ScalarEvolutionAliasAnalysis.cpp [plain text]
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Pass.h"
using namespace llvm;
namespace {
class ScalarEvolutionAliasAnalysis : public FunctionPass,
public AliasAnalysis {
ScalarEvolution *SE;
public:
static char ID; ScalarEvolutionAliasAnalysis() : FunctionPass(&ID), SE(0) {}
virtual void *getAdjustedAnalysisPointer(const PassInfo *PI) {
if (PI->isPassID(&AliasAnalysis::ID))
return (AliasAnalysis*)this;
return this;
}
private:
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual bool runOnFunction(Function &F);
virtual AliasResult alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size);
Value *GetBaseValue(const SCEV *S);
};
}
char ScalarEvolutionAliasAnalysis::ID = 0;
static RegisterPass<ScalarEvolutionAliasAnalysis>
X("scev-aa", "ScalarEvolution-based Alias Analysis", false, true);
static RegisterAnalysisGroup<AliasAnalysis> Y(X);
FunctionPass *llvm::createScalarEvolutionAliasAnalysisPass() {
return new ScalarEvolutionAliasAnalysis();
}
void
ScalarEvolutionAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredTransitive<ScalarEvolution>();
AU.setPreservesAll();
AliasAnalysis::getAnalysisUsage(AU);
}
bool
ScalarEvolutionAliasAnalysis::runOnFunction(Function &F) {
InitializeAliasAnalysis(this);
SE = &getAnalysis<ScalarEvolution>();
return false;
}
Value *
ScalarEvolutionAliasAnalysis::GetBaseValue(const SCEV *S) {
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
return GetBaseValue(AR->getStart());
} else if (const SCEVAddExpr *A = dyn_cast<SCEVAddExpr>(S)) {
const SCEV *Last = A->getOperand(A->getNumOperands()-1);
if (Last->getType()->isPointerTy())
return GetBaseValue(Last);
} else if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
return U->getValue();
}
return 0;
}
AliasAnalysis::AliasResult
ScalarEvolutionAliasAnalysis::alias(const Value *A, unsigned ASize,
const Value *B, unsigned BSize) {
const SCEV *AS = SE->getSCEV(const_cast<Value *>(A));
const SCEV *BS = SE->getSCEV(const_cast<Value *>(B));
if (AS == BS) return MustAlias;
if (SE->getEffectiveSCEVType(AS->getType()) ==
SE->getEffectiveSCEVType(BS->getType())) {
unsigned BitWidth = SE->getTypeSizeInBits(AS->getType());
APInt AI(BitWidth, ASize);
const SCEV *BA = SE->getMinusSCEV(BS, AS);
if (AI.ule(SE->getUnsignedRange(BA).getUnsignedMin())) {
APInt BI(BitWidth, BSize);
const SCEV *AB = SE->getMinusSCEV(AS, BS);
if (BI.ule(SE->getUnsignedRange(AB).getUnsignedMin()))
return NoAlias;
}
}
Value *AO = GetBaseValue(AS);
Value *BO = GetBaseValue(BS);
if ((AO && AO != A) || (BO && BO != B))
if (alias(AO ? AO : A, AO ? ~0u : ASize,
BO ? BO : B, BO ? ~0u : BSize) == NoAlias)
return NoAlias;
return AliasAnalysis::alias(A, ASize, B, BSize);
}