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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2021-11-08 05:08:57 -08:00
parent e1bc9cc0bb
commit 57c40e480b
8 changed files with 120 additions and 96 deletions
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92
src/math/polysat/solver.cpp
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@ -126,7 +126,7 @@ namespace polysat {
set_conflict(c /*, dep */);
return;
}
m_bvars.assign(lit, m_level, nullptr, nullptr, dep);
m_bvars.asserted(lit, m_level, dep);
m_trail.push_back(trail_instr_t::assign_bool_i);
m_search.push_boolean(lit);
@ -206,7 +206,7 @@ namespace polysat {
if (m_bvars.is_false(cl[idx]))
set_conflict(cl);
else
assign_bool(level(cl), cl[idx], &cl, nullptr);
assign_propagate(cl[idx], cl);
return false;
}
@ -539,7 +539,11 @@ namespace polysat {
break;
case l_undef:
num_choices++;
if (!lit2cnstr(lit).is_currently_false(*this))
if (lit2cnstr(lit).is_currently_false(*this)) {
unsigned level = m_level; // TODO
assign_eval(level, lit);
}
else
choice = lit;
break;
}
@ -558,9 +562,9 @@ namespace polysat {
push_cjust(lemma.justified_var(), c);
if (num_choices == 1)
assign_bool(level(lemma), choice, &lemma, nullptr);
assign_propagate(choice, lemma);
else
assign_bool(m_level, choice, nullptr, &lemma);
assign_decision(choice, &lemma);
}
/**
@ -597,48 +601,31 @@ namespace polysat {
return m_bvars.is_decision(item.lit().var());
}
// Current situation: we have a decision for boolean literal L on top of the stack, and a conflict core.
//
// In a CDCL solver, this means ~L is in the lemma (actually, as the asserting literal). We drop the decision and replace it by the propagation (~L)^lemma.
//
// - we know L must be false
// - if L isn't in the core, we can still add it (weakening the lemma) to obtain "core => ~L"
// - then we can add the propagation (~L)^lemma and continue with the next guess
// Note that if we arrive at this point, the variables in L are "relevant" to the conflict (otherwise we would have skipped L).
// So the subsequent steps must have contained one of these:
// - propagation of some variable v from L (and maybe other constraints)
// (v := val)^{L, ...}
// this means L is in core, unless we core-reduced it away
// - propagation of L' from L
// (L')^{L' \/ ¬L \/ ...}
// again L is in core, unless we core-reduced it away
void solver::revert_bool_decision(sat::literal lit) {
sat::bool_var const var = lit.var();
LOG_H3("Reverting boolean decision: " << lit << " " << m_conflict);
SASSERT(m_bvars.is_decision(var));
// Current situation: we have a decision for boolean literal L on top of the stack, and a conflict core.
//
// In a CDCL solver, this means ~L is in the lemma (actually, as the asserting literal). We drop the decision and replace it by the propagation (~L)^lemma.
//
// - we know L must be false
// - if L isn't in the core, we can still add it (weakening the lemma) to obtain "core => ~L"
// - then we can add the propagation (~L)^lemma and continue with the next guess
// Note that if we arrive at this point, the variables in L are "relevant" to the conflict (otherwise we would have skipped L).
// So the subsequent steps must have contained one of these:
// - propagation of some variable v from L (and maybe other constraints)
// (v := val)^{L, ...}
// this means L is in core, unless we core-reduced it away
// - propagation of L' from L
// (L')^{L' \/ ¬L \/ ...}
// again L is in core, unless we core-reduced it away
clause_builder reason_builder = m_conflict.build_lemma();
clause_builder reason_builder = m_conflict.build_lemma();
SASSERT(std::find(reason_builder.begin(), reason_builder.end(), ~lit));
#if 0
if (!contains_lit) {
// At this point, we do not have ~lit in the reason.
// For now, we simply add it (thus weakening the reason)
//
// Alternative (to be considered later):
// - 'reason' itself (without ~L) would already be an explanation for ~L
// - however if it doesn't contain ~L, it breaks the boolean resolution invariant
// - would need to check what we can gain by relaxing that invariant
// - drawback: might have to bail out at boolean resolution
// Also: maybe we can skip ~L in some cases? but in that case it shouldn't be marked.
//
std::cout << "ADD extra " << ~lit << "\n";
reason_builder.push(~lit);
}
#endif
clause_ref reason = reason_builder.build();
if (reason->empty()) {
@ -666,7 +653,7 @@ namespace polysat {
SASSERT(!can_propagate());
SASSERT(!is_conflict());
push_level();
assign_bool(m_level, lit, nullptr, lemma);
assign_decision(lit, lemma);
}
unsigned solver::level(clause const& cl) {
@ -679,15 +666,20 @@ namespace polysat {
return lvl;
}
/// Assign a boolean literal and put it on the search stack
void solver::assign_bool(unsigned level, sat::literal lit, clause* reason, clause* lemma) {
SASSERT(!m_bvars.is_true(lit));
if (reason)
LOG("Propagate literal " << lit << " @ " << level << " by " << *reason);
else
LOG("Decide literal " << lit << " @ " << m_level);
m_bvars.assign(lit, level, reason, lemma);
void solver::assign_propagate(sat::literal lit, clause& reason) {
m_bvars.propagate(lit, level(reason), reason);
m_trail.push_back(trail_instr_t::assign_bool_i);
m_search.push_boolean(lit);
}
void solver::assign_decision(sat::literal lit, clause* lemma) {
m_bvars.decide(lit, m_level, lemma);
m_trail.push_back(trail_instr_t::assign_bool_i);
m_search.push_boolean(lit);
}
void solver::assign_eval(unsigned level, sat::literal lit) {
m_bvars.eval(lit, level);
m_trail.push_back(trail_instr_t::assign_bool_i);
m_search.push_boolean(lit);
}