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[InstCombine] Use APInt bit counting methods to avoid a temporary APInt. NFC 

llvm-svn: 301516
This commit is contained in:
Craig Topper 2017-04-27 04:51:25 +00:00
parent 42fca6e794
commit 9474e9b6c8
1 changed files with 6 additions and 6 deletions
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12
llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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@ -1384,17 +1384,17 @@ static Instruction *foldCttzCtlz(IntrinsicInst &II, InstCombiner &IC) {
// Create a mask for bits above (ctlz) or below (cttz) the first known one.
bool IsTZ = II.getIntrinsicID() == Intrinsic::cttz;
unsigned NumMaskBits = IsTZ ? Known.One.countTrailingZeros()
: Known.One.countLeadingZeros();
APInt Mask = IsTZ ? APInt::getLowBitsSet(BitWidth, NumMaskBits)
: APInt::getHighBitsSet(BitWidth, NumMaskBits);
unsigned PossibleZeros = IsTZ ? Known.One.countTrailingZeros()
: Known.One.countLeadingZeros();
unsigned DefiniteZeros = IsTZ ? Known.Zero.countTrailingOnes()
: Known.Zero.countLeadingOnes();
// If all bits above (ctlz) or below (cttz) the first known one are known
// zero, this value is constant.
// FIXME: This should be in InstSimplify because we're replacing an
// instruction with a constant.
if (Mask.isSubsetOf(Known.Zero)) {
auto *C = ConstantInt::get(IT, APInt(BitWidth, NumMaskBits));
if (PossibleZeros == DefiniteZeros) {
auto *C = ConstantInt::get(IT, DefiniteZeros);
return IC.replaceInstUsesWith(II, C);
}