z3/src/muz/spacer/spacer_context.h

/**++
Copyright (c) 2017 Microsoft Corporation and Arie Gurfinkel

Module Name:

    spacer_context.h

Abstract:

    SPACER predicate transformers and search context.

Author:

    Arie Gurfinkel
    Anvesh Komuravelli

    Based on muz/pdr/pdr_context.h by Nikolaj Bjorner (nbjorner)

Notes:

--*/

#pragma once
// clang-format off

#include <algorithm>
#include <fstream>
#include <queue>

#include "muz/spacer/spacer_cluster.h"
#include "muz/spacer/spacer_manager.h"
#include "muz/spacer/spacer_prop_solver.h"
#include "muz/spacer/spacer_sem_matcher.h"
#include "util/scoped_ptr_vector.h"

#include "muz/base/fp_params.hpp"

namespace datalog {
class rule_set;
class context;
}; // namespace datalog

namespace spacer {

class model_search;

class pred_transformer;
class derivation;
class pob_queue;
class context;
class lemma_cluster;
class lemma_cluster_finder;
class lemma_global_generalizer;

typedef obj_map<datalog::rule const, app_ref_vector *> rule2inst;
typedef obj_map<func_decl, pred_transformer *> decl2rel;

class pob;
typedef ref<pob> pob_ref;
typedef sref_vector<pob> pob_ref_vector;
typedef sref_buffer<pob> pob_ref_buffer;

class reach_fact;
typedef ref<reach_fact> reach_fact_ref;
typedef sref_vector<reach_fact> reach_fact_ref_vector;

class lemma;
using lemma_ref = ref<lemma>;
using lemma_ref_vector = sref_vector<lemma>;

class reach_fact {
    unsigned m_ref_count;

    expr_ref m_fact;
    ptr_vector<app> m_aux_vars;

    const datalog::rule &m_rule;
    reach_fact_ref_vector m_justification;

    // variable used to tag this reach fact in an incremental disjunction
    app_ref m_tag;

    bool m_init;

  public:
    reach_fact(ast_manager &m, const datalog::rule &rule, expr *fact,
               const ptr_vector<app> &aux_vars, bool init = false)
        : m_ref_count(0), m_fact(fact, m), m_aux_vars(aux_vars), m_rule(rule),
          m_tag(m), m_init(init) {}
    reach_fact(ast_manager &m, const datalog::rule &rule, expr *fact,
               bool init = false)
        : m_ref_count(0), m_fact(fact, m), m_rule(rule), m_tag(m),
          m_init(init) {}

    bool is_init() { return m_init; }
    const datalog::rule &get_rule() { return m_rule; }

    void add_justification(reach_fact *f) { m_justification.push_back(f); }
    const reach_fact_ref_vector &get_justifications() {
        return m_justification;
    }

    expr *get() { return m_fact.get(); }
    const ptr_vector<app> &aux_vars() { return m_aux_vars; }

    app *tag() const {
        SASSERT(m_tag);
        return m_tag;
    }
    void set_tag(app *tag) { m_tag = tag; }

    void inc_ref() { ++m_ref_count; }
    void dec_ref() {
        SASSERT(m_ref_count > 0);
        --m_ref_count;
        if (m_ref_count == 0) { dealloc(this); }
    }
};

// a lemma
class lemma {
    // clang-format off
    unsigned m_ref_count;

    ast_manager &m;
    expr_ref m_body;
    expr_ref_vector m_cube;
    app_ref_vector m_zks;
    app_ref_vector m_bindings;
    pob_ref m_pob;
    model_ref m_ctp;           // counter-example to pushing
    unsigned m_lvl;            // current level of the lemma
    unsigned m_init_lvl;       // level at which lemma was created
    unsigned m_bumped:16;
    unsigned m_weakness:16;
    unsigned m_external:1;    // external lemma from another solver
    unsigned m_blocked:1;     // blocked by CTP
    unsigned m_background:1;  // background assumed fact
    // clang-format on
    // clang-format off

    void mk_expr_core();
    void mk_cube_core();

  public:
    lemma(ast_manager &manager, expr *fml, unsigned lvl);
    lemma(pob_ref const &p);
    lemma(pob_ref const &p, expr_ref_vector &cube, unsigned lvl);
    //    lemma(const lemma &other) = delete;

    ast_manager &get_ast_manager() { return m; }

    model_ref &get_ctp() { return m_ctp; }
    bool has_ctp() { return !is_inductive() && m_ctp; }
    void set_ctp(model_ref &v) { m_ctp = v; }
    void reset_ctp() { m_ctp.reset(); }

    void bump() { m_bumped++; }
    unsigned get_bumped() { return m_bumped; }

    expr *get_expr();
    bool is_false();
    expr_ref_vector const &get_cube();
    void update_cube(pob_ref const &p, expr_ref_vector &cube);

    bool has_pob() { return !!m_pob; }
    pob_ref &get_pob() { return m_pob; }
    unsigned weakness() { return m_weakness; }

    void add_skolem(app *zk, app *b);

    void set_external(bool ext) { m_external = ext; }
    bool external() { return m_external; }

    void set_background(bool v) { m_background = v; }
    bool is_background() { return m_background; }

    bool is_blocked() { return m_blocked; }
    void set_blocked(bool v) { m_blocked = v; }

    bool is_inductive() const { return is_infty_level(m_lvl); }
    unsigned level() const { return m_lvl; }
    unsigned init_level() const { return m_init_lvl; }
    void set_level(unsigned lvl);
    app_ref_vector &get_bindings() { return m_bindings; }
    bool has_binding(app_ref_vector const &binding);
    void add_binding(app_ref_vector const &binding);
    void instantiate(expr *const *exprs, expr_ref &result, expr *e = nullptr);
    void mk_insts(expr_ref_vector &inst, expr *e = nullptr);
    bool is_ground() { return !is_quantifier(get_expr()); }

    void inc_ref() { ++m_ref_count; }
    void dec_ref() {
        SASSERT(m_ref_count > 0);
        --m_ref_count;
        if (m_ref_count == 0) { dealloc(this); }
    }
};

struct lemma_lt_proc {
    bool operator()(lemma *a, lemma *b) {
        return (a->level() < b->level()) ||
               (a->level() == b->level() &&
                ast_lt_proc()(a->get_expr(), b->get_expr()));
    }
};

