Let meet in UnionDomain.Map throw Uncomparable in case different fiel…

…ds are set.

Fixes an issue where meet in branch refinement yielded bot on unions where different fields were set.

src/cdomains/unionDomain.ml

@@ -192,6 +192,16 @@ struct
   let join =
     Map.join
 
+  let meet a b =
+    if a == b then
+      a
+    else
+      let merge_pair _ x y = match x, y with
+        | Some x, Some y -> Some (Values.meet x y)
+        | _, _ -> raise Lattice.Uncomparable
+      in
+      Map.merge merge_pair a b
+
   (** Performs join or widen operation using per element merge function *)
   let merge ~merge_values x y =
     if is_top x || is_top y then