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testing lookahead
Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner
parent
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42deeb3498
13 changed files with 456 additions and 15 deletions
394
src/sat/sat_lookahead.h
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394
src/sat/sat_lookahead.h
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/*++
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Copyright (c) 2017 Microsoft Corporation
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Module Name:
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sat_lookahead.h
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Abstract:
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Lookahead SAT solver in the style of March.
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Author:
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Nikolaj Bjorner (nbjorner) 2017-2-11
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Notes:
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--*/
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#ifndef _SAT_LOOKAHEAD_H_
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#define _SAT_LOOKAHEAD_H_
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namespace sat {
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class lookahead {
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solver& s;
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struct config {
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double m_dl_success;
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};
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config m_config;
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double m_delta_trigger;
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literal_vector m_trail;
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literal_vector m_units;
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unsigned_vector m_units_lim;
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unsigned_vector m_learned_lim;
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void init() {
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m_delta_trigger = s.num_vars()/10;
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m_config.m_dl_success = 0.8;
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}
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void push(literal lit) {
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m_learned_lim.push_back(s.m_learned.size());
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m_units_lim.push_back(m_units.size());
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m_trail.push_back(lit);
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s.push();
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assign(lit);
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}
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void pop() {
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s.pop(1);
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unsigned old_sz = m_learned_lim.back();
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m_learned_lim.pop_back();
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for (unsigned i = old_sz; i < s.m_learned.size(); ++i) {
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clause* r = s.m_learned[i];
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s.dettach_clause(*r);
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s.m_cls_allocator.del_clause(r);
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}
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s.m_learned.shrink(old_sz);
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literal lits[2] = { m_trail.back(), null_literal };
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unsigned new_unit_sz = m_units_lim.back();
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for (unsigned i = m_units.size(); i > new_unit_sz; ) {
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--i;
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lits[1] = m_units[i];
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clause * r = s.m_cls_allocator.mk_clause(2, lits, true);
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s.m_learned.push_back(r);
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}
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m_units.shrink(new_unit_sz);
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m_units_lim.pop_back();
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m_trail.pop_back();
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}
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unsigned diff(unsigned value0) const {
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unsigned value1 = get_state_value();
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SASSERT(value1 >= value0);
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return value1 - value0;
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}
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unsigned mix_diff(unsigned l, unsigned r) const {
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return l + r + (1 << 10) * l * r;
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}
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void get_resolvent_units(literal lit) {
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if (inconsistent()) return;
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for (unsigned i = s.m_trail.size(); i > 0; ) {
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--i;
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literal l = s.m_trail[i];
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if (l == lit) break;
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SASSERT(s.lvl(l) == s.scope_lvl());
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watch_list& wlist = s.m_watches[(~l).index()];
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watch_list::iterator it = wlist.begin(), end = wlist.end();
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for (; it != end; ++it) {
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switch (it->get_kind()) {
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case watched::TERNARY:
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if (s.value(it->get_literal1()) == l_false &&
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s.value(it->get_literal()) == l_false) {
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m_units.push_back(l);
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goto done_watch_list;
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}
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break;
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case watched::CLAUSE: {
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clause_offset cls_off = it->get_clause_offset();
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clause & c = *(s.m_cls_allocator.get_clause(cls_off));
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if (c.size() == 2) break;
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SASSERT(c.size() > 2);
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if (c[0] == l && s.value(c[1]) == l_false) {
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DEBUG_CODE(for (unsigned j = 2; j < c.size(); ++j) SASSERT(s.value(c[j]) == l_false););
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m_units.push_back(l);
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goto done_watch_list;
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}
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if (c[1] == l && s.value(c[0]) == l_false) {
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DEBUG_CODE(for (unsigned j = 2; j < c.size(); ++j) SASSERT(s.value(c[j]) == l_false););
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m_units.push_back(l);
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goto done_watch_list;
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}
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break;
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}
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default:
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break;
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}
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}
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done_watch_list:
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continue;
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}
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}
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literal choose() {
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literal l;
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while (!choose1(l)) {};
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return l;
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}
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unsigned get_state_value() const {
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return s.m_learned.size();
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}
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bool choose1(literal& l) {
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literal_vector P;
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pre_select(P);
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l = null_literal;
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if (P.empty()) {
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return true;
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}
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unsigned value0 = get_state_value();
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unsigned h = 0, count = 1;
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literal_vector& units = m_units;;
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for (unsigned i = 0; i < P.size(); ++i) {
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literal lit = P[i];
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push(lit);
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if (do_double(value0)) double_look();
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if (inconsistent()) {
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pop();
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assign(~lit);
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if (do_double(value0)) double_look();
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if (inconsistent()) return true;
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continue;
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}
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unsigned diff1 = diff(value0);
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pop();
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push(~lit);
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if (do_double(value0)) double_look();
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bool unsat2 = inconsistent();
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unsigned diff2 = diff(value0);
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pop();
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if (unsat2) {
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assign(lit);
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continue;
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}
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unsigned mixd = mix_diff(diff1, diff2);
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if (mixd > h || (mixd == h && s.m_rand(count) == 0)) {
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h = mixd;
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l = diff1 < diff2 ? lit : ~lit;
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++count;
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}
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}
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return l != null_literal;
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}
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void double_look() {
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literal_vector P;
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pre_select(P);
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for (unsigned i = 0; !inconsistent() && i < P.size(); ++i) {
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literal lit = P[i];
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push(lit);
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bool unsat = inconsistent();
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pop();
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if (unsat) {
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assign(~lit);
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continue;
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}
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push(~lit);
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unsat = inconsistent();
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pop();
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if (unsat) {
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assign(lit);
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}
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}
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update_delta_trigger();
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}
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void assign(literal l) {
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s.assign(l, justification());
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s.propagate(false);
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get_resolvent_units(l);
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}
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bool inconsistent() { return s.inconsistent(); }
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void pre_select(literal_vector& P) {
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select_variables(P);
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order_by_implication_trees(P);
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}
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void order_by_implication_trees(literal_vector& P) {
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literal_set roots;
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literal_vector nodes, parent;
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//
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// Extract binary clauses in watch list.