//
// Predicate transformer state.
// A predicate transformer corresponds to the
// set of rules that have the same head predicates.
//

class pred_transformer {

    struct stats {
        // clang-format off
        unsigned m_num_propagations;     // num of times lemma is pushed higher
        unsigned m_num_invariants;       // num of infty lemmas found
        unsigned m_num_ctp_blocked;      // num of time ctp blocked lemma pushing
        unsigned m_num_is_invariant;     // num of times lemmas are pushed
        unsigned m_num_lemma_level_jump; // lemma learned at higher level than
                                         // expected
        unsigned m_num_reach_queries;
        // clang-format on
        // clang-format off

        stats() { reset(); }
        void reset() { memset(this, 0, sizeof(*this)); }
    };

    /// manager of the lemmas in all the frames
#include "muz/spacer/spacer_legacy_frames.h"
    class frames {
      private:
        // clang-format off
        pred_transformer &m_pt;            // parent pred_transformer
        lemma_ref_vector m_pinned_lemmas;  // all created lemmas
        lemma_ref_vector m_lemmas;         // active lemmas
        lemma_ref_vector m_bg_invs;        // background (assumed) invariants
        unsigned m_size;                   // num of frames

        bool m_sorted;                     // true if m_lemmas is sorted by m_lt
        lemma_lt_proc m_lt;                // sort order for m_lemmas
        // clang-format on
        // clang-format off

        void sort();

      public:
        frames(pred_transformer &pt) : m_pt(pt), m_size(0), m_sorted(true) {}
        void simplify_formulas();

        pred_transformer &pt() const { return m_pt; }
        const lemma_ref_vector &lemmas() const { return m_lemmas; }

        void get_frame_lemmas(unsigned level, expr_ref_vector &out) const {
            for (auto &lemma : m_lemmas) {
                if (lemma->level() == level) {
                    out.push_back(lemma->get_expr());
                }
            }
        }
        void get_frame_geq_lemmas(unsigned level, expr_ref_vector &out,
                                  bool with_bg = false) const {
            for (auto &lemma : m_lemmas) {
                if (lemma->level() >= level) {
                    out.push_back(lemma->get_expr());
                }
            }
            if (with_bg) {
                for (auto &lemma : m_bg_invs) out.push_back(lemma->get_expr());
            }
        }

        void get_frame_all_lemmas(lemma_ref_vector &out,
                                  bool with_bg = false) const {
            for (auto &lemma : m_lemmas) { out.push_back(lemma); }
            if (with_bg) {
                for (auto &lemma : m_bg_invs) out.push_back(lemma);
            }
        }
        const lemma_ref_vector &get_bg_invs() const { return m_bg_invs; }
        unsigned size() const { return m_size; }
        unsigned lemma_size() const { return m_lemmas.size(); }
        unsigned bg_invs_size() const { return m_bg_invs.size(); }

        void add_frame() { m_size++; }
        void inherit_frames(frames &other) {
            for (auto &other_lemma : other.m_lemmas) {
                lemma_ref new_lemma =
                    alloc(lemma, m_pt.get_ast_manager(),
                          other_lemma->get_expr(), other_lemma->level());
                new_lemma->add_binding(other_lemma->get_bindings());
                add_lemma(new_lemma.get());
            }
            m_sorted = false;
            m_bg_invs.append(other.m_bg_invs);
        }

        bool add_lemma(lemma *new_lemma);
        void propagate_to_infinity(unsigned level);
        bool propagate_to_next_level(unsigned level);
    };

    /**
        manager of proof-obligations (pob_manager)

        Pobs are determined uniquely by their post-condition and a parent pob.
        They are managed by pob_manager and remain live through the
        life of the manager
     */
    class pob_manager {
        // a buffer that contains space for one pob and allocates more
        // space if needed
        typedef ptr_buffer<pob, 1> pob_buffer;
        // Type for the map from post-conditions to pobs. The common
        // case is that each post-condition corresponds to a single
        // pob. Other cases are handled by expanding the buffer
        typedef obj_map<expr, pob_buffer> expr2pob_buffer;

        // parent predicate transformer
        pred_transformer &m_pt;

        // map from post-conditions to pobs
        expr2pob_buffer m_pobs;

        // a store
        pob_ref_vector m_pinned;

      public:
        pob_manager(pred_transformer &pt) : m_pt(pt) {}
        pob *mk_pob(pob *parent, unsigned level, unsigned depth, expr *post,
                    app_ref_vector const &b);

        pob *mk_pob(pob *parent, unsigned level, unsigned depth, expr *post) {
            app_ref_vector b(m_pt.get_ast_manager());
            return mk_pob(parent, level, depth, post, b);
        }
        unsigned size() const { return m_pinned.size(); }

        pob *find_pob(pob *parent, expr *post);
    };

    class pt_rule {
        // clang-format off
        const datalog::rule &m_rule;
        expr_ref m_trans;        // ground version of m_rule
        ptr_vector<app> m_auxs;  // auxiliary variables in m_trans
        app_ref_vector m_reps;   // map from fv in m_rule to ground constants
        app_ref m_tag;           // a unique tag for the rule
        // clang-format on
        // clang-format off

      public:
        pt_rule(ast_manager &m, const datalog::rule &r)
            : m_rule(r), m_trans(m), m_reps(m), m_tag(m) {}

        const datalog::rule &rule() const { return m_rule; }

        void set_tag(expr *tag) {
            SASSERT(is_app(tag));
            set_tag(to_app(tag));
        }
        void set_tag(app *tag) { m_tag = tag; }
        app *tag() const { return m_tag; }
        ptr_vector<app> &auxs() { return m_auxs; }
        void set_auxs(ptr_vector<app> &v) {
            m_auxs.reset();
            m_auxs.append(v);
        }
        void set_reps(app_ref_vector &v) {
            m_reps.reset();
            m_reps.append(v);
        }

