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[X86] combineGatherScatter - use FoldConstantArithmetic for truncation of constant build vectors #136033

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Merged
RKSimon merged 2 commits into from
Apr 17, 2025
Merged

[X86] combineGatherScatter - use FoldConstantArithmetic for truncation of constant build vectors #136033

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a05211d
[X86] combineGatherScatter - use FoldConstantArithmetic for truncatio…
RKSimon Apr 16, 2025
541664d
Merge branch 'main' into x86-gather-scatter-index-constant-fold
RKSimon Apr 17, 2025
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11 changes: 4 additions & 7 deletions llvm/lib/Target/X86/X86ISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -56529,16 +56529,13 @@ static SDValue combineGatherScatter(SDNode *N, SelectionDAG &DAG,
if (IndexWidth > 32 && DAG.ComputeNumSignBits(Index) > (IndexWidth - 32)) {
EVT NewVT = IndexVT.changeVectorElementType(MVT::i32);

// FIXME: We could support more than just constant vectors, but we need to
// FIXME: We could support more than just constant fold, but we need to
// careful with costing. A truncate that can be optimized out would be
// fine. Otherwise we might only want to create a truncate if it avoids a
// split.
if (auto *BV = dyn_cast<BuildVectorSDNode>(Index)) {
if (BV->isConstant()) {
Index = DAG.getNode(ISD::TRUNCATE, DL, NewVT, Index);
return rebuildGatherScatter(GorS, Index, Base, Scale, DAG);
}
}
if (SDValue TruncIndex =
DAG.FoldConstantArithmetic(ISD::TRUNCATE, DL, NewVT, Index))
return rebuildGatherScatter(GorS, TruncIndex, Base, Scale, DAG);

// Shrink any sign/zero extends from 32 or smaller to larger than 32 if
// there are sufficient sign bits. Only do this before legalize types to
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