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Diffstat (limited to 'llvm/lib/Analysis/ScopedNoAliasAA.cpp')
-rw-r--r-- | llvm/lib/Analysis/ScopedNoAliasAA.cpp | 210 |
1 files changed, 210 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/ScopedNoAliasAA.cpp b/llvm/lib/Analysis/ScopedNoAliasAA.cpp new file mode 100644 index 000000000000..094e4a3d5dc8 --- /dev/null +++ b/llvm/lib/Analysis/ScopedNoAliasAA.cpp @@ -0,0 +1,210 @@ +//===- ScopedNoAliasAA.cpp - Scoped No-Alias Alias Analysis ---------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This file defines the ScopedNoAlias alias-analysis pass, which implements +// metadata-based scoped no-alias support. +// +// Alias-analysis scopes are defined by an id (which can be a string or some +// other metadata node), a domain node, and an optional descriptive string. +// A domain is defined by an id (which can be a string or some other metadata +// node), and an optional descriptive string. +// +// !dom0 = metadata !{ metadata !"domain of foo()" } +// !scope1 = metadata !{ metadata !scope1, metadata !dom0, metadata !"scope 1" } +// !scope2 = metadata !{ metadata !scope2, metadata !dom0, metadata !"scope 2" } +// +// Loads and stores can be tagged with an alias-analysis scope, and also, with +// a noalias tag for a specific scope: +// +// ... = load %ptr1, !alias.scope !{ !scope1 } +// ... = load %ptr2, !alias.scope !{ !scope1, !scope2 }, !noalias !{ !scope1 } +// +// When evaluating an aliasing query, if one of the instructions is associated +// has a set of noalias scopes in some domain that is a superset of the alias +// scopes in that domain of some other instruction, then the two memory +// accesses are assumed not to alias. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Analysis/ScopedNoAliasAA.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/Analysis/MemoryLocation.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/Metadata.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/CommandLine.h" + +using namespace llvm; + +// A handy option for disabling scoped no-alias functionality. The same effect +// can also be achieved by stripping the associated metadata tags from IR, but +// this option is sometimes more convenient. +static cl::opt<bool> EnableScopedNoAlias("enable-scoped-noalias", + cl::init(true), cl::Hidden); + +namespace { + +/// This is a simple wrapper around an MDNode which provides a higher-level +/// interface by hiding the details of how alias analysis information is encoded +/// in its operands. +class AliasScopeNode { + const MDNode *Node = nullptr; + +public: + AliasScopeNode() = default; + explicit AliasScopeNode(const MDNode *N) : Node(N) {} + + /// Get the MDNode for this AliasScopeNode. + const MDNode *getNode() const { return Node; } + + /// Get the MDNode for this AliasScopeNode's domain. + const MDNode *getDomain() const { + if (Node->getNumOperands() < 2) + return nullptr; + return dyn_cast_or_null<MDNode>(Node->getOperand(1)); + } +}; + +} // end anonymous namespace + +AliasResult ScopedNoAliasAAResult::alias(const MemoryLocation &LocA, + const MemoryLocation &LocB, + AAQueryInfo &AAQI) { + if (!EnableScopedNoAlias) + return AAResultBase::alias(LocA, LocB, AAQI); + + // Get the attached MDNodes. + const MDNode *AScopes = LocA.AATags.Scope, *BScopes = LocB.AATags.Scope; + + const MDNode *ANoAlias = LocA.AATags.NoAlias, *BNoAlias = LocB.AATags.NoAlias; + + if (!mayAliasInScopes(AScopes, BNoAlias)) + return NoAlias; + + if (!mayAliasInScopes(BScopes, ANoAlias)) + return