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z3/src/smt/smt_model_checker.cpp
2020-04-26 12:59:51 -07:00

566 lines
21 KiB
C++

/*++
Copyright (c) 2006 Microsoft Corporation
Module Name:
smt_model_checker.cpp
Abstract:
Model checker
Author:
Leonardo de Moura (leonardo) 2010-12-03.
Revision History:
- to support lambdas/array models:
binding sk -> (as-array k!0)
then include definition for k!0 as part of binding.
Binding instance can be a pointer into m_pinned expressions.
--*/
#include "ast/normal_forms/pull_quant.h"
#include "ast/for_each_expr.h"
#include "ast/rewriter/var_subst.h"
#include "ast/rewriter/rewriter_def.h"
#include "ast/ast_pp.h"
#include "ast/array_decl_plugin.h"
#include "ast/ast_smt2_pp.h"
#include "smt/smt_model_checker.h"
#include "smt/smt_context.h"
#include "smt/smt_model_finder.h"
#include "model/model_pp.h"
#include <tuple>
namespace smt {
model_checker::model_checker(ast_manager & m, qi_params const & p, model_finder & mf):
m(m),
m_params(p),
m_autil(m),
m_qm(nullptr),
m_context(nullptr),
m_root2value(nullptr),
m_model_finder(mf),
m_max_cexs(1),
m_iteration_idx(0),
m_curr_model(nullptr),
m_fresh_exprs(m),
m_pinned_exprs(m) {
}
model_checker::~model_checker() {
m_aux_context = nullptr; // delete aux context before fparams
m_fparams = nullptr;
}
quantifier * model_checker::get_flat_quantifier(quantifier * q) {
return m_model_finder.get_flat_quantifier(q);
}
void model_checker::set_qm(quantifier_manager & qm) {
SASSERT(m_qm == nullptr);
SASSERT(m_context == nullptr);
m_qm = &qm;
m_context = &(m_qm->get_context());
}
/**
\brief Return a term in the context that evaluates to val.
*/
expr * model_checker::get_term_from_ctx(expr * val) {
init_value2expr();
expr * t = nullptr;
m_value2expr.find(val, t);
return t;
}
expr * model_checker::get_type_compatible_term(expr * val) {
app* fresh_term;
if (is_app(val) && to_app(val)->get_num_args() > 0) {
ptr_buffer<expr> args;
for (expr* arg : *to_app(val)) {
args.push_back(get_type_compatible_term(arg));
}
fresh_term = m.mk_app(to_app(val)->get_decl(), args.size(), args.c_ptr());
}
else {
expr * sk_term = get_term_from_ctx(val);
if (sk_term != nullptr) {
return sk_term;
}
for (expr* f : m_fresh_exprs) {
if (m.get_sort(f) == m.get_sort(val)) {
return f;
}
}
fresh_term = m.mk_fresh_const("sk", m.get_sort(val));
}
m_fresh_exprs.push_back(fresh_term);
m_context->ensure_internalized(fresh_term);
return fresh_term;
}
void model_checker::init_value2expr() {
if (m_value2expr.empty()) {
// populate m_value2expr
for (auto const& kv : *m_root2value) {
enode * n = kv.m_key;
expr * val = kv.m_value;
n = n->get_eq_enode_with_min_gen();
m_value2expr.insert(val, n->get_owner());
}
}
}
expr_ref model_checker::replace_value_from_ctx(expr * e) {
init_value2expr();
struct beta_reducer_cfg : default_rewriter_cfg {
model_checker& mc;
beta_reducer_cfg(model_checker& mc):mc(mc) {}
bool get_subst(expr * e, expr* & t, proof *& pr) {
t = nullptr; pr = nullptr;
mc.m_value2expr.find(e, t);
return t != nullptr;
}
};
struct beta_reducer : public rewriter_tpl<beta_reducer_cfg> {
beta_reducer_cfg m_cfg;
beta_reducer(model_checker& m):
rewriter_tpl<beta_reducer_cfg>(m.m, false, m_cfg), m_cfg(m) {}
};
beta_reducer br(*this);
expr_ref result(m);
br(e, result);
return result;
}
/**
\brief Assert in m_aux_context, the constraint
sk = e_1 OR ... OR sk = e_n
where {e_1, ..., e_n} is the universe.
