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[SCEV] Commute sign extends through nsw multiplication #163840

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[SCEV] Commute sign extends through nsw multiplication #163840

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14 changes: 14 additions & 0 deletions llvm/lib/Analysis/ScalarEvolution.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1988,6 +1988,20 @@ const SCEV *ScalarEvolution::getSignExtendExprImpl(const SCEV *Op, Type *Ty,
}
}
}

if (auto *SA = dyn_cast<SCEVMulExpr>(Op)) {
// sext((A * B * ...)<nsw>) --> (sext(A) * sext(B) * ...)<nsw>
if (SA->hasNoSignedWrap()) {
// If the multiplication does not sign overflow then we can, by
// definition, commute the sign extension with the multiplication
// operation.
SmallVector<const SCEV *, 4> Ops;
for (const auto *Op : SA->operands())
Ops.push_back(getSignExtendExpr(Op, Ty, Depth + 1));
return getMulExpr(Ops, SCEV::FlagNSW, Depth + 1);
}
}

// If the input value is a chrec scev, and we can prove that the value
// did not overflow the old, smaller, value, we can sign extend all of the
// operands (often constants). This allows analysis of something like
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