        void set_trans(expr_ref &v) { m_trans = v; }
        expr *trans() const { return m_trans; }
        bool is_init() const {
            return m_rule.get_uninterpreted_tail_size() == 0;
        }
    };

    class pt_rules {
        typedef obj_map<datalog::rule const, pt_rule *> rule2ptrule;
        typedef obj_map<const expr, pt_rule *> tag2ptrule;
        typedef rule2ptrule::iterator iterator;
        rule2ptrule m_rules;
        tag2ptrule m_tags;

      public:
        ~pt_rules() {
            for (auto &kv : m_rules) { dealloc(kv.m_value); }
        }

        bool find_by_rule(const datalog::rule &r, pt_rule *&ptr) {
            return m_rules.find(&r, ptr);
        }
        bool find_by_tag(const expr *tag, pt_rule *&ptr) {
            return m_tags.find(tag, ptr);
        }
        pt_rule &mk_rule(ast_manager &m, const datalog::rule &r) {
            return mk_rule(pt_rule(m, r));
        }
        pt_rule &mk_rule(const pt_rule &v);
        void set_tag(expr *tag, pt_rule &v) {
            pt_rule *p;
            VERIFY(find_by_rule(v.rule(), p));
            p->set_tag(tag);
            m_tags.insert(tag, p);
        }

        bool empty() { return m_rules.empty(); }
        iterator begin() { return m_rules.begin(); }
        iterator end() { return m_rules.end(); }
    };

    /// Clusters of lemmas
    class cluster_db {
        sref_vector<lemma_cluster> m_clusters;
        unsigned m_max_cluster_size;

      public:
        cluster_db() : m_max_cluster_size(0) {}
        unsigned get_max_cluster_size() const { return m_max_cluster_size; }

        /// Return the smallest cluster than can contain \p lemma
        lemma_cluster *can_contain(const lemma_ref &lemma) {
            unsigned sz = UINT_MAX;
            lemma_cluster *res = nullptr;
            for (auto *c : m_clusters) {
                if (c->get_gas() > 0 && c->get_size() < sz &&
                    c->can_contain(lemma)) {
                    res = c;
                    sz = res->get_size();
                }
            }
            return res;
        }

        bool contains(const lemma_ref &lemma) {
            for (auto *c : m_clusters) {
                if (c->contains(lemma)) { return true; }
            }
            return false;
        }

        /// The number of clusters with pattern \p pattern
        unsigned clstr_count(const expr_ref &pattern) {
            unsigned count = 0;
            for (auto c : m_clusters) {
                if (c->get_pattern() == pattern) count++;
            }
            return count;
        }

        lemma_cluster *mk_cluster(const expr_ref &pattern) {
            m_clusters.push_back(alloc(lemma_cluster, pattern));
            return m_clusters.back();
        }

        /// Return the smallest cluster containing \p lemma
        lemma_cluster *get_cluster(const lemma_ref &lemma) {
            unsigned sz = UINT_MAX;
            lemma_cluster *res = nullptr;
            for (auto *c : m_clusters) {
                if (c->get_size() < sz && c->contains(lemma)) {
                    res = c;
                    sz = res->get_size();
                }
            }
            return res;
        }

        lemma_cluster *get_cluster(const expr *pattern) {
            for (lemma_cluster *lc : m_clusters) {
                if (lc->get_pattern().get() == pattern) return lc;
            }
            return nullptr;
        }
    };
    // clang-format off
    manager&                     pm;                // spacer::manager
    ast_manager&                 m;                 // ast_manager
    context&                     ctx;               // spacer::context

    func_decl_ref                m_head;            // predicate
    func_decl_ref_vector         m_sig;             // signature
    ptr_vector<pred_transformer> m_use;             // places where 'this' is referenced.
    pt_rules                     m_pt_rules;           // pt rules used to derive transformer
    ptr_vector<datalog::rule>    m_rules;           // rules used to derive transformer
    scoped_ptr<prop_solver>      m_solver;          // solver context
    ref<solver>                  m_reach_solver;       // context for reachability facts
    pob_manager                         m_pobs;            // proof obligations created so far
    frames                       m_frames;          // frames with lemmas
    reach_fact_ref_vector        m_reach_facts;     // reach facts
    unsigned                     m_rf_init_sz;      // number of reach fact from INIT
    expr_ref_vector              m_transition_clause; // extra clause for trans
    expr_ref                     m_transition;      // transition relation
    expr_ref                     m_init;            // initial condition
    app_ref                      m_extend_lit0;     // first literal used to extend initial state
    app_ref                      m_extend_lit;      // current literal to extend initial state
    bool                         m_all_init;        // true if the pt has no uninterpreted body in any rule
    ptr_vector<func_decl>        m_predicates;      // temp vector used with find_predecessors()
    stats                        m_stats;
    stopwatch                    m_initialize_watch;
    stopwatch                    m_must_reachable_watch;
    stopwatch                    m_ctp_watch;
    stopwatch                    m_mbp_watch;
    bool                         m_has_quantified_frame; // True when a quantified lemma is in the frame
    cluster_db                   m_cluster_db;
    // clang-format on
    // clang-format off

    void init_sig();
    app_ref mk_extend_lit();
    void ensure_level(unsigned level);
    void add_lemma_core(lemma *lemma, bool ground_only = false);
    void add_lemma_from_child(pred_transformer &child, lemma *lemma,
                              unsigned lvl, bool ground_only = false);

    void mk_assumptions(func_decl *head, expr *fml, expr_ref_vector &result);

    // Initialization
    void init_rules(decl2rel const &pts);
    void init_rule(decl2rel const &pts, datalog::rule const &rule);
    void init_atom(decl2rel const &pts, app *atom, app_ref_vector &var_reprs,
                   expr_ref_vector &side, unsigned tail_idx);

    void simplify_formulas(tactic &tac, expr_ref_vector &fmls);

    void add_premises(decl2rel const &pts, unsigned lvl, datalog::rule &rule,
                      expr_ref_vector &r);

    app_ref mk_fresh_rf_tag();

