Constant *computeLoadValue(LoadInst *LI, unsigned Iteration) {
if (!LI)
return nullptr;
Value *BaseAddr = LoadBaseAddresses[LI];
if (!BaseAddr)
return nullptr;
auto GV = dyn_cast<GlobalVariable>(BaseAddr);
if (!GV)
return nullptr;
ConstantDataSequential *CDS =
dyn_cast<ConstantDataSequential>(GV->getInitializer());
if (!CDS)
return nullptr;
const SCEV *BaseAddrSE = SE.getSCEV(BaseAddr);
const SCEV *S = SE.getSCEV(LI->getPointerOperand());
const SCEV *OffSE = SE.getMinusSCEV(S, BaseAddrSE);
APInt StepC, StartC;
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(OffSE);
if (!AR)
return nullptr;
if (const SCEVConstant *StepSE =
dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
StepC = StepSE->getValue()->getValue();
else
return nullptr;
if (const SCEVConstant *StartSE = dyn_cast<SCEVConstant>(AR->getStart()))
StartC = StartSE->getValue()->getValue();
else
return nullptr;
unsigned ElemSize = CDS->getElementType()->getPrimitiveSizeInBits() / 8U;
unsigned Start = StartC.getLimitedValue();
unsigned Step = StepC.getLimitedValue();
unsigned Index = (Start + Step * Iteration) / ElemSize;
if (Index >= CDS->getNumElements())
return nullptr;
Constant *CV = CDS->getElementAsConstant(Index);
return CV;
}
/// Try to fold load I.
bool UnrolledInstAnalyzer::visitLoad(LoadInst &I) {
Value *AddrOp = I.getPointerOperand();
auto AddressIt = SimplifiedAddresses.find(AddrOp);
if (AddressIt == SimplifiedAddresses.end())
return false;
ConstantInt *SimplifiedAddrOp = AddressIt->second.Offset;
auto *GV = dyn_cast<GlobalVariable>(AddressIt->second.Base);
// We're only interested in loads that can be completely folded to a
// constant.
if (!GV || !GV->hasDefinitiveInitializer() || !GV->isConstant())
return false;
ConstantDataSequential *CDS =
dyn_cast<ConstantDataSequential>(GV->getInitializer());
if (!CDS)
return false;
// We might have a vector load from an array. FIXME: for now we just bail
// out in this case, but we should be able to resolve and simplify such
// loads.
if(!CDS->isElementTypeCompatible(I.getType()))
return false;
int ElemSize = CDS->getElementType()->getPrimitiveSizeInBits() / 8U;
if (SimplifiedAddrOp->getValue().getActiveBits() >= 64)
return false;
int64_t Index = SimplifiedAddrOp->getSExtValue() / ElemSize;
if (Index >= CDS->getNumElements()) {
// FIXME: For now we conservatively ignore out of bound accesses, but
// we're allowed to perform the optimization in this case.
return false;
}
Constant *CV = CDS->getElementAsConstant(Index);
assert(CV && "Constant expected.");
SimplifiedValues[&I] = CV;
return true;
}
