesWith(UserInst->getArgOperand(1)); + break; + case IC_DestroyWeak: + // No return value. + break; + default: + llvm_unreachable("alloca really is used!"); + } + UserInst->eraseFromParent(); + } + Alloca->eraseFromParent(); + done:; + } + } + + DEBUG(dbgs() << "ObjCARCOpt::OptimizeWeakCalls: Finished List.\n\n"); + +} + +/// Identify program paths which execute sequences of retains and releases which +/// can be eliminated. +bool ObjCARCOpt::OptimizeSequences(Function &F) { + /// Releases, Retains - These are used to store the results of the main flow + /// analysis. These use Value* as the key instead of Instruction* so that the + /// map stays valid when we get around to rewriting code and calls get + /// replaced by arguments. + DenseMap<Value *, RRInfo> Releases; + MapVector<Value *, RRInfo> Retains; + + /// This is used during the traversal of the function to track the + /// states for each identified object at each block. + DenseMap<const BasicBlock *, BBState> BBStates; + + // Analyze the CFG of the function, and all instructions. + bool NestingDetected = Visit(F, BBStates, Retains, Releases); + + // Transform. + return PerformCodePlacement(BBStates, Retains, Releases, F.getParent()) && + NestingDetected; +} + +/// Look for this pattern: +/// \code +/// %call = call i8* @something(...) +/// %2 = call i8* @objc_retain(i8* %call) +/// %3 = call i8* @objc_autorelease(i8* %2) +/// ret i8* %3 +/// \endcode +/// And delete the retain and autorelease. +/// +/// Otherwise if it's just this: +/// \code +/// %3 = call i8* @objc_autorelease(i8* %2) +/// ret i8* %3 +/// \endcode +/// convert the autorelease to autoreleaseRV. +void ObjCARCOpt::OptimizeReturns(Function &F) { + if (!F.getReturnType()->isPointerTy()) + return; + + SmallPtrSet<Instruction *, 4> DependingInstructions; + SmallPtrSet<const BasicBlock *, 4> Visited; + for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) { + BasicBlock *BB = FI; + ReturnInst *Ret = dyn_cast<ReturnInst>(&BB->back()); + + DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Visiting: " << *Ret << "\n"); + + if (!Ret) continue; + + const Value *Arg = StripPointerCastsAndObjCCalls(Ret->getOperand(0)); + FindDependencies(NeedsPositiveRetainCount, Arg, + BB, Ret, DependingInstructions, Visited, PA); + if (DependingInstructions.size() != 1) + goto next_block; + + { + CallInst *Autorelease = + dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); + if (!Autorelease) + goto next_block; + InstructionClass AutoreleaseClass = GetBasicInstructionClass(Autorelease); + if (!IsAutorelease(AutoreleaseClass)) + goto next_block; + if (GetObjCArg(Autorelease) != Arg) + goto next_block; + + DependingInstructions.clear(); + Visited.clear(); + + // Check that there is nothing that can affect the reference + // count between the autorelease and the retain. + FindDependencies(CanChangeRetainCount, Arg, + BB, Autorelease, DependingInstructions, Visited, PA); + if (DependingInstructions.size() != 1) + goto next_block; + + { + CallInst *Retain = + dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); + + // Check that we found a retain with the same argument. + if (!Retain || + !IsRetain(GetBasicInstructionClass(Retain)) || + GetObjCArg(Retain) != Arg) + goto next_block; + + DependingInstructions.clear(); + Visited.clear(); + + // Convert the autorelease to an autoreleaseRV, since it's + // returning the value. + if (AutoreleaseClass == IC_Autorelease) { + DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Converting autorelease " + "=> autoreleaseRV since it's returning a value.