z3/src/sat/smt/euf_internalize.cpp

/*++
Copyright (c) 2020 Microsoft Corporation

Module Name:

    euf_internalize.cpp

Abstract:

    Internalize utilities for EUF solver plugin.

Author:

    Nikolaj Bjorner (nbjorner) 2020-08-25

--*/

#include "ast/ast_pp.h"
#include "ast/pb_decl_plugin.h"
#include "sat/smt/euf_solver.h"

namespace euf {

    void solver::internalize(expr* e, bool redundant) {
        if (si.is_bool_op(e))
            attach_lit(si.internalize(e, redundant), e);
        else if (auto* ext = get_solver(e))
            ext->internalize(e, redundant);
        else
            visit_rec(m, e, false, false, redundant);
        SASSERT(m_egraph.find(e));
    }

    sat::literal solver::internalize(expr* e, bool sign, bool root, bool redundant) {
        if (si.is_bool_op(e))
            return attach_lit(si.internalize(e, redundant), e);
        if (auto* ext = get_solver(e))
            return ext->internalize(e, sign, root, redundant);
        if (!visit_rec(m, e, sign, root, redundant))
            return sat::null_literal;
        SASSERT(m_egraph.find(e));
        if (m.is_bool(e))
            return literal(si.to_bool_var(e), sign);
        return sat::null_literal;
    }

    bool solver::visit(expr* e) {
        euf::enode* n = m_egraph.find(e);
        if (n)
            return true;
        if (si.is_bool_op(e)) {
            attach_lit(si.internalize(e, m_is_redundant), e);
            return true;
        }
        if (is_app(e) && to_app(e)->get_num_args() > 0) {
            m_stack.push_back(sat::eframe(e));
            return false;
        }
        n = m_egraph.mk(e, 0, nullptr);
        attach_node(n);
        return true;
    }

    bool solver::post_visit(expr* e, bool sign, bool root) {
        unsigned num = is_app(e) ? to_app(e)->get_num_args() : 0;
        m_args.reset();
        for (unsigned i = 0; i < num; ++i)
            m_args.push_back(m_egraph.find(to_app(e)->get_arg(i)));
        if (root && internalize_root(to_app(e), sign, m_args))
            return false;
        if (auto* s = get_solver(e)) {
            s->internalize(e, m_is_redundant);
            return true;
        }
        enode* n = m_egraph.mk(e, num, m_args.c_ptr());
        attach_node(n);
        return true;
    }

    bool solver::visited(expr* e) {
        return m_egraph.find(e) != nullptr;
    }

    void solver::attach_node(euf::enode* n) {
        expr* e = n->get_expr();
        if (!m.is_bool(e))
            drat_log_node(e);
        else
            attach_lit(literal(si.add_bool_var(e), false), e);

        if (!m.is_bool(e) && m.get_sort(e)->get_family_id() != null_family_id) {
            auto* e_ext = get_solver(e);
            auto* s_ext = get_solver(m.get_sort(e));
            if (s_ext && s_ext != e_ext)
                s_ext->apply_sort_cnstr(n, m.get_sort(e));
        }
        axiomatize_basic(n);
    }

    sat::literal solver::attach_lit(literal lit, expr* e) {
        sat::bool_var v = lit.var();
        s().set_external(v);
        s().set_eliminated(v, false);

        if (lit.sign()) {
            v = si.add_bool_var(e);
            s().set_external(v);
            s().set_eliminated(v, false);
            sat::literal lit2 = literal(v, false);
            s().mk_clause(~lit, lit2, sat::status::th(m_is_redundant, m.get_basic_family_id()));
            s().mk_clause(lit, ~lit2, sat::status::th(m_is_redundant, m.get_basic_family_id()));
            lit = lit2;
        }
        m_var2expr.reserve(v + 1, nullptr);
        SASSERT(m_var2expr[v] == nullptr);
        m_var2expr[v] = e;
        m_var_trail.push_back(v);
        if (!m_egraph.find(e)) {
            enode* n = m_egraph.mk(e, 0, nullptr);
            m_egraph.set_merge_enabled(n, false);
        }
        return lit;
    }

