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Teach instcombine propagate zeroness through shl instructions, implementing

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and.ll:test31

llvm-svn: 21717
This commit is contained in:
Chris Lattner 2005-05-06 04:53:20 +00:00
parent d3797164f9
commit 2b4c801d10
1 changed files with 4 additions and 8 deletions
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12
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -1361,14 +1361,10 @@ static bool MaskedValueIsZero(Value *V, ConstantIntegral *Mask) {
break;
}
case Instruction::Shl:
// (shl X, C1) & C2 == 0 iff (-1 << C1) & C2 == 0
if (ConstantUInt *SA = dyn_cast<ConstantUInt>(I->getOperand(1))) {
Constant *C1 = ConstantIntegral::getAllOnesValue(I->getType());
C1 = ConstantExpr::getShl(C1, SA);
C1 = ConstantExpr::getAnd(C1, Mask);
if (C1->isNullValue())
return true;
}
// (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
if (ConstantUInt *SA = dyn_cast<ConstantUInt>(I->getOperand(1)))
return MaskedValueIsZero(I->getOperand(0),
cast<ConstantIntegral>(ConstantExpr::getUShr(Mask, SA)));
break;
case Instruction::Shr:
// (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0