Existing Instance NullExtension.Espec.
Instance CompSpecs : compspecs. make_compspecs prog. Defined.
Definition Vprog : varspecs. mk_varspecs prog. Defined.
Definition twice_spec :=
DECLARE _twice
WITH n : Z
PRE [ _n OF tint ]
PROP  (Int.min_signed <= n+n <= Int.max_signed)
LOCAL (temp _n (Vint (Int.repr n)))
SEP ()
POST [ tint ]
PROP ()
LOCAL (temp ret_temp (Vint (Int.repr (n+n))))
SEP ().
Definition f_spec :=
DECLARE _f
WITH x : Z
PRE [ _x OF tuint ]
PROP  (0 <= x <= Int.max_unsigned)
LOCAL (temp _x (Vint (Int.repr x)))
SEP ()
POST [ tint ]
PROP ()
LOCAL (temp ret_temp (Vint (Int.repr 1)))
SEP ().
Definition Gprog : funspecs :=   ltac:(with_library prog [twice_spec]).

Lemma body_twice: semax_body Vprog Gprog f_twice twice_spec.