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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner
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1 changed files with 560 additions and 0 deletions
560
src/sat/smt/xor_solver.cpp
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560
src/sat/smt/xor_solver.cpp
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/*++
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Copyright (c) 2017 Microsoft Corporation
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Module Name:
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xor_solver.cpp
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Abstract:
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Extension for xr reasoning.
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Author:
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Nikolaj Bjorner (nbjorner) 2017-01-30
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Revision History:
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--*/
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#include "sat/sat_types.h"
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#include "sat/smt/ba_solver.h"
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#include "sat/sat_simplifier_params.hpp"
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#include "sat/sat_xor_finder.h"
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namespace sat {
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ba_solver::xr& ba_solver::constraint::to_xr() {
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SASSERT(is_xr());
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return static_cast<xr&>(*this);
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}
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ba_solver::xr const& ba_solver::constraint::to_xr() const{
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SASSERT(is_xr());
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return static_cast<xr const&>(*this);
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}
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ba_solver::xr::xr(extension* e, unsigned id, literal_vector const& lits):
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constraint(e, xr_t, id, null_literal, lits.size(), get_obj_size(lits.size())) {
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for (unsigned i = 0; i < size(); ++i) {
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m_lits[i] = lits[i];
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}
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}
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bool ba_solver::xr::is_watching(literal l) const {
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return
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l == (*this)[0] || l == (*this)[1] ||
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~l == (*this)[0] || ~l == (*this)[1];
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}
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bool ba_solver::xr::well_formed() const {
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uint_set vars;
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if (lit() != null_literal) vars.insert(lit().var());
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for (literal l : *this) {
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bool_var v = l.var();
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if (vars.contains(v)) return false;
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vars.insert(v);
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}
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return true;
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}
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// --------------------
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// xr:
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void ba_solver::clear_watch(xr& x) {
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x.clear_watch();
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unwatch_literal(x[0], x);
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unwatch_literal(x[1], x);
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unwatch_literal(~x[0], x);
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unwatch_literal(~x[1], x);
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}
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bool ba_solver::parity(xr const& x, unsigned offset) const {
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bool odd = false;
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unsigned sz = x.size();
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for (unsigned i = offset; i < sz; ++i) {
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SASSERT(value(x[i]) != l_undef);
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if (value(x[i]) == l_true) {
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odd = !odd;
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}
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}
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return odd;
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}
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bool ba_solver::init_watch(xr& x) {
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clear_watch(x);
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VERIFY(x.lit() == null_literal);
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TRACE("ba", display(tout, x, true););
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unsigned sz = x.size();
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unsigned j = 0;
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for (unsigned i = 0; i < sz && j < 2; ++i) {
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if (value(x[i]) == l_undef) {
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x.swap(i, j);
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++j;
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}
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}
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switch (j) {
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case 0:
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if (!parity(x, 0)) {
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unsigned l = lvl(x[0]);
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j = 1;
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for (unsigned i = 1; i < sz; ++i) {
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if (lvl(x[i]) > l) {
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j = i;
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l = lvl(x[i]);
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}
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}
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set_conflict(x, x[j]);
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}
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return false;
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case 1:
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SASSERT(x.lit() == null_literal || value(x.lit()) == l_true);
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assign(x, parity(x, 1) ? ~x[0] : x[0]);
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return false;
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default:
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SASSERT(j == 2);
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watch_literal(x[0], x);
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watch_literal(x[1], x);
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watch_literal(~x[0], x);
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watch_literal(~x[1], x);
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return true;
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}
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}
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lbool ba_solver::add_assign(xr& x, literal alit) {
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// literal is assigned
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unsigned sz = x.size();
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TRACE("ba", tout << "assign: " << ~alit << "@" << lvl(~alit) << " " << x << "\n"; display(tout, x, true); );
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VERIFY(x.lit() == null_literal);
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SASSERT(value(alit) != l_undef);
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unsigned index = (x[1].var() == alit.var()) ? 1 : 0;
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VERIFY(x[index].var() == alit.var());
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// find a literal to swap with:
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for (unsigned i = 2; i < sz; ++i) {
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literal lit = x[i];
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if (value(lit) == l_undef) {
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x.swap(index, i);
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unwatch_literal(~alit, x);
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// alit gets unwatched by propagate_core because we return l_undef
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watch_literal(lit, x);
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watch_literal(~lit, x);
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TRACE("ba", tout << "swap in: " << lit << " " << x << "\n";);
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return l_undef;
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}
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}
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if (index == 0) {
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x.swap(0, 1);
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}
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// alit resides at index 1.
