z3/src/sat/sat_model_converter.h

/*++
Copyright (c) 2011 Microsoft Corporation

Module Name:

    sat_model_converter.h

Abstract:

    Low level model converter for SAT solver.

Author:

    Leonardo de Moura (leonardo) 2011-05-26.

Revision History:

--*/
#pragma once

#include "sat/sat_types.h"
#include "util/ref_vector.h"

namespace sat {
    /**
       \brief Stores eliminated variables and Blocked clauses.
       It uses these clauses to extend/patch the model produced for the
       simplified CNF formula.

       This information may also be used to support incremental solving.
       If new clauses are asserted into the SAT engine, then we can
       restore the state by re-asserting all clauses in the model
       converter.

       This is a low-level model_converter. Given a mapping from bool_var to expr,
       it can be converted into a general Z3 model_converter
    */

    class solver;

    static unsigned counter = 0;

    class model_converter {
        
    public:
        typedef svector<std::pair<unsigned, literal>> elim_stackv;


        class elim_stack {
            unsigned        m_counter;
            unsigned        m_refcount;
            elim_stackv     m_stack;
        public:
            elim_stack(elim_stack const&) = delete;
            elim_stack(elim_stackv && stack):
                m_counter(0),
                m_refcount(0), 
                m_stack(std::move(stack)) {
                m_counter = ++counter;
            }
            ~elim_stack() { }
            void inc_ref() { ++m_refcount; }
            void dec_ref() { if (0 == --m_refcount) { dealloc(this); } }
            elim_stackv const& stack() const { return m_stack; }
            unsigned ref_count() const { return m_refcount; }
        };

        enum kind { ELIM_VAR = 0, BCE, CCE, ACCE, ABCE, ATE };
        class entry {
            friend class model_converter;
            bool_var                m_var;
            kind                    m_kind;
            literal_vector          m_clauses; // the different clauses are separated by null_literal
            literal_vector          m_clause;  // original clause in case of CCE
            sref_vector<elim_stack> m_elim_stack;
            entry(kind k, bool_var v): m_var(v), m_kind(k) {}
        public:
            bool_var var() const { return m_var; }
            kind get_kind() const { return m_kind; }
        };
    private:
        vector<entry>          m_entries;           // entries accumulated during SAT search
        unsigned               m_exposed_lim;       // last entry that was exposed to model converter.
        bool_vector            m_mark;              // literals that are used in asserted clauses.
        solver const*          m_solver;
        elim_stackv            m_elim_stack;

        void process_stack(model & m, literal_vector const& clause, elim_stackv const& stack) const;

        std::ostream& display(std::ostream & out, entry const& entry) const;

        bool legal_to_flip(bool_var v) const;

        void swap(bool_var v, unsigned sz, literal_vector& clause);

        void add_elim_stack(entry & e);

    public:
        model_converter();
        ~model_converter();
        void set_solver(solver const* s) { m_solver = s; }
        void operator()(model & m) const;
        model_converter& operator=(model_converter const& other);

        elim_stackv& stackv() { return m_elim_stack; }

        entry & mk(kind k, bool_var v);
        void insert(entry & e, clause const & c);
        void insert(entry & e, literal l1, literal l2);
        void insert(entry & e, clause_wrapper const & c);
        void insert(entry & c, literal_vector const& covered_clause);
        void set_clause(entry & e, literal l1, literal l2);
        void set_clause(entry & e, clause const & c);

        void add_ate(literal_vector const& lits);
        void add_ate(literal l1, literal l2);
        void add_ate(clause const& c);

        bool empty() const { return m_entries.empty(); }
        unsigned size() const { return m_entries.size(); }

        void init_search(solver& s);
        void add_clause(unsigned n, literal const* lits);

        bool check_invariant(unsigned num_vars) const;
        void display(std::ostream & out) const;
        bool check_model(model const & m) const;
        void copy(model_converter const & src);
        
        /*
          \brief Append entries from src, then remove entries in src.
        */
        void flush(model_converter& src);
        void collect_vars(bool_var_set & s) const;
        unsigned max_var(unsigned min) const;
        /*
         * \brief expand entries to a list of clauses, such that
         *  the first literal in each clause is the literal whose
         *  truth value is updated as follows:
         *  
         *     lit0 := lit0 or (~lit1 & ~lit2 & ... & ~lit_k)
         *  
         */
        void expand(literal_vector& update_stack);
    };

    inline std::ostream& operator<<(std::ostream& out, model_converter::kind k) {
        switch (k) {
        case model_converter::ELIM_VAR: out << "elim"; break;
        case model_converter::BCE: out << "bce"; break;
        case model_converter::CCE: out << "cce"; break;
        case model_converter::ACCE: out << "acce"; break;
        case model_converter::ABCE: out << "abce"; break;
        case model_converter::ATE: out << "ate"; break;
        }
        return out;
    }

};