\n" + " In: " << *Autorelease + << "\n"); + Autorelease->setCalledFunction(getAutoreleaseRVCallee(F.getParent())); + DEBUG(dbgs() << " Out: " << *Autorelease + << "\n"); + Autorelease->setTailCall(); // Always tail call autoreleaseRV. + AutoreleaseClass = IC_AutoreleaseRV; + } + + // Check that there is nothing that can affect the reference + // count between the retain and the call. + // Note that Retain need not be in BB. + FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain, + DependingInstructions, Visited, PA); + if (DependingInstructions.size() != 1) + goto next_block; + + { + CallInst *Call = + dyn_cast_or_null<CallInst>(*DependingInstructions.begin()); + + // Check that the pointer is the return value of the call. + if (!Call || Arg != Call) + goto next_block; + + // Check that the call is a regular call. + InstructionClass Class = GetBasicInstructionClass(Call); + if (Class != IC_CallOrUser && Class != IC_Call) + goto next_block; + + // If so, we can zap the retain and autorelease. + Changed = true; + ++NumRets; + DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Erasing: " << *Retain + << "\n Erasing: " + << *Autorelease << "\n"); + EraseInstruction(Retain); + EraseInstruction(Autorelease); + } + } + } + + next_block: + DependingInstructions.clear(); + Visited.clear(); + } + + DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Finished List.\n\n"); + +} + +bool ObjCARCOpt::doInitialization(Module &M) { + if (!EnableARCOpts) + return false; + + // If nothing in the Module uses ARC, don't do anything. + Run = ModuleHasARC(M); + if (!Run) + return false; + + // Identify the imprecise release metadata kind. + ImpreciseReleaseMDKind = + M.getContext().getMDKindID("clang.imprecise_release"); + CopyOnEscapeMDKind = + M.getContext().getMDKindID("clang.arc.copy_on_escape"); + NoObjCARCExceptionsMDKind = + M.getContext().getMDKindID("clang.arc.no_objc_arc_exceptions"); + + // Intuitively, objc_retain and others are nocapture, however in practice + // they are not, because they return their argument value. And objc_release + // calls finalizers which can have arbitrary side effects. + + // These are initialized lazily. + RetainRVCallee = 0; + AutoreleaseRVCallee = 0; + ReleaseCallee = 0; + RetainCallee = 0; + RetainBlockCallee = 0; + AutoreleaseCallee = 0; + + return false; +} + +bool ObjCARCOpt::runOnFunction(Function &F) { + if (!EnableARCOpts) + return false; + + // If nothing in the Module uses ARC, don't do anything. + if (!Run) + return false; + + Changed = false; + + DEBUG(dbgs() << "ObjCARCOpt: Visiting Function: " << F.getName() << "\n"); + + PA.setAA(&getAnalysis<AliasAnalysis>()); + + // This pass performs several distinct transformations. As a compile-time aid + // when compiling code that isn't ObjC, skip these if the relevant ObjC + // library functions aren't declared. + + // Preliminary optimizations. This also computs UsedInThisFunction. + OptimizeIndividualCalls(F); + + // Optimizations for weak pointers. + if (UsedInThisFunction & ((1 << IC_LoadWeak) | + (1 << IC_LoadWeakRetained) | + (1 << IC_StoreWeak) | + (1 << IC_InitWeak) | + (1 << IC_CopyWeak) | + (1 << IC_MoveWeak) | + (1 << IC_DestroyWeak))) + OptimizeWeakCalls(F); + + // Optimizations for retain+release pairs. + if (UsedInThisFunction & ((1 << IC_Retain) | + (1 << IC_RetainRV) | + (1 << IC_RetainBlock))) + if (UsedInThisFunction & (1 << IC_Release)) + // Run OptimizeSequences until it either stops making changes or + // no retain+release pair nesting is detected. + while (OptimizeSequences(F)) {} + + // Optimizations if objc_autorelease is used. + if (UsedInThisFunction & ((1 << IC_Autorelease) | + (1 << IC_AutoreleaseRV))) + OptimizeReturns(F); + + DEBUG(dbgs() << "\n"); + + return Changed; +} + +void ObjCARCOpt::releaseMemory() { + PA.clear(); +} + +/// @} +/// +/// \defgroup ARCContract ARC Contraction. +/// @{ + +// TODO: ObjCARCContract could insert PHI nodes when uses aren't +// dominated by single calls. + +#include "llvm/Analysis/Dominators.h" +#include "llvm/IR/InlineAsm.h" +#include "llvm/IR/Operator.h" + +STATISTIC(NumStoreStrongs, "Number objc_storeStrong calls formed"); + +namespace { + /// \brief 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; + + /// A flag indicating whether this