[PATCH] Convert a vselect into a concat_vector if possible

[hfinkel at anl.gov]

================
Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:4634
@@ +4633,3 @@
+         "One half of the selector was all UNDEFs and the other was all the "
+         "same value. This should have been addressed before this function.");
+  return DAG.getNode(
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Are you sure this is always true on all possible code paths? If you are sure, please add a comment explaining where this is handled and why it will always happen first. Otherwise, please just make this a normal check.

http://reviews.llvm.org/D3916