[SelectionDAG] Don't use simple VT in generic shuffle code

Better to assume that any value type may be commuted, not just MVTs.

No test case right now, but discovered while investigating possible shuffle combines.

llvm-svn: 324179

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -1644,7 +1644,7 @@ SDValue SelectionDAG::getVectorShuffle(EVT VT, const SDLoc &dl, SDValue N1,
 }
 
 SDValue SelectionDAG::getCommutedVectorShuffle(const ShuffleVectorSDNode &SV) {
-  MVT VT = SV.getSimpleValueType(0);
+  EVT VT = SV.getValueType(0);
   SmallVector<int, 8> MaskVec(SV.getMask().begin(), SV.getMask().end());
   ShuffleVectorSDNode::commuteMask(MaskVec);