253 lines
8.8 KiB
C++
253 lines
8.8 KiB
C++
//===- ScopedNoAliasAA.cpp - Scoped No-Alias Alias Analysis ---------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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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 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/ADT/SmallPtrSet.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/IR/Constants.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/IR/Module.h"
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#include "llvm/Pass.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>
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EnableScopedNoAlias("enable-scoped-noalias", cl::init(true));
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namespace {
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/// AliasScopeNode - This is a simple wrapper around an MDNode which provides
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/// a higher-level interface by hiding the details of how alias analysis
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/// information is encoded in its operands.
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class AliasScopeNode {
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const MDNode *Node;
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public:
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AliasScopeNode() : Node(0) {}
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explicit AliasScopeNode(const MDNode *N) : Node(N) {}
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/// getNode - Get the MDNode for this AliasScopeNode.
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const MDNode *getNode() const { return Node; }
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/// getDomain - 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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/// ScopedNoAliasAA - This is a simple alias analysis
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/// implementation that uses scoped-noalias metadata to answer queries.
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class ScopedNoAliasAA : public ImmutablePass, public AliasAnalysis {
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public:
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static char ID; // Class identification, replacement for typeinfo
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ScopedNoAliasAA() : ImmutablePass(ID) {
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initializeScopedNoAliasAAPass(*PassRegistry::getPassRegistry());
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}
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bool doInitialization(Module &M) override;
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/// getAdjustedAnalysisPointer - This method is used when a pass implements
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/// an analysis interface through multiple inheritance. If needed, it
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/// should override this to adjust the this pointer as needed for the
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/// specified pass info.
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void *getAdjustedAnalysisPointer(const void *PI) override {
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if (PI == &AliasAnalysis::ID)
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return (AliasAnalysis*)this;
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return this;
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}
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protected:
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bool mayAliasInScopes(const MDNode *Scopes, const MDNode *NoAlias) const;
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void collectMDInDomain(const MDNode *List, const MDNode *Domain,
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SmallPtrSetImpl<const MDNode *> &Nodes) const;
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private:
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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AliasResult alias(const MemoryLocation &LocA,
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const MemoryLocation &LocB) override;
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bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal) override;
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ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override;
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ModRefBehavior getModRefBehavior(const Function *F) override;
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ModRefResult getModRefInfo(ImmutableCallSite CS,
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const MemoryLocation &Loc) override;
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ModRefResult getModRefInfo(ImmutableCallSite CS1,
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ImmutableCallSite CS2) override;
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};
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} // End of anonymous namespace
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// Register this pass...
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char ScopedNoAliasAA::ID = 0;
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INITIALIZE_AG_PASS(ScopedNoAliasAA, AliasAnalysis, "scoped-noalias",
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"Scoped NoAlias Alias Analysis", false, true, false)
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ImmutablePass *llvm::createScopedNoAliasAAPass() {
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return new ScopedNoAliasAA();
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}
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bool ScopedNoAliasAA::doInitialization(Module &M) {
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InitializeAliasAnalysis(this, &M.getDataLayout());
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return true;
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}
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void
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ScopedNoAliasAA::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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AliasAnalysis::getAnalysisUsage(AU);
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}
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void
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ScopedNoAliasAA::collectMDInDomain(const MDNode *List, const MDNode *Domain,
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SmallPtrSetImpl<const MDNode *> &Nodes) const {
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for (unsigned i = 0, ie = List->getNumOperands(); i != ie; ++i)
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if (const MDNode *MD = dyn_cast<MDNode>(List->getOperand(i)))
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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
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ScopedNoAliasAA::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 (unsigned i = 0, ie = NoAlias->getNumOperands(); i != ie; ++i)
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if (const MDNode *NAMD = dyn_cast<MDNode>(NoAlias->getOperand(i)))
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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> NANodes, ScopeNodes;
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collectMDInDomain(NoAlias, Domain, NANodes);
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collectMDInDomain(Scopes, Domain, ScopeNodes);
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if (!ScopeNodes.size())
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continue;
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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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AliasResult ScopedNoAliasAA::alias(const MemoryLocation &LocA,
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const MemoryLocation &LocB) {
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if (!EnableScopedNoAlias)
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return AliasAnalysis::alias(LocA, LocB);
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// Get the attached MDNodes.
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const MDNode *AScopes = LocA.AATags.Scope,
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*BScopes = LocB.AATags.Scope;
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const MDNode *ANoAlias = LocA.AATags.NoAlias,
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*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 AliasAnalysis::alias(LocA, LocB);
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}
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bool ScopedNoAliasAA::pointsToConstantMemory(const MemoryLocation &Loc,
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bool OrLocal) {
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return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
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}
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AliasAnalysis::ModRefBehavior
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ScopedNoAliasAA::getModRefBehavior(ImmutableCallSite CS) {
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return AliasAnalysis::getModRefBehavior(CS);
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}
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AliasAnalysis::ModRefBehavior
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ScopedNoAliasAA::getModRefBehavior(const Function *F) {
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return AliasAnalysis::getModRefBehavior(F);
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}
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AliasAnalysis::ModRefResult
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ScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS,
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const MemoryLocation &Loc) {
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if (!EnableScopedNoAlias)
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return AliasAnalysis::getModRefInfo(CS, Loc);
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if (!mayAliasInScopes(Loc.AATags.Scope, CS.getInstruction()->getMetadata(
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LLVMContext::MD_noalias)))
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return NoModRef;
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if (!mayAliasInScopes(
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CS.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
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Loc.AATags.NoAlias))
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return NoModRef;
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return AliasAnalysis::getModRefInfo(CS, Loc);
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}
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AliasAnalysis::ModRefResult
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ScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) {
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if (!EnableScopedNoAlias)
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return AliasAnalysis::getModRefInfo(CS1, CS2);
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if (!mayAliasInScopes(
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CS1.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
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CS2.getInstruction()->getMetadata(LLVMContext::MD_noalias)))
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return NoModRef;
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if (!mayAliasInScopes(
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CS2.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
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CS1.getInstruction()->getMetadata(LLVMContext::MD_noalias)))
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return NoModRef;
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return AliasAnalysis::getModRefInfo(CS1, CS2);
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}
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