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Fix for semantic conflict and decision levels
When faced with a semantic conflict, a new decision must be made to solve the conflict, however, because we just backtracked, it is not ensured that the solver is in a correct state to add a new level, so the decision is now delayed until propagation has been done.
This commit is contained in:
Guillaume Bury
parent
df1f28ccb1
commit
a21807c624
1 changed files with 106 additions and 93 deletions
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@ -40,8 +40,8 @@ module Make
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mutable unsat_conflict : clause option;
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(* conflict clause at decision level 0, if any *)
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mutable next_decision : atom option;
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(* When the last conflict was a semantic one, this stores the next decision to make *)
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elt_queue : t Vec.t;
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(* decision stack + propagated elements (atoms or assignments) *)
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@ -110,6 +110,7 @@ module Make
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let env = {
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unsat_conflict = None;
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next_decision = None;
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clauses_hyps = Vec.make 0 dummy_clause;
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clauses_learnt = Vec.make 0 dummy_clause;
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@ -158,13 +159,14 @@ module Make
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nb_init_clauses = 0;
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}
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let is_unsat () = match env.unsat_conflict with Some _ -> true | None -> false
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let is_unsat () =
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match env.unsat_conflict with
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| Some _ -> true
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| None -> false
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(* Level for push/pop operations *)
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type level = int
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let base_level = 0
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let current_level () = Vec.size env.user_levels
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(* Iteration over subterms *)
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@ -253,6 +255,67 @@ module Make
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let nb_learnts () = Vec.size env.clauses_learnt
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let nb_vars () = St.nb_elt ()
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(* Simplify clauses *)
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exception Trivial
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let simplify_zero atoms level0 =
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(* Eliminates dead litterals from clauses when at decision level 0 *)
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assert (decision_level () = 0);
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let aux (atoms, init, lvl) a =
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if a.is_true then raise Trivial;
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if a.neg.is_true then begin
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match a.var.reason with
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| Bcp (Some cl) -> atoms, false, max lvl cl.c_level
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| Semantic 0 -> atoms, init, lvl
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| _ ->
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L.debug 0 "Unexpected semantic propagation at level 0: %a" St.pp_atom a;
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assert false
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end else
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a::atoms, init, lvl
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in
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let atoms, init, lvl = List.fold_left aux ([], true, level0) atoms in
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List.fast_sort (fun a b -> a.var.vid - b.var.vid) atoms, init, lvl
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let partition atoms init0 =
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(* Parittion litterals for new clauses *)
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let rec partition_aux trues unassigned falses init lvl = function
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| [] -> trues @ unassigned @ falses, init, lvl
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| a :: r ->
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if a.is_true then
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if a.var.level = 0 then raise Trivial
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else (a::trues) @ unassigned @ falses @ r, init, lvl
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else if a.neg.is_true then
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if a.var.level = 0 then begin
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match a.var.reason with
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| Bcp (Some cl) ->
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partition_aux trues unassigned falses false (max lvl cl.c_level) r
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| Semantic 0 ->
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partition_aux trues unassigned falses init lvl r
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| _ -> assert false
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end else
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partition_aux trues unassigned (a::falses) init lvl r
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else
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partition_aux trues (a::unassigned) falses init lvl r
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in
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if decision_level () = 0 then
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simplify_zero atoms init0
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else
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partition_aux [] [] [] false init0 atoms
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(* Compute a progess estimate *)
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let progress_estimate () =
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let prg = ref 0. in
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let nbv = to_float (nb_vars()) in
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let lvl = decision_level () in
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let _F = 1. /. nbv in
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for i = 0 to lvl do
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let _beg = if i = 0 then 0 else Vec.get env.elt_levels (i-1) in
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let _end = if i=lvl then Vec.size env.elt_queue else Vec.get env.elt_levels i in
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prg := !prg +. _F**(to_float i) *. (to_float (_end - _beg))
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done;
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!prg /. nbv
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(* Manipulating decision levels *)
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let new_decision_level() =
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assert (env.th_head = Vec.size env.elt_queue);
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@ -493,15 +556,14 @@ module Make
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if is_uip then
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enqueue_bool fuip blevel (Bcp (Some lclause))
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else begin
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env.decisions <- env.decisions + 1;
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new_decision_level();
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enqueue_bool fuip.neg (decision_level ()) (Bcp None)
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env.next_decision <- Some fuip.neg
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end
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end;
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var_decay_activity ();
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clause_decay_activity ()
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let add_boolean_conflict confl =
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env.next_decision <- None;
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env.conflicts <- env.conflicts + 1;
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if decision_level() = 0 || Vec.for_all (fun a -> a.var.level = 0) confl.atoms then
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report_unsat confl; (* Top-level conflict *)
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@ -510,50 +572,6 @@ module Make
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record_learnt_clause confl blevel learnt (History history) is_uip lvl
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(* Add a new clause *)
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exception Trivial
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let simplify_zero atoms level0 =
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assert (decision_level () = 0);
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let aux (atoms, init, lvl) a =
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if a.is_true then raise Trivial;
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if a.neg.is_true then begin
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match a.var.reason with
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| Bcp (Some cl) -> atoms, false, max lvl cl.c_level
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| Semantic 0 -> atoms, init, lvl
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| _ ->
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L.debug 0 "Unexpected semantic propagation at level 0: %a" St.pp_atom a;
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assert false
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end else
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a::atoms, init, lvl
