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Backtrack/backjump based on accumulated lemmas

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This commit is contained in:
Jakob Rath 2022-11-23 12:49:36 +01:00
parent fdc186b204
commit 2787a22007
4 changed files with 202 additions and 134 deletions
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51
src/math/polysat/solver.h
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@ -46,6 +46,52 @@ namespace polysat {
bool m_log_conflicts = false;
};
/**
* A metric to evaluate lemmas from conflict analysis.
* Lower is better.
*
* Comparison criterion:
* - Lowest jump level has priority, because otherwise, some of the accumulated lemmas may still be false after backjumping.
* - To break ties on jump level, choose clause with the fewest literals at its highest decision level;
* to limit case splits.
*/
class lemma_score {
unsigned m_jump_level;
unsigned m_literals_at_max_level;
public:
lemma_score(unsigned jump_level, unsigned at_max_level)
: m_jump_level(jump_level), m_literals_at_max_level(at_max_level)
{ }
unsigned jump_level() const { return m_jump_level; }
unsigned literals_at_max_level() const { return m_literals_at_max_level; }
static lemma_score max() {
return {UINT_MAX, UINT_MAX};
}
bool operator==(lemma_score const& other) const {
return m_jump_level == other.m_jump_level
&& m_literals_at_max_level == other.m_literals_at_max_level;
}
bool operator!=(lemma_score const& other) const { return !operator==(other); }
bool operator<(lemma_score const& other) const {
return m_jump_level < other.m_jump_level
|| (m_jump_level == other.m_jump_level && m_literals_at_max_level < other.m_literals_at_max_level);
}
bool operator>(lemma_score const& other) const { return other.operator<(*this); }
bool operator<=(lemma_score const& other) const { return operator==(other) || operator<(other); }
bool operator>=(lemma_score const& other) const { return operator==(other) || operator>(other); }
std::ostream& display(std::ostream& out) const {
return out << "jump_level=" << m_jump_level << " at_max_level=" << m_literals_at_max_level;
}
};
inline std::ostream& operator<<(std::ostream& out, lemma_score const& ls) { return ls.display(out); }
class solver {
struct stats {
@ -214,6 +260,8 @@ namespace polysat {
void revert_decision(pvar v);
void revert_bool_decision(sat::literal lit);
void backjump_and_learn(unsigned jump_level, clause& lemma);
void backjump_and_learn(unsigned max_jump_level);
std::optional<lemma_score> compute_lemma_score(clause const& lemma);
// activity of variables based on standard VSIDS
unsigned m_activity_inc = 128;
@ -237,9 +285,6 @@ namespace polysat {
bool invariant();
static bool invariant(signed_constraints const& cs);
bool lemma_invariant(clause const& lemma, polysat::assignment const& a);
bool lemma_invariant_part1(clause const& lemma, polysat::assignment const& a, sat::literal_vector& out_todo);
bool lemma_invariant_part2(sat::literal_vector const& todo);
bool wlist_invariant();
bool assignment_invariant();
bool verify_sat();