Instance CompSpecs : compspecs. make_compspecs prog. Defined.
Definition Vprog : varspecs. mk_varspecs prog. Defined.
Local Open Scope Z.
Local Open Scope logic.
Definition myspec :=
WITH i: Z
PRE [ _i OF tint ]
PROP (Int.min_signed <= i < Int.max_signed)
LOCAL (temp _i (Vint (Int.repr i)))
SEP ()
POST [ tint ]
PROP() LOCAL (temp ret_temp (Vint (Int.repr (i+1))))
SEP().
Definition myfunc_spec := DECLARE _myfunc myspec.
Definition main_spec :=
DECLARE _main
WITH gv : globals
PRE  [] main_pre prog tt nil gv
POST [ tint ] main_post prog nil gv.
Definition Gprog : funspecs :=   ltac:(with_library prog [
myfunc_spec; main_spec]).

Lemma body_myfunc: semax_body Vprog Gprog f_myfunc myfunc_spec.