    // get tagged formulae of all of the background invariants for all of the
    // predecessors of the current transformer
    void get_pred_bg_invs(expr_ref_vector &out);
    const lemma_ref_vector &get_bg_invs() const {
        return m_frames.get_bg_invs();
    }

  public:
    pred_transformer(context &ctx, manager &pm, func_decl *head);

    inline bool use_native_mbp();
    bool mk_mdl_rf_consistent(const datalog::rule *r, model &mdl);
    reach_fact *get_rf(expr *v) {
        for (auto *rf : m_reach_facts) {
            if (v == rf->get()) { return rf; }
        }
        return nullptr;
    }
    void find_predecessors(datalog::rule const &r,
                           ptr_vector<func_decl> &predicates) const;

    void add_rule(datalog::rule *r) { m_rules.push_back(r); }
    void add_use(pred_transformer *pt) {
        if (!m_use.contains(pt)) { m_use.insert(pt); }
    }
    void initialize(decl2rel const &pts);

    func_decl *head() const { return m_head; }
    ptr_vector<datalog::rule> const &rules() const { return m_rules; }
    func_decl *sig(unsigned i) const { return m_sig[i]; } // signature
    func_decl *const *sig() { return m_sig.data(); }
    unsigned sig_size() const { return m_sig.size(); }
    expr *transition() const { return m_transition; }
    expr *init() const { return m_init; }
    expr *rule2tag(datalog::rule const *r) {
        pt_rule *p;
        return m_pt_rules.find_by_rule(*r, p) ? p->tag() : nullptr;
    }
    unsigned get_num_levels() const { return m_frames.size(); }
    expr_ref get_cover_delta(func_decl *p_orig, int level);
    void add_cover(unsigned level, expr *property, bool bg = false);
    expr_ref get_reachable();

    std::ostream &display(std::ostream &strm) const;

    void collect_statistics(statistics &st) const;
    void reset_statistics();

    bool is_must_reachable(expr *state, model_ref *model = nullptr);
    /// \brief Returns reachability fact active in the given model
    /// all determines whether initial reachability facts are included as well
    reach_fact *get_used_rf(model &mdl, bool all = true);
    /// \brief Returns reachability fact active in the origin of the given model
    reach_fact *get_used_origin_rf(model &mdl, unsigned oidx);
    /// \brief Collects all the reachable facts used in mdl
    void get_all_used_rf(model &mdl, unsigned oidx, reach_fact_ref_vector &res);
    void get_all_used_rf(model &mdl, reach_fact_ref_vector &res);
    expr_ref get_origin_summary(model &mdl, unsigned level, unsigned oidx,
                                bool must, const ptr_vector<app> **aux);

    bool is_ctp_blocked(lemma *lem);
    const datalog::rule *find_rule(model &mdl);
    const datalog::rule *find_rule(model &mev, bool &is_concrete,
                                   bool_vector &reach_pred_used,
                                   unsigned &num_reuse_reach);
    expr *get_transition(datalog::rule const &r) {
        pt_rule *p;
        return m_pt_rules.find_by_rule(r, p) ? p->trans() : nullptr;
    }
    ptr_vector<app> &get_aux_vars(datalog::rule const &r) {
        pt_rule *p = nullptr;
        VERIFY(m_pt_rules.find_by_rule(r, p));
        return p->auxs();
    }

    bool propagate_to_next_level(unsigned level);
    void propagate_to_infinity(unsigned level);
    /// \brief  Add a lemma to the current context and all users
    bool add_lemma(expr *e, unsigned lvl, bool bg);
    bool add_lemma(lemma *lem) { return m_frames.add_lemma(lem); }
    expr *get_reach_case_var(unsigned idx) const;
    bool has_rfs() const { return !m_reach_facts.empty(); }

    /// initialize reachability facts using initial rules
    void init_rfs();
    reach_fact *mk_rf(pob &n, model &mdl, const datalog::rule &r);
    void add_rf(reach_fact *fact, bool force = false); // add reachability fact
    reach_fact *get_last_rf() const { return m_reach_facts.back(); }
    expr *get_last_rf_tag() const;

    pob *mk_pob(pob *parent, unsigned level, unsigned depth, expr *post,
                app_ref_vector const &b) {
        return m_pobs.mk_pob(parent, level, depth, post, b);
    }
    pob *find_pob(pob *parent, expr *post) {
        return m_pobs.find_pob(parent, post);
    }

    pob *mk_pob(pob *parent, unsigned level, unsigned depth, expr *post) {
        return m_pobs.mk_pob(parent, level, depth, post);
    }

    lbool is_reachable(pob& n, expr_ref_vector* core, model_ref *model,
                       unsigned& uses_level, bool& is_concrete,
                       datalog::rule const *&r, bool_vector &reach_pred_used,
                       unsigned& num_reuse_reach, bool use_iuc = true);
    bool is_invariant(unsigned level, lemma *lem, unsigned &solver_level,
                      expr_ref_vector* core = nullptr);

    bool is_invariant(unsigned level, expr *lem, unsigned &solver_level,
                      expr_ref_vector *core = nullptr) {
        // XXX only needed for legacy_frames to compile
        UNREACHABLE();
        return false;
    }

    bool check_inductive(unsigned level, expr_ref_vector &state,
                         unsigned &assumes_level, unsigned weakness = UINT_MAX);

    expr_ref get_formulas(unsigned level, bool bg = false) const;

    void simplify_formulas();

    context &get_context() const { return ctx; }
    manager &get_manager() const { return pm; }
    ast_manager &get_ast_manager() const { return m; }

    void add_premises(decl2rel const &pts, unsigned lvl, expr_ref_vector &r);

    void inherit_lemmas(pred_transformer &other);

    void ground_free_vars(expr *e, app_ref_vector &vars,
                          ptr_vector<app> &aux_vars, bool is_init);

    /// \brief Adds a given expression to the set of initial rules
    app *extend_initial(expr *e);

