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/LLVMContext.h" 40 #include "llvm/IR/Metadata.h" 41 #include "llvm/InitializePasses.h" 42 #include "llvm/Pass.h" 43 #include "llvm/Support/Casting.h" 44 #include "llvm/Support/CommandLine.h" 45 46 using namespace llvm; 47 48 // A handy option for disabling scoped no-alias functionality. The same effect 49 // can also be achieved by stripping the associated metadata tags from IR, but 50 // this option is sometimes more convenient. 51 static cl::opt<bool> EnableScopedNoAlias("enable-scoped-noalias", 52 cl::init(true), cl::Hidden); 53 54 AliasResult ScopedNoAliasAAResult::alias(const MemoryLocation &LocA, 55 const MemoryLocation &LocB, 56 AAQueryInfo &AAQI, 57 const Instruction *) { 58 if (!EnableScopedNoAlias) 59 return AliasResult::MayAlias; 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 return AliasResult::MayAlias; 73 } 74 75 ModRefInfo ScopedNoAliasAAResult::getModRefInfo(const CallBase *Call, 76 const MemoryLocation &Loc, 77 AAQueryInfo &AAQI) { 78 if (!EnableScopedNoAlias) 79 return ModRefInfo::ModRef; 80 81 if (!mayAliasInScopes(Loc.AATags.Scope, 82 Call->getMetadata(LLVMContext::MD_noalias))) 83 return ModRefInfo::NoModRef; 84 85 if (!mayAliasInScopes(Call->getMetadata(LLVMContext::MD_alias_scope), 86 Loc.AATags.NoAlias)) 87 return ModRefInfo::NoModRef; 88 89 return ModRefInfo::ModRef; 90 } 91 92 ModRefInfo ScopedNoAliasAAResult::getModRefInfo(const CallBase *Call1, 93 const CallBase *Call2, 94 AAQueryInfo &AAQI) { 95 if (!EnableScopedNoAlias) 96 return ModRefInfo::ModRef; 97 98 if (!mayAliasInScopes(Call1->getMetadata(LLVMContext::MD_alias_scope), 99 Call2->getMetadata(LLVMContext::MD_noalias))) 100 return ModRefInfo::NoModRef; 101 102 if (!mayAliasInScopes(Call2->getMetadata(LLVMContext::MD_alias_scope), 103 Call1->getMetadata(LLVMContext::MD_noalias))) 104 return ModRefInfo::NoModRef; 105 106 return ModRefInfo::ModRef; 107 } 108 109 static void collectMDInDomain(const MDNode *List, const MDNode *Domain, 110 SmallPtrSetImpl<const MDNode *> &Nodes) { 111 for (const MDOperand &MDOp : List->operands()) 112 if (const MDNode *MD = dyn_cast<MDNode>(MDOp)) 113 if (AliasScopeNode(MD).getDomain() == Domain) 114 Nodes.insert(MD); 115 } 116 117 bool ScopedNoAliasAAResult::mayAliasInScopes(const MDNode *Scopes, 118 const MDNode *NoAlias) const { 119 if (!Scopes || !NoAlias) 120 return true; 121 122 // Collect the set of scope domains relevant to the noalias scopes. 123 SmallPtrSet<const MDNode *, 16> Domains; 124 for (const MDOperand &MDOp : NoAlias->operands()) 125 if (const MDNode *NAMD = dyn_cast<MDNode>(MDOp)) 126 if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain()) 127 Domains.insert(Domain); 128 129 // We alias unless, for some domain, the set of noalias scopes in that domain 130 // is a superset of the set of alias scopes in that domain. 131 for (const MDNode *Domain : Domains) { 132 SmallPtrSet<const MDNode *, 16> ScopeNodes; 133 collectMDInDomain(Scopes, Domain, ScopeNodes); 134 if (ScopeNodes.empty()) 135 continue; 136 137 SmallPtrSet<const MDNode *, 16> NANodes; 138 collectMDInDomain(NoAlias, Domain, NANodes); 139 140 // To not alias, all of the nodes in ScopeNodes must be in NANodes. 141 if (llvm::set_is_subset(ScopeNodes, NANodes)) 142 return false; 143 } 144 145 return true; 146 } 147 148 AnalysisKey ScopedNoAliasAA::Key; 149 150 ScopedNoAliasAAResult ScopedNoAliasAA::run(Function &F, 151 FunctionAnalysisManager &AM) { 152 return ScopedNoAliasAAResult(); 153 } 154 155 char ScopedNoAliasAAWrapperPass::ID = 0; 156 157 INITIALIZE_PASS(ScopedNoAliasAAWrapperPass, "scoped-noalias-aa", 158 "Scoped NoAlias Alias Analysis", false, true) 159 160 ImmutablePass *llvm::createScopedNoAliasAAWrapperPass() { 161 return new ScopedNoAliasAAWrapperPass(); 162 } 163 164 ScopedNoAliasAAWrapperPass::ScopedNoAliasAAWrapperPass() : ImmutablePass(ID) { 165 initializeScopedNoAliasAAWrapperPassPass(*PassRegistry::getPassRegistry()); 166 } 167 168 bool ScopedNoAliasAAWrapperPass::doInitialization(Module &M) { 169 Result.reset(new ScopedNoAliasAAResult()); 170 return false; 171 } 172 173 bool ScopedNoAliasAAWrapperPass::doFinalization(Module &M) { 174 Result.reset(); 175 return false; 176 } 177 178 void ScopedNoAliasAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { 179 AU.setPreservesAll(); 180 } 181