1 //===- ObjCARCAliasAnalysis.cpp - ObjC ARC Optimization -------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 /// \file 9 /// This file defines a simple ARC-aware AliasAnalysis using special knowledge 10 /// of Objective C to enhance other optimization passes which rely on the Alias 11 /// Analysis infrastructure. 12 /// 13 /// WARNING: This file knows about certain library functions. It recognizes them 14 /// by name, and hardwires knowledge of their semantics. 15 /// 16 /// WARNING: This file knows about how certain Objective-C library functions are 17 /// used. Naive LLVM IR transformations which would otherwise be 18 /// behavior-preserving may break these assumptions. 19 /// 20 /// TODO: Theoretically we could check for dependencies between objc_* calls 21 /// and FMRB_OnlyAccessesArgumentPointees calls or other well-behaved calls. 22 /// 23 //===----------------------------------------------------------------------===// 24 25 #include "llvm/Analysis/ObjCARCAliasAnalysis.h" 26 #include "llvm/Analysis/ObjCARCAnalysisUtils.h" 27 #include "llvm/Analysis/Passes.h" 28 #include "llvm/IR/Function.h" 29 #include "llvm/IR/Instruction.h" 30 #include "llvm/IR/Value.h" 31 #include "llvm/InitializePasses.h" 32 #include "llvm/Pass.h" 33 34 #define DEBUG_TYPE "objc-arc-aa" 35 36 using namespace llvm; 37 using namespace llvm::objcarc; 38 39 AliasResult ObjCARCAAResult::alias(const MemoryLocation &LocA, 40 const MemoryLocation &LocB, 41 AAQueryInfo &AAQI) { 42 if (!EnableARCOpts) 43 return AAResultBase::alias(LocA, LocB, AAQI); 44 45 // First, strip off no-ops, including ObjC-specific no-ops, and try making a 46 // precise alias query. 47 const Value *SA = GetRCIdentityRoot(LocA.Ptr); 48 const Value *SB = GetRCIdentityRoot(LocB.Ptr); 49 AliasResult Result = 50 AAResultBase::alias(MemoryLocation(SA, LocA.Size, LocA.AATags), 51 MemoryLocation(SB, LocB.Size, LocB.AATags), AAQI); 52 if (Result != AliasResult::MayAlias) 53 return Result; 54 55 // If that failed, climb to the underlying object, including climbing through 56 // ObjC-specific no-ops, and try making an imprecise alias query. 57 const Value *UA = GetUnderlyingObjCPtr(SA); 58 const Value *UB = GetUnderlyingObjCPtr(SB); 59 if (UA != SA || UB != SB) { 60 Result = AAResultBase::alias(MemoryLocation::getBeforeOrAfter(UA), 61 MemoryLocation::getBeforeOrAfter(UB), AAQI); 62 // We can't use MustAlias or PartialAlias results here because 63 // GetUnderlyingObjCPtr may return an offsetted pointer value. 64 if (Result == AliasResult::NoAlias) 65 return AliasResult::NoAlias; 66 } 67 68 // If that failed, fail. We don't need to chain here, since that's covered 69 // by the earlier precise query. 70 return AliasResult::MayAlias; 71 } 72 73 bool ObjCARCAAResult::pointsToConstantMemory(const MemoryLocation &Loc, 74 AAQueryInfo &AAQI, bool OrLocal) { 75 if (!EnableARCOpts) 76 return AAResultBase::pointsToConstantMemory(Loc, AAQI, OrLocal); 77 78 // First, strip off no-ops, including ObjC-specific no-ops, and try making 79 // a precise alias query. 80 const Value *S = GetRCIdentityRoot(Loc.Ptr); 81 if (AAResultBase::pointsToConstantMemory( 82 MemoryLocation(S, Loc.Size, Loc.AATags), AAQI, OrLocal)) 83 return true; 84 85 // If that failed, climb to the underlying object, including climbing through 86 // ObjC-specific no-ops, and try making an imprecise alias query. 87 const Value *U = GetUnderlyingObjCPtr(S); 88 if (U != S) 89 return AAResultBase::pointsToConstantMemory( 90 MemoryLocation::getBeforeOrAfter(U), AAQI, OrLocal); 91 92 // If that failed, fail. We don't need to chain here, since that's covered 93 // by the earlier precise query. 94 return false; 95 } 96 97 FunctionModRefBehavior ObjCARCAAResult::getModRefBehavior(const Function *F) { 98 if (!EnableARCOpts) 99 return AAResultBase::getModRefBehavior(F); 100 101 switch (GetFunctionClass(F)) { 102 case ARCInstKind::NoopCast: 103 return FMRB_DoesNotAccessMemory; 104 default: 105 break; 106 } 107 108 return AAResultBase::getModRefBehavior(F); 109 } 110 111 ModRefInfo ObjCARCAAResult::getModRefInfo(const CallBase *Call, 112 const MemoryLocation &Loc, 113 AAQueryInfo &AAQI) { 114 if (!EnableARCOpts) 115 return AAResultBase::getModRefInfo(Call, Loc, AAQI); 116 117 switch (GetBasicARCInstKind(Call)) { 118 case ARCInstKind::Retain: 119 case ARCInstKind::RetainRV: 120 case ARCInstKind::Autorelease: 121 case ARCInstKind::AutoreleaseRV: 122 case ARCInstKind::NoopCast: 123 case ARCInstKind::AutoreleasepoolPush: 124 case ARCInstKind::FusedRetainAutorelease: 125 case ARCInstKind::FusedRetainAutoreleaseRV: 126 // These functions don't access any memory visible to the compiler. 127 // Note that this doesn't include objc_retainBlock, because it updates 128 // pointers when it copies block data. 129 return ModRefInfo::NoModRef; 130 default: 131 break; 132 } 133 134 return AAResultBase::getModRefInfo(Call, Loc, AAQI); 135 } 136 137 AnalysisKey ObjCARCAA::Key; 138 139 ObjCARCAAResult ObjCARCAA::run(Function &F, FunctionAnalysisManager &AM) { 140 return ObjCARCAAResult(F.getParent()->getDataLayout()); 141 } 142 143 char ObjCARCAAWrapperPass::ID = 0; 144 INITIALIZE_PASS(ObjCARCAAWrapperPass, "objc-arc-aa", 145 "ObjC-ARC-Based Alias Analysis", false, true) 146 147 ImmutablePass *llvm::createObjCARCAAWrapperPass() { 148 return new ObjCARCAAWrapperPass(); 149 } 150 151 ObjCARCAAWrapperPass::ObjCARCAAWrapperPass() : ImmutablePass(ID) { 152 initializeObjCARCAAWrapperPassPass(*PassRegistry::getPassRegistry()); 153 } 154 155 bool ObjCARCAAWrapperPass::doInitialization(Module &M) { 156 Result.reset(new ObjCARCAAResult(M.getDataLayout())); 157 return false; 158 } 159 160 bool ObjCARCAAWrapperPass::doFinalization(Module &M) { 161 Result.reset(); 162 return false; 163 } 164 165 void ObjCARCAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { 166 AU.setPreservesAll(); 167 } 168