Optimize mask generation for one of the DAG combiner shufflevector cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187961 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index cb8894105b15087f4b03527ba32dc2297515e1e6..0d71761fd0f6fe0d61e4bca8aebb1fcfc5be9043 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9358,10 +9358,10 @@ SDValue DAGCombiner::visitVECTOR_SHUFFLE(SDNode *N) {
     for (unsigned i = 0; i != NumElts; ++i) {
       int Idx = SVN->getMaskElt(i);
       if (Idx >= 0) {
-        if (Idx < (int)NumElts)
-          Idx += NumElts;
-        else
+        if (Idx >= (int)NumElts)
           Idx -= NumElts;
+        else
+          Idx = -1; // remove reference to lhs
       }
       NewMask.push_back(Idx);
     }