Prevent visitSIGN_EXTEND from generating ISD::SELECT for vectors

[Relph, Richard]

Per discussion on LLVMDev, implement Nadav's suggested fix to DAGCombiner::visitSIGN_EXTEND() to prevent 'optimization' of SIGN_EXTEND to SELECT if we are sign-extending a vector…

Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp	(revision 176837)
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp	(working copy)
@@ -4496,8 +4496,8 @@
                        NegOne, DAG.getConstant(0, VT),
                        cast<CondCodeSDNode>(N0.getOperand(2))->get(), true);
     if (SCC.getNode()) return SCC;
-    if (!LegalOperations ||
-        TLI.isOperationLegal(ISD::SETCC, TLI.getSetCCResultType(VT)))
+    if (!VT.isVector() && (!LegalOperations ||
+        TLI.isOperationLegal(ISD::SETCC, TLI.getSetCCResultType(VT))))
       return DAG.getNode(ISD::SELECT, N->getDebugLoc(), VT,
                          DAG.getSetCC(N->getDebugLoc(),
                                       TLI.getSetCCResultType(VT),