let data_in_visible ff data_in = match data_in with
| None -> true
| Some data_in ->
(* it is too difficult to know if the callers of this slice
* compute [data_in] or not, but let's see if, by chance,
* some data have been selected manually... *)
let m = Fct_slice.get_input_loc_under_mark ff data_in in
let v = visible_mark m in
SlicingParameters.debug ~level:2
"[SlicingTransform.Visibility.data_in_visible] data %a is %svisible"
Locations.Zone.pretty data_in (if v then "" else "in");
v