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in
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let atoms, init, lvl = List.fold_left aux ([], true, level0) atoms in
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List.fast_sort (fun a b -> a.var.vid - b.var.vid) atoms, init, lvl
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let partition atoms init0 =
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let rec partition_aux trues unassigned falses init lvl = function
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| [] -> trues @ unassigned @ falses, init, lvl
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| a :: r ->
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if a.is_true then
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if a.var.level = 0 then raise Trivial
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else (a::trues) @ unassigned @ falses @ r, init, lvl
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else if a.neg.is_true then
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if a.var.level = 0 then begin
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match a.var.reason with
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| Bcp (Some cl) ->
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partition_aux trues unassigned falses false (max lvl cl.c_level) r
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| Semantic 0 ->
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partition_aux trues unassigned falses init lvl r
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| _ -> assert false
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end else
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partition_aux trues unassigned (a::falses) init lvl r
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else
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partition_aux trues (a::unassigned) falses init lvl r
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in
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if decision_level () = 0 then
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simplify_zero atoms init0
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else
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partition_aux [] [] [] false init0 atoms
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let add_clause ?(force=false) init0 =
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let vec = match init0.cpremise with
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| Lemma _ -> env.clauses_learnt
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@ -592,18 +610,6 @@ module Make
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enqueue_bool a 0 (Bcp (Some init0))
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with Trivial -> L.debug 5 "Trivial clause ignored : %a" St.pp_clause init0
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let progress_estimate () =
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let prg = ref 0. in
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let nbv = to_float (nb_vars()) in
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let lvl = decision_level () in
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let _F = 1. /. nbv in
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for i = 0 to lvl do
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let _beg = if i = 0 then 0 else Vec.get env.elt_levels (i-1) in
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let _end = if i=lvl then Vec.size env.elt_queue else Vec.get env.elt_levels i in
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prg := !prg +. _F**(to_float i) *. (to_float (_end - _beg))
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done;
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!prg /. nbv
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let propagate_in_clause a c i watched new_sz =
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let atoms = c.atoms in
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let first = Vec.get atoms 0 in
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@ -741,6 +747,7 @@ module Make
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| _ -> !res
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end
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(*
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(* heuristic comparison between clauses, by their size (unary/binary or not)
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and activity *)
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let f_sort_db c1 c2 =
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@ -762,6 +769,7 @@ module Make
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| _ -> false
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) env.vars
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*)
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*)
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(* remove some learnt clauses *)
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let reduce_db () = () (*
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@ -794,9 +802,6 @@ module Make
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if satisfied c then remove_clause c
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done
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module HUC = Hashtbl.Make
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(struct type t = clause let equal = (==) let hash = Hashtbl.hash end)
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let simplify () =
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assert (decision_level () = 0);
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if is_unsat () then raise Unsat;
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@ -814,32 +819,40 @@ module Make
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end
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(* Decide on a new litteral *)
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let rec pick_branch_lit () =
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let max = Iheap.remove_min f_weight env.order in
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destruct_elt (St.get_elt max)
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(fun v ->
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if v.level >= 0 then
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pick_branch_lit ()
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else begin
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let value = Th.assign v.term in
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env.decisions <- env.decisions + 1;
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new_decision_level();
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let current_level = decision_level () in
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enqueue_assign v value current_level
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end)
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(fun v ->
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if v.level >= 0 then begin
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assert (v.pa.is_true || v.na.is_true);
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pick_branch_lit ()
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end else match Th.eval v.pa.lit with
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| Th.Unknown ->
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env.decisions <- env.decisions + 1;
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new_decision_level();
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let current_level = decision_level () in
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enqueue_bool v.pa current_level (Bcp None)
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| Th.Valued (b, lvl) ->
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let a = if b then v.pa else v.na in
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enqueue_bool a lvl (Semantic lvl))
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let rec pick_branch_aux atom =
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let v = atom.var in
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if v.level >= 0 then begin
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assert (v.pa.is_true || v.na.is_true);
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pick_branch_lit ()
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end else match Th.eval atom.lit with
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| Th.Unknown ->
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env.decisions <- env.decisions + 1;
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new_decision_level();
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let current_level = decision_level () in
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enqueue_bool atom current_level (Bcp None)
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| Th.Valued (b, lvl) ->
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let a = if b then atom else atom.neg in
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enqueue_bool a lvl (Semantic lvl)
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and pick_branch_lit () =
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match env.next_decision with
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| Some atom ->
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env.next_decision <- None;
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pick_branch_aux atom
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| None ->
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destruct_elt (
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St.get_elt @@ Iheap.remove_min f_weight env.order)
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(fun v ->
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if v.level >= 0 then
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pick_branch_lit ()
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else begin
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let value = Th.assign v.term in
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env.decisions <- env.decisions + 1;
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new_decision_level();
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let current_level = decision_level () in
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enqueue_assign v value current_level
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end)
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(fun v -> pick_branch_aux v.pa)
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let search n_of_conflicts n_of_learnts =
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let conflictC = ref 0 in
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