*/
void model_checker::restrict_to_universe(expr * sk, obj_hashtable<expr> const & universe) {
SASSERT(!universe.empty());
ptr_buffer<expr> eqs;
for (expr * e : universe) {
eqs.push_back(m.mk_eq(sk, e));
}
expr_ref fml(m.mk_or(eqs.size(), eqs.c_ptr()), m);
m_aux_context->assert_expr(fml);
}
/**
\brief Assert the negation of q after applying the interpretation in m_curr_model to the uninterpreted symbols in q.
The variables are replaced by skolem constants. These constants are stored in sks.
*/
void model_checker::assert_neg_q_m(quantifier * q, expr_ref_vector & sks) {
expr_ref tmp(m);
TRACE("model_checker", tout << "curr_model:\n"; model_pp(tout, *m_curr_model););
if (!m_curr_model->eval(q->get_expr(), tmp, true)) {
return;
}
TRACE("model_checker", tout << "q after applying interpretation:\n" << mk_ismt2_pp(tmp, m) << "\n";);
ptr_buffer<expr> subst_args;
unsigned num_decls = q->get_num_decls();
subst_args.resize(num_decls, nullptr);
sks.resize(num_decls, nullptr);
for (unsigned i = 0; i < num_decls; i++) {
sort * s = q->get_decl_sort(num_decls - i - 1);
expr * sk = m.mk_fresh_const(nullptr, s);
sks[num_decls - i - 1] = sk;
subst_args[num_decls - i - 1] = sk;
if (m_curr_model->is_finite(s)) {
restrict_to_universe(sk, m_curr_model->get_known_universe(s));
}
}
var_subst s(m);
expr_ref sk_body = s(tmp, subst_args.size(), subst_args.c_ptr());
expr_ref r(m);
r = m.mk_not(sk_body);
TRACE("model_checker", tout << "mk_neg_q_m:\n" << mk_ismt2_pp(r, m) << "\n";);
m_aux_context->assert_expr(r);
}
bool model_checker::add_instance(quantifier * q, model * cex, expr_ref_vector & sks, bool use_inv) {
if (cex == nullptr || sks.empty()) {
TRACE("model_checker", tout << "no model is available\n";);
return false;
}
array_util autil(m);
unsigned num_decls = q->get_num_decls();
// Remark: sks were created for the flat version of q.
SASSERT(sks.size() >= num_decls);
expr_ref_vector bindings(m), defs(m);
expr_ref def(m);
bindings.resize(num_decls);
unsigned max_generation = 0;
for (unsigned i = 0; i < num_decls; i++) {
expr * sk = sks.get(num_decls - i - 1);
func_decl * sk_d = to_app(sk)->get_decl();
expr_ref sk_value(cex->get_some_const_interp(sk_d), m);
if (!sk_value) {
TRACE("model_checker", tout << "Could not get value for " << sk_d->get_name() << "\n";);
return false; // get_some_value failed... giving up
}
TRACE("model_checker", tout << "Got some value " << sk_value << "\n";);
if (use_inv) {
unsigned sk_term_gen;
expr * sk_term = m_model_finder.get_inv(q, i, sk_value, sk_term_gen);
if (sk_term != nullptr) {
TRACE("model_checker", tout << "Found inverse " << mk_pp(sk_term, m) << "\n";);
SASSERT(!m.is_model_value(sk_term));
max_generation = std::max(sk_term_gen, max_generation);
sk_value = sk_term;
}
else {
TRACE("model_checker", tout << "no inverse value for " << sk_value << "\n";);
return false;
}
}
else {
expr * sk_term = get_term_from_ctx(sk_value);
if (sk_term != nullptr) {
sk_value = sk_term;
}
}
if (contains_model_value(sk_value)) {
sk_value = get_type_compatible_term(sk_value);
}
func_decl * f = nullptr;
if (autil.is_as_array(sk_value, f) && cex->get_func_interp(f) && cex->get_func_interp(f)->get_interp()) {
expr_ref body(cex->get_func_interp(f)->get_interp(), m);
ptr_vector<sort> sorts(f->get_arity(), f->get_domain());
