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