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[DAG] visitTRUNCATE - test abd legality early to avoid unnecessary computeKnownBits/ComputeNumSignBits calls. NFC. #154085

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Merged
RKSimon merged 1 commit into from
Aug 18, 2025
Merged

[DAG] visitTRUNCATE - test abd legality early to avoid unnecessary computeKnownBits/ComputeNumSignBits calls. NFC. #154085

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7 changes: 4 additions & 3 deletions llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16329,8 +16329,9 @@ SDValue DAGCombiner::visitTRUNCATE(SDNode *N) {
break;
case ISD::ABDU:
case ISD::ABDS:
// (trunc (abdu/abds a, b)) → (abdu/abds (trunc a), (trunc b))
if (!LegalOperations || N0.hasOneUse()) {
// (trunc (abdu/abds a, b)) -> (abdu/abds (trunc a), (trunc b))
if ((!LegalOperations || N0.hasOneUse()) &&
TLI.isOperationLegal(N0.getOpcode(), VT)) {
EVT SrcVT = N0.getValueType();
EVT TruncVT = VT;
unsigned SrcBits = SrcVT.getScalarSizeInBits();
Expand All @@ -16352,7 +16353,7 @@ SDValue DAGCombiner::visitTRUNCATE(SDNode *N) {
CanFold = SignBitsA > NeededBits && SignBitsB > NeededBits;
}

if (CanFold && TLI.isOperationLegal(N0.getOpcode(), VT)) {
if (CanFold) {
SDValue NewA = DAG.getNode(ISD::TRUNCATE, DL, TruncVT, A);
SDValue NewB = DAG.getNode(ISD::TRUNCATE, DL, TruncVT, B);
return DAG.getNode(N0.getOpcode(), DL, TruncVT, NewA, NewB);
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