#5809: remove hash-consing of environments, replaced by a much cheaper one-slot memoization.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13078 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

typing/cmt_format.ml

@@ -62,30 +62,11 @@ type cmt_infos = {
 type error =
     Not_a_typedtree of string
 
-
-
-
-
-(*
-  Keeping all the environments in the typedtree can result in
-  huge typedtrees.
-*)
-
-
 let need_to_clear_env =
   try ignore (Sys.getenv "OCAML_BINANNOT_WITHENV"); false
   with Not_found -> true
 
-(* Re-introduce sharing after clearing environments *)
-let env_hcons = Hashtbl.create 133
-let keep_only_summary env =
-  let new_env = Env.keep_only_summary env in
-  try
-    Hashtbl.find env_hcons new_env
-  with Not_found ->
-    Hashtbl.add env_hcons new_env new_env;
-    new_env
-let clear_env_hcons () = Hashtbl.clear env_hcons
+let keep_only_summary = Env.keep_only_summary
 
 module ClearEnv  = TypedtreeMap.MakeMap (struct
   open TypedtreeMap
@@ -242,7 +223,6 @@ let save_cmt filename modname binary_annots sourcefile initial_env sg =
       cmt_interface_digest = this_crc;
       cmt_use_summaries = need_to_clear_env;
     } in
-    clear_env_hcons ();
     output_cmt oc cmt;
     close_out oc;
     set_saved_types [];

typing/env.ml

@@ -1313,12 +1313,25 @@ let initial = Predef.build_initial_env add_type add_exception empty
 
 let summary env = env.summary
 
+let last_env = ref empty
+let last_reduced_env = ref empty
+
 let keep_only_summary env =
-  { empty with
-    summary = env.summary;
-    local_constraints = env.local_constraints;
-    in_signature = env.in_signature;
-  }
+  if !last_env == env then !last_reduced_env
+  else begin
+    let new_env =
+      {
+       empty with
+       summary = env.summary;
+       local_constraints = env.local_constraints;
+       in_signature = env.in_signature;
+      }
+    in
+    last_env := env;
+    last_reduced_env := new_env;
+    new_env
+  end
+
 
 let env_of_only_summary env_from_summary env =
   let new_env = env_from_summary env.summary Subst.identity in