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Fix a mistake in the computation of leading zeros for udiv.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50591 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2008-05-02 21:30:02 +00:00
parent 48e8c80e17
commit 1d9cd50677
4 changed files with 49 additions and 6 deletions
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8
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -780,7 +780,7 @@ void InstCombiner::ComputeMaskedBits(Value *V, const APInt &Mask,
case Instruction::UDiv: {
// For the purposes of computing leading zeros we can conservatively
// treat a udiv as a logical right shift by the power of 2 known to
// be greater than the denominator.
// be less than the denominator.
APInt AllOnes = APInt::getAllOnesValue(BitWidth);
ComputeMaskedBits(I->getOperand(0),
AllOnes, KnownZero2, KnownOne2, Depth+1);
@ -790,8 +790,10 @@ void InstCombiner::ComputeMaskedBits(Value *V, const APInt &Mask,
KnownZero2.clear();
ComputeMaskedBits(I->getOperand(1),
AllOnes, KnownZero2, KnownOne2, Depth+1);
LeadZ = std::min(BitWidth,
LeadZ + BitWidth - KnownOne2.countLeadingZeros());
unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
if (RHSUnknownLeadingOnes != BitWidth)
LeadZ = std::min(BitWidth,
LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask;
return;