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[LLVM][SCEV] Look through common multiplicand when simplifying compares. #141798

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[LLVM][SCEV] Look through common multiplicand when simplifying compares. #141798

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47a151e
Add dedicated SCEV tests.
paulwalker-arm May 30, 2025
cfcd9df
[LLVM][SCEV] Look through common multiplicand when simplifying compares.
paulwalker-arm May 15, 2025
c1a0135
Extend to cover signed comparisons.
paulwalker-arm May 30, 2025
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26 changes: 26 additions & 0 deletions llvm/lib/Analysis/ScalarEvolution.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -10748,6 +10748,32 @@ bool ScalarEvolution::SimplifyICmpOperands(CmpPredicate &Pred, const SCEV *&LHS,
if (Depth >= 3)
return false;

if (isa<SCEVMulExpr>(LHS) && isa<SCEVMulExpr>(RHS)) {
const SCEVMulExpr *LMul = cast<SCEVMulExpr>(LHS);
const SCEVMulExpr *RMul = cast<SCEVMulExpr>(RHS);

if (LMul->getNumOperands() == 2 && RMul->getNumOperands() == 2 &&
LMul->getOperand(1) == RMul->getOperand(1)) {
// (X * Z) uicmp (Y * Z) ==> X uicmp Y
// when neither multiply wraps and Z is non-zero.
if (ICmpInst::isUnsigned(Pred) && isKnownNonZero(LMul->getOperand(1)) &&
LMul->hasNoUnsignedWrap() && RMul->hasNoUnsignedWrap()) {
LHS = LMul->getOperand(0);
RHS = RMul->getOperand(0);
Changed = true;
}
// (X * Z) sicmp (Y * Z) ==> X sicmp Y
// when neither multiply wraps and Z is positive.
else if (ICmpInst::isSigned(Pred) &&
isKnownPositive(LMul->getOperand(1)) &&
LMul->hasNoSignedWrap() && RMul->hasNoSignedWrap()) {
LHS = LMul->getOperand(0);
RHS = RMul->getOperand(0);
Changed = true;
}
}
}

// Canonicalize a constant to the right side.
if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS)) {
// Check for both operands constant.
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