[SelectionDAG] Improve asserts in SelectionDAG::getSelect.

The VT passed in must match the type of LHS and RHS.
Previously we only checked that the vectorness matched.

llvm/include/llvm/CodeGen/SelectionDAG.h

@@ -1103,10 +1103,8 @@ public:
   /// operands and don't want to check for vector.
   SDValue getSelect(const SDLoc &DL, EVT VT, SDValue Cond, SDValue LHS,
                     SDValue RHS) {
-    assert(LHS.getValueType() == RHS.getValueType() &&
+    assert(LHS.getValueType() == VT && RHS.getValueType() == VT &&
            "Cannot use select on differing types");
-    assert(VT.isVector() == LHS.getValueType().isVector() &&
-           "Cannot mix vectors and scalars");
     auto Opcode = Cond.getValueType().isVector() ? ISD::VSELECT : ISD::SELECT;
     return getNode(Opcode, DL, VT, Cond, LHS, RHS);
   }