[llvm] r327251 - [X86] Don't compute known bits twice for the same SDValue in LowerMUL.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Sun Mar 11 22:35:02 2018
New Revision: 327251

URL: http://llvm.org/viewvc/llvm-project?rev=327251&view=rev
Log:
[X86] Don't compute known bits twice for the same SDValue in LowerMUL.

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.

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=327251&r1=327250&r2=327251&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Sun Mar 11 22:35:02 2018
@@ -22532,13 +22532,17 @@ static SDValue LowerMUL(SDValue Op, cons
   //
   //  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.