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//! Vivification
#![allow(dead_code)]
use crate::{
assign::{AssignIF, AssignStack, PropagateIF, VarManipulateIF},
cdb::{ClauseDB, ClauseDBIF, ClauseIF},
state::{Stat, State, StateIF},
types::*,
};
const VIVIFY_LIMIT: usize = 80_000;
pub trait VivifyIF {
fn vivify(&mut self, asg: &mut AssignStack, state: &mut State) -> MaybeInconsistent;
}
impl VivifyIF for ClauseDB {
/// vivify clauses under `asg`
fn vivify(&mut self, asg: &mut AssignStack, state: &mut State) -> MaybeInconsistent {
const NUM_TARGETS: Option<usize> = Some(VIVIFY_LIMIT);
if asg.remains() {
asg.propagate_sandbox(self).map_err(|cc| {
state.log(None, "By vivifier");
SolverError::RootLevelConflict(cc)
})?;
}
let mut clauses: Vec<OrderedProxy<ClauseId>> =
select_targets(asg, self, state[Stat::Restart] == 0, NUM_TARGETS);
if clauses.is_empty() {
return Ok(());
}
let num_target = clauses.len();
state[Stat::Vivification] += 1;
// This is a reusable vector to reduce memory consumption,
// the key is the number of invocation
let mut seen: Vec<usize> = vec![0; asg.num_vars + 1];
let display_step: usize = 1000;
let mut num_check = 0;
let mut num_shrink = 0;
let mut num_assert = 0;
let mut to_display = 0;
'next_clause: while let Some(cp) = clauses.pop() {
asg.backtrack_sandbox();
debug_assert_eq!(asg.decision_level(), asg.root_level());
if asg.remains() {
asg.propagate_sandbox(self)
.map_err(SolverError::RootLevelConflict)?;
}
debug_assert!(asg.stack_is_empty() || !asg.remains());
debug_assert_eq!(asg.root_level(), asg.decision_level());
let cid = cp.to();
let c = &mut self[cid];
if c.is_dead() {
continue;
}
let is_learnt = c.is(FlagClause::LEARNT);
c.vivified();
let clits = c.iter().copied().collect::<Vec<Lit>>();
if to_display <= num_check {
state.flush("");
state.flush(format!(
"clause vivifying(assert:{num_assert} shorten:{num_shrink}, check:{num_check}/{num_target})..."
));
to_display = num_check + display_step;
}
num_check += 1;
debug_assert!(clits.iter().all(|l| !clits.contains(&!*l)));
let mut decisions: Vec<Lit> = Vec::new();
for lit in clits.iter().copied() {
// assert!(!asg.var(lit.vi()).is(FlagVar::ELIMINATED));
match asg.assigned(!lit) {
//## Rule 1
Some(false) => (),
//## Rule 2
Some(true) => break,
None => {
decisions.push(!lit);
asg.assign_by_decision(!lit);
//## Rule 3
if let Err(cc) = asg.propagate_sandbox(self) {
let mut vec: Vec<Lit>;
match cc.1 {
AssignReason::BinaryLink(l) => {
let cnfl_lits = vec![cc.0, !l];
// vec = asg.analyze_sandbox(self, &decisions, &cnfl_lits, &mut seen);
// asg.backtrack_sandbox();
if clits.len() == 2
&& cnfl_lits.contains(&clits[0])
&& cnfl_lits.contains(&clits[1])
{
asg.backtrack_sandbox();
continue 'next_clause;
} else {
debug_assert!(clits.len() != 2 || decisions.len() != 2);
seen[0] = num_check;
vec = asg.analyze_sandbox(
self, &decisions, &cnfl_lits, &mut seen,
);
asg.backtrack_sandbox();
}
}
AssignReason::Implication(ci) => {
if ci == cid && clits.len() == decisions.len() {
asg.backtrack_sandbox();
continue 'next_clause;
} else {
let cnfl_lits =
&self[ci].iter().copied().collect::<Vec<Lit>>();
seen[0] = num_check;
vec = asg.analyze_sandbox(
self, &decisions, cnfl_lits, &mut seen,
);
asg.backtrack_sandbox();
}
}
AssignReason::Decision(_) | AssignReason::None => {
unreachable!("vivify")
}
}
match vec.len() {
0 => {
state.flush("");
