From 6bca8ef6670f3a524c30d68eb7962f4a1dd1b099 Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Sun, 27 Apr 2014 11:41:06 +0000
Subject: SelectionDAG: Aggressively fold shuffles of constant splats.

llvm-svn: 207352
---
 llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 5 +++++
 1 file changed, 5 insertions(+)

(limited to 'llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp')

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 3f68d49da68..46d0fcac410 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1441,6 +1441,11 @@ SDValue SelectionDAG::getVectorShuffle(EVT VT, SDLoc dl, SDValue N1,
   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);
-- 
cgit v1.2.3