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[InstCombine][ValueTracking] When computing known bits for Srem make sure we don't compute known bits for the LHS twice.

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If we already called computeKnownBits for the RHS being a constant power of 2, we've already computed everything we can and should just stop. I think previously we would still recurse if we had determined the result was negative or had not determined the sign bit at all.

llvm-svn: 300432
This commit is contained in:
Craig Topper 2017-04-16 21:46:12 +00:00
parent 2ddcbb2d22
commit 8a80f26229
2 changed files with 7 additions and 10 deletions
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13
lib/Analysis/ValueTracking.cpp
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@ -1178,19 +1178,16 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
KnownOne |= ~LowBits;
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
break;
}
}
// The sign bit is the LHS's sign bit, except when the result of the
// remainder is zero.
if (KnownZero.isNonNegative()) {
APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth + 1,
Q);
// If it's known zero, our sign bit is also zero.
if (LHSKnownZero.isNegative())
KnownZero.setSignBit();
}
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
// If it's known zero, our sign bit is also zero.
if (KnownZero2.isNegative())
KnownZero.setSignBit();
break;
case Instruction::URem: {

4
lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
View File

@ -644,13 +644,13 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
KnownOne |= ~LowBits;
assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?");
break;
}
}
// The sign bit is the LHS's sign bit, except when the result of the
// remainder is zero.
if (DemandedMask.isNegative() && KnownZero.isNonNegative()) {
APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
if (DemandedMask.isNegative()) {
computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth + 1,
CxtI);
// If it's known zero, our sign bit is also zero.