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// Produce implication graph between literals in P.
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//
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for (unsigned i = 0; i < P.size(); ++i) {
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literal lit1 = P[i], lit2;
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//
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// lit2 => lit1, where lit2 is a root.
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// make lit1 a root instead of lit2
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//
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watch_list& wlist = s.m_watches[(~lit1).index()];
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watch_list::iterator it = wlist.begin(), end = wlist.end();
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lit2 = null_literal;
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for (; it != end; ++it) {
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switch (it->get_kind()) {
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case watched::BINARY:
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lit2 = it->get_literal();
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break;
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case watched::CLAUSE: {
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clause_offset cls_off = it->get_clause_offset();
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clause & c = *(s.m_cls_allocator.get_clause(cls_off));
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if (c.size() == 2) {
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if (c[0] == ~lit1) {
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lit2 = c[1];
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}
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else {
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SASSERT(c[1] == ~lit1);
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lit2 = c[0];
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}
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}
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break;
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}
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default:
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break;
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}
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if (lit2 != null_literal && roots.contains(lit2)) {
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// lit2 => lit1
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// if lit2 is a root, put it under lit2
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parent.setx(lit2.index(), lit1, null_literal);
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roots.remove(lit2);
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roots.insert(lit1);
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goto found;
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}
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}
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//
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// lit1 => lit2.
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// if lit2 is a node, put lit1 above lit2
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//
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it = s.m_watches[lit1.index()].begin();
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end = s.m_watches[lit1.index()].end();
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for (; it != end; ++it) {
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lit2 = null_literal;
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switch (it->get_kind()) {
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case watched::BINARY:
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lit2 = it->get_literal();
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break;
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case watched::CLAUSE: {
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clause_offset cls_off = it->get_clause_offset();
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clause & c = *(s.m_cls_allocator.get_clause(cls_off));
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if (c.size() == 2) {
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if (c[0] == lit1) {
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lit2 = c[1];
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}
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else {
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SASSERT(c[1] == lit1);
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lit2 = c[0];
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}
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}
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break;
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}
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default:
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break;
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}
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if (lit2 != null_literal && nodes.contains(lit2)) {
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// lit1 => lit2
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parent.setx(lit1.index(), lit2, null_literal);
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nodes.insert(lit1);
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goto found;
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}
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}
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std::cout << "no parents or children of literal " << lit1 << "\n";
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nodes.push_back(lit1);
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roots.insert(lit1);
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found:
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;
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}
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std::cout << "implication trees\n";
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for (unsigned i = 0; i < parent.size(); ++i) {
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literal p = parent[i];
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if (p != null_literal) {
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std::cout << to_literal(i) << " |-> " << p << "\n";
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}
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}
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}
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void select_variables(literal_vector& P) {
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for (unsigned i = 0; i < s.num_vars(); ++i) {
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if (s.value(i) == l_undef) {
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P.push_back(literal(i, false));
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}
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}
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}
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bool do_double(unsigned value0) {
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unsigned value1 = get_state_value();
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return !inconsistent() && value1 - value0 > m_delta_trigger;
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}
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void update_delta_trigger() {
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if (inconsistent()) {
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m_delta_trigger -= (1 - m_config.m_dl_success) / m_config.m_dl_success;
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}
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else {
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m_delta_trigger += 1;
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}
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if (m_delta_trigger >= s.num_vars()) {
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// reset it.
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}
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}
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lbool search() {
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literal_vector trail;
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#define BACKTRACK \
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if (inconsistent()) { \
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if (trail.empty()) return l_false; \
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pop(); \
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assign(~trail.back()); \
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trail.pop_back(); \
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continue; \
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} \
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while (true) {
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s.checkpoint();
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BACKTRACK;
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literal l = choose();
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TRACE("sat", tout << l << "\n";);
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BACKTRACK;
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if (l == null_literal) {
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return l_true;
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}
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push(l);
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trail.push_back(l);
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}
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}
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public:
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lookahead(solver& s) : s(s) {
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init();
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}
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lbool check() {
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return search();
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}
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};
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}
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#endif
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