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Give higher priority to boolean propagation and bool/eval conflicts

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This commit is contained in:
Jakob Rath 2023-03-10 15:30:01 +01:00
parent 538c4ee25f
commit c8c40f0154
1 changed files with 38 additions and 7 deletions
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45
src/math/polysat/solver.cpp
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@ -206,12 +206,45 @@ namespace polysat {
flet<bool> save_(m_is_propagating, true);
#endif
push_qhead();
unsigned bool_qhead = m_qhead;
unsigned eval_qhead = m_qhead;
while (can_propagate()) {
auto const& item = m_search[m_qhead++];
if (item.is_assignment())
propagate(item.var());
else
propagate(item.lit());
SASSERT(bool_qhead >= eval_qhead);
SASSERT(eval_qhead >= m_qhead);
if (bool_qhead < m_search.size()) {
// First priority: propagate boolean values
auto const& item = m_search[bool_qhead++];
if (item.is_boolean())
propagate(item.lit());
}
else if (eval_qhead < m_search.size()) {
// Second priority: check for bool/eval conflicts
//
// Why do we do this here? Consider the situation:
// - Literal L is bool-propagated by some clause, so L is put on the propagation queue (m_search)
// - Before we get to activate/narrow L, we reach another constraint L' in the queue
// - Narrowing L' causes a viable conflict
// - When building the viable lemma, one of the linking constraints happens to be L
// - L is bool-true but eval-false --> we actually have a bool/eval conflict that we didn't detect
// - the viable lemma is problematic because L is bool-true
auto const& item = m_search[eval_qhead++];
if (item.is_boolean()) {
// TODO: what happens if evaluation depends on a variable assignment that occurs later in m_search? can that happen? should not happen because we only narrow after exhausting this branch; and narrow is the only place where we do value propagation.
signed_constraint c = lit2cnstr(item.lit());
if (c.is_currently_false(*this))
set_conflict(c);
}
}
else {
// Third priority: activate/narrow
auto const& item = m_search[m_qhead++];
if (item.is_assignment())
propagate(item.var());
else {
signed_constraint c = lit2cnstr(item.lit());
activate_constraint(c);
}
}
}
if (!is_conflict())
linear_propagate();
@ -279,8 +312,6 @@ namespace polysat {
void solver::propagate(sat::literal lit) {
LOG_H2("Propagate bool " << lit << "@" << m_bvars.level(lit) << " " << m_level << " qhead: " << m_qhead);
LOG("Literal " << lit_pp(*this, lit));
signed_constraint c = lit2cnstr(lit);
activate_constraint(c);
auto& wlist = m_bvars.watch(~lit);
LOG("wlist[" << ~lit << "]: " << wlist);
unsigned i = 0, j = 0, sz = wlist.size();