Use String.sub alternatives found by semgrep

src/cdomain/value/cdomains/addressDomain.ml

@@ -277,7 +277,7 @@ struct
     let compute_substring s1 s2 =
       try
         let i = Str.search_forward (Str.regexp_string s2) s1 0 in
-        Some (String.sub s1 i (String.length s1 - i))
+        Some (Str.string_after s1 i)
       with Not_found -> None in
 
     (* if any of the input address sets contains an element that isn't a StrPtr, return top *)

src/cdomain/value/cdomains/stringDomain.ml

@@ -62,7 +62,7 @@ let to_n_c_string n x =
     else if n < 0 then
       None
     else
-      Some (String.sub x 0 n)
+      Some (Str.first_chars x n)
   | None -> None
 
 let to_string_length x =

src/cdomains/apron/affineEqualityDomain.apron.ml

@@ -282,7 +282,7 @@ struct
       let res = (String.concat "" @@ Array.to_list @@ Array.map dim_to_str vars)
                 ^ (const_to_str arr.(Array.length arr - 1)) ^ "=0" in
       if String.starts_with res "+" then
-        String.sub res 1 (String.length res - 1)
+        Str.string_after res 1
       else
         res
     in

src/config/gobConfig.ml

@@ -140,7 +140,7 @@ struct
     let rec split' i =
       if i<l then begin
         if xs.[i]=c1 || xs.[i]=c2 then
-          (String.sub xs 0 i, String.sub xs i (l-i))
+          (Str.first_chars xs i, Str.string_after xs i)
         else
           split' (i+1)
       end else