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[X86] Don't compute known bits twice for the same SDValue in LowerMUL.

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We called MaskedValueIsZero with two different masks, but underneath that calls computeKnownBits before applying the mask. This means we compute the same known bits twice due to the two calls. Instead just call computeKnownBits directly and apply the two masks ourselves.

llvm-svn: 327251
This commit is contained in:
Craig Topper 2018-03-12 05:35:02 +00:00
parent b9becfb692
commit 94bcc98a97
1 changed files with 8 additions and 4 deletions
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12
lib/Target/X86/X86ISelLowering.cpp
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@ -22532,13 +22532,17 @@ static SDValue LowerMUL(SDValue Op, const X86Subtarget &Subtarget,
//
// Hi = psllqi(AloBhi + AhiBlo, 32);
// return AloBlo + Hi;
KnownBits AKnown, BKnown;
DAG.computeKnownBits(A, AKnown);
DAG.computeKnownBits(B, BKnown);
APInt LowerBitsMask = APInt::getLowBitsSet(64, 32);
bool ALoIsZero = DAG.MaskedValueIsZero(A, LowerBitsMask);
bool BLoIsZero = DAG.MaskedValueIsZero(B, LowerBitsMask);
bool ALoIsZero = LowerBitsMask.isSubsetOf(AKnown.Zero);
bool BLoIsZero = LowerBitsMask.isSubsetOf(BKnown.Zero);
APInt UpperBitsMask = APInt::getHighBitsSet(64, 32);
bool AHiIsZero = DAG.MaskedValueIsZero(A, UpperBitsMask);
bool BHiIsZero = DAG.MaskedValueIsZero(B, UpperBitsMask);
bool AHiIsZero = UpperBitsMask.isSubsetOf(AKnown.Zero);
bool BHiIsZero = UpperBitsMask.isSubsetOf(BKnown.Zero);
// If DQI is supported we can use MULLQ, but MULUDQ is still better if the
// the high bits are known to be zero.