optimization pass should run. + bool Run; + + /// Declarations for ObjC runtime functions, for use in creating calls to + /// them. These are initialized lazily to avoid cluttering up the Module + /// with unused declarations. + + /// Declaration for objc_storeStrong(). + Constant *StoreStrongCallee; + /// Declaration for objc_retainAutorelease(). + Constant *RetainAutoreleaseCallee; + /// Declaration for objc_retainAutoreleaseReturnValue(). + Constant *RetainAutoreleaseRVCallee; + + /// The inline asm string to insert between calls and RetainRV calls to make + /// the optimization work on targets which need it. + const MDString *RetainRVMarker; + + /// 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; + + Constant *getStoreStrongCallee(Module *M); + Constant *getRetainAutoreleaseCallee(Module *M); + Constant *getRetainAutoreleaseRVCallee(Module *M); + + bool ContractAutorelease(Function &F, Instruction *Autorelease, + InstructionClass Class, + SmallPtrSet<Instruction *, 4> + &DependingInstructions, + SmallPtrSet<const BasicBlock *, 4> + &Visited); + + void ContractRelease(Instruction *Release, + inst_iterator &Iter); + + virtual void getAnalysisUsage(AnalysisUsage &AU) const; + virtual bool doInitialization(Module &M); + virtual bool runOnFunction(Function &F); + + public: + static char ID; + ObjCARCContract() : FunctionPass(ID) { + initializeObjCARCContractPass(*PassRegistry::getPassRegistry()); + } + }; +} + +char ObjCARCContract::ID = 0; +INITIALIZE_PASS_BEGIN(ObjCARCContract, + "objc-arc-contract", "ObjC ARC contraction", false, false) +INITIALIZE_AG_DEPENDENCY(AliasAnalysis) +INITIALIZE_PASS_DEPENDENCY(DominatorTree) +INITIALIZE_PASS_END(ObjCARCContract, + "objc-arc-contract", "ObjC ARC contraction", false, false) + +Pass *llvm::createObjCARCContractPass() { + return new ObjCARCContract(); +} + +void ObjCARCContract::getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequired<AliasAnalysis>(); + AU.addRequired<DominatorTree>(); + AU.setPreservesCFG(); +} + +Constant *ObjCARCContract::getStoreStrongCallee(Module *M) { + if (!StoreStrongCallee) { + LLVMContext &C = M->getContext(); + Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); + Type *I8XX = PointerType::getUnqual(I8X); + Type *Params[] = { I8XX, I8X }; + + AttributeSet Attr = AttributeSet() + .addAttribute(M->getContext(), AttributeSet::FunctionIndex, + Attribute::NoUnwind) + .addAttribute(M->getContext(), 1, Attribute::NoCapture); + + StoreStrongCallee = + M->getOrInsertFunction( + "objc_storeStrong", + FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false), + Attr); + } + return StoreStrongCallee; +} + +Constant *ObjCARCContract::getRetainAutoreleaseCallee(Module *M) { + if (!RetainAutoreleaseCallee) { + LLVMContext &C = M->getContext(); + Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); + Type *Params[] = { I8X }; + FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false); + AttributeSet Attribute = + AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex, + Attribute::NoUnwind); + RetainAutoreleaseCallee = + M->getOrInsertFunction("objc_retainAutorelease", FTy, Attribute); + } + return RetainAutoreleaseCallee; +} + +Constant *ObjCARCContract::getRetainAutoreleaseRVCallee(Module *M) { + if (!RetainAutoreleaseRVCallee) { + LLVMContext &C = M->getContext(); + Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C)); + Type *Params[] = { I8X }; + FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false); + AttributeSet Attribute = + AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex, + Attribute::NoUnwind); + RetainAutoreleaseRVCallee = + M->getOrInsertFunction("objc_retainAutoreleaseReturnValue", FTy, + Attribute); + } + return RetainAutoreleaseRVCallee; +} + +/// Merge an autorelease with a retain into a fused call. +bool +ObjCARCContract::ContractAutorelease(Function &F, Instruction *Autorelease, + InstructionClass Class, + SmallPtrSet<Instruction *, 4> + &DependingInstructions, + SmallPtrSet<const BasicBlock *, 4> + &Visited) { + const Value *Arg = GetObjCArg(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 = 0; + if (Class == IC_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 || + GetBasicInstructionClass(Retain) != IC_Retain || + GetObjCArg(Retain) != Arg) + return false; + + Changed = true; + ++NumPeeps; + + DEBUG(dbgs() << "ObjCARCContract::ContractAutorelease: Fusing " + "retain/autorelease. Erasing: " << *Autorelease << "\n" + " Old Retain: " + << *Retain << "\n"); + + if (Class == IC_AutoreleaseRV) + Retain->setCalledFunction(getRetainAutoreleaseRVCallee(F.getParent())); + else + Retain->setCalledFunction(getRetainAutoreleaseCallee(F.getParent())); + + DEBUG(dbgs() << " New Retain: " + << *Retain << "\n"); + + EraseInstruction(Autorelease); + return true; +} + +/// Attempt to merge an objc_release with a store, load, and objc_retain to form +/// an objc_storeStrong. This can be a little tricky because the instructions +/// don't always appear in order, and there may be unrelated intervening +/// instructions. +void ObjCARCContract::ContractRelease(Instruction *Release, + inst_iterator &Iter) { + LoadInst *Load = dyn_cast<LoadInst>(GetObjCArg(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; + + // Walk down to find the store and the release, which may be in either order. + BasicBlock::iterator I = Load, End = BB->end(); + ++I; + AliasAnalysis::Location Loc = AA->getLocation(Load); + StoreInst *Store = 0; + bool SawRelease = false; + for (; !Store || !SawRelease; ++I) { + if (I == End) + return; + + Instruction *Inst = I; + if (Inst == Release) { + SawRelease = true; + continue; + } + + InstructionClass Class = GetBasicInstructionClass(Inst); + + // Unrelated retains are harmless. + if (IsRetain(Class)) + continue; + + if (Store) { + // The store is the point where we're going to put the objc_storeStrong, + // so make sure there are no uses after it. + if (CanUse(Inst, Load, PA, Class)) + return; + } else if (AA->getModRefInfo(Inst, Loc) & AliasAnalysis::Mod) { + // We are moving the load down to the store, so check for anything + // else which writes to the memory between the load and the store. + Store = dyn_cast<StoreInst>(Inst); + if (!Store || !Store->isSimple()) return; + if (Store->getPointerOperand() != Loc.Ptr) return; + } + } + + Value *New = StripPointerCastsAndObjCCalls(Store->getValueOperand()); + + // Walk up to find the retain. + I = Store; + BasicBlock::iterator Begin = BB->begin(); + while (I != Begin && GetBasicInstructionClass(I) != IC_Retain) + --I; + Instruction *Retain = I; + if (GetBasicInstructionClass(Retain) != IC_Retain) return; + if (GetObjCArg(Retain) != New) return; + + Changed = true; + ++NumStoreStrongs; + + 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); + CallInst *StoreStrong = + CallInst::Create(getStoreStrongCallee(BB->getParent()->getParent()), + Args, "", Store); + 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); + + if (&*Iter == Store) ++Iter; + Store->eraseFromParent(); + Release->eraseFromParent(); + EraseInstruction(Retain); + if (Load->use_empty()) + Load->eraseFromParent(); +} + +bool ObjCARCContract::doInitialization(Module &M) { + // If nothing in the Module uses ARC, don't do anything. + Run = ModuleHasARC(M); + if (!Run) + return false; + + // These are initialized lazily. + StoreStrongCallee = 0; + RetainAutoreleaseCallee = 0; + RetainAutoreleaseRVCallee = 0; + + // Initialize RetainRVMarker. + RetainRVMarker = 0; + if (NamedMDNode *NMD = + M.getNamedMetadata("clang.arc.retainAutoreleasedReturnValueMarker")) + if (NMD->getNumOperands() == 1) { + const MDNode *N = NMD->getOperand(0); + if (N->getNumOperands() == 1) + if (const MDString *S = dyn_cast<MDString>(N->getOperand(0))) + RetainRVMarker = S; + } + + return false; +} + +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<AliasAnalysis>(); + DT = &getAnalysis<DominatorTree>(); + + PA.setAA(&getAnalysis<AliasAnalysis>()); + + // 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++; + + DEBUG(dbgs() << "ObjCARCContract: Visiting: " << *Inst << "\n"); + + // Only these library routines return their argument. In particular, + // objc_retainBlock does not necessarily return its argument. + InstructionClass Class = GetBasicInstructionClass(Inst); + switch (Class) { + case IC_Retain: + case IC_FusedRetainAutorelease: + case IC_FusedRetainAutoreleaseRV: + break; + case IC_Autorelease: + case IC_AutoreleaseRV: + if (ContractAutorelease(F, Inst, Class, DependingInstructions, Visited)) + continue; + break; + case IC_RetainRV: { + // If we're compiling for a target which needs a special inline-asm + // marker to do the retainAutoreleasedReturnValue optimization, + // insert it now. + if (!RetainRVMarker) + break; + BasicBlock::iterator BBI = Inst; + BasicBlock *InstParent = Inst->getParent(); + + // Step up to see if the call immediately precedes the RetainRV 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(); + break; + } + --BBI; + } while (isNoopInstruction(BBI)); + + if (&*BBI == GetObjCArg(Inst)) { + DEBUG(dbgs() << "ObjCARCContract: Adding inline asm marker for " + "retainAutoreleasedReturnValue optimization.\n"); + Changed = true; + InlineAsm *IA = + InlineAsm::get(FunctionType::get(Type::getVoidTy(Inst->getContext()), + /*isVarArg=*/false), + RetainRVMarker->getString(), + /*Constraints=*/"", /*hasSideEffects=*/true); + CallInst::Create(IA, "", Inst); + } + decline_rv_optimization: + break; + } + case IC_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); + + DEBUG(dbgs() << "OBJCARCContract: Old = " << *CI << "\n" + << " New = " << *Null << "\n"); + + CI->replaceAllUsesWith(Null); + CI->eraseFromParent(); + } + continue; + } + case IC_Release: + ContractRelease(Inst, I); + continue; + case IC_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; + continue; + default: + continue; + } + + DEBUG(dbgs() << "ObjCARCContract: Finished List.\n\n"); + + // Don't use GetObjCArg because we don't want to look through bitcasts + // and such; to do the replacement, the argument must have type i8*. + const Value *Arg = cast<CallInst>(Inst)->getArgOperand(0); + for (;;) { + // If we're compiling bugpointed code, don't get in trouble. + if (!isa<Instruction>(Arg) && !isa<Argument>(Arg)) + break; + // Look through the uses of the pointer. + for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end(); + UI != UE; ) { + Use &U = UI.getUse(); + unsigned OperandNo = UI.getOperandNo(); + ++UI; // Increment UI now, because we may unlink its element. + + // 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 GetObjCArg. + if (DT->isReachableFromEntry(U) && DT->dominates(Inst, U)) { + 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 *BB = PHI->getIncomingBlock(ValNo); + if (Replacement->getType() != UseTy) + Replacement = new BitCastInst(Replacement, UseTy, "", + &BB->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) == BB) { + // Keep the UI iterator valid. + if (&PHI->getOperandUse( + PHINode::getOperandNumForIncomingValue(i)) == + &UI.getUse()) + ++UI; + PHI->setIncomingValue(i, Replacement); + } + } else { + if (Replacement->getType() != UseTy) + Replacement = new BitCastInst(Replacement, UseTy, "", + cast<Instruction>(U.getUser())); + U.set(Replacement); + } + } + } + + // 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)->mayBeOverridden()) + Arg = cast<GlobalAlias>(Arg)->getAliasee(); + else + break; + } + } + + // If this function has no escaping allocas or suspicious vararg usage, + // objc_storeStrong calls can be marked with the "tail" keyword. + if (TailOkForStoreStrongs) + for (SmallPtrSet<CallInst *, 8>::iterator I = StoreStrongCalls.begin(), + E = StoreStrongCalls.end(); I != E; ++I) + (*I)->setTailCall(); + StoreStrongCalls.clear(); + + return Changed; +} + +/// @} +/// |