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better encodings for at-most-1, #755

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2016-10-10 23:46:03 -07:00
parent 5d9820f3e2
commit 8d2b70a5e2
17 changed files with 232 additions and 253 deletions
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244
src/smt/smt_consequences.cpp
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@ -251,191 +251,6 @@ namespace smt {
expr_ref_vector& conseq,
expr_ref_vector& unfixed) {
m_antecedents.reset();
pop_to_base_lvl();
lbool is_sat = check(assumptions.size(), assumptions.c_ptr());
if (is_sat != l_true) {
return is_sat;
}
obj_map<expr, expr*> var2val;
index_set _assumptions;
for (unsigned i = 0; i < assumptions.size(); ++i) {
_assumptions.insert(get_literal(assumptions[i]).var());
}
model_ref mdl;
get_model(mdl);
ast_manager& m = m_manager;
expr_ref_vector trail(m);
model_evaluator eval(*mdl.get());
expr_ref val(m);
TRACE("context", model_pp(tout, *mdl););
for (unsigned i = 0; i < vars.size(); ++i) {
eval(vars[i], val);
if (m.is_value(val)) {
trail.push_back(val);
var2val.insert(vars[i], val);
}
else {
unfixed.push_back(vars[i]);
}
}
unsigned num_units = 0;
extract_fixed_consequences(num_units, var2val, _assumptions, conseq);
app_ref eq(m);
TRACE("context",
tout << "vars: " << vars.size() << "\n";
tout << "lits: " << num_units << "\n";);
m_case_split_queue->init_search_eh();
unsigned num_iterations = 0;
unsigned model_threshold = 2;
unsigned num_fixed_eqs = 0;
unsigned num_reiterations = 0;
while (!var2val.empty()) {
obj_map<expr,expr*>::iterator it = var2val.begin();
expr* e = it->m_key;
expr* val = it->m_value;
TRACE("context", tout << "scope level: " << get_scope_level() << "\n";);
SASSERT(!inconsistent());
//
// The current variable is checked to be a backbone
// We add the negation of the reference assignment to the variable.
// If the variable is a Boolean, it means adding literal that has
// the opposite value of the current reference model.
// If the variable is a non-Boolean, it means adding a disequality.
//
literal lit = mk_diseq(e, val);
mark_as_relevant(lit);
push_scope();
assign(lit, b_justification::mk_axiom(), true);
flet<bool> l(m_searching, true);
//
// We check if the current assignment stack can be extended to a
// satisfying assignment. bounded search may decide to restart,
// in which case it returns l_undef and clears search failure.
//
while (true) {
is_sat = bounded_search();
TRACE("context", tout << "search result: " << is_sat << "\n";);
if (is_sat != l_true && m_last_search_failure != OK) {
return is_sat;
}
if (is_sat == l_undef) {
TRACE("context", tout << "restart\n";);
inc_limits();
continue;
}
break;
}
//
// If the state is satisfiable with the current variable assigned to
// a different value from the reference model, it is unfixed.
//
// If it is assigned above the search level we can't conclude anything
// about its value.
// extract_fixed_consequences pops the assignment stack to the search level
// so this sets up the state to retry finding fixed values.
//
// Otherwise, the variable is fixed.
// - it is either assigned at the search level to l_false, or
// - the state is l_false, which means that the variable is fixed by
// the background constraints (and does not depend on assumptions).
//
if (is_sat == l_true && get_assignment(lit) == l_true && is_relevant(lit)) {
var2val.erase(e);
unfixed.push_back(e);
SASSERT(!are_equal(e, val));
TRACE("context", tout << mk_pp(e, m) << " is unfixed\n";
display_literal_verbose(tout, lit); tout << "\n";
tout << "relevant: " << is_relevant(lit) << "\n";
display(tout););
}
else if (is_sat == l_true && (get_assign_level(lit) > get_search_level() || !is_relevant(lit))) {
TRACE("context", tout << "Retry fixing: " << mk_pp(e, m) << "\n";);
extract_fixed_consequences(num_units, var2val, _assumptions, conseq);
++num_reiterations;
continue;
}
else {
//
// The state can be labeled as inconsistent when the implied consequence does
// not depend on assumptions, then the conflict level sits at the search level
// which causes the conflict resolver to decide that the state is unsat.
