From dcb325fd6ef432cd3717264c1547b94c7da2f396 Mon Sep 17 00:00:00 2001
From: Pierre-Marie Pédrot
Date: Mon, 19 Oct 2020 15:44:19 +0200
Subject: Restore the List.Smart.map original implementation.

Commit 56ff0c9 mangled the code claiming to make it tail-rec, but this is not
the case. In addition to make the code convoluted it also over-allocates for
nothing and breaks the write barrier for fun.

We simply rollback to the (slightly cleaned-up) previous code, that was simpler,
likely faster, and as much tail-rec as the one introduced in 56ff0c9.
---
 clib/cList.ml | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/clib/cList.ml b/clib/cList.ml
index 057200f83e..6b13fac48c 100644
--- a/clib/cList.ml
+++ b/clib/cList.ml
@@ -1019,20 +1019,12 @@ let rec factorize_left cmp = function
 module Smart =
 struct
 
-  let rec map_loop f p = function
-    | [] -> ()
-    | x :: l' as l ->
-      let x' = f x in
-      map_loop f p l';
-      if x' == x && !p == l' then p := l else p := x' :: !p
-
-  let map f = function
-    | [] -> []
-    | x :: l' as l ->
-      let p = ref [] in
-      let x' = f x in
-      map_loop f p l';
-      if x' == x && !p == l' then l else x' :: !p
+  let rec map f l = match l with
+  | [] -> l
+  | h :: tl ->
+    let h' = f h in
+    let tl' = map f tl in
+    if h' == h && tl' == tl then l else h' :: tl'
 
 end
 
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