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+//===- 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();
+}