commit 6bca8ef6670f3a524c30d68eb7962f4a1dd1b099
author Benjamin Kramer <benny.kra@googlemail.com> Sun Apr 27 11:41:06 2014 +0000
committer Benjamin Kramer <benny.kra@googlemail.com> Sun Apr 27 11:41:06 2014 +0000
tree 61c7219c77e513ad05c21e2c890048bf1902b742
parent 66935020c4241bb8cb0478cd6bbaf0a9f90d02f7

SelectionDAG: Aggressively fold shuffles of constant splats.

llvm-svn: 207352

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 3f68d49..46d0fca 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1441,6 +1441,11 @@
   if (Identity && NElts)
     return N1;
 
+  // Shuffling a constant splat doesn't change the result.
+  if (N2Undef && N1.getOpcode() == ISD::BUILD_VECTOR)
+    if (cast<BuildVectorSDNode>(N1)->getConstantSplatValue())
+      return N1;
+
   FoldingSetNodeID ID;
   SDValue Ops[2] = { N1, N2 };
   AddNodeIDNode(ID, ISD::VECTOR_SHUFFLE, getVTList(VT), Ops, 2);