NoAlias; + + // If they may alias, chain to the next AliasAnalysis. + return AAResultBase::alias(LocA, LocB, AAQI); +} + +ModRefInfo ScopedNoAliasAAResult::getModRefInfo(const CallBase *Call, + const MemoryLocation &Loc, + AAQueryInfo &AAQI) { + if (!EnableScopedNoAlias) + return AAResultBase::getModRefInfo(Call, Loc, AAQI); + + if (!mayAliasInScopes(Loc.AATags.Scope, + Call->getMetadata(LLVMContext::MD_noalias))) + return ModRefInfo::NoModRef; + + if (!mayAliasInScopes(Call->getMetadata(LLVMContext::MD_alias_scope), + Loc.AATags.NoAlias)) + return ModRefInfo::NoModRef; + + return AAResultBase::getModRefInfo(Call, Loc, AAQI); +} + +ModRefInfo ScopedNoAliasAAResult::getModRefInfo(const CallBase *Call1, + const CallBase *Call2, + AAQueryInfo &AAQI) { + if (!EnableScopedNoAlias) + return AAResultBase::getModRefInfo(Call1, Call2, AAQI); + + if (!mayAliasInScopes(Call1->getMetadata(LLVMContext::MD_alias_scope), + Call2->getMetadata(LLVMContext::MD_noalias))) + return ModRefInfo::NoModRef; + + if (!mayAliasInScopes(Call2->getMetadata(LLVMContext::MD_alias_scope), + Call1->getMetadata(LLVMContext::MD_noalias))) + return ModRefInfo::NoModRef; + + return AAResultBase::getModRefInfo(Call1, Call2, AAQI); +} + +static void collectMDInDomain(const MDNode *List, const MDNode *Domain, + SmallPtrSetImpl<const MDNode *> &Nodes) { + for (const MDOperand &MDOp : List->operands()) + if (const MDNode *MD = dyn_cast<MDNode>(MDOp)) + if (AliasScopeNode(MD).getDomain() == Domain) + Nodes.insert(MD); +} + +bool ScopedNoAliasAAResult::mayAliasInScopes(const MDNode *Scopes, + const MDNode *NoAlias) const { + if (!Scopes || !NoAlias) + return true; + + // Collect the set of scope domains relevant to the noalias scopes. + SmallPtrSet<const MDNode *, 16> Domains; + for (const MDOperand &MDOp : NoAlias->operands()) + if (const MDNode *NAMD = dyn_cast<MDNode>(MDOp)) + if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain()) + Domains.insert(Domain); + + // We alias unless, for some domain, the set of noalias scopes in that domain + // is a superset of the set of alias scopes in that domain. + for (const MDNode *Domain : Domains) { + SmallPtrSet<const MDNode *, 16> ScopeNodes; + collectMDInDomain(Scopes, Domain, ScopeNodes); + if (ScopeNodes.empty()) + continue; + + SmallPtrSet<const MDNode *, 16> NANodes; + collectMDInDomain(NoAlias, Domain, NANodes); + + // To not alias, all of the nodes in ScopeNodes must be in NANodes. + bool FoundAll = true; + for (const MDNode *SMD : ScopeNodes) + if (!NANodes.count(SMD)) { + FoundAll = false; + break; + } + + if (FoundAll) + return false; + } + + return true; +} + +AnalysisKey ScopedNoAliasAA::Key; + +ScopedNoAliasAAResult ScopedNoAliasAA::run(Function &F, + FunctionAnalysisManager &AM) { + return ScopedNoAliasAAResult(); +} + +char ScopedNoAliasAAWrapperPass::ID = 0; + +INITIALIZE_PASS(ScopedNoAliasAAWrapperPass, "scoped-noalias", + "Scoped NoAlias Alias Analysis", false, true) + +ImmutablePass *llvm::createScopedNoAliasAAWrapperPass() { + return new ScopedNoAliasAAWrapperPass(); +} + +ScopedNoAliasAAWrapperPass::ScopedNoAliasAAWrapperPass() : ImmutablePass(ID) { + initializeScopedNoAliasAAWrapperPassPass(*PassRegistry::getPassRegistry()); +} + +bool ScopedNoAliasAAWrapperPass::doInitialization(Module &M) { + Result.reset(new ScopedNoAliasAAResult()); + return false; +} + +bool ScopedNoAliasAAWrapperPass::doFinalization(Module &M) { + Result.reset(); + return false; +} + +void ScopedNoAliasAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesAll(); +} |