[PATCH] Convert a vselect into a concat_vector if possible

[hfinkel at anl.gov]

================
Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:4637
@@ +4636,3 @@
+      ISD::CONCAT_VECTORS, dl, VT,
+      BottomHalf->isNullValue() ? LHS->getOperand(1) : RHS->getOperand(1),
+      TopHalf->isNullValue() ? LHS->getOperand(0) : RHS->getOperand(0));
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Why does operand 0 derive from operand 1 of the inputs?

http://reviews.llvm.org/D3916