Additional fixes for bug 15155.

This handles the cases where the 6-bit splat element is odd, converting
to a three-instruction sequence to add or subtract two splats.  With this
fix, the XFAIL in test/CodeGen/PowerPC/vec_constants.ll is removed.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175663 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/PPCISelLowering.h b/lib/Target/PowerPC/PPCISelLowering.h
index 7cc2d1a..1fa88f3 100644
--- a/lib/Target/PowerPC/PPCISelLowering.h
+++ b/lib/Target/PowerPC/PPCISelLowering.h
@@ -238,8 +238,9 @@
       ADDI_DTPREL_L,
 
       /// VRRC = VADD_SPLAT Elt, EltSize - Temporary node to be expanded
-      /// into an ADD of a VSPLTI with itself during instruction selection.
-      /// Necessary to avoid losing this optimization due to constant folds.
+      /// during instruction selection to optimize a BUILD_VECTOR into
+      /// operations on splats.  This is necessary to avoid losing these
+      /// optimizations due to constant folding.
       VADD_SPLAT,
 
       /// STD_32 - This is the STD instruction for use with "32-bit" registers.