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Merge branch 'polysat' of https://github.com/z3prover/z3 into polysat

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Nikolaj Bjorner 2021-09-13 13:14:29 +02:00
commit 6ffcea0bde
3 changed files with 27 additions and 77 deletions
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74
src/math/polysat/conflict_core.cpp
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@ -16,11 +16,6 @@ Notes:
TODO: try a final core reduction step or other core minimization
TODO: fallback lemma is redundant:
The core lemma uses m_vars and m_conflict directly instead of walking the stack.
It should be an invariant that the core is false (the negation of the core is valid modulo assertions).
The fallback lemma prunes at least the last value assignment.
TODO: If we have e.g. 4x+y=2 and y=0, then we have a conflict no matter the value of x, so we should drop x=? from the core.
(works currently if x is unassigned; for other cases we would need extra info from constraint::is_currently_false)
@ -209,41 +204,9 @@ namespace polysat {
s().propagate_bool_at(active_level, c.blit(), cl);
}
/** Create fallback lemma that excludes the current search state */
/**
* revisit: can prune literals further by slicing base on cone of influence
* based on marked literals/variables on the stack. Only decisions that affect
* marked items need to be included.
*/
clause_builder conflict_core::build_fallback_lemma(unsigned lvl) {
LOG_H3("Creating fallback lemma for level " << lvl);
LOG_V("m_search: " << s().m_search);
clause_builder lemma(s());
unsigned todo = lvl;
unsigned i = 0;
while (todo > 0) {
auto const& item = s().m_search[i++];
if (!s().is_decision(item))
continue;
LOG_V("Adding: " << item);
if (item.is_assignment()) {
pvar v = item.var();
auto c = ~s().eq(s().var(v), s().get_value(v));
cm().ensure_bvar(c.get());
lemma.push(c.blit());
} else {
sat::literal lit = item.lit();
lemma.push(~lit);
}
--todo;
}
return lemma;
}
clause_builder conflict_core::build_core_lemma(unsigned model_level) {
clause_builder conflict_core::build_core_lemma() {
LOG_H3("Build lemma from core");
LOG("core: " << *this);
LOG("model_level: " << model_level);
clause_builder lemma(s());
for (auto c : m_constraints) {
@ -258,8 +221,6 @@ namespace polysat {
SASSERT(s().is_assigned(v)); // note that we may have added too many variables: e.g., y disappears in x*y if x=0
if (!s().is_assigned(v))
continue;
if (s().get_level(v) > model_level)
continue;
auto diseq = ~s().eq(s().var(v), s().get_value(v));
cm().ensure_bvar(diseq.get());
lemma.push(diseq);
@ -268,13 +229,11 @@ namespace polysat {
return lemma;
}
clause_builder conflict_core::build_lemma(unsigned reverted_level) {
if (!is_bailout())
return build_core_lemma(reverted_level);
else if (m_bailout_lemma)
clause_builder conflict_core::build_lemma() {
if (m_bailout_lemma)
return *std::move(m_bailout_lemma);
else
return build_fallback_lemma(reverted_level);
return build_core_lemma();
}
bool conflict_core::resolve_value(pvar v, vector<signed_constraint> const& cjust_v) {
@ -298,18 +257,23 @@ namespace polysat {
for (auto c : cjust_v)
insert(c);
for (auto* engine : ex_engines)
if (engine->try_explain(v, *this))
return true;
if (!is_bailout()) {
for (auto* engine : ex_engines)
if (engine->try_explain(v, *this))
return true;
// No value resolution method was successful => fall back to saturation and variable elimination
while (s().inc()) {
// TODO: as a last resort, substitute v by m_value[v]?
if (try_eliminate(v))
return true;
if (!try_saturate(v))
break;
// No value resolution method was successful => fall back to saturation and variable elimination
while (s().inc()) {
// TODO: as a last resort, substitute v by m_value[v]?
if (try_eliminate(v))
return true;
if (!try_saturate(v))
break;
}
set_bailout();
}
m_vars.insert(v);
return false;
}