state[Stat::VivifiedClause] += num_shrink;
state[Stat::VivifiedVar] += num_assert;
state.log(None, "RootLevelConflict By vivify");
return Err(SolverError::EmptyClause);
}
1 => {
self.certificate_add_assertion(vec[0]);
asg.assign_at_root_level(vec[0])?;
num_assert += 1;
}
_ => {
#[cfg(feature = "clause_rewarding")]
if let Some(ci) =
self.new_clause(asg, &mut vec, is_learnt).is_new()
{
self.set_activity(ci, cp.value());
}
#[cfg(not(feature = "clause_rewarding"))]
self.new_clause(asg, &mut vec, is_learnt);
self.remove_clause(cid);
num_shrink += 1;
}
}
continue 'next_clause;
}
//## Rule 4
}
}
}
if VIVIFY_LIMIT < num_check {
break;
}
}
asg.backtrack_sandbox();
if asg.remains() {
asg.propagate_sandbox(self)
.map_err(SolverError::RootLevelConflict)?;
}
asg.clear_asserted_literals(self)?;
debug_assert!(asg.stack_is_empty() || !asg.remains());
state.flush("");
state.flush(format!(
"vivification(assert:{num_assert} shorten:{num_shrink}), "
));
// state.log(
// asg.num_conflict,
// format!(
// "vivify:{:5}, pick:{:>8}, assert:{:>8}, shorten:{:>8}",
// state[Stat::Vivification],
// num_check,
// num_assert,
// num_shrink,
// ),
// );
state[Stat::VivifiedClause] += num_shrink;
state[Stat::VivifiedVar] += num_assert;
Ok(())
}
}
fn select_targets(
asg: &mut AssignStack,
cdb: &mut ClauseDB,
initial_stage: bool,
len: Option<usize>,
) -> Vec<OrderedProxy<ClauseId>> {
if initial_stage {
let mut seen: Vec<Option<OrderedProxy<ClauseId>>> = vec![None; 2 * (asg.num_vars + 1)];
for (i, c) in cdb.iter().enumerate().skip(1) {
if let Some(rank) = c.to_vivify(true) {
let p = &mut seen[usize::from(c.lit0())];
if p.as_ref().map_or(0.0, |r| r.value()) < rank {
*p = Some(OrderedProxy::new(ClauseId::from(i), rank));
}
}
}
let mut clauses = seen.iter().filter_map(|p| p.clone()).collect::<Vec<_>>();
if let Some(max_len) = len {
if 10 * max_len < clauses.len() {
clauses.sort();
clauses.truncate(max_len);
}
}
clauses
} else {
let mut clauses: Vec<OrderedProxy<ClauseId>> = cdb
.iter()
.enumerate()
.skip(1)
.filter_map(|(i, c)| {
c.to_vivify(false)
.map(|r| OrderedProxy::new_invert(ClauseId::from(i), r))
})
.collect::<Vec<_>>();
if let Some(max_len) = len {
if max_len < clauses.len() {
clauses.sort();
clauses.truncate(max_len);
}
}
clauses
}
}
impl AssignStack {
/// inspect the complete implication graph to collect a disjunction of a subset of
/// negated literals of `lits`
fn analyze_sandbox(
&self,
cdb: &ClauseDB,
decisions: &[Lit],
conflicting: &[Lit],
seen: &mut [usize],
) -> Vec<Lit> {
let key = seen[0];
let mut learnt: Vec<Lit> = Vec::new();
for l in conflicting {
seen[l.vi()] = key;
}
let last_decision = decisions.last().unwrap();
let from = self.len_upto(self.root_level());
let all = self.stack_iter().map(|l| !*l).collect::<Vec<_>>();
let assumes = &all[from..];
debug_assert!(
all.iter().all(|l| !assumes.contains(&!*l)),
"vivify252\n{:?}, {:?}",
assumes
.iter()
.filter(|l| all.contains(&!**l))
.collect::<Vec<_>>(),
assumes
.iter()
.filter(|l| all.contains(&!**l))
.map(|l| self.reason(l.vi()))
.collect::<Vec<_>>(),
// am.iter().filter(|l| am.contains(&!**l)).collect::<Vec<_>>(),
);
// sweep in the reverse order
for l in self.stack_iter().skip(self.len_upto(0)).rev() {
if seen[l.vi()] != key {
continue;
}
if decisions.contains(l) {
// || assert!(!learnt.contains(l));
// Quiz: which is the correct learnt clause here?
