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[SelectionDAGBuilder] Propagate fast-math flags to fpext #167574

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Merged
merged 3 commits into from
Nov 15, 2025
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[SelectionDAGBuilder] Propagate fast-math flags to fpext #167574

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2cc7c09
Propagate fast-math flags through fpext
mikolaj-pirog Nov 11, 2025
bf228bb
Check for arcp on fpext on fdiv combine
mikolaj-pirog Nov 13, 2025
31250ab
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mikolaj-pirog Nov 13, 2025
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4 changes: 3 additions & 1 deletion llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -18673,11 +18673,13 @@ SDValue DAGCombiner::visitFDIV(SDNode *N) {
if (Flags.hasAllowReciprocal()) {
// If this FDIV is part of a reciprocal square root, it may be folded
// into a target-specific square root estimate instruction.
bool N1AllowReciprocal = N1->getFlags().hasAllowReciprocal();
if (N1.getOpcode() == ISD::FSQRT) {
if (SDValue RV = buildRsqrtEstimate(N1.getOperand(0)))
return DAG.getNode(ISD::FMUL, DL, VT, N0, RV);
} else if (N1.getOpcode() == ISD::FP_EXTEND &&
N1.getOperand(0).getOpcode() == ISD::FSQRT) {
N1.getOperand(0).getOpcode() == ISD::FSQRT &&
N1AllowReciprocal) {
if (SDValue RV = buildRsqrtEstimate(N1.getOperand(0).getOperand(0))) {
RV = DAG.getNode(ISD::FP_EXTEND, SDLoc(N1), VT, RV);
AddToWorklist(RV.getNode());
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5 changes: 4 additions & 1 deletion llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
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Expand Up @@ -3976,7 +3976,10 @@ void SelectionDAGBuilder::visitFPExt(const User &I) {
SDValue N = getValue(I.getOperand(0));
EVT DestVT = DAG.getTargetLoweringInfo().getValueType(DAG.getDataLayout(),
I.getType());
setValue(&I, DAG.getNode(ISD::FP_EXTEND, getCurSDLoc(), DestVT, N));
SDNodeFlags Flags;
if (auto *TruncInst = dyn_cast<FPMathOperator>(&I))
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@bjope bjope Nov 16, 2025

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TruncInst is confusing here (I guess it has been copied from somewhere). You could perhaps all it Operator or FPExtInst or something, but it seems like FPOp is a common variable name when dyn_cast-ing to a FPMathOperator. So I would suggest FPOp.

Flags.copyFMF(*TruncInst);
setValue(&I, DAG.getNode(ISD::FP_EXTEND, getCurSDLoc(), DestVT, N, Flags));
}

void SelectionDAGBuilder::visitFPToUI(const User &I) {
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2 changes: 1 addition & 1 deletion llvm/test/CodeGen/PowerPC/recipest.ll
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Expand Up @@ -164,7 +164,7 @@ define double @foof_fmf(double %a, float %b) nounwind {
; CHECK-P9-NEXT: xsmuldp f1, f1, f0
; CHECK-P9-NEXT: blr
%x = call contract reassoc arcp float @llvm.sqrt.f32(float %b)
%y = fpext float %x to double
%y = fpext arcp float %x to double
%r = fdiv contract reassoc arcp double %a, %y
ret double %r
}
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