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[InstCombine] Use a more targeted fix instead of r235544

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Only clear out the NSW/NUW flags if we are optimizing 'add'/'sub' while
taking advantage that the sign bit is not set.  We do this optimization
to further shrink the mask but shrinking the mask isn't NSW/NUW
preserving in this case.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235558 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2015-04-22 22:42:05 +00:00
parent d9b72fea11
commit f9c92b069a
2 changed files with 20 additions and 9 deletions
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17
lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
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@ -88,13 +88,6 @@ bool InstCombiner::SimplifyDemandedBits(Use &U, APInt DemandedMask,
KnownOne, Depth, UserI);
if (!NewVal) return false;
U = NewVal;
// Shrinking a constant might cause a nsw/nuw violation to occur in
// instructions which are themselves demanded.
if (auto *UserOBO = dyn_cast<OverflowingBinaryOperator>(UserI)) {
cast<BinaryOperator>(UserOBO)->setHasNoSignedWrap(false);
cast<BinaryOperator>(UserOBO)->setHasNoUnsignedWrap(false);
}
return true;
}
@ -607,8 +600,11 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
if (SimplifyDemandedBits(I->getOperandUse(0), DemandedFromOps,
LHSKnownZero, LHSKnownOne, Depth + 1) ||
SimplifyDemandedBits(I->getOperandUse(1), DemandedFromOps,
LHSKnownZero, LHSKnownOne, Depth + 1))
LHSKnownZero, LHSKnownOne, Depth + 1)) {
cast<BinaryOperator>(I)->setHasNoSignedWrap(false);
cast<BinaryOperator>(I)->setHasNoUnsignedWrap(false);
return I;
}
}
}
break;
@ -624,8 +620,11 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
if (SimplifyDemandedBits(I->getOperandUse(0), DemandedFromOps,
LHSKnownZero, LHSKnownOne, Depth + 1) ||
SimplifyDemandedBits(I->getOperandUse(1), DemandedFromOps,
LHSKnownZero, LHSKnownOne, Depth + 1))
LHSKnownZero, LHSKnownOne, Depth + 1)) {
cast<BinaryOperator>(I)->setHasNoSignedWrap(false);
cast<BinaryOperator>(I)->setHasNoUnsignedWrap(false);
return I;
}
}
// Otherwise just hand the sub off to computeKnownBits to fill in