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//! Vivification
#![allow(dead_code)]
use crate::{
assign::{AssignIF, AssignStack, PropagateIF, VarManipulateIF},
cdb::{ClauseDB, ClauseDBIF, clause::ClauseIF},
state::{Stat, State, StateIF},
types::*,
};
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 {
// This is a reusable vector to reduce memory consumption,
// the key is the number of invocation
// let db_skip: usize = 1 + self.num_clause / 1_000_000;
let mut seen: Vec<usize> = vec![0; asg.num_vars + 1];
let display_step: usize = 1000;
let mut num_check: usize = 0;
let mut num_shrink: usize = 0;
let mut num_assert: usize = 0;
let mut to_display: usize = display_step;
state[Stat::Vivification] += 1;
if asg.remains() {
asg.propagate_sandbox(self).map_err(|cc| {
state.log(None, "By vivifier");
SolverError::RootLevelConflict(cc)
})?;
}
// Inlined target selection (formerly `select_targets`).
// Pick clauses that haven't been vivified recently. We deliberately
// do NOT sort the candidates: the per-clause filter in the loop below
// decides which ones are actually worth processing.
'next_clause: for i in 1..self.clause.len() {
let cid = ClauseId::from(i);
let c = &mut self[cid];
if c.is_dead() {
continue;
}
let span: usize = 10_000 * c.len() * 2_usize.pow(c.vivify_age as u32 + 1);
if c.vivify_at + span > asg.num_conflict
|| (c.referred_at <= c.vivify_at && (c.is(FlagClause::LEARNT) || c.vivify_age != 0))
{
continue;
}
num_check += 1;
let c = &mut self[cid];
// c.update_reference_rate(asg.num_conflict);
// Skip clauses that are unlikely to be improved by vivification.
// Empirically success concentrates on clauses
// that are not too short and have a moderate LBD; outside this band
// the success rate collapses, so skipping them saves work without
// losing many improvable clauses.
// assert!(!c.is(FlagClause::ASSIGN_REASON));
c.vivify_at = asg.num_conflict;
c.vivify_age += 1;
let is_learnt = c.is(FlagClause::LEARNT);
let lbd = c.lbd;
let referred = c.referred;
let referred_at = c.referred_at;
let vivify_age = c.vivify_age;
let vivify_at = c.vivify_at;
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})..."
));
to_display = num_check + display_step;
}
// debug_assert!(clits.iter().all(|l| !clits.contains(&!*l)));
// Build a clean environment
// debug_assert!(asg.stack_is_empty() || !asg.remains());
// debug_assert_eq!(asg.root_level(), asg.decision_level());
asg.backtrack_sandbox();
debug_assert_eq!(asg.decision_level(), asg.root_level());
if asg.remains() {
asg.propagate_sandbox(self)
.map_err(SolverError::RootLevelConflict)?;
}
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[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(self, vec[0])?;
num_assert += 1;
}
_ => {
if let Some(cid) = self.new_clause(&mut vec, is_learnt).is_new()
{
self[cid].lbd = lbd.min(decisions.len() as DecisionLevel);
self[cid].referred = referred;
self[cid].referred_at = referred_at;
self[cid].vivify_age = vivify_age;
self[cid].vivify_at = vivify_at;
}
self.remove_clause(cid);
num_shrink += 1;
}
}
continue 'next_clause;
}
//## Rule 4
}
}
}
}
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(())
}
}
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
}
}