flambda-backend: Review changes of term directory (#602)

Author: chambart

utils/misc.ml

@@ -148,6 +148,14 @@ module Stdlib = struct
       in
       aux n [] l
 
+    let rec map_sharing f l0 =
+      match l0 with
+      | a :: l ->
+        let a' = f a in
+        let l' = map_sharing f l in
+        if a' == a && l' == l then l0 else a' :: l'
+      | [] -> []
+
     let rec is_prefix ~equal t ~of_ =
       match t, of_ with
       | [], [] -> true

utils/misc.mli

@@ -116,6 +116,10 @@ module Stdlib : sig
         the [n] first elements of [l] and [after] the remaining ones.
         If [l] has less than [n] elements, raises Invalid_argument. *)
 
+    val map_sharing : ('a -> 'a) -> 'a t -> 'a t
+    (** [map_sharing f l] is [map f l]. If for all elements of the list
+        [f e == e] then [map_sharing f l == l] *)
+
     val is_prefix
        : equal:('a -> 'a -> bool)
       -> 'a list