//===- ScopedNoAliasAA.cpp - Scoped No-Alias Alias Analysis ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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 superset of the alias
// scopes in that domain of some other instruction, then the two memory
// accesses are assumed not to alias.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.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));
namespace {
/// AliasScopeNode - 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;
public:
AliasScopeNode() : Node(0) {}
explicit AliasScopeNode(const MDNode *N) : Node(N) {}
/// getNode - Get the MDNode for this AliasScopeNode.
const MDNode *getNode() const { return Node; }
/// getDomain - 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));
}
};
/// ScopedNoAliasAA - This is a simple alias analysis
/// implementation that uses scoped-noalias metadata to answer queries.
class ScopedNoAliasAA : public ImmutablePass, public AliasAnalysis {
public:
static char ID; // Class identification, replacement for typeinfo
ScopedNoAliasAA() : ImmutablePass(ID) {
initializeScopedNoAliasAAPass(*PassRegistry::getPassRegistry());
}
bool doInitialization(Module &M) override;
/// getAdjustedAnalysisPointer - This method is used when a pass implements
/// an analysis interface through multiple inheritance. If needed, it
/// should override this to adjust the this pointer as needed for the
/// specified pass info.
void *getAdjustedAnalysisPointer(const void *PI) override {
if (PI == &AliasAnalysis::ID)
return (AliasAnalysis*)this;
return this;
}
protected:
bool mayAliasInScopes(const MDNode *Scopes, const MDNode *NoAlias) const;
void collectMDInDomain(const MDNode *List, const MDNode *Domain,
SmallPtrSetImpl<const MDNode *> &Nodes) const;
private:
void getAnalysisUsage(AnalysisUsage &AU) const override;
AliasResult alias(const MemoryLocation &LocA,
const MemoryLocation &LocB) override;
bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal) override;
ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override;
ModRefBehavior getModRefBehavior(const Function *F) override;
ModRefResult getModRefInfo(ImmutableCallSite CS,
const MemoryLocation &Loc) override;
ModRefResult getModRefInfo(ImmutableCallSite CS1,
ImmutableCallSite CS2) override;
};
} // End of anonymous namespace
// Register this pass...
char ScopedNoAliasAA::ID = 0;
INITIALIZE_AG_PASS(ScopedNoAliasAA, AliasAnalysis, "scoped-noalias",
"Scoped NoAlias Alias Analysis", false, true, false)
ImmutablePass *llvm::createScopedNoAliasAAPass() {
return new ScopedNoAliasAA();
}
bool ScopedNoAliasAA::doInitialization(Module &M) {
InitializeAliasAnalysis(this, &M.getDataLayout());
return true;
}
void
ScopedNoAliasAA::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AliasAnalysis::getAnalysisUsage(AU);
}
void
ScopedNoAliasAA::collectMDInDomain(const MDNode *List, const MDNode *Domain,
SmallPtrSetImpl<const MDNode *> &Nodes) const {
for (unsigned i = 0, ie = List->getNumOperands(); i != ie; ++i)
if (const MDNode *MD = dyn_cast<MDNode>(List->getOperand(i)))
if (AliasScopeNode(MD).getDomain() == Domain)
Nodes.insert(MD);
}
bool
ScopedNoAliasAA::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 (unsigned i = 0, ie = NoAlias->getNumOperands(); i != ie; ++i)
if (const MDNode *NAMD = dyn_cast<MDNode>(NoAlias->getOperand(i)))
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> NANodes, ScopeNodes;
collectMDInDomain(NoAlias, Domain, NANodes);
collectMDInDomain(Scopes, Domain, ScopeNodes);
if (!ScopeNodes.size())
continue;
// 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;
}
AliasAnalysis::AliasResult ScopedNoAliasAA::alias(const MemoryLocation &LocA,
const MemoryLocation &LocB) {
if (!EnableScopedNoAlias)
return AliasAnalysis::alias(LocA, LocB);
// 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 AliasAnalysis::alias(LocA, LocB);
}
bool ScopedNoAliasAA::pointsToConstantMemory(const MemoryLocation &Loc,
bool OrLocal) {
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
}
AliasAnalysis::ModRefBehavior
ScopedNoAliasAA::getModRefBehavior(ImmutableCallSite CS) {
return AliasAnalysis::getModRefBehavior(CS);
}
AliasAnalysis::ModRefBehavior
ScopedNoAliasAA::getModRefBehavior(const Function *F) {
return AliasAnalysis::getModRefBehavior(F);
}
AliasAnalysis::ModRefResult
ScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS,
const MemoryLocation &Loc) {
if (!EnableScopedNoAlias)
return AliasAnalysis::getModRefInfo(CS, Loc);
if (!mayAliasInScopes(Loc.AATags.Scope, CS.getInstruction()->getMetadata(
LLVMContext::MD_noalias)))
return NoModRef;
if (!mayAliasInScopes(
CS.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
Loc.AATags.NoAlias))
return NoModRef;
return AliasAnalysis::getModRefInfo(CS, Loc);
}
AliasAnalysis::ModRefResult
ScopedNoAliasAA::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) {
if (!EnableScopedNoAlias)
return AliasAnalysis::getModRefInfo(CS1, CS2);
if (!mayAliasInScopes(
CS1.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
CS2.getInstruction()->getMetadata(LLVMContext::MD_noalias)))
return NoModRef;
if (!mayAliasInScopes(
CS2.getInstruction()->getMetadata(LLVMContext::MD_alias_scope),
CS1.getInstruction()->getMetadata(LLVMContext::MD_noalias)))
return NoModRef;
return AliasAnalysis::getModRefInfo(CS1, CS2);
}
