Add a simplification pass in the pretty-printer, to prevent generating

exponentially large types in some cases. This simplifies types of the form:
T & 'a | T \ 'a into T.

types/types.ml

@@ -1936,6 +1936,26 @@ module Print = struct
           ) h; h'
         with Not_found -> h
       in
+      let tt, rm_keys =
+        (* Simplify types of the form 'a & T | T \'a *)
+        VarTable.fold (fun (v1, v2) tt1 ((acc_empty, acc_keys) as acc) ->
+            match Var.Set.length v1, Var.Set.length v2 with
+              0, 1 | 1, 0 ->
+                let k2 = (v2, v1) in
+                begin try
+                        let tt2 = VarTable.find h k2 in
+                        if equiv tt2 tt1 then
+                          (cup acc_empty tt1, k2::acc_keys)
+                        else acc
+                  with Not_found -> acc
+                end
+            | _ -> acc
+
+        ) h ((try VarTable.find h Key.empty with Not_found -> empty), [])
+      in
+      if non_empty tt then VarTable.replace h Key.empty tt;
+      List.iter (fun (v1, v2) -> VarTable.remove h (v1, v2);
+                               VarTable.remove h (v2, v1)) rm_keys;
       let found_any, all_descrs =
         try
           let res =