add clause persistence to sat/smt solver

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/sat/smt/user_solver.cpp

@@ -178,8 +178,10 @@ namespace user_solver {
     void solver::propagate_consequence(prop_info const& prop) {
         sat::literal lit = ctx.internalize(prop.m_conseq, false, false);
         if (s().value(lit) != l_true) {
-            s().assign(lit, mk_justification(m_qhead));
+            auto j = mk_justification(m_qhead);
+            s().assign(lit, j);
             ++m_stats.m_num_propagations;
+            persist_clause(lit, j);
         }
     }
 
@@ -188,9 +190,17 @@ namespace user_solver {
     }
 
     bool solver::unit_propagate() {
-        if (m_qhead == m_prop.size())
+        if (m_qhead == m_prop.size() && m_replay_qhead == m_clauses_to_replay.size())
             return false;
         force_push();
+
+        bool replayed = false;
+        if (m_replay_qhead < m_clauses_to_replay.size()) {
+            replayed = true;
+            ctx.push(value_trail<unsigned>(m_replay_qhead));
+            for (; m_replay_qhead < m_clauses_to_replay.size(); ++m_replay_qhead) 
+                replay_clause(m_clauses_to_replay.get(m_replay_qhead));
+        }
         ctx.push(value_trail<unsigned>(m_qhead));
         unsigned np = m_stats.m_num_propagations;
         for (; m_qhead < m_prop.size() && !s().inconsistent(); ++m_qhead) {
@@ -200,7 +210,37 @@ namespace user_solver {
             else
                 propagate_new_fixed(prop);
         }
-        return np < m_stats.m_num_propagations;
+        return np < m_stats.m_num_propagations || replayed;
+    }
+
+    void solver::replay_clause(expr_ref_vector const& clause) {
+        sat::literal_vector lits;
+        for (expr* e : clause)
+            lits.push_back(ctx.mk_literal(e));
+        add_clause(lits);
+    }    
+
+    void solver::persist_clause(sat::literal lit, sat::justification const& sj) {
+        if (!ctx.get_config().m_up_persist_clauses) 
+            return;
+        
+        expr_ref_vector clause(m);
+        auto idx = sj.get_ext_justification_idx();
+        auto& j = justification::from_index(idx);
+        auto const& prop = m_prop[j.m_propagation_index];
+        sat::literal_vector r;
+        for (unsigned id : prop.m_ids)
+            r.append(m_id2justification[id]);
+        for (auto lit : r)
+            clause.push_back(ctx.literal2expr(~lit));
+        for (auto const& [a,b] : prop.m_eqs)
+            clause.push_back(m.mk_not(m.mk_eq(a, b)));
+        clause.push_back(ctx.literal2expr(lit));
+
+        m_clauses_to_replay.push_back(clause);
+        if (m_replay_qhead + 1 < m_clauses_to_replay.size()) 
+            std::swap(m_clauses_to_replay[m_replay_qhead], m_clauses_to_replay[m_clauses_to_replay.size()-1]);
+        ++m_replay_qhead;
     }
 
     void solver::collect_statistics(::statistics& st) const {

src/sat/smt/user_solver.h

@@ -77,6 +77,8 @@ namespace user_solver {
         stats                           m_stats;
         sat::bool_var                   m_next_split_var = sat::null_bool_var;
         lbool                           m_next_split_phase = l_undef;
+        vector<expr_ref_vector> m_clauses_to_replay;
+        unsigned                m_replay_qhead = 0;
 
         struct justification {
             unsigned m_propagation_index { 0 };
@@ -105,6 +107,9 @@ namespace user_solver {
 
         sat::bool_var enode_to_bool(euf::enode* n, unsigned idx);
 
+        void replay_clause(expr_ref_vector const& clause);
+        void persist_clause(sat::literal lit, sat::justification const& j);
+
     public:
         solver(euf::solver& ctx);