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[RISCV] Fix incorrect folding of select on ctlz/cttz #155231

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Merged
merged 4 commits into from
Sep 3, 2025
+766 −1
Merged

[RISCV] Fix incorrect folding of select on ctlz/cttz #155231

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dc3d14a
Add tests for wrong fold
MitchBriles Aug 25, 2025
7fecf8e
[RISCV] Fix incorrect folding of select on ctlz/cttz
MitchBriles Aug 25, 2025
a2adc64
Remove unnecessary intrinsic declarations
MitchBriles Aug 25, 2025
ad1df8f
Move tests to existing file
MitchBriles Sep 2, 2025
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5 changes: 4 additions & 1 deletion llvm/lib/Target/RISCV/RISCVISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -18746,6 +18746,10 @@ static SDValue foldSelectOfCTTZOrCTLZ(SDNode *N, SelectionDAG &DAG) {
if (Cond->getOperand(0) != CountZeroesArgument)
return SDValue();

unsigned BitWidth = CountZeroes.getValueSizeInBits();
if (!isPowerOf2_32(BitWidth))
return SDValue();

if (CountZeroes.getOpcode() == ISD::CTTZ_ZERO_UNDEF) {
CountZeroes = DAG.getNode(ISD::CTTZ, SDLoc(CountZeroes),
CountZeroes.getValueType(), CountZeroesArgument);
Expand All @@ -18754,7 +18758,6 @@ static SDValue foldSelectOfCTTZOrCTLZ(SDNode *N, SelectionDAG &DAG) {
CountZeroes.getValueType(), CountZeroesArgument);
}

unsigned BitWidth = CountZeroes.getValueSizeInBits();
SDValue BitWidthMinusOne =
DAG.getConstant(BitWidth - 1, SDLoc(N), CountZeroes.getValueType());

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