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backtrack_fi

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This commit is contained in:
Jakob Rath 2022-04-25 17:37:50 +02:00
parent fc2633c964
commit 6bf897aad8
6 changed files with 113 additions and 15 deletions
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76
src/math/polysat/solver.cpp
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@ -559,7 +559,7 @@ namespace polysat {
/**
* Conflict resolution.
*/
void solver::resolve_conflict() {
void solver::resolve_conflict() {
LOG_H2("Resolve conflict");
LOG("\n" << *this);
LOG(search_state_pp(m_search, true));
@ -572,8 +572,9 @@ namespace polysat {
pvar v = m_conflict.conflict_var();
// This case corresponds to a propagation of conflict_var, except it's not explicitly on the stack.
// TODO: use unsat core from m_viable_fallback if the conflict is from there
// TODO: we could try simpler backtracking loop if we get a lemma from forbidden intervals
VERIFY(m_viable.resolve(v, m_conflict));
backtrack_fi();
return;
}
search_iterator search_it(m_search);
@ -630,6 +631,74 @@ namespace polysat {
report_unsat();
}
/**
* Simpler backracking for forbidden interval lemmas:
* since forbidden intervals already gives us a lemma where the conflict variable has been eliminated,
* we can backtrack to the last relevant decision and learn this lemma.
*/
void solver::backtrack_fi() {
uint_set relevant_vars;
search_iterator search_it(m_search);
while (search_it.next()) {
auto& item = *search_it;
search_it.set_resolved();
if (item.is_assignment()) {
// Resolve over variable assignment
pvar v = item.var();
if (!m_conflict.pvar_occurs_in_constraints(v) && !relevant_vars.contains(v)) {
m_search.pop_assignment();
continue;
}
LOG_H2("Working on " << search_item_pp(m_search, item));
LOG(m_justification[v]);
LOG("Conflict: " << m_conflict);
inc_activity(v);
justification& j = m_justification[v];
if (j.level() > base_level() && j.is_decision()) {
m_conflict.end_conflict();
revert_decision(v);
return;
}
SASSERT(j.is_propagation());
// If a variable was propagated:
// we don't really care about the constraints in this case, but just about the variables it depends on
for (auto const& c : m_viable.get_constraints(v))
for (pvar v : c->vars()) {
relevant_vars.insert(v);
m_conflict.log_var(v);
}
m_search.pop_assignment();
}
else {
// Resolve over boolean literal
SASSERT(item.is_boolean());
sat::literal const lit = item.lit();
sat::bool_var const var = lit.var();
if (!m_conflict.is_marked(var))
continue;
LOG_H2("Working on " << search_item_pp(m_search, item));
LOG(bool_justification_pp(m_bvars, lit));
LOG("Literal " << lit << " is " << lit2cnstr(lit));
LOG("Conflict: " << m_conflict);
if (m_bvars.is_assumption(var))
continue;
else if (m_bvars.is_decision(var)) {
m_conflict.end_conflict();
revert_bool_decision(lit);
return;
}
else if (m_bvars.is_bool_propagation(var))
m_conflict.resolve(lit, *m_bvars.reason(lit));
else {
SASSERT(m_bvars.is_value_propagation(var));
continue;
}
}
}
m_conflict.end_conflict();
report_unsat();
}
/**
* Variable activity accounting.
* As a placeholder we increment activity
@ -706,8 +775,6 @@ namespace polysat {
void solver::decide_on_lemma(clause& lemma) {
LOG_H3("Guessing literal in lemma: " << lemma);
IF_LOGGING(m_viable.log());
LOG("Boolean assignment: " << m_bvars);
// To make a guess, we need to find an unassigned literal that is not false in the current model.
@ -717,6 +784,7 @@ namespace polysat {
for (sat::literal lit : lemma) {
switch (m_bvars.value(lit)) {
case l_true:
LOG("Already satisfied because literal " << lit << " is true");
return;
case l_false:
break;