let rec stars_exp = function
| Lval (Var x,off ) -> Some(x,Cil.typeOfLval (Var x,off),0)
| Lval (Mem e, _) ->
(match stars_exp (Cil.stripInfo e).enode with
| None -> None
| Some (x,ty,n) -> Some (x, ty ,n+1))
| _ -> None