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[TargetLowering] SimplifyDemandedBits ADD/SUB/MUL - correctly inherit SDNodeFlags from the original node. 

Just disable NSW/NUW flags. This matches what we're already doing for the other situations for these nodes, it was just missed for the demanded constant case.

Noticed by inspection - confirmed in offline discussion with @spatel. I've checked we have test coverage in the x86 extract-bits.ll and extract-lowbits.ll tests

llvm-svn: 370497
This commit is contained in:
Simon Pilgrim 2019-08-30 17:58:55 +00:00
parent 466ec2d552
commit 2d1e0899e9
1 changed files with 2 additions and 4 deletions
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6
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -1953,10 +1953,8 @@ bool TargetLowering::SimplifyDemandedBits(
if (C && !C->isAllOnesValue() && !C->isOne() &&
(C->getAPIntValue() | HighMask).isAllOnesValue()) {
SDValue Neg1 = TLO.DAG.getAllOnesConstant(dl, VT);
// We can't guarantee that the new math op doesn't wrap, so explicitly
// clear those flags to prevent folding with a potential existing node
// that has those flags set.
SDNodeFlags Flags;
// Disable the nsw and nuw flags. We can no longer guarantee that we
// won't wrap after simplification.
Flags.setNoSignedWrap(false);
Flags.setNoUnsignedWrap(false);
SDValue NewOp = TLO.DAG.getNode(Op.getOpcode(), dl, VT, Op0, Neg1, Flags);