svector<symbol> names;
for (unsigned i = 0; i < f->get_arity(); ++i) {
names.push_back(symbol(i));
}
defined_names dn(m);
body = replace_value_from_ctx(body);
body = m.mk_lambda(sorts.size(), sorts.c_ptr(), names.c_ptr(), body);
// sk_value = m.mk_fresh_const(0, m.get_sort(sk_value)); // get rid of as-array
body = dn.mk_definition(body, to_app(sk_value));
defs.push_back(body);
}
bindings.set(num_decls - i - 1, sk_value);
}
TRACE("model_checker", tout << q->get_qid() << " found (use_inv: " << use_inv << ") new instance: " << bindings << "\n" << defs << "\n";);
if (!defs.empty()) def = mk_and(defs);
max_generation = std::max(m_qm->get_generation(q), max_generation);
add_instance(q, bindings, max_generation, def.get());
return true;
}
void model_checker::add_instance(quantifier* q, expr_ref_vector const& bindings, unsigned max_generation, expr* def) {
SASSERT(q->get_num_decls() == bindings.size());
unsigned offset = m_pinned_exprs.size();
m_pinned_exprs.append(bindings);
m_pinned_exprs.push_back(q);
m_pinned_exprs.push_back(def);
m_new_instances.push_back(instance(q, offset, def, max_generation));
}
void model_checker::operator()(expr *n) {
if (m.is_model_value(n) /*|| m_autil.is_as_array(n)*/) {
throw is_model_value();
}
}
bool model_checker::contains_model_value(expr* n) {
if (m.is_model_value(n) /*|| m_autil.is_as_array(n)*/) {
return true;
}
if (is_app(n) && to_app(n)->get_num_args() == 0) {
return false;
}
m_visited.reset();
try {
for_each_expr(*this, m_visited, n);
}
catch (const is_model_value &) {
return true;
}
return false;
}
bool model_checker::add_blocking_clause(model * cex, expr_ref_vector & sks) {
SASSERT(cex != nullptr);
expr_ref_buffer diseqs(m);
for (expr * sk : sks) {
func_decl * sk_d = to_app(sk)->get_decl();
expr_ref sk_value(cex->get_some_const_interp(sk_d), m);
if (!sk_value) {
TRACE("model_checker", tout << "no constant interpretation for " << mk_pp(sk, m) << "\n";);
return false; // get_some_value failed... aborting add_blocking_clause
}
diseqs.push_back(m.mk_not(m.mk_eq(sk, sk_value)));
}
expr_ref blocking_clause(m);
blocking_clause = m.mk_or(diseqs.size(), diseqs.c_ptr());
TRACE("model_checker", tout << "blocking clause:\n" << mk_ismt2_pp(blocking_clause, m) << "\n";);
m_aux_context->assert_expr(blocking_clause);
return true;
}
struct scoped_ctx_push {
context* c;
scoped_ctx_push(context* c): c(c) { c->push(); }
~scoped_ctx_push() { c->pop(1); }
};
/**
\brief Return true if q is satisfied by m_curr_model.
*/
bool model_checker::check(quantifier * q) {
SASSERT(!m_aux_context->relevancy());
scoped_ctx_push _push(m_aux_context.get());
quantifier * flat_q = get_flat_quantifier(q);
TRACE("model_checker", tout << "model checking:\n" << expr_ref(flat_q->get_expr(), m) << "\n";);
expr_ref_vector sks(m);
assert_neg_q_m(flat_q, sks);
TRACE("model_checker", tout << "skolems:\n" << sks << "\n";);
flet<bool> l(m_aux_context->get_fparams().m_array_fake_support, true);
lbool r = m_aux_context->check();
TRACE("model_checker", tout << "[complete] model-checker result: " << to_sat_str(r) << "\n";);
if (r != l_true) {
return r == l_false; // quantifier is satisfied by m_curr_model
}
model_ref complete_cex;
m_aux_context->get_model(complete_cex);
// try to find new instances using instantiation sets.