// 1. [decision1, decision2, !last_decision]
// 2. [!decision1, !decision2, !last_decision]
// Since `conflict::conflict_analyze` sweeps *reason clauses*,
// it collects positive literals out of the clauses in the dependency graph,
// while we collect decision literals in *trail* here.
// Thus we must negate the literals.
learnt.push(!*l);
}
match self.reason(l.vi()) {
AssignReason::Decision(_) => (),
AssignReason::BinaryLink(bil) => {
seen[bil.vi()] = key;
}
AssignReason::Implication(cid) => {
for r in cdb[cid].iter().skip(1) {
seen[r.vi()] = key;
}
}
AssignReason::None => unreachable!("analyze_sandbox::AssignReason::None"),
}
}
// cnfs/unsat.cnf can panic at
//
// clause vivifying(assert:0 shorten:0, check:0/12)...thread 'main' panicked at '
// [-17L, -5L, 25L, -29L, 50L, 51L, -61L, 63L]
// [Some(false), Some(false), Some(false), Some(false), Some(false), Some(false), Some(false), Some(false)]
// [0, 0, 0, 0, 0, 0, 0, 0]',
// src/solver/vivify.rs:297:13
//
// This conflicting clause which consists of implicated literals is found
// before finding a conflict by the target clause.
// So we must skip this conflict.
if learnt.is_empty() {
debug_assert_eq!(self.num_conflict, 0);
// panic!("\n{:?}\n{:?}\n{:?}",
// conflicting,
// conflicting.iter().map(|l| self.assigned(*l)).collect::<Vec<_>>(),
// conflicting.iter().map(|l| self.level(l.vi())).collect::<Vec<_>>(),
// );
return learnt;
}
// make sure the decision var is at the top of list
debug_assert!(
!learnt.is_empty(),
"empty learnt, conflict: {conflicting:?}, assumed: {decisions:?}"
);
debug_assert!(
learnt.contains(&!*last_decision),
"\nThe negation of the last decision {last_decision} isn't contained in {learnt:?}"
);
// Since we don't assign the right value of the 'reason' literal after conflict analysis,
// we need not to swap locations.
// learnt.swap(0, lst);
// assert!(matches!(self.reason(learnt[0].vi()), AssignReason::None));
debug_assert!(
learnt.iter().all(|l| !learnt.contains(&!*l)),
"res: {learnt:?} from: {decisions:?} and trail: {assumes:?}"
);
learnt
}
}
impl Clause {
/// return `true` if the clause should try vivification.
/// smaller is better.
#[cfg(feature = "clause_rewarding")]
fn to_vivify(&self, initial_stage: bool) -> Option<f64> {
if initial_stage {
(!self.is_dead()).then(|| self.len() as f64)
} else {
(!self.is_dead()
&& self.rank * 2 <= self.rank_old
&& (self.is(FlagClause::LEARNT) || self.is(FlagClause::DERIVE20)))
.then(|| self.reward)
}
}
#[cfg(not(feature = "clause_rewarding"))]
fn to_vivify(&self, initial_stage: bool) -> Option<f64> {
if initial_stage {
(!self.is_dead()).then(|| self.len() as f64)
} else {
(!self.is_dead()
&& self.rank * 2 <= self.rank_old
&& (self.is(FlagClause::LEARNT) || self.is(FlagClause::DERIVE20)))
.then(|| -((self.rank_old - self.rank) as f64 / self.rank as f64))
}
}
/// clear flags about vivification
fn vivified(&mut self) {
self.rank_old = self.rank;
if !self.is(FlagClause::LEARNT) {
self.turn_off(FlagClause::DERIVE20);
}
}
}