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Don't do: "(X & 4) >> 1 == 2 --> (X & 4) == 4" if there are more than one uses of the shift result.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50118 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2008-04-23 00:38:06 +00:00
parent a5ddb59a13
commit f30752cbcc
2 changed files with 32 additions and 2 deletions
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5
lib/Transforms/Scalar/InstructionCombining.cpp
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@@ -6065,13 +6065,14 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
// Otherwise, check to see if the bits shifted out are known to be zero.
// If so, we can compare against the unshifted value:
// (X & 4) >> 1 == 2 --> (X & 4) == 4.
if (MaskedValueIsZero(LHSI->getOperand(0),
if (LHSI->hasOneUse() &&
MaskedValueIsZero(LHSI->getOperand(0),
APInt::getLowBitsSet(Comp.getBitWidth(), ShAmtVal))) {
return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0),
ConstantExpr::getShl(RHS, ShAmt));
}
if (LHSI->hasOneUse() || RHSV == 0) {
if (LHSI->hasOneUse()) {
// Otherwise strength reduce the shift into an and.
APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
Constant *Mask = ConstantInt::get(Val);