[PowerPC] Cannonicalize applicable vector shift immediates as swaps

This patch corresponds to review:
http://reviews.llvm.org/D21358

Vector shifts that have the same semantics as a vector swap are cannonicalized
as such to provide additional opportunities for swap removal optimization to
remove unnecessary swaps.

llvm-svn: 275168
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index 4e51141..8a48320 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -311,6 +311,10 @@
       /// of outputs.
       XXSWAPD,
 
+      /// An SDNode for swaps that are not associated with any loads/stores
+      /// and thereby have no chain.
+      SWAP_NO_CHAIN,
+
       /// QVFPERM = This corresponds to the QPX qvfperm instruction.
       QVFPERM,