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VERIFY(x[1].var() == alit.var());
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if (value(x[0]) == l_undef) {
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bool p = parity(x, 1);
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assign(x, p ? ~x[0] : x[0]);
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}
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else if (!parity(x, 0)) {
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set_conflict(x, ~x[1]);
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}
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return inconsistent() ? l_false : l_true;
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}
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void ba_solver::add_xr(literal_vector const& lits) {
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add_xr(lits, false);
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}
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bool ba_solver::all_distinct(literal_vector const& lits) {
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return s().all_distinct(lits);
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}
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bool ba_solver::all_distinct(clause const& c) {
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return s().all_distinct(c);
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}
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bool ba_solver::all_distinct(xr const& x) {
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init_visited();
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for (literal l : x) {
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if (is_visited(l.var())) {
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return false;
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}
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mark_visited(l.var());
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}
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return true;
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}
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literal ba_solver::add_xor_def(literal_vector& lits, bool learned) {
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unsigned sz = lits.size();
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SASSERT (sz > 1);
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VERIFY(all_distinct(lits));
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init_visited();
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bool parity1 = true;
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for (literal l : lits) {
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mark_visited(l.var());
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parity1 ^= l.sign();
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}
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for (auto const & w : get_wlist(lits[0])) {
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if (w.get_kind() != watched::EXT_CONSTRAINT) continue;
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constraint& c = index2constraint(w.get_ext_constraint_idx());
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if (!c.is_xr()) continue;
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xr& x = c.to_xr();
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if (sz + 1 != x.size()) continue;
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bool is_match = true;
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literal l0 = null_literal;
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bool parity2 = true;
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for (literal l : x) {
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if (!is_visited(l.var())) {
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if (l0 == null_literal) {
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l0 = l;
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}
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else {
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is_match = false;
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break;
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}
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}
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else {
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parity2 ^= l.sign();
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}
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}
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if (is_match) {
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SASSERT(all_distinct(x));
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if (parity1 == parity2) l0.neg();
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if (!learned && x.learned()) {
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set_non_learned(x);
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}
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return l0;
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}
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}
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bool_var v = s().mk_var(true, true);
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literal lit(v, false);
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lits.push_back(~lit);
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add_xr(lits, learned);
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return lit;
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}
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ba_solver::constraint* ba_solver::add_xr(literal_vector const& _lits, bool learned) {
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literal_vector lits;
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u_map<bool> var2sign;
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bool sign = false, odd = false;
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for (literal lit : _lits) {
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if (var2sign.find(lit.var(), sign)) {
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var2sign.erase(lit.var());
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odd ^= (sign ^ lit.sign());
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}
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else {
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var2sign.insert(lit.var(), lit.sign());
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}
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}
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for (auto const& kv : var2sign) {
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lits.push_back(literal(kv.m_key, kv.m_value));
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}
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if (odd && !lits.empty()) {
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lits[0].neg();
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}
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switch (lits.size()) {
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case 0:
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if (!odd)
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s().set_conflict(justification(0));
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return nullptr;
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case 1:
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s().assign_scoped(lits[0]);
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return nullptr;
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default:
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break;
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}
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void * mem = m_allocator.allocate(xr::get_obj_size(lits.size()));
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xr* x = new (mem) xr(this, next_id(), lits);
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x->set_learned(learned);
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add_constraint(x);
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return x;
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}
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/**
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\brief perform parity resolution on xr premises.
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The idea is to collect premises based on xr resolvents.
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Variables that are repeated an even number of times cancel out.