    /// \brief Returns true if the obligation is already blocked by current
    /// lemmas
    bool is_blocked(pob &n, unsigned &uses_level, model_ref *model = nullptr);
    /// \brief Returns true if the obligation is already blocked by current
    /// quantified lemmas
    bool is_qblocked(pob &n);

    /// \brief interface to Model Based Projection
    void mbp(app_ref_vector &vars, expr_ref &fml, model &mdl,
             bool reduce_all_selects, bool force = false);

    void updt_solver(prop_solver *solver);

    void updt_solver_with_lemmas(prop_solver *solver,
                                 const pred_transformer &pt, app *rule_tag,
                                 unsigned pos);
    // exposing ACTIVE lemmas (alternatively, one can expose `m_pinned_lemmas`
    // for ALL lemmas)
    void get_all_lemmas(lemma_ref_vector &out, bool with_bg = false) const {
        m_frames.get_frame_all_lemmas(out, with_bg);
    }
    void update_solver_with_rfs(prop_solver *solver, const pred_transformer &pt,
                                app *rule_tag, unsigned pos);

    lemma_cluster *mk_cluster(const expr_ref &pattern) {
        return m_cluster_db.mk_cluster(pattern);
    }

    // Checks whether \p lemma is in any existing cluster
    bool clstr_contains(const lemma_ref &lemma) {
        return m_cluster_db.contains(lemma);
    }

    /// The number of clusters with pattern \p pattern
    unsigned clstr_count(const expr_ref &pattern) {
        return m_cluster_db.clstr_count(pattern);
    }

    /// Checks whether \p lemma matches any cluster
    lemma_cluster *clstr_match(const lemma_ref &lemma) {
        lemma_cluster *res = m_cluster_db.get_cluster(lemma);
        if (!res) res = m_cluster_db.can_contain(lemma);
        return res;
    }

    /// Returns a cluster with pattern \p pattern
    lemma_cluster *get_cluster(const expr *pattern) {
        return m_cluster_db.get_cluster(pattern);
    }
};

/**
 * A proof obligation.
 */
class pob {
    // clang-format off
    // TBD: remove this
    friend class context;
    unsigned m_ref_count;
    /// parent node
    pob_ref          m_parent;
    /// predicate transformer
    pred_transformer&       m_pt;
    /// post-condition decided by this node
    expr_ref                m_post;
    // if m_post is not ground, then m_binding is an instantiation for
    // all quantified variables
    app_ref_vector          m_binding;
    /// new post to be swapped in for m_post
    expr_ref                m_new_post;
    /// level at which to decide the post
    unsigned                m_level:16;
    unsigned                m_depth:16;

    unsigned                 m_desired_level:16;

    /// whether a concrete answer to the post is found
    unsigned                m_open:1;
    /// whether to use farkas generalizer to construct a lemma blocking this
    /// node
    unsigned                m_use_farkas:1;
    /// true if this pob is in pob_queue
    unsigned                m_in_queue:1;
    // true if this pob is a conjecture
    unsigned                m_is_conjecture:1;
    // should do local generalizations on pob
    unsigned                m_enable_local_gen:1;
    // should concretize cube
    unsigned                m_enable_concretize:1;
    // is a subsume pob
    unsigned                m_is_subsume:1;
    // should apply expand bnd generalization on pob
    unsigned                m_enable_expand_bnd_gen:1;

    unsigned                m_weakness;
    /// derivation representing the position of this node in the parent's rule
    scoped_ptr<derivation>   m_derivation;

    /// pobs created as children of this pob (at any time, not
    /// necessarily currently active)
    ptr_vector<pob>  m_kids;
    // lemmas created to block this pob (at any time, not necessarily active)
    ptr_vector<lemma> m_lemmas;

    unsigned m_blocked_lvl;
    // clang-format on
    // clang-format off

    // pattern identified for one of its lemmas
    expr_ref m_concretize_pat;

    // gas decides how much time is spent in blocking this (may) pob
    unsigned m_gas;

    // additional data used by global (and other) generalizations
    scoped_ptr<pob> m_data;
public:
    pob(pob *parent, pred_transformer &pt, unsigned level, unsigned depth = 0,
        bool add_to_parent = true);

    // no copy constructor
    pob(const pob&) = delete;
    // no move constructor
    pob(pob &&) = delete;

    ~pob() {
        if (m_parent) { m_parent->erase_child(*this); }
    }

    void set_data(pob* v) { m_data = v; }
    void reset_data() { set_data(nullptr); }
    pob* get_data() { return m_data.get(); }
    bool has_data() { return m_data; }

    // TBD: move into constructor and make private
    void set_post(expr *post, app_ref_vector const &binding);
    void set_post(expr *post);

    unsigned weakness() { return m_weakness; }
    void bump_weakness() { m_weakness++; }
    void reset_weakness() { m_weakness = 0; }

    void inc_level() {
        SASSERT(!is_in_queue());
        m_level++;
        m_depth++;
        reset_weakness();
    }

    void inherit(pob const &p);
    void set_derivation(derivation *d) { m_derivation = d; }
    bool has_derivation() const { return (bool)m_derivation; }
    derivation &get_derivation() const { return *m_derivation.get (); }
    void reset_derivation() { set_derivation (nullptr); }
    /// detaches derivation from the node without deallocating
    derivation* detach_derivation() { return m_derivation.detach (); }

    pob* parent() const { return m_parent.get (); }

    bool is_conjecture() const { return m_is_conjecture; }
    void set_conjecture(bool v = true) { m_is_conjecture = v; }

    void disable_expand_bnd_gen() { m_enable_expand_bnd_gen = false; }
    bool is_expand_bnd_enabled() { return m_enable_expand_bnd_gen; }
    void set_expand_bnd(bool v = true) { m_enable_expand_bnd_gen = v; }
    void set_concretize_pattern(const expr_ref &pattern) { m_concretize_pat = pattern; }
    const expr_ref &get_concretize_pattern() const { return m_concretize_pat; }
    bool is_subsume() const { return m_is_subsume; }
    void set_subsume(bool v = true) { m_is_subsume = v; }
    bool is_may_pob() const { return is_subsume() || is_conjecture(); }
    unsigned get_gas() const { return m_gas; }
    void set_gas(unsigned n) { m_gas = n; }

