1 //===- ScopedNoAliasAA.cpp - Scoped No-Alias Alias Analysis ---------------===// 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 // 9 // This file defines the ScopedNoAlias alias-analysis pass, which implements 10 // metadata-based scoped no-alias support. 11 // 12 // Alias-analysis scopes are defined by an id (which can be a string or some 13 // other metadata node), a domain node, and an optional descriptive string. 14 // A domain is defined by an id (which can be a string or some other metadata 15 // node), and an optional descriptive string. 16 // 17 // !dom0 = metadata !{ metadata !"domain of foo()" } 18 // !scope1 = metadata !{ metadata !scope1, metadata !dom0, metadata !"scope 1" } 19 // !scope2 = metadata !{ metadata !scope2, metadata !dom0, metadata !"scope 2" } 20 // 21 // Loads and stores can be tagged with an alias-analysis scope, and also, with 22 // a noalias tag for a specific scope: 23 // 24 // ... = load %ptr1, !alias.scope !{ !scope1 } 25 // ... = load %ptr2, !alias.scope !{ !scope1, !scope2 }, !noalias !{ !scope1 } 26 // 27 // When evaluating an aliasing query, if one of the instructions is associated 28 // has a set of noalias scopes in some domain that is a superset of the alias 29 // scopes in that domain of some other instruction, then the two memory 30 // accesses are assumed not to alias. 31 // 32 //===----------------------------------------------------------------------===// 33 34 #include "llvm/Analysis/ScopedNoAliasAA.h" 35 #include "llvm/ADT/SetOperations.h" 36 #include "llvm/ADT/SmallPtrSet.h" 37 #include "llvm/Analysis/MemoryLocation.h" 38 #include "llvm/IR/InstrTypes.h" 39 #include "llvm/IR/Instruction.h" 40 #include "llvm/IR/LLVMContext.h" 41 #include "llvm/IR/Metadata.h" 42 #include "llvm/InitializePasses.h" 43 #include "llvm/Pass.h" 44 #include "llvm/Support/Casting.h" 45 #include "llvm/Support/CommandLine.h" 46 47 using namespace llvm; 48 49 // A handy option for disabling scoped no-alias functionality. The same effect 50 // can also be achieved by stripping the associated metadata tags from IR, but 51 // this option is sometimes more convenient. 52 static cl::opt<bool> EnableScopedNoAlias("enable-scoped-noalias", 53 cl::init(true), cl::Hidden); 54 55 AliasResult ScopedNoAliasAAResult::alias(const MemoryLocation &LocA, 56 const MemoryLocation &LocB, 57 AAQueryInfo &AAQI) { 58 if (!EnableScopedNoAlias) 59 return AAResultBase::alias(LocA, LocB, AAQI); 60 61 // Get the attached MDNodes. 62 const MDNode *AScopes = LocA.AATags.Scope, *BScopes = LocB.AATags.Scope; 63 64 const MDNode *ANoAlias = LocA.AATags.NoAlias, *BNoAlias = LocB.AATags.NoAlias; 65 66 if (!mayAliasInScopes(AScopes, BNoAlias)) 67 return AliasResult::NoAlias; 68 69 if (!mayAliasInScopes(BScopes, ANoAlias)) 70 return AliasResult::NoAlias; 71 72 // If they may alias, chain to the next AliasAnalysis. 