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*/
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void ba_solver::get_xr_antecedents(literal l, unsigned index, justification js, literal_vector& r) {
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unsigned level = lvl(l);
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bool_var v = l.var();
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SASSERT(js.get_kind() == justification::EXT_JUSTIFICATION);
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TRACE("ba", tout << l << ": " << js << "\n";
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for (unsigned i = 0; i <= index; ++i) tout << s().m_trail[i] << " "; tout << "\n";
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s().display_units(tout);
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);
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unsigned num_marks = 0;
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while (true) {
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TRACE("ba", tout << "process: " << l << " " << js << "\n";);
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if (js.get_kind() == justification::EXT_JUSTIFICATION) {
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constraint& c = index2constraint(js.get_ext_justification_idx());
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TRACE("ba", tout << c << "\n";);
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if (!c.is_xr()) {
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r.push_back(l);
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}
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else {
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xr& x = c.to_xr();
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if (x[1].var() == l.var()) {
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x.swap(0, 1);
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}
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VERIFY(x[0].var() == l.var());
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for (unsigned i = 1; i < x.size(); ++i) {
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literal lit(value(x[i]) == l_true ? x[i] : ~x[i]);
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inc_parity(lit.var());
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if (lvl(lit) == level) {
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TRACE("ba", tout << "mark: " << lit << "\n";);
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++num_marks;
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}
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else {
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m_parity_trail.push_back(lit);
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}
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}
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}
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}
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else {
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r.push_back(l);
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}
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bool found = false;
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while (num_marks > 0) {
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l = s().m_trail[index];
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v = l.var();
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unsigned n = get_parity(v);
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if (n > 0 && lvl(l) == level) {
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reset_parity(v);
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num_marks -= n;
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if (n % 2 == 1) {
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found = true;
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break;
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}
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}
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--index;
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}
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if (!found) {
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break;
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}
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--index;
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js = s().m_justification[v];
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}
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// now walk the defined literals
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for (literal lit : m_parity_trail) {
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if (get_parity(lit.var()) % 2 == 1) {
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r.push_back(lit);
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}
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else {
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// IF_VERBOSE(2, verbose_stream() << "skip even parity: " << lit << "\n";);
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}
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reset_parity(lit.var());
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}
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m_parity_trail.reset();
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TRACE("ba", tout << r << "\n";);
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}
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void ba_solver::pre_simplify() {
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VERIFY(s().at_base_lvl());
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if (s().inconsistent())
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return;
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m_constraint_removed = false;
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xor_finder xf(s());
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for (unsigned sz = m_constraints.size(), i = 0; i < sz; ++i) pre_simplify(xf, *m_constraints[i]);
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for (unsigned sz = m_learned.size(), i = 0; i < sz; ++i) pre_simplify(xf, *m_learned[i]);
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bool change = m_constraint_removed;
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cleanup_constraints();
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if (change) {
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// remove non-used variables.
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init_use_lists();
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remove_unused_defs();
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set_non_external();
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}
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}
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void ba_solver::simplify(xr& x) {
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if (x.learned()) {
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x.set_removed();
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m_constraint_removed = true;
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}
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}
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void ba_solver::get_antecedents(literal l, xr const& x, literal_vector& r) {
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if (x.lit() != null_literal) r.push_back(x.lit());
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// TRACE("ba", display(tout << l << " ", x, true););
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SASSERT(x.lit() == null_literal || value(x.lit()) == l_true);
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SASSERT(x[0].var() == l.var() || x[1].var() == l.var());
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if (x[0].var() == l.var()) {
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SASSERT(value(x[1]) != l_undef);
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r.push_back(value(x[1]) == l_true ? x[1] : ~x[1]);