    bool is_local_gen_enabled() const { return m_enable_local_gen; }
    void disable_local_gen() { m_enable_local_gen = false; }
    void get_post_simplified(expr_ref_vector &res);
    bool is_concretize_enabled() const { return m_enable_concretize && m_gas > 0; }
    void set_concretize(bool v = true) { m_enable_concretize = v; }
    pred_transformer& pt() const { return m_pt; }
    ast_manager& get_ast_manager() const { return m_pt.get_ast_manager(); }
    manager& get_manager() const { return m_pt.get_manager(); }
    context& get_context() const { return m_pt.get_context(); }

    unsigned level() const { return m_level; }
    unsigned depth() const { return m_depth; }
    unsigned desired_level() const { return m_desired_level; }
    void set_desired_level(unsigned v) { m_desired_level = v; }
    unsigned width() const { return m_kids.size(); }
    unsigned blocked_at(unsigned lvl = 0) {
        return (m_blocked_lvl = std::max(lvl, m_blocked_lvl));
    }

    bool is_in_queue() const { return m_in_queue; }
    void set_in_queue(bool v) { m_in_queue = v; }
    bool use_farkas_generalizer() const { return m_use_farkas; }
    void set_farkas_generalizer(bool v) { m_use_farkas = v; }

    expr *post() const { return m_post.get(); }

    bool is_closed() const { return !m_open; }
    void close();

    const ptr_vector<pob> &children() const { return m_kids; }
    void add_child(pob &v) { m_kids.push_back(&v); }
    void erase_child(pob &v) { m_kids.erase(&v); }

    const ptr_vector<lemma> &lemmas() const { return m_lemmas; }
    void add_lemma(lemma *new_lemma) { m_lemmas.push_back(new_lemma); }

    bool is_ground() const { return m_binding.empty(); }
    unsigned get_free_vars_size() const { return m_binding.size(); }
    app_ref_vector const &get_binding() const { return m_binding; }
    /*
     * Returns a map from variable id to skolems that implicitly
     * represent them in the pob. Note that only some (or none) of the
     * skolems returned actually appear in the post of the pob.
     */
    void get_skolems(app_ref_vector &v);

    void on_expand() {
        if (m_parent.get()) { m_parent.get()->on_expand(); }
    }
    void off_expand() {
        if (m_parent.get()) { m_parent.get()->off_expand(); }
    }

    void inc_ref() { ++m_ref_count; }
    void dec_ref() {
        --m_ref_count;
        if (m_ref_count == 0) { dealloc(this); }
    }

    std::ostream &display(std::ostream &out, bool full = false) const;
    class on_expand_event {
        pob &m_p;

      public:
        on_expand_event(pob &p) : m_p(p) { m_p.on_expand(); }
        ~on_expand_event() { m_p.off_expand(); }
    };
};

inline std::ostream &operator<<(std::ostream &out, pob const &p) {
    return p.display(out);
}

struct pob_lt_proc {
    bool operator()(const pob *pn1, const pob *pn2) const;
};

struct pob_gt_proc {
    bool operator()(const pob *n1, const pob *n2) const {
        return pob_lt_proc()(n2, n1);
    }
};

/**
 */
class derivation {
    /// a single premise of a derivation
    class premise {
        pred_transformer &m_pt;
        /// origin order in the rule
        unsigned m_oidx;
        /// summary fact corresponding to the premise
        expr_ref m_summary;
        ///  whether this is a must or may premise
        bool m_must;
        app_ref_vector m_ovars;

      public:
        premise(pred_transformer &pt, unsigned oidx, expr *summary, bool must,
                const ptr_vector<app> *aux_vars = nullptr);

        bool is_must() { return m_must; }
        expr *get_summary() { return m_summary.get(); }
        app_ref_vector &get_ovars() { return m_ovars; }
        unsigned get_oidx() { return m_oidx; }
        pred_transformer &pt() { return m_pt; }

        /// \brief Updated the summary.
        /// The new summary is over n-variables.
        void set_summary(expr *summary, bool must,
                         const ptr_vector<app> *aux_vars = nullptr);
    };

    // clang-format off
    /// parent model node
    pob&                         m_parent;

    /// the rule corresponding to this derivation
    const datalog::rule &m_rule;

    /// the premises
    vector<premise>                     m_premises;
    /// pointer to the active premise
    unsigned                            m_active;
    // transition relation over origin variables
    expr_ref                            m_trans;
    //  implicitly existentially quantified variables in m_trans
    app_ref_vector                      m_evars;
    // clang-format on
    // clang-format off

    /// -- create next child using given model as the guide
    /// -- returns NULL if there is no next child
    pob *create_next_child(model &mdl);
    /// existentially quantify vars and skolemize the result
    void exist_skolemize(expr *fml, app_ref_vector &vars, expr_ref &res);

  public:
    derivation(pob &parent, datalog::rule const &rule, expr *trans,
               app_ref_vector const &evars);
    void add_premise(pred_transformer &pt, unsigned oidx, expr *summary,
                     bool must, const ptr_vector<app> *aux_vars = nullptr);

    /// creates the first child. Must be called after all the premises
    /// are added. The model must be valid for the premises
    /// Returns NULL if no child exits
    pob *create_first_child(model &mdl);

