[llvm] r294745 - [X86][SSE] Add missing comment describing combing to SHUFPS. NFCI

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Fri Feb 10 07:16:01 2017
New Revision: 294745

URL: http://llvm.org/viewvc/llvm-project?rev=294745&view=rev
Log:
[X86][SSE] Add missing comment describing combing to SHUFPS. NFCI

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=294745&r1=294744&r2=294745&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Fri Feb 10 07:16:01 2017
@@ -26759,6 +26759,8 @@ static bool matchBinaryPermuteVectorShuf
       (MaskVT == MVT::v16f32 && Subtarget.hasAVX512())) {
     SmallVector<int, 4> RepeatedMask;
     if (isRepeatedTargetShuffleMask(128, MaskVT, Mask, RepeatedMask)) {
+      // Match each half of the repeated mask, to determine if its just
+      // referencing one of the vectors, is zeroable or entirely undef.
       auto MatchHalf = [&](unsigned Offset, int &S0, int &S1) {
         int M0 = RepeatedMask[Offset];
         int M1 = RepeatedMask[Offset + 1];