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[SelectionDAG] Use KnownBits::countMinSignBits() to simplify the end of ComputeNumSignBits. 

This matches what is done in ValueTracking.cpp

Reviewed By: RKSimon, foad

Differential Revision: https://reviews.llvm.org/D116423
This commit is contained in:
Craig Topper 2021-12-31 17:29:57 -08:00
parent d00e438cfe
commit 243b7aaf51
1 changed files with 1 additions and 15 deletions
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16
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -4294,21 +4294,7 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, const APInt &DemandedElts,
// Finally, if we can prove that the top bits of the result are 0's or 1's,
// use this information.
KnownBits Known = computeKnownBits(Op, DemandedElts, Depth);
APInt Mask;
if (Known.isNonNegative()) { // sign bit is 0
Mask = Known.Zero;
} else if (Known.isNegative()) { // sign bit is 1;
Mask = Known.One;
} else {
// Nothing known.
return FirstAnswer;
}
// Okay, we know that the sign bit in Mask is set. Use CLO to determine
// the number of identical bits in the top of the input value.
Mask <<= Mask.getBitWidth()-VTBits;
return std::max(FirstAnswer, Mask.countLeadingOnes());
return std::max(FirstAnswer, Known.countMinSignBits());
}
unsigned SelectionDAG::ComputeMinSignedBits(SDValue Op, unsigned Depth) const {