73 return AAResultBase::alias(LocA, LocB, AAQI); 74 } 75 76 ModRefInfo ScopedNoAliasAAResult::getModRefInfo(const CallBase *Call, 77 const MemoryLocation &Loc, 78 AAQueryInfo &AAQI) { 79 if (!EnableScopedNoAlias) 80 return AAResultBase::getModRefInfo(Call, Loc, AAQI); 81 82 if (!mayAliasInScopes(Loc.AATags.Scope, 83 Call->getMetadata(LLVMContext::MD_noalias))) 84 return ModRefInfo::NoModRef; 85 86 if (!mayAliasInScopes(Call->getMetadata(LLVMContext::MD_alias_scope), 87 Loc.AATags.NoAlias)) 88 return ModRefInfo::NoModRef; 89 90 return AAResultBase::getModRefInfo(Call, Loc, AAQI); 91 } 92 93 ModRefInfo ScopedNoAliasAAResult::getModRefInfo(const CallBase *Call1, 94 const CallBase *Call2, 95 AAQueryInfo &AAQI) { 96 if (!EnableScopedNoAlias) 97 return AAResultBase::getModRefInfo(Call1, Call2, AAQI); 98 99 if (!mayAliasInScopes(Call1->getMetadata(LLVMContext::MD_alias_scope), 100 Call2->getMetadata(LLVMContext::MD_noalias))) 101 return ModRefInfo::NoModRef; 102 103 if (!mayAliasInScopes(Call2->getMetadata(LLVMContext::MD_alias_scope), 104 Call1->getMetadata(LLVMContext::MD_noalias))) 105 return ModRefInfo::NoModRef; 106 107 return AAResultBase::getModRefInfo(Call1, Call2, AAQI); 108 } 109 110 static void collectMDInDomain(const MDNode *List, const MDNode *Domain, 111 SmallPtrSetImpl<const MDNode *> &Nodes) { 112 for (const MDOperand &MDOp : List->operands()) 113 if (const MDNode *MD = dyn_cast<MDNode>(MDOp)) 114 if (AliasScopeNode(MD).getDomain() == Domain) 115 Nodes.insert(MD); 116 } 117 118 bool ScopedNoAliasAAResult::mayAliasInScopes(const MDNode *Scopes, 119 const MDNode *NoAlias) const { 120 if (!Scopes || !NoAlias) 121 return true; 122 123 // Collect the set of scope domains relevant to the noalias scopes. 124 SmallPtrSet<const MDNode *, 16> Domains; 125 for (const MDOperand &MDOp : NoAlias->operands()) 126 if (const MDNode *NAMD = dyn_cast<MDNode>(MDOp)) 127 if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain()) 128 Domains.insert(Domain); 129 130 // We alias unless, for some domain, the set of noalias scopes in that domain 131 // is a superset of the set of alias scopes in that domain. 132 for (const MDNode *Domain : Domains) { 133 SmallPtrSet<const MDNode *, 16> ScopeNodes; 134 collectMDInDomain(Scopes, Domain, ScopeNodes); 135 if (ScopeNodes.empty()) 136 continue; 137 138 SmallPtrSet<const MDNode *, 16> NANodes; 139 collectMDInDomain(NoAlias, Domain, NANodes); 140 141 // To not alias, all of the nodes in ScopeNodes must be in NANodes. 142 if (llvm::set_is_subset(ScopeNodes, NANodes)) 143 return false; 144 } 145 146 return true; 147 } 148 149 AnalysisKey ScopedNoAliasAA::Key; 150 151 ScopedNoAliasAAResult ScopedNoAliasAA::run(Function &F, 152 FunctionAnalysisManager &AM) { 153 return ScopedNoAliasAAResult(); 154 } 155 156 char ScopedNoAliasAAWrapperPass::ID = 0; 157 158 INITIALIZE_PASS(ScopedNoAliasAAWrapperPass, "scoped-noalias-aa", 159 "Scoped NoAlias Alias Analysis", false, true) 160 161 ImmutablePass *llvm::createScopedNoAliasAAWrapperPass() { 162 return new ScopedNoAliasAAWrapperPass(); 163 } 164 165 ScopedNoAliasAAWrapperPass::ScopedNoAliasAAWrapperPass() : ImmutablePass(ID) { 166 initializeScopedNoAliasAAWrapperPassPass(*PassRegistry::getPassRegistry()); 167 } 168 169 bool ScopedNoAliasAAWrapperPass::doInitialization(Module &M) { 170 Result.reset(new ScopedNoAliasAAResult()); 171 return false; 172 } 173 174 bool ScopedNoAliasAAWrapperPass::doFinalization(Module &M) { 175 Result.reset(); 176 return false; 177 } 178 179 void ScopedNoAliasAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { 180 AU.setPreservesAll(); 181 } 182