Merge pull request #463 from mshinwell/flambda2-flambda2-name-occurrences-diff

Speed up Name_occurrences.diff

Author: mshinwell

middle_end/flambda/compilenv_deps/patricia_tree.ml

@@ -1139,7 +1139,7 @@ struct
   let transpose_keys_and_data_set _ =
     Misc.fatal_error "transpose_keys_and_data_set not yet implemented"
 
-  let diff_domains _ _ = Misc.fatal_error "diff_domains not yet implemented"
+  let diff_domains = diff
 
   let fold2_stop_on_key_mismatch _ _ _ _ =
     Misc.fatal_error "fold2_stop_on_key_mismatch not yet implemented"

middle_end/flambda/naming/name_occurrences.ml

@@ -363,12 +363,9 @@ end = struct
       if N.Map.is_empty map then Empty
       else Potentially_many map
     | Potentially_many map1, Potentially_many map2 ->
-      let map =
-        N.Map.fold (fun name _ map -> N.Map.remove name map)
-          map2
-          map1
-      in
-      Potentially_many map
+      let map = N.Map.diff_domains map1 map2 in
+      if N.Map.is_empty map then Empty
+      else Potentially_many map
 
   let union t1 t2 =
     match t1, t2 with