10BC0 [DAGCombiner] Fold subtraction if above threshold to `umin` by pfusik · Pull Request #134235 · llvm/llvm-project · GitHub
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[DAGCombiner] Fold subtraction if above threshold to umin #134235

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Merged
pfusik merged 5 commits into from
Apr 10, 2025
Merged

[DAGCombiner] Fold subtraction if above threshold to umin #134235

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d67978a
[RISCV] Fold subtraction if above threshold to Zbb `minu`
pfusik Apr 3, 2025
75b5292
[RISCV] Prevent transform on >XLEN types
pfusik Apr 3, 2025
130bbb6
[DAGCombiner] Move the transform from RISCVISelLowering
pfusik Apr 7, 2025
d797364
[RISCV][test] Add `uge` test for subtraction if above threshold
pfusik Apr 10, 2025
0a1c55b
[RISCV] Handle a variant with inverse comparison
pfusik Apr 10, 2025
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[DAGCombiner] Move the transform from RISCVISelLowering
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@pfusik
pfusik committed Apr 9, 2025
commit 130bbb6b57939086280fb0279e9419c18028e640
13 changes: 13 additions & 0 deletions llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4251,6 +4251,19 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
sd_match(N1, m_UMaxLike(m_Specific(A), m_Specific(B))))
return DAG.getNegative(DAG.getNode(ISD::ABDU, DL, VT, A, B), DL, VT);

// (sub x, (select (ult x, y), 0, y)) -> (umin x, (sub x, y))
auto LK = TLI.getTypeConversion(*DAG.getContext(), VT);
if ((LK.first == TargetLoweringBase::TypeLegal ||
LK.first == TargetLoweringBase::TypePromoteInteger) &&
TLI.isOperationLegal(ISD::UMIN, LK.second)) {
SDValue Y;
if (sd_match(N1, m_OneUse(m_Select(m_SetCC(m_Specific(N0), m_Value(Y),
m_SpecificCondCode(ISD::SETULT)),
m_Zero(), m_Deferred(Y)))))
return DAG.getNode(ISD::UMIN, DL, VT, N0,
DAG.getNode(ISD::SUB, DL, VT, N0, Y));
}

return SDValue();
}

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17 changes: 0 additions & 17 deletions llvm/lib/Target/RISCV/RISCVISelLowering.cpp
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Expand Up @@ -14917,23 +14917,6 @@ static SDValue performSUBCombine(SDNode *N, SelectionDAG &DAG,
if (SDValue V = combineSubShiftToOrcB(N, DAG, Subtarget))
return V;

const TargetLowering &TLI = DAG.getTargetLoweringInfo();
auto LK = TLI.getTypeConversion(*DAG.getContext(), VT);
if ((LK.first == TargetLoweringBase::TypeLegal ||
LK.first == TargetLoweringBase::TypePromoteInteger) &&
TLI.isOperationLegal(ISD::UMIN, LK.second)) {
// fold (sub x, (select (ult x, y), 0, y)) -> (umin x, (sub x, y))
using namespace llvm::SDPatternMatch;
SDValue Y;
if (sd_match(N1, m_OneUse(m_Select(m_SetCC(m_Specific(N0), m_Value(Y),
m_SpecificCondCode(ISD::SETULT)),
m_Zero(), m_Deferred(Y))))) {
SDLoc DL(N);
return DAG.getNode(ISD::UMIN, DL, VT, N0,
DAG.getNode(ISD::SUB, DL, VT, N0, Y));
}
}

// fold (sub x, (select lhs, rhs, cc, 0, y)) ->
// (select lhs, rhs, cc, x, (sub x, y))
return combineSelectAndUse(N, N1, N0, DAG, /*AllOnes*/ false, Subtarget);
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