m_model_finder.restrict_sks_to_inst_set(m_aux_context.get(), q, sks);
unsigned num_new_instances = 0;
while (true) {
flet<bool> l(m_aux_context->get_fparams().m_array_fake_support, true);
lbool r = m_aux_context->check();
TRACE("model_checker", tout << "[restricted] model-checker (" << (num_new_instances+1) << ") result: " << to_sat_str(r) << "\n";);
if (r != l_true)
break;
model_ref cex;
m_aux_context->get_model(cex);
if (!add_instance(q, cex.get(), sks, true)) {
break;
}
num_new_instances++;
if (num_new_instances >= m_max_cexs || !add_blocking_clause(cex.get(), sks)) {
TRACE("model_checker", tout << "Add blocking clause failed new-instances: " << num_new_instances << " max-cex: " << m_max_cexs << "\n";);
// add_blocking_clause failed... stop the search for new counter-examples...
break;
}
}
if (num_new_instances == 0) {
// failed to create instances when restricting to inst sets... then use result of the complete model check
TRACE("model_checker", tout << "using complete_cex result:\n"; model_pp(tout, *complete_cex););
add_instance(q, complete_cex.get(), sks, false);
}
return false;
}
void model_checker::init_aux_context() {
if (!m_fparams) {
m_fparams = alloc(smt_params, m_context->get_fparams());
m_fparams->m_relevancy_lvl = 0; // no relevancy since the model checking problems are quantifier free
m_fparams->m_case_split_strategy = CS_ACTIVITY; // avoid warning messages about smt.case_split >= 3.
m_fparams->m_arith_dump_lemmas = false;
}
if (!m_aux_context) {
symbol logic;
params_ref p;
p.set_bool("arith.dump_lemmas", false);
m_aux_context = m_context->mk_fresh(&logic, m_fparams.get(), p);
}
}
bool model_checker::check(proto_model * md, obj_map<enode, app *> const & root2value) {
SASSERT(md != nullptr);
m_root2value = &root2value;
if (m_qm->num_quantifiers() == 0)
return true;
if (m_iteration_idx >= m_params.m_mbqi_max_iterations) {
IF_VERBOSE(1, verbose_stream() << "(smt.mbqi \"max instantiations " << m_iteration_idx << " reached\")\n";);
m_context->set_reason_unknown("max mbqi instantiations reached");
return false;
}
m_curr_model = md;
m_value2expr.reset();
TRACE("model_checker", tout << "MODEL_CHECKER INVOKED\n";
tout << "model:\n"; model_pp(tout, *m_curr_model););
md->compress();
TRACE("model_checker", tout << "MODEL_CHECKER INVOKED\n";
tout << "model:\n"; model_pp(tout, *m_curr_model););
if (m_params.m_mbqi_trace) {
verbose_stream() << "(smt.mbqi \"started\")\n";
}
init_aux_context();
bool found_relevant = false;
unsigned num_failures = 0;
check_quantifiers(found_relevant, num_failures);
if (found_relevant)
m_iteration_idx++;
TRACE("model_checker", tout << "model after check:\n"; model_pp(tout, *md););
TRACE("model_checker", tout << "model checker result: " << (num_failures == 0) << "\n";);
m_max_cexs += m_params.m_mbqi_max_cexs;
if (num_failures == 0 && (!m_context->validate_model())) {
num_failures = 1;
// this time force expanding recursive function definitions
// that are not forced true in the current model.
check_quantifiers(found_relevant, num_failures);
}
if (num_failures == 0)
m_curr_model->cleanup();
if (m_params.m_mbqi_trace) {
if (num_failures == 0)
verbose_stream() << "(smt.mbqi :succeeded true)\n";
else
verbose_stream() << "(smt.mbqi :num-failures " << num_failures << ")\n";
}
return num_failures == 0;
}
//
// (repeated from defined_names.cpp)
// NB. The pattern for lambdas is incomplete.
