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[SelectionDAG] add ISD::BITCAST handling for isGuaranteedNotToBeUndefOrPoison #161745

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[SelectionDAG] add ISD::BITCAST handling for isGuaranteedNotToBeUndefOrPoison #161745

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[SelectionDAG] add ISD::BITCAST handling for isGuaranteedNotToBeUndef…
yichi170 Oct 2, 2025
2b946f2
fix for scalable vector
yichi170 Oct 3, 2025
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25 changes: 25 additions & 0 deletions llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5636,6 +5636,31 @@ bool SelectionDAG::isGuaranteedNotToBeUndefOrPoison(SDValue Op,
});
}

case ISD::BITCAST: {
SDValue Src = Op.getOperand(0);
EVT SrcVT = Src.getValueType();
EVT TgtVT = Op.getValueType();

// Case 1: Scalar -> Vector, or Scalar -> Scalar
if (!SrcVT.isVector()) {
APInt DemandedSrcElts(1, 1);
return isGuaranteedNotToBeUndefOrPoison(Src, DemandedSrcElts, PoisonOnly,
Depth + 1);
}

// Case 2: Vector -> Scalar, or Scalable Vector -> Scalable Vector
if ((SrcVT.isVector() && !TgtVT.isVector()) ||
(SrcVT.isScalableVT() && TgtVT.isScalableVT()))
return isGuaranteedNotToBeUndefOrPoison(Src, PoisonOnly, Depth + 1);

// Case 3: Vector -> Vector
unsigned NumSrcElts = SrcVT.getVectorNumElements();
APInt ScaledDemandedElts = APIntOps::ScaleBitMask(DemandedElts, NumSrcElts);

return isGuaranteedNotToBeUndefOrPoison(Src, ScaledDemandedElts, PoisonOnly,
Depth + 1);
}

// TODO: Search for noundef attributes from library functions.

// TODO: Pointers dereferenced by ISD::LOAD/STORE ops are noundef.
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