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}
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else {
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SASSERT(value(x[0]) != l_undef);
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r.push_back(value(x[0]) == l_true ? x[0] : ~x[0]);
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}
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for (unsigned i = 2; i < x.size(); ++i) {
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SASSERT(value(x[i]) != l_undef);
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r.push_back(value(x[i]) == l_true ? x[i] : ~x[i]);
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}
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}
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lbool ba_solver::eval(xr const& x) const {
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bool odd = false;
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for (auto l : x) {
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switch (value(l)) {
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case l_true: odd = !odd; break;
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case l_false: break;
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default: return l_undef;
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}
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}
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return odd ? l_true : l_false;
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}
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lbool ba_solver::eval(model const& m, xr const& x) const {
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bool odd = false;
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for (auto l : x) {
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switch (value(m, l)) {
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case l_true: odd = !odd; break;
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case l_false: break;
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default: return l_undef;
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}
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}
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return odd ? l_true : l_false;
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}
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void ba_solver::pre_simplify(xor_finder& xf, constraint& c) {
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if (c.is_xr() && c.size() <= xf.max_xor_size()) {
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unsigned sz = c.size();
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literal_vector lits;
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bool parity = false;
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xr const& x = c.to_xr();
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for (literal lit : x) {
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parity ^= lit.sign();
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}
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// IF_VERBOSE(0, verbose_stream() << "blast: " << c << "\n");
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for (unsigned i = 0; i < (1ul << sz); ++i) {
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if (xf.parity(sz, i) == parity) {
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lits.reset();
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for (unsigned j = 0; j < sz; ++j) {
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lits.push_back(literal(x[j].var(), (0 != (i & (1 << j)))));
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}
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// IF_VERBOSE(0, verbose_stream() << lits << "\n");
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s().mk_clause(lits);
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}
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}
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c.set_removed();
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m_constraint_removed = true;
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}
|
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}
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bool ba_solver::clausify(xr& x) {
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return false;
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}
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// merge xors that contain cut variable
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void ba_solver::merge_xor() {
|
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unsigned sz = s().num_vars();
|
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for (unsigned i = 0; i < sz; ++i) {
|
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literal lit(i, false);
|
||||
unsigned index = lit.index();
|
||||
if (m_cnstr_use_list[index].size() == 2) {
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constraint& c1 = *m_cnstr_use_list[index][0];
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constraint& c2 = *m_cnstr_use_list[index][1];
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if (c1.is_xr() && c2.is_xr() &&
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m_clause_use_list.get(lit).empty() &&
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m_clause_use_list.get(~lit).empty()) {
|
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bool unique = true;
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||||
for (watched w : get_wlist(lit)) {
|
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if (w.is_binary_clause()) unique = false;
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}
|
||||
for (watched w : get_wlist(~lit)) {
|
||||
if (w.is_binary_clause()) unique = false;
|
||||
}
|
||||
if (!unique) continue;
|
||||
xr const& x1 = c1.to_xr();
|
||||
xr const& x2 = c2.to_xr();
|
||||
literal_vector lits, dups;
|
||||
bool parity = false;
|
||||
init_visited();
|
||||
for (literal l : x1) {
|
||||
mark_visited(l.var());
|
||||
lits.push_back(l);
|
||||
}
|
||||
for (literal l : x2) {
|
||||
if (is_visited(l.var())) {
|
||||
dups.push_back(l);
|
||||
}
|
||||
else {
|
||||
lits.push_back(l);
|
||||
}
|
||||
}
|
||||
init_visited();
|
||||
for (literal l : dups) mark_visited(l);
|
||||
unsigned j = 0;
|
||||
for (unsigned i = 0; i < lits.size(); ++i) {
|
||||
literal l = lits[i];
|
||||
if (is_visited(l)) {
|
||||
// skip
|
||||
}
|
||||
else if (is_visited(~l)) {
|
||||
parity ^= true;
|
||||
}
|
||||
else {
|
||||
lits[j++] = l;
|
||||
}
|
||||
}
|
||||
lits.shrink(j);
|
||||
if (!parity) lits[0].neg();
|
||||
IF_VERBOSE(1, verbose_stream() << "binary " << lits << " : " << c1 << " " << c2 << "\n");
|
||||
c1.set_removed();
|
||||
c2.set_removed();
|
||||
add_xr(lits, !c1.learned() && !c2.learned());
|
||||
m_constraint_removed = true;
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
void ba_solver::extract_xor() {
|
||||
xor_finder xf(s());
|
||||
std::function<void (literal_vector const&)> f = [this](literal_vector const& l) { add_xr(l, false); };
|
||||
xf.set(f);
|
||||
clause_vector clauses(s().clauses());
|
||||
xf(clauses);
|
||||
for (clause* cp : xf.removed_clauses()) {
|
||||
cp->set_removed(true);
|
||||
m_clause_removed = true;
|
||||
}
|
||||
}
|
||||
|
||||
void ba_solver::display(std::ostream& out, xr const& x, bool values) const {
|
||||
out << "xr: ";
|
||||
for (literal l : x) {
|
||||
out << l;
|
||||
if (values) {
|
||||
out << "@(" << value(l);
|
||||
if (value(l) != l_undef) {
|
||||
out << ":" << lvl(l);
|
||||
}
|
||||
out << ") ";
|
||||
}
|
||||
else {
|
||||
out << " ";
|
||||
}
|
||||
}
|
||||
out << "\n";
|
||||
}
|
||||
|
||||
bool ba_solver::validate_unit_propagation(xr const& x, literal alit) const {
|
||||
if (value(x.lit()) != l_true) return false;
|
||||
for (unsigned i = 1; i < x.size(); ++i) {
|
||||
if (value(x[i]) == l_undef) return false;
|
||||
}
|
||||
return true;
|
||||
}
|
||||
|
||||
}
|
||||
Loading…
Add table
Add a link
Reference in a new issue