// consider store(a, i, v) == \lambda j . if i = j then v else a[j]
// the instantiation rules for store(a, i, v) are:
// sotre(a, i, v)[j] = if i = j then v else a[j] with patterns {a[j], store(a, i, v)} { store(a, i, v)[j] }
// The first pattern is not included.
// TBD use a model-based scheme for extracting instantiations instead of
// using multi-patterns.
//
void model_checker::check_quantifiers(bool& found_relevant, unsigned& num_failures) {
for (quantifier * q : *m_qm) {
if (!(m_qm->mbqi_enabled(q) &&
m_context->is_relevant(q) &&
m_context->get_assignment(q) == l_true &&
(!m_context->get_fparams().m_ematching || !m.is_lambda_def(q)))) {
continue;
}
TRACE("model_checker",
tout << "Check: " << mk_pp(q, m) << "\n";
tout << m_context->get_assignment(q) << "\n";);
if (m_params.m_mbqi_trace && q->get_qid() != symbol::null) {
verbose_stream() << "(smt.mbqi :checking " << q->get_qid() << ")\n";
}
found_relevant = true;
if (!check(q)) {
if (m_params.m_mbqi_trace || get_verbosity_level() >= 5) {
IF_VERBOSE(0, verbose_stream() << "(smt.mbqi :failed " << q->get_qid() << ")\n");
}
TRACE("model_checker", tout << "checking quantifier " << mk_pp(q, m) << " failed\n";);
num_failures++;
}
}
}
void model_checker::init_search_eh() {
m_max_cexs = m_params.m_mbqi_max_cexs;
m_iteration_idx = 0;
}
void model_checker::restart_eh() {
IF_VERBOSE(100, if (has_new_instances()) verbose_stream() << "(smt.mbqi \"instantiating new instances...\")\n";);
assert_new_instances();
reset_new_instances();
}
bool model_checker::has_new_instances() {
TRACE("model_checker", tout << "instances: " << m_new_instances.size() << "\n";);
return !m_new_instances.empty();
}
void model_checker::reset_new_instances() {
m_pinned_exprs.reset();
m_new_instances.reset();
}
void model_checker::reset() {
reset_new_instances();
}
void model_checker::assert_new_instances() {
TRACE("model_checker_bug_detail", tout << "assert_new_instances, inconsistent: " << m_context->inconsistent() << "\n";);
ptr_buffer<enode> bindings;
vector<std::tuple<enode *, enode *>> dummy;
for (instance const& inst : m_new_instances) {
quantifier * q = inst.m_q;
if (m_context->b_internalized(q)) {
bindings.reset();
unsigned num_decls = q->get_num_decls();
unsigned gen = inst.m_generation;
unsigned offset = inst.m_bindings_offset;
for (unsigned i = 0; i < num_decls; i++) {
expr * b = m_pinned_exprs.get(offset + i);
if (!m_context->e_internalized(b)) {
TRACE("model_checker", tout << "internalizing b:\n" << mk_pp(b, m) << "\n";);
m_context->internalize(b, false, gen);
}
bindings.push_back(m_context->get_enode(b));
}
if (inst.m_def) {
unsigned n = 1;
expr* const* args = &inst.m_def;
if (m.is_and(inst.m_def)) {
n = to_app(inst.m_def)->get_num_args();
args = to_app(inst.m_def)->get_args();
}
for (unsigned i = 0; i < n; ++i) {
proof* pr = nullptr;
expr* arg = args[i];
if (m.proofs_enabled()) {
pr = m.mk_def_intro(arg);
}
m_context->internalize_assertion(arg, pr, gen);
}
}
TRACE("model_checker_bug_detail", tout << "instantiating... q:\n" << mk_pp(q, m) << "\n";
tout << "inconsistent: " << m_context->inconsistent() << "\n";
tout << "bindings:\n" << expr_ref_vector(m, num_decls, m_pinned_exprs.c_ptr() + offset) << "\n";);
m_context->add_instance(q, nullptr, num_decls, bindings.c_ptr(), inst.m_def, gen, gen, gen, dummy);
TRACE("model_checker_bug_detail", tout << "after instantiating, inconsistent: " << m_context->inconsistent() << "\n";);
}
}
}
};