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feat(solver): eager checking of proofs for theory propagation

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bugs where a literal is propagated "too late" (at current level)
when the cause stems from previous levels, thus leading to invalid
clause learning (non UIP clauses) since some literals are not resolved
away as they're "too low", are hard to debug.
so we just check that propagation level coincides with current level.
This commit is contained in:
Simon Cruanes 2022-01-11 12:21:17 -05:00
parent a33029129e
commit 1ffe778951
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GPG key ID: EBFFF6F283F3A2B4
1 changed files with 22 additions and 14 deletions
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36
src/sat/Solver.ml
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@ -1738,10 +1738,10 @@ module Make(Plugin : PLUGIN)
(Clause.debug self.store) c);
raise_notrace (Th_conflict c)
let check_consequence_lits_false_ self l : unit =
let check_consequence_lits_false_ self l p : unit =
let store = self.store in
Log.debugf 50 (fun k->k "(@[sat.check-consequence-lits: %a@])"
(Util.pp_list (Atom.debug store)) l);
Log.debugf 50 (fun k->k "(@[sat.check-consequence-lits: %a@ :for %a@])"
(Util.pp_list (Atom.debug store)) l (Atom.debug store) p);
match List.find (fun a -> Atom.is_true store a) l with
| a ->
invalid_argf
@ -1761,24 +1761,32 @@ module Make(Plugin : PLUGIN)
else if Atom.is_false store p then (
let lits, proof = mk_expl() in
let guard = List.rev_map (fun f -> Atom.neg @@ make_atom_ self f) lits in
check_consequence_lits_false_ self guard;
check_consequence_lits_false_ self guard p;
let c = Clause.make_l store ~removable:true (p::guard) proof in
raise_notrace (Th_conflict c)
) else (
insert_var_order self (Atom.var p);
let c = lazy (
let level = decision_level self in
let c = (
(* Check literals + proof eagerly, as it's safer.
We could check invariants in a [lazy] block,
as conflict analysis would run in an environment where
the literals should be true anyway, since it's an extension of the
current trail.
(otherwise the propagated lit would have been backtracked and
discarded already.)
However it helps catching propagation bugs to verify truthiness
of the guard (and level) eagerly.
*)
let lits, proof = mk_expl () in
let guard = List.rev_map (fun f -> Atom.neg @@ make_atom_ self f) lits in
(* note: we can check that invariant here in the [lazy] block,
as conflict analysis will run in an environment where
the literals should be true anyway, since it's an extension of the
current trail
(otherwise the propagated lit would have been backtracked and
discarded already.) *)
check_consequence_lits_false_ self guard;
Clause.make_l store ~removable:true (p::guard) proof
check_consequence_lits_false_ self guard p;
assert (List.fold_left (fun l a -> max l (Atom.level store a)) 0 guard = level);
(* delay creating the actual clause. *)
lazy (Clause.make_l store ~removable:true (p::guard) proof)
) in
let level = decision_level self in
Stat.incr self.n_propagations;
enqueue_bool self p ~level (Bcp_lazy c)
)