    /// Create the next child. Must summary of the currently active
    /// premise must be consistent with the transition relation
    pob *create_next_child();

    datalog::rule const &get_rule() const { return m_rule; }
    pob &get_parent() const { return m_parent; }
    ast_manager &get_ast_manager() const { return m_parent.get_ast_manager(); }
    manager &get_manager() const { return m_parent.get_manager(); }
    context &get_context() const { return m_parent.get_context(); }
    pred_transformer &pt() const { return m_parent.pt(); }
};

class pob_queue {

    typedef std::priority_queue<pob *, std::vector<pob *>, pob_gt_proc>
        pob_queue_ty;
    pob_ref m_root;
    unsigned m_max_level;
    unsigned m_min_depth;

    pob_queue_ty m_data;

  public:
    pob_queue() : m_root(nullptr), m_max_level(0), m_min_depth(0) {}

    void reset();
    pob *top();
    void pop();
    void push(pob &n);

    void inc_level() {
        SASSERT(!m_data.empty() || m_root);
        m_max_level++;
        m_min_depth++;
        if (m_root && m_data.empty()) {
            SASSERT(!m_root->is_in_queue());
            m_root->set_in_queue(true);
            m_data.push(m_root.get());
        }
    }

    pob &get_root() const { return *m_root.get(); }
    void set_root(pob &n);
    bool is_root(pob &n) const { return m_root.get() == &n; }

    unsigned max_level() const { return m_max_level; }
    unsigned min_depth() const { return m_min_depth; }
    size_t size() const { return m_data.size(); }
};

/**
 * Generalizers (strengthens) a lemma
 */
class lemma_generalizer {
  protected:
    context &m_ctx;

  public:
    lemma_generalizer(context &ctx) : m_ctx(ctx) {}
    virtual ~lemma_generalizer() = default;
    virtual void operator()(lemma_ref &lemma) = 0;
    virtual void collect_statistics(statistics &st) const {}
    virtual void reset_statistics() {}
};

class spacer_callback {
  protected:
    context &m_context;

  public:
    spacer_callback(context &context) : m_context(context) {}

    virtual ~spacer_callback() = default;

    context &get_context() { return m_context; }

    virtual inline bool new_lemma() { return false; }

    virtual void new_lemma_eh(expr *lemma, unsigned level) {}

    virtual inline bool predecessor() { return false; }

    virtual void predecessor_eh() {}

    virtual inline bool unfold() { return false; }

    virtual void unfold_eh() {}

    virtual inline bool propagate() { return false; }

    virtual void propagate_eh() {}
};

// order in which children are processed
enum spacer_children_order {
    CO_RULE,     // same order as in the rule
    CO_REV_RULE, // reverse order of the rule
    CO_RANDOM    // random shuffle
};

class context {
    friend class pred_transformer;
    struct stats {
        unsigned m_num_queries;
        unsigned m_num_reuse_reach;
        unsigned m_max_query_lvl;
        unsigned m_max_depth;
        unsigned m_cex_depth;
        unsigned m_expand_pob_undef;
        unsigned m_num_lemmas;
        unsigned m_num_restarts;
        unsigned m_num_lemmas_imported;
        unsigned m_num_lemmas_discarded;
        unsigned m_num_conj;
        unsigned m_num_conj_success;
        unsigned m_num_conj_failed;
        unsigned m_num_subsume_pobs;
        unsigned m_num_subsume_pob_reachable;
        unsigned m_num_subsume_pob_blckd;
        unsigned m_num_concretize;
        unsigned m_num_pob_ofg;
        unsigned m_non_local_gen;
        stats() { reset(); }
        void reset() { memset(this, 0, sizeof(*this)); }
    };

    // clang-format off
    // stat watches
    stopwatch m_solve_watch;
    stopwatch m_propagate_watch;
    stopwatch m_reach_watch;
    stopwatch m_is_reach_watch;
    stopwatch m_create_children_watch;
    stopwatch m_init_rules_watch;

    fp_params const&     m_params;
    ast_manager&         m;
    datalog::context*    m_context;
    manager              m_pm;

    // three solver pools for different queries
    scoped_ptr<solver_pool> m_pool0;
    scoped_ptr<solver_pool> m_pool1;
    scoped_ptr<solver_pool> m_pool2;

    random_gen           m_random;
    spacer_children_order m_children_order;
    decl2rel             m_rels;         // Map from relation predicate to fp-operator.
    func_decl_ref        m_query_pred;
    pred_transformer*    m_query;
    mutable pob_queue    m_pob_queue;
    lbool                m_last_result;
    unsigned             m_inductive_lvl;
    unsigned             m_expanded_lvl;
    ptr_buffer<lemma_generalizer>  m_lemma_generalizers;
    lemma_global_generalizer *m_global_gen;
    lemma_generalizer    *m_expand_bnd_gen;
    lemma_cluster_finder *m_lmma_cluster;
    stats                m_stats;
    model_converter_ref  m_mc;
    proof_converter_ref  m_pc;
    bool                 m_use_native_mbp;
    bool                 m_instantiate;
    bool                 m_use_qlemmas;
    bool                 m_weak_abs;
    bool                 m_use_restarts;
    bool                 m_simplify_pob;
    bool                 m_use_euf_gen;
    bool                 m_use_lim_num_gen;
    bool                 m_use_ctp;
    bool                 m_use_inc_clause;
    bool                 m_use_ind_gen;
    bool                 m_use_array_eq_gen;
    bool                 m_validate_lemmas;
    bool                 m_use_propagate;
    bool                 m_reset_obligation_queue;
    bool                 m_push_pob;
    bool                 m_use_lemma_as_pob;
    bool                 m_elim_aux;
    bool                 m_reach_dnf;
    bool                 m_use_derivations;
    bool                 m_validate_result;
    bool                 m_use_eq_prop;
    bool                 m_ground_pob;
    bool                 m_q3_qgen;
    bool                 m_use_gpdr;
    bool                 m_simplify_formulas_pre;
    bool                 m_simplify_formulas_post;
    bool                 m_pdr_bfs;
    bool                 m_use_bg_invs;
    bool                 m_global;
    bool                 m_expand_bnd;
    bool                 m_gg_conjecture;
    bool                 m_gg_subsume;
    bool                 m_gg_concretize;
    bool                 m_use_iuc;
    unsigned             m_push_pob_max_depth;
    unsigned             m_max_level;
    unsigned             m_restart_initial_threshold;
    unsigned             m_blast_term_ite_inflation;
    scoped_ptr_vector<spacer_callback> m_callbacks;
    std::fstream*        m_trace_stream;
    // clang-format on
    // clang-format off

    // Solve using gpdr strategy
    lbool gpdr_solve_core();
    bool gpdr_check_reachability(unsigned lvl, model_search &ms);
    bool gpdr_create_split_children(pob &n, const datalog::rule &r, expr *trans,
                                    model &mdl, pob_ref_buffer &out);

