Fix issue with vector bitcast.

Ensure that types are evenly divisible so the vector is appropriately
sized.

All QC tests seem to be passing again.

src/coq/QC/GenAST.v

@@ -2675,7 +2675,8 @@ Section InstrGenerators.
               let trivial_typs := [(* (1%N, TYPE_I 1); *) (8%N, TYPE_I 8); (32%N, TYPE_I 32); (32%N, TYPE_Float); (64%N, TYPE_I 64) (* ; (64%N, TYPE_Double) *)] in
               let size_of_vec := get_bit_size_from_typ t_from in
               let choices := fold_left (fun acc '(s,t) => let sz' := (size_of_vec / s)%N in
-                                                          if (sz' =? 0)%N then acc else ((TYPE_Vector sz' t) :: acc)%list) trivial_typs [] in
+                                                       let rem := (size_of_vec mod s)%N in
+                                                       if ((sz' =? 0) || negb (rem =? 0))%N then acc else ((TYPE_Vector sz' t) :: acc)%list) trivial_typs [] in
               ret (t_from :: choices) (* I think adding t_from here slightly biases the generator sometimes *)
           end
       | TYPE_Pointer subtyp =>