//
if (l_false == is_sat) {
SASSERT(inconsistent());
m_conflict = null_b_justification;
m_not_l = null_literal;
}
TRACE("context", tout << "Fixed: " << mk_pp(e, m) << " " << is_sat << "\n";
if (is_sat == l_false) display(tout););
}
++num_iterations;
//
// Check the slow pass: it retrieves an updated model and checks if the
// values in the updated model differ from the values in the reference
// model.
//
bool apply_slow_pass = model_threshold <= num_iterations || num_iterations <= 2;
if (apply_slow_pass && is_sat == l_true) {
delete_unfixed(var2val, unfixed);
// The next time we check the model is after 1.5 additional iterations.
model_threshold *= 3;
model_threshold /= 2;
}
//
// Walk the assignment stack at level 1 for learned consequences.
// The current literal should be assigned at the search level unless
// the state is is_sat == l_true and the assignment to lit is l_true.
// This condition is checked above.
//
extract_fixed_consequences(num_units, var2val, _assumptions, conseq);
//
// Fixed equalities can be extracted by walking all variables and checking
// if the congruence roots are equal at the search level.
//
if (apply_slow_pass) {
num_fixed_eqs += extract_fixed_eqs(var2val, conseq);
IF_VERBOSE(1, display_consequence_progress(verbose_stream(), num_iterations, var2val.size(), conseq.size(),
unfixed.size(), num_fixed_eqs););
TRACE("context", display_consequence_progress(tout, num_iterations, var2val.size(), conseq.size(),
unfixed.size(), num_fixed_eqs););
}
TRACE("context", tout << "finishing " << mk_pp(e, m) << "\n";);
SASSERT(!inconsistent());
//
// This becomes unnecessary when the fixed consequence are
// completely extracted.
//
if (var2val.contains(e)) {
TRACE("context", tout << "Fixed value to " << mk_pp(e, m) << " was not processed\n";);
expr_ref fml(m);
fml = m.mk_eq(e, var2val.find(e));
if (!m_antecedents.contains(lit.var())) {
extract_fixed_consequences(lit, var2val, _assumptions, conseq);
}
fml = m.mk_implies(antecedent2fml(m_antecedents[lit.var()]), fml);
conseq.push_back(fml);
var2val.erase(e);
}
}
end_search();
DEBUG_CODE(validate_consequences(assumptions, vars, conseq, unfixed););
return l_true;
}
lbool context::get_consequences2(expr_ref_vector const& assumptions,
expr_ref_vector const& vars,
expr_ref_vector& conseq,
expr_ref_vector& unfixed) {
m_antecedents.reset();
pop_to_base_lvl();
lbool is_sat = check(assumptions.size(), assumptions.c_ptr());
@ -552,6 +367,65 @@ namespace smt {
}
lbool context::find_mutexes(expr_ref_vector const& vars, vector<expr_ref_vector>& mutexes) {
index_set lits;
for (unsigned i = 0; i < vars.size(); ++i) {
expr* n = vars[i];
bool neg = m_manager.is_not(n, n);
if (b_internalized(n)) {
lits.insert(literal(get_bool_var(n), !neg).index());
}
}
while (!lits.empty()) {
literal_vector mutex;
index_set other(lits);
while (!other.empty()) {
index_set conseq;
literal p = to_literal(*other.begin());
other.erase(p.index());
mutex.push_back(p);
if (other.empty()) {
break;
}
get_reachable(p, other, conseq);
other = conseq;
}
if (mutex.size() > 1) {
expr_ref_vector mux(m_manager);
for (unsigned i = 0; i < mutex.size(); ++i) {
expr_ref e(m_manager);
literal2expr(mutex[i], e);
mux.push_back(e);
}
mutexes.push_back(mux);
}
for (unsigned i = 0; i < mutex.size(); ++i) {
lits.remove(mutex[i].index());
}
}
return l_true;
}
void context::get_reachable(literal p, index_set& goal, index_set& reachable) {
index_set seen;
literal_vector todo;
todo.push_back(p);
while (!todo.empty()) {
p = todo.back();
todo.pop_back();
if (seen.contains(p.index())) {
continue;
}
seen.insert(p.index());
literal np = ~p;
if (goal.contains(np.index())) {
reachable.insert(np.index());
}
watch_list & w = m_watches[np.index()];
todo.append(static_cast<unsigned>(w.end_literals() - w.begin_literals()), w.begin_literals());
}
}
//
// Validate, in a slow pass, that the current consequences are correctly
// extracted.