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Merge branch 'unstable' of https://git01.codeplex.com/z3 into unstable

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This commit is contained in:
Nikolaj Bjorner 2013-04-09 10:15:38 -07:00
commit 312e052788
2 changed files with 51 additions and 5 deletions
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2
src/cmd_context/basic_cmds.cpp
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@ -568,7 +568,7 @@ public:
ctx.regular_stream() << "(:authors \"Leonardo de Moura and Nikolaj Bjorner\")" << std::endl;
}
else if (opt == m_version) {
ctx.regular_stream() << "(:version \"" << Z3_MAJOR_VERSION << "." << Z3_MINOR_VERSION << "\")" << std::endl;
ctx.regular_stream() << "(:version \"" << Z3_MAJOR_VERSION << "." << Z3_MINOR_VERSION << "." << Z3_BUILD_NUMBER << "\")" << std::endl;
}
else if (opt == m_status) {
ctx.regular_stream() << "(:status " << ctx.get_status() << ")" << std::endl;

54
src/sat/sat_solver.cpp
View file

@ -1745,6 +1745,12 @@ namespace sat {
mark_lit(m_lemma[i]);
}
literal l0 = m_lemma[0];
// l0 is the FUIP, and we never remove the FUIP.
//
// In the following loop, we use unmark_lit(l) to remove a
// literal from m_lemma.
for (unsigned i = 0; i < sz; i++) {
literal l = m_lemma[i];
if (!is_marked_lit(l))
@ -1754,9 +1760,15 @@ namespace sat {
watch_list::const_iterator it = wlist.begin();
watch_list::const_iterator end = wlist.end();
for (; it != end; ++it) {
// In this for-loop, the conditions l0 != ~l2 and l0 != ~l3
// are not really needed if the solver does not miss unit propagations.
// However, we add them anyway because we don't want to rely on this
// property of the propagator.
// For example, if this property is relaxed in the future, then the code
// without the conditions l0 != ~l2 and l0 != ~l3 may remove the FUIP
if (it->is_binary_clause()) {
literal l2 = it->get_literal();
if (is_marked_lit(~l2)) {
if (is_marked_lit(~l2) && l0 != ~l2) {
// eliminate ~l2 from lemma because we have the clause l \/ l2
unmark_lit(~l2);
}
@ -1764,11 +1776,11 @@ namespace sat {
else if (it->is_ternary_clause()) {
literal l2 = it->get_literal1();
literal l3 = it->get_literal2();
if (is_marked_lit(l2) && is_marked_lit(~l3)) {
if (is_marked_lit(l2) && is_marked_lit(~l3) && l0 != ~l3) {
// eliminate ~l3 from lemma because we have the clause l \/ l2 \/ l3
unmark_lit(~l3);
}
else if (is_marked_lit(~l2) && is_marked_lit(l3)) {
else if (is_marked_lit(~l2) && is_marked_lit(l3) && l0 != ~l2) {
// eliminate ~l2 from lemma because we have the clause l \/ l2 \/ l3
unmark_lit(~l2);
}
@ -1786,7 +1798,41 @@ namespace sat {
literal_vector::iterator end = implied_lits->end();
for (; it != end; ++it) {
literal l2 = *it;
if (is_marked_lit(~l2)) {
// Here, we must check l0 != ~l2.
// l \/ l2 is an implied binary clause.
// However, it may have been deduced using a lemma that has been deleted.
// For example, consider the following sequence of events:
//
// 1. Initial clause database:
//
// l \/ ~p1
// p1 \/ ~p2
// p2 \/ ~p3
// p3 \/ ~p4
// q1 \/ q2 \/ p1 \/ p2 \/ p3 \/ p4 \/ l2
// q1 \/ ~q2 \/ p1 \/ p2 \/ p3 \/ p4 \/ l2
// ~q1 \/ q2 \/ p1 \/ p2 \/ p3 \/ p4 \/ l2
// ~q1 \/ ~q2 \/ p1 \/ p2 \/ p3 \/ p4 \/ l2
// ...
//
// 2. Now suppose we learned the lemma
//
// p1 \/ p2 \/ p3 \/ p4 \/ l2 (*)
//
// 3. Probing is executed and we notice hat (~l => l2) when we assign l to false.
// That is, l \/ l2 is an implied clause. Note that probing does not add
// this clause to the clause database (there are too many).
//
// 4. Lemma (*) is deleted (garbage collected).
//
// 5. l is decided to be false, p1, p2, p3 and p4 are propagated using BCP,
// but l2 is not since the lemma (*) was deleted.
//
// Probing module still "knows" that l \/ l2 is valid binary clause
//
// 6. A new lemma is created where ~l2 is the FUIP and the lemma also contains l.
// If we remove l0 != ~l2 may try to delete the FUIP.
if (is_marked_lit(~l2) && l0 != ~l2) {
// eliminate ~l2 from lemma because we have the clause l \/ l2
unmark_lit(~l2);
}