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LAA: improve code in getStrideFromPointer (NFC) #124780

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Merged
artagnon merged 3 commits into from
Jan 31, 2025
Merged

LAA: improve code in getStrideFromPointer (NFC) #124780

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616eb80
LAA: improve code in getStrideFromPointer (NFC)
artagnon Jan 28, 2025
0a48a23
LAA: fix style; address review
artagnon Jan 31, 2025
7605406
LAA: add comment
artagnon Jan 31, 2025
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27 changes: 9 additions & 18 deletions llvm/lib/Analysis/LoopAccessAnalysis.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2859,26 +2859,23 @@ static Value *stripGetElementPtr(Value *Ptr, ScalarEvolution *SE, Loop *Lp) {
/// strides "a[i*stride]". Returns the symbolic stride, or null otherwise.
static const SCEV *getStrideFromPointer(Value *Ptr, ScalarEvolution *SE, Loop *Lp) {
auto *PtrTy = dyn_cast<PointerType>(Ptr->getType());
if (!PtrTy || PtrTy->isAggregateType())
if (!PtrTy)
return nullptr;

// Try to remove a gep instruction to make the pointer (actually index at this
// point) easier analyzable. If OrigPtr is equal to Ptr we are analyzing the
// pointer, otherwise, we are analyzing the index.
Value *OrigPtr = Ptr;

// The size of the pointer access.
int64_t PtrAccessSize = 1;

Ptr = stripGetElementPtr(Ptr, SE, Lp);
const SCEV *V = SE->getSCEV(Ptr);

if (Ptr != OrigPtr)
// Strip off casts.
while (const SCEVIntegralCastExpr *C = dyn_cast<SCEVIntegralCastExpr>(V))
while (auto *C = dyn_cast<SCEVIntegralCastExpr>(V))
V = C->getOperand();

const SCEVAddRecExpr *S = dyn_cast<SCEVAddRecExpr>(V);
auto *S = dyn_cast<SCEVAddRecExpr>(V);
if (!S)
return nullptr;

Expand All @@ -2888,25 +2885,19 @@ static const SCEV *getStrideFromPointer(Value *Ptr, ScalarEvolution *SE, Loop *L
return nullptr;

V = S->getStepRecurrence(*SE);
if (!V)
return nullptr;

// Strip off the size of access multiplication if we are still analyzing the
// pointer.
if (OrigPtr == Ptr) {
if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(V)) {
if (M->getOperand(0)->getSCEVType() != scConstant)
if (auto *M = dyn_cast<SCEVMulExpr>(V)) {
auto *StepConst = dyn_cast<SCEVConstant>(M->getOperand(0));
if (!StepConst)
return nullptr;

const APInt &APStepVal = cast<SCEVConstant>(M->getOperand(0))->getAPInt();

// Huge step value - give up.
if (APStepVal.getBitWidth() > 64)
auto StepVal = StepConst->getAPInt().trySExtValue();
if (!StepVal || StepVal != 1)
return nullptr;

int64_t StepVal = APStepVal.getSExtValue();
if (PtrAccessSize != StepVal)
return nullptr;
V = M->getOperand(1);
}
}
Expand All @@ -2920,7 +2911,7 @@ static const SCEV *getStrideFromPointer(Value *Ptr, ScalarEvolution *SE, Loop *L
if (isa<SCEVUnknown>(V))
return V;

if (const auto *C = dyn_cast<SCEVIntegralCastExpr>(V))
if (auto *C = dyn_cast<SCEVIntegralCastExpr>(V))
if (isa<SCEVUnknown>(C->getOperand()))
return V;

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