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feat: minimize conflicts

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similar to minisat's level 2 of minimization.
This commit is contained in:
Simon Cruanes 2021-07-19 22:35:23 -04:00
parent 5080195c5b
commit 350a23d99e
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GPG key ID: 4AC01D0849AA62B6
1 changed files with 38 additions and 30 deletions
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68
src/sat/Solver.ml
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@ -698,6 +698,7 @@ module Make(Plugin : PLUGIN)
n_propagations : int Stat.counter;
n_decisions : int Stat.counter;
n_restarts : int Stat.counter;
n_minimized_away : int Stat.counter;
}
type solver = t
@ -748,6 +749,7 @@ module Make(Plugin : PLUGIN)
n_decisions = Stat.mk_int stat "sat.n-decisions";
n_propagations = Stat.mk_int stat "sat.n-propagations";
n_restarts = Stat.mk_int stat "sat.n-restarts";
n_minimized_away = Stat.mk_int stat "sat.n-confl-minimized-away";
on_conflict = None;
on_decision= None;
@ -1121,8 +1123,11 @@ module Make(Plugin : PLUGIN)
let store = self.store in
let to_unmark = self.to_clear in
(* save current state of [to_unmark] *)
let top = Vec.size to_unmark in
Log.debugf 1 (fun k->k"lit.redundant v%d abstract_levels 0x%xd" (v:var:>int) abstract_levels);
let rec aux v =
Log.debugf 1 (fun k->k"lit.redundant.aux v%d" (v:var:>int));
match Var.reason store v with
| None -> assert false
| Some Decision -> raise_notrace Non_redundant
@ -1146,46 +1151,48 @@ module Make(Plugin : PLUGIN)
)
done
in
try aux v; true
try aux v; Log.debug 1 "redundant"; true
with Non_redundant ->
(* clear new marks, they are not actually redundant *)
Log.debug 1 "non redundant";
for i = top to Vec.size to_unmark-1 do
Var.unmark store (Vec.get to_unmark i)
done;
Vec.shrink to_unmark top;
false
(* minimize conflict by removing atoms whose propagation history
is ultimately self-subsuming with [lits] *)
let minimize_conflict (self:t) (c_level:int) (learnt: atom Vec.t) : unit =
let store = self.store in
let to_unmark = self.to_clear in
assert (Vec.is_empty to_unmark);
(* minimize conflict by removing atoms whose propagation history
is ultimately self-subsuming with [lits] *)
let minimize_conflict (self:t) (c_level:int)
(learnt: atom Vec.t) : unit =
let store = self.store in
Vec.iter
(fun a ->
if Atom.level store a < c_level then (
Vec.push to_unmark (Atom.var a);
Var.mark store (Atom.var a)
))
learnt;
(* abstraction of the levels involved in the conflict at all,
as logical "or" of each literal's approximate level *)
let abstract_levels =
Vec.fold (fun lvl a -> lvl lor abstract_level_ self (Atom.var a)) 0 learnt
in
(* abstraction of the levels involved in the conflict at all,
as logical "or" of each literal's approximate level *)
let abstract_levels =
Vec.fold (fun lvl a -> lvl lor abstract_level_ self (Atom.var a)) 0 learnt
in
Vec.filter_in_place
(fun a ->
Atom.level store a = c_level ||
let j = ref 1 in
for i=1 to Vec.size learnt - 1 do
let a = Vec.get learnt i in
let keep =
begin match Atom.reason store a with
| Some Decision -> true (* always keep decisions *)
| _ ->
| Some (Bcp _ | Bcp_lazy _) ->
not (lit_redundant self abstract_levels (Atom.var a))
end)
learnt;
()
| None -> assert false
end
in
if keep then (
Vec.set learnt !j a;
incr j
) else (
Stat.incr self.n_minimized_away;
)
done;
Vec.shrink learnt !j;
()
(* result of conflict analysis, containing the learnt clause and some
additional info. *)
@ -1286,12 +1293,13 @@ module Make(Plugin : PLUGIN)
| _, (None | Some Decision) -> assert false
done;
Vec.iter (Store.clear_var store) to_unmark;
Vec.clear to_unmark;
(* minimize conflict, to get a more general lemma *)
minimize_conflict self conflict_level learnt;
(* cleanup marks *)
Vec.iter (Store.clear_var store) to_unmark;
Vec.clear to_unmark;
(* put high-level literals first, so that:
- they make adequate watch lits
- the first literal is the UIP, if any *)