188 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8//9// This file defines the ScopedNoAlias alias-analysis pass, which implements10// metadata-based scoped no-alias support.11//12// Alias-analysis scopes are defined by an id (which can be a string or some13// 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 metadata15// 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, with22// 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 associated28// has a set of noalias scopes in some domain that is a superset of the alias29// scopes in that domain of some other instruction, then the two memory30// 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 46using namespace llvm;47 48// A handy option for disabling scoped no-alias functionality. The same effect49// can also be achieved by stripping the associated metadata tags from IR, but50// this option is sometimes more convenient.51static cl::opt<bool> EnableScopedNoAlias("enable-scoped-noalias",52 cl::init(true), cl::Hidden);53 54AliasResult 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 75ModRefInfo 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 92ModRefInfo 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 109static 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/// Collect the set of scoped domains relevant to the noalias scopes.118void ScopedNoAliasAAResult::collectScopedDomains(119 const MDNode *NoAlias, SmallPtrSetImpl<const MDNode *> &Domains) {120 if (!NoAlias)121 return;122 assert(Domains.empty() && "Domains should be empty");123 for (const MDOperand &MDOp : NoAlias->operands())124 if (const MDNode *NAMD = dyn_cast<MDNode>(MDOp))125 if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain())126 Domains.insert(Domain);127}128 129bool ScopedNoAliasAAResult::mayAliasInScopes(const MDNode *Scopes,130 const MDNode *NoAlias) {131 if (!Scopes || !NoAlias)132 return true;133 134 // Collect the set of scope domains relevant to the noalias scopes.135 SmallPtrSet<const MDNode *, 16> Domains;136 collectScopedDomains(NoAlias, Domains);137 138 // We alias unless, for some domain, the set of noalias scopes in that domain139 // is a superset of the set of alias scopes in that domain.140 for (const MDNode *Domain : Domains) {141 SmallPtrSet<const MDNode *, 16> ScopeNodes;142 collectMDInDomain(Scopes, Domain, ScopeNodes);143 if (ScopeNodes.empty())144 continue;145 146 SmallPtrSet<const MDNode *, 16> NANodes;147 collectMDInDomain(NoAlias, Domain, NANodes);148 149 // To not alias, all of the nodes in ScopeNodes must be in NANodes.150 if (llvm::set_is_subset(ScopeNodes, NANodes))151 return false;152 }153 154 return true;155}156 157AnalysisKey ScopedNoAliasAA::Key;158 159ScopedNoAliasAAResult ScopedNoAliasAA::run(Function &F,160 FunctionAnalysisManager &AM) {161 return ScopedNoAliasAAResult();162}163 164char ScopedNoAliasAAWrapperPass::ID = 0;165 166INITIALIZE_PASS(ScopedNoAliasAAWrapperPass, "scoped-noalias-aa",167 "Scoped NoAlias Alias Analysis", false, true)168 169ImmutablePass *llvm::createScopedNoAliasAAWrapperPass() {170 return new ScopedNoAliasAAWrapperPass();171}172 173ScopedNoAliasAAWrapperPass::ScopedNoAliasAAWrapperPass() : ImmutablePass(ID) {}174 175bool ScopedNoAliasAAWrapperPass::doInitialization(Module &M) {176 Result.reset(new ScopedNoAliasAAResult());177 return false;178}179 180bool ScopedNoAliasAAWrapperPass::doFinalization(Module &M) {181 Result.reset();182 return false;183}184 185void ScopedNoAliasAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {186 AU.setPreservesAll();187}188