refactor(cc): merge the two task queues

src/smt/Congruence_closure.ml

@@ -16,9 +16,6 @@ end
 
 module Sig_tbl = CCHashtbl.Make(Signature)
 
-type merge_op = node * node * explanation
-(* a merge operation to perform *)
-
 module type ACTIONS = sig
   val on_backtrack: (unit -> unit) -> unit
   (** Register a callback to be invoked upon backtracking below the current level *)
@@ -35,6 +32,10 @@ end
 
 type actions = (module ACTIONS)
 
+type task =
+  | T_pending of node
+  | T_merge of node * node * explanation
+
 type t = {
   tst: Term.state;
   acts: actions;
@@ -48,10 +49,8 @@ type t = {
      The critical property is that all members of an equivalence class
      that have the same "shape" (including head symbol)
      have the same signature *)
-  pending: node Vec.t;
-  (* nodes to check, maybe their new signature is in {!signatures_tbl} *)
-  combine: merge_op Vec.t;
-  (* pairs of terms to merge *)
+  tasks: task Vec.t;
+  (* tasks to perform *)
   mutable ps_lits: Lit.Set.t;
   (* proof state *)
   ps_queue: (node*node) Vec.t;
@@ -146,22 +145,18 @@ let add_signature cc (t:term) (r:node): unit =
         assert (same_class cc r r');
     end
 
-let[@inline] is_done (cc:t): bool =
-  Vec.is_empty cc.pending &&
-  Vec.is_empty cc.combine
-
 let push_pending cc t : unit =
   if not @@ Equiv_class.get_field Equiv_class.field_is_pending t then (
     Log.debugf 5 (fun k->k "(@[<hv1>cc.push_pending@ %a@])" Equiv_class.pp t);
     Equiv_class.set_field Equiv_class.field_is_pending true t;
-    Vec.push cc.pending t
+    Vec.push cc.tasks (T_pending t)
   )
 
 let push_combine cc t u e : unit =
   Log.debugf 5
     (fun k->k "(@[<hv1>cc.push_combine@ :t1 %a@ :t2 %a@ :expl %a@])"
       Equiv_class.pp t Equiv_class.pp u Explanation.pp e);
-  Vec.push cc.combine (t,u,e)
+  Vec.push cc.tasks @@ T_merge (t,u,e)
 
 (* re-root the explanation tree of the equivalence class of [n]
    so that it points to [n].
@@ -296,11 +291,17 @@ let add_tag_n cc (n:node) (tag:int) (expl:explanation) : unit =
 
 (* main CC algo: add terms from [pending] to the signature table,
    check for collisions *)
-let rec update_pending (cc:t): unit =
+let rec update_tasks (cc:t): unit =
   (* step 2 deal with pending (parent) terms whose equiv class
      might have changed *)
-  while not (Vec.is_empty cc.pending) do
-    let n = Vec.pop_last cc.pending in
+  while not (Vec.is_empty cc.tasks) do
+    let task = Vec.pop_last cc.tasks in
+    match task with 
+    | T_pending n -> task_pending_ cc n
+    | T_merge (t,u,expl) -> task_merge_ cc t u expl
+  done
+
+and task_pending_ cc n =
   Equiv_class.set_field Equiv_class.field_is_pending false n;
   (* check if some parent collided *)
   begin match find_by_signature cc n.n_term with
@@ -328,16 +329,11 @@ let rec update_pending (cc:t): unit =
   (* FIXME: when to actually evaluate?
      eval_pending cc;
   *)
-  done;
-  if not (is_done cc) then (
-    update_combine cc (* repeat *)
-  )
+  ()
 
 (* main CC algo: merge equivalence classes in [st.combine].
    @raise Exn_unsat if merge fails *)
-and update_combine cc =
-  while not (Vec.is_empty cc.combine) do
-    let a, b, e_ab = Vec.pop_last cc.combine in
+and task_merge_ cc a b e_ab : unit =
   let ra = find cc a in
   let rb = find cc b in
   if not (Equiv_class.equal ra rb) then (
@@ -395,9 +391,6 @@ and update_combine cc =
     (* notify listeners of the merge *)
     notify_merge cc r_from ~into:r_into e_ab;
   )
-  done;
-  (* now update pending terms again *)
-  update_pending cc
 
 (* Checks if [ra] and [~into] have compatible normal forms and can
    be merged w.r.t. the theories.
@@ -452,12 +445,12 @@ and[@inline] add_ cc t : node =
 
 let add cc t : node =
   let n = add_ cc t in
-  update_pending cc;
+  update_tasks cc;
   n
 
 let add_seq cc seq =
   seq (fun t -> ignore @@ add_ cc t);
-  update_pending cc
+  update_tasks cc
 
 (* assert that this boolean literal holds *)
 let assert_lit cc lit : unit =
@@ -473,7 +466,7 @@ let assert_lit cc lit : unit =
      the corresponding value, so its superterms (like [ite]) can evaluate
      properly *)
   push_combine cc n rhs (E_lit lit);
-  update_combine cc
+  update_tasks cc
 
 let assert_eq cc (t:term) (u:term) e : unit =
   let n1 = add_ cc t in
@@ -482,7 +475,7 @@ let assert_eq cc (t:term) (u:term) e : unit =
     let e = Explanation.E_lits e in
     push_combine cc n1 n2 e;
   );
-  update_pending cc
+  update_tasks cc
 
 let assert_distinct cc (l:term list) ~neq (lit:Lit.t) : unit =
   assert (match l with[] | [_] -> false | _ -> true);
@@ -513,8 +506,7 @@ let create ?(size=2048) ~actions (tst:Term.state) : t =
     acts=actions;
     tbl = Term.Tbl.create size;
     signatures_tbl = Sig_tbl.create size;
-    pending=Vec.make_empty Equiv_class.dummy;
-    combine= Vec.make_empty (nd,nd,E_reduction);
+    tasks=Vec.make_empty (T_pending Equiv_class.dummy);
     ps_lits=Lit.Set.empty;
     ps_queue=Vec.make_empty (nd,nd);
     true_ = Equiv_class.dummy;
@@ -526,7 +518,7 @@ let create ?(size=2048) ~actions (tst:Term.state) : t =
 
 let final_check cc : unit =
   Log.debug 5 "(CC.final_check)";
-  update_pending cc
+  update_tasks cc
 
 (* model: map each uninterpreted equiv class to some ID *)
 let mk_model (cc:t) (m:Model.t) : Model.t =