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It looks like the changes to the SRem logic of SimplifyDemandedUseBits 

(fix for PR6165) are needed here too.

llvm-svn: 94801
This commit is contained in:
Duncan Sands 2010-01-29 06:18:37 +00:00
parent 42c876dff2
commit 26cd6bd0b0
1 changed files with 18 additions and 9 deletions
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27
llvm/lib/Analysis/ValueTracking.cpp
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@ -421,20 +421,29 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
}
case Instruction::SRem:
if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
APInt RA = Rem->getValue();
if (RA.isPowerOf2() || (-RA).isPowerOf2()) {
APInt LowBits = RA.isStrictlyPositive() ? (RA - 1) : ~RA;
APInt RA = Rem->getValue().abs();
if (RA.isPowerOf2()) {
APInt LowBits = RA - 1;
APInt Mask2 = LowBits | APInt::getSignBit(BitWidth);
ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
Depth+1);
// If the sign bit of the first operand is zero, the sign bit of
// the result is zero. If the first operand has no one bits below
// the second operand's single 1 bit, its sign will be zero.
if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
KnownZero2 |= ~LowBits;
// The low bits of the first operand are unchanged by the srem.
KnownZero = KnownZero2 & LowBits;
KnownOne = KnownOne2 & LowBits;
KnownZero |= KnownZero2 & Mask;
// If the first operand is non-negative or has all low bits zero, then
// the upper bits are all zero.
if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
KnownZero |= ~LowBits;
// If the first operand is negative and not all low bits are zero, then
// the upper bits are all one.
if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0))
KnownOne |= ~LowBits;
KnownZero &= Mask;
KnownOne &= Mask;
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
}