    // progress logging
    void log_enter_level(unsigned lvl);
    void log_propagate();
    void log_expand_pob(pob &);
    void log_add_lemma(pred_transformer &, lemma &);

    // Functions used by search.
    lbool solve_core(unsigned from_lvl = 0);
    bool is_requeue(pob &n);
    bool check_reachability();
    bool propagate(unsigned min_prop_lvl, unsigned max_prop_lvl,
                   unsigned full_prop_lvl);
    bool is_reachable(pob &n);
    lbool expand_pob(pob &n, pob_ref_buffer &out);
    bool create_children(pob &n, const datalog::rule &r, model &mdl,
                         const bool_vector &reach_pred_used,
                         pob_ref_buffer &out);

    /**
       \brief Retrieve satisfying assignment with explanation.
    */
    expr_ref mk_sat_answer() const {
        proof_ref pr = get_ground_refutation();
        return expr_ref(pr.get(), pr.get_manager());
    }
    expr_ref mk_unsat_answer() const;
    unsigned get_cex_depth();

    // Generate inductive property
    void get_level_property(unsigned lvl, expr_ref_vector &res,
                            vector<relation_info> &rs,
                            bool with_bg = false) const;

    // Initialization
    void init_lemma_generalizers();
    void reset_lemma_generalizers();
    void inherit_lemmas(const decl2rel &rels);
    void init_global_smt_params();
    void init_rules(datalog::rule_set &rules, decl2rel &transformers);
    // (re)initialize context with new relations
    void init(const decl2rel &rels);

    bool validate();
    bool check_invariant(unsigned lvl);
    bool check_invariant(unsigned lvl, func_decl *fn);

    void checkpoint();

    void simplify_formulas();

    void predecessor_eh();

    void updt_params();
    lbool handle_unknown(pob &n, const datalog::rule *r, model &model);
    bool mk_mdl_rf_consistent(model &mdl);

  public:
    /**
       Initial values of predicates are stored in corresponding relations in
       dctx. We check whether there is some reachable state of the relation
       checked_relation.
    */
    context(fp_params const &params, ast_manager &m);
    ~context();

    const fp_params &get_params() const { return m_params; }
    bool use_eq_prop() const { return m_use_eq_prop; }
    bool use_native_mbp() const { return m_use_native_mbp; }
    bool use_ground_pob() const { return m_ground_pob; }
    bool use_instantiate() const { return m_instantiate; }
    bool weak_abs() const { return m_weak_abs; }
    bool use_qlemmas() const { return m_use_qlemmas; }
    bool use_euf_gen() const { return m_use_euf_gen; }
    bool use_lim_num_gen() const { return m_use_lim_num_gen; }
    bool simplify_pob() const { return m_simplify_pob; }
    bool use_ctp() const { return m_use_ctp; }
    bool use_inc_clause() const { return m_use_inc_clause; }
    unsigned blast_term_ite_inflation() const {
        return m_blast_term_ite_inflation;
    }
    bool elim_aux() const { return m_elim_aux; }
    bool reach_dnf() const { return m_reach_dnf; }
    bool use_bg_invs() const { return m_use_bg_invs; }
    bool do_subsume() const { return m_gg_subsume; }

    ast_manager &get_ast_manager() const { return m; }
    manager &get_manager() { return m_pm; }
    const manager &get_manager() const { return m_pm; }
    decl2rel const &get_pred_transformers() const { return m_rels; }
    pred_transformer &get_pred_transformer(func_decl *p) const {
        return *m_rels.find(p);
    }

    datalog::context &get_datalog_context() const {
        SASSERT(m_context);
        return *m_context;
    }

    void update_rules(datalog::rule_set &rules);
    lbool solve(unsigned from_lvl = 0);
    lbool solve_from_lvl(unsigned from_lvl);

    expr_ref get_answer();
    /**
     * get bottom-up (from query) sequence of ground predicate instances
     * (for e.g. P(0,1,0,0,3)) that together form a ground derivation to query
     */
    expr_ref get_ground_sat_answer() const;
    proof_ref get_ground_refutation() const;
    void get_rules_along_trace(datalog::rule_ref_vector &rules);

    void collect_statistics(statistics &st) const;
    void reset_statistics();
    void reset();

    std::ostream &display(std::ostream &out) const;
    void display_certificate(std::ostream &out) const;

    pob &get_root() const { return m_pob_queue.get_root(); }
    void set_query(func_decl *q) { m_query_pred = q; }
    void set_unsat() { m_last_result = l_false; }
    void set_model_converter(model_converter_ref &mc) { m_mc = mc; }
    model_converter_ref get_model_converter() { return m_mc; }
    void set_proof_converter(proof_converter_ref &pc) { m_pc = pc; }
    scoped_ptr_vector<spacer_callback> &callbacks() { return m_callbacks; }

    unsigned get_num_levels(func_decl *p);

    expr_ref get_cover_delta(int level, func_decl *p_orig, func_decl *p);
    void add_cover(int level, func_decl *pred, expr *property, bool bg = false);
    expr_ref get_reachable(func_decl *p);
    void add_invariant(func_decl *pred, expr *property);
    model_ref get_model();
    proof_ref get_proof() const { return get_ground_refutation(); }

    expr_ref get_constraints(unsigned lvl);
    void add_constraint(expr *c, unsigned lvl);

    void new_lemma_eh(pred_transformer &pt, lemma *lem);
    void new_pob_eh(pob *p);

    bool is_inductive();

    // close all parents of may pob when gas runs out
    void close_all_may_parents(pob_ref node);

    // three different solvers with three different sets of parameters
    // different solvers are used for different types of queries in spacer
    solver *mk_solver0() { return m_pool0->mk_solver(); }
    solver *mk_solver1() { return m_pool1->mk_solver(); }
    solver *mk_solver2() { return m_pool2->mk_solver(); }
};

inline bool pred_transformer::use_native_mbp() { return ctx.use_native_mbp(); }
} // namespace spacer