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) {
initializeScalarEvolutionAliasAnalysisPass(
*PassRegistry::getPassRegistry());
}
virtual void *getAdjustedAnalysisPointer(AnalysisID PI) {
if (PI == &AliasAnalysis::ID)
return (AliasAnalysis*)this;
return this;
}
private:
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual bool runOnFunction(Function &F);
virtual AliasResult alias(const Location &LocA, const Location &LocB);
Value *GetBaseValue(const SCEV *S);
};
}
char ScalarEvolutionAliasAnalysis::ID = 0;
INITIALIZE_AG_PASS_BEGIN(ScalarEvolutionAliasAnalysis, AliasAnalysis, "scev-aa",
"ScalarEvolution-based Alias Analysis", false, true, false)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_AG_PASS_END(ScalarEvolutionAliasAnalysis, AliasAnalysis, "scev-aa",
"ScalarEvolution-based Alias Analysis", false, true, false)
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 Location &LocA,
const Location &LocB) {
if (LocA.Size == 0 || LocB.Size == 0)
return NoAlias;
const SCEV *AS = SE->getSCEV(const_cast<Value *>(LocA.Ptr));
const SCEV *BS = SE->getSCEV(const_cast<Value *>(LocB.Ptr));
if (AS == BS) return MustAlias;
if (SE->getEffectiveSCEVType(AS->getType()) ==
SE->getEffectiveSCEVType(BS->getType())) {
unsigned BitWidth = SE->getTypeSizeInBits(AS->getType());
APInt ASizeInt(BitWidth, LocA.Size);
APInt BSizeInt(BitWidth, LocB.Size);
const SCEV *BA = SE->getMinusSCEV(BS, AS);
if (ASizeInt.ule(SE->getUnsignedRange(BA).getUnsignedMin()) &&
(-BSizeInt).uge(SE->getUnsignedRange(BA).getUnsignedMax()))
return NoAlias;
const SCEV *AB = SE->getMinusSCEV(AS, BS);
if (BSizeInt.ule(SE->getUnsignedRange(AB).getUnsignedMin()) &&
(-ASizeInt).uge(SE->getUnsignedRange(AB).getUnsignedMax()))
return NoAlias;
}
Value *AO = GetBaseValue(AS);
Value *BO = GetBaseValue(BS);
if ((AO && AO != LocA.Ptr) || (BO && BO != LocB.Ptr))
if (alias(Location(AO ? AO : LocA.Ptr,
AO ? +UnknownSize : LocA.Size,
AO ? 0 : LocA.TBAATag),
Location(BO ? BO : LocB.Ptr,
BO ? +UnknownSize : LocB.Size,
BO ? 0 : LocB.TBAATag)) == NoAlias)
return NoAlias;
return AliasAnalysis::alias(LocA, LocB);
}