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z3str3: make counterexamples less naive, and check regex membership more efficiently (#4358)

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* z3str3: make counterexamples less naive, and check regex membership more efficiently

* z3str3: construct even better counterexamples for regex membership
This commit is contained in:
Murphy Berzish 2020-05-28 11:57:08 -05:00 • committed by GitHub
parent 56bf4c144b
commit f3b2a082ae
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3 changed files with 94 additions and 83 deletions
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65
src/smt/theory_str_regex.cpp
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@ -206,69 +206,8 @@ namespace smt {
regex_inc_counter(regex_length_attempt_count, re);
continue;
} else {
expr_ref pathConstraint(m);
expr_ref characterConstraints(m);
pathConstraint = generate_regex_path_constraints(str, assumption.get_automaton(), exact_length_value, characterConstraints);
TRACE("str", tout << "generated regex path constraint " << mk_pp(pathConstraint, m) << std::endl;);
TRACE("str", tout << "character constraints are " << mk_pp(characterConstraints, m) << std::endl;);
expr_ref_vector lhs_terms(m);
if (current_assignment == l_true) {
lhs_terms.push_back(str_in_re);
} else {
lhs_terms.push_back(m.mk_not(str_in_re));
}
lhs_terms.push_back(ctx.mk_eq_atom(mk_strlen(str), m_autil.mk_numeral(exact_length_value, true)));
expr_ref lhs(mk_and(lhs_terms), m);
// If the path constraint comes out as "false", this means there are no paths of that length
// in the automaton. If the polarity is the same, we can assert a conflict clause.
// If the polarity is opposite, we ignore the path constraint.
if (m.is_false(pathConstraint)) {
if ( (current_assignment == l_true && assumption.get_polarity())
|| (current_assignment == l_false && !assumption.get_polarity())) {
// automaton and constraint have same polarity -- assert conflict clause
TRACE("str", tout << "path constraint is false with matching polarity; asserting conflict clause" << std::endl;);
expr_ref conflict(m.mk_not(mk_and(lhs_terms)), m);
assert_axiom(conflict);
// don't set up "regex_terms_with_path_constraints" as a conflict clause is not a path constraint
} else {
// automaton and constraint have opposite polarity -- ignore path constraint
TRACE("str", tout << "path constraint is false with opposite polarity; ignoring path constraint" << std::endl;);
assert_implication(lhs, characterConstraints);
regex_terms_with_path_constraints.insert(str_in_re);
m_trail_stack.push(insert_obj_trail<theory_str, expr>(regex_terms_with_path_constraints, str_in_re));
}
regex_axiom_add = true;
} else {
// If the automaton was built with the same polarity as the constraint,
// assert directly. Otherwise, negate the path constraint
if ( (current_assignment == l_true && assumption.get_polarity())
|| (current_assignment == l_false && !assumption.get_polarity())) {
TRACE("str", tout << "automaton and regex term have same polarity" << std::endl;);
expr_ref rhs(m.mk_and(pathConstraint, characterConstraints), m);
assert_implication(lhs, rhs);
} else {
TRACE("str", tout << "automaton and regex term have opposite polarity" << std::endl;);
expr_ref rhs(m.mk_and(m.mk_not(pathConstraint), characterConstraints), m);
assert_implication(lhs, rhs);
}
regex_terms_with_path_constraints.insert(str_in_re);
m_trail_stack.push(insert_obj_trail<theory_str, expr>(regex_terms_with_path_constraints, str_in_re));
regex_axiom_add = true;
}
// increment LengthAttemptCount
regex_inc_counter(regex_length_attempt_count, re);
TRACE("str",
{
unsigned v = regex_get_counter(regex_length_attempt_count, re);
tout << "length attempt count for " << mk_pp(re, m) << " is " << v << std::endl;
});
continue;
// fixed-length model construction handles path constraints on our behalf, and with a better reduction
return;
}
} else {
// no automata available, or else all bounds assumptions are invalid