Hint Rewrite sem_cast_neutral_int using
  (auto;
   match goal with H: is_int ?i ?s ?v |- isVint ?v => apply (is_int_is_Vint i s v H) end) : norm.

Lemma eval_expr_unop: forall {cs: compspecs} op a1 t, eval_expr (Eunop op a1 t) = lift1 (eval_unop op (typeof a1)) (eval_expr a1).