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Teach ValueTracking to look at the dividend when determining the sign bit of an 

srem instruction.

llvm-svn: 126637
This commit is contained in:
Nick Lewycky 2011-02-28 06:52:12 +00:00
parent 75a800d3bf
commit 29dbbd12c1
1 changed files with 12 additions and 0 deletions
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12
llvm/lib/Analysis/ValueTracking.cpp
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@ -460,6 +460,18 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
} }
} }
if (Mask.isNegative()) { // We're looking for the sign bit.
APInt Mask2 = APInt::getSignBit(BitWidth);
KnownZero2 = 0;
KnownOne2 = 0;
ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
Depth+1);
if (KnownOne2[BitWidth-1])
KnownOne |= Mask2;
if (KnownZero2[BitWidth-1])
KnownZero |= Mask2;
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
}
break; break;
case Instruction::URem: { case Instruction::URem: {
if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) { if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {