[llvm] r298910 - [X86][SSE] Set second operand to undef instead of first operand in unary shuffle combines.

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Tue Mar 28 07:16:42 2017
New Revision: 298910

URL: http://llvm.org/viewvc/llvm-project?rev=298910&view=rev
Log:
[X86][SSE] Set second operand to undef instead of first operand in unary shuffle combines.

Copy isn't necessary after the matchVectorShuffleWithUNPCK refactor and undef value will make some future undef/zero handling easier.

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=298910&r1=298909&r2=298910&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Tue Mar 28 07:16:42 2017
@@ -27269,7 +27269,8 @@ static bool combineX86ShuffleChain(Array
   // here, we're not going to remove the operands we find.
   bool UnaryShuffle = (Inputs.size() == 1);
   SDValue V1 = peekThroughBitcasts(Inputs[0]);
-  SDValue V2 = (UnaryShuffle ? V1 : peekThroughBitcasts(Inputs[1]));
+  SDValue V2 = (UnaryShuffle ? DAG.getUNDEF(V1.getValueType())
+                             : peekThroughBitcasts(Inputs[1]));
 
   MVT VT1 = V1.getSimpleValueType();
   MVT VT2 = V2.getSimpleValueType();