Hint Resolve isptr_is_pointer_or_null.
Definition add_ptr_int  {cs: compspecs}  (ty: type) (v: val) (i: Z) : val :=
eval_binop Cop.Oadd (tptr ty) tint v (Vint (Int.repr i)).

Lemma add_ptr_int_offset:
forall  {cs: compspecs}  t v n,
repable_signed (sizeof t) ->
repable_signed n ->
add_ptr_int t v n = offset_val (sizeof t * n) v.