    bool solver::internalize_root(app* e, bool sign, enode_vector const& args) {
        if (m.is_distinct(e)) {
            enode_vector _args(args);
            if (sign)
                add_not_distinct_axiom(e, _args.c_ptr());
            else
                add_distinct_axiom(e, _args.c_ptr());
            return true;
        }
        return false;
    }

    void solver::add_not_distinct_axiom(app* e, enode* const* args) {
        SASSERT(m.is_distinct(e));
        unsigned sz = e->get_num_args();
        if (sz <= 1)
            return;

        sat::status st = sat::status::th(m_is_redundant, m.get_basic_family_id());
        static const unsigned distinct_max_args = 32;
        if (sz <= distinct_max_args) {
            sat::literal_vector lits;
            for (unsigned i = 0; i < sz; ++i) {
                for (unsigned j = i + 1; j < sz; ++j) {
                    expr_ref eq(m.mk_eq(args[i]->get_expr(), args[j]->get_expr()), m);
                    sat::literal lit = internalize(eq, false, false, m_is_redundant);
                    lits.push_back(lit);
                }
            }
            s().mk_clause(lits, st);
        }
        else {
            // g(f(x_i)) = x_i
            // f(x_1) = a + .... + f(x_n) = a >= 2
            sort* srt = m.get_sort(e->get_arg(0));
            SASSERT(!m.is_bool(srt));
            sort_ref u(m.mk_fresh_sort("distinct-elems"), m);
            sort* u_ptr = u.get();
            func_decl_ref f(m.mk_fresh_func_decl("dist-f", "", 1, &srt, u), m);
            func_decl_ref g(m.mk_fresh_func_decl("dist-g", "", 1, &u_ptr, srt), m);
            expr_ref a(m.mk_fresh_const("a", u), m);
            expr_ref_vector eqs(m);
            for (expr* arg : *e) {
                expr_ref fapp(m.mk_app(f, arg), m);
                expr_ref gapp(m.mk_app(g, fapp.get()), m);
                expr_ref eq(m.mk_eq(gapp, arg), m);
                sat::literal lit = internalize(eq, false, false, m_is_redundant);
                s().add_clause(1, &lit, st);
                eqs.push_back(m.mk_eq(fapp, a));
            }
            pb_util pb(m);
            expr_ref at_least2(pb.mk_at_least_k(eqs.size(), eqs.c_ptr(), 2), m);
            sat::literal lit = si.internalize(at_least2, m_is_redundant);
            s().mk_clause(1, &lit, st);
        }
    }

    void solver::add_distinct_axiom(app* e, enode* const* args) {
        SASSERT(m.is_distinct(e));
        static const unsigned distinct_max_args = 32;
        unsigned sz = e->get_num_args();
        sat::status st = sat::status::th(m_is_redundant, m.get_basic_family_id());
        if (sz <= 1) {
            s().mk_clause(0, nullptr, st);
            return;
        }
        if (sz <= distinct_max_args) {
            for (unsigned i = 0; i < sz; ++i) {
                for (unsigned j = i + 1; j < sz; ++j) {
                    expr_ref eq(m.mk_eq(args[i]->get_expr(), args[j]->get_expr()), m);
                    sat::literal lit = internalize(eq, true, false, m_is_redundant);
                    s().add_clause(1, &lit, st);
                }
            }
        }
        else {
            // dist-f(x_1) = v_1 & ... & dist-f(x_n) = v_n
            sort* srt = m.get_sort(e->get_arg(0));
            SASSERT(!m.is_bool(srt));
            sort_ref u(m.mk_fresh_sort("distinct-elems"), m);
            func_decl_ref f(m.mk_fresh_func_decl("dist-f", "", 1, &srt, u), m);
            for (unsigned i = 0; i < sz; ++i) {
                expr_ref fapp(m.mk_app(f, e->get_arg(i)), m);
                expr_ref fresh(m.mk_fresh_const("dist-value", u), m);
                enode* n = m_egraph.mk(fresh, 0, nullptr);
                n->mark_interpreted();
                expr_ref eq(m.mk_eq(fapp, fresh), m);
                sat::literal lit = internalize(eq, false, false, m_is_redundant);
                s().add_clause(1, &lit, st);
            }
        }
    }

    void solver::axiomatize_basic(enode* n) {
        expr* e = n->get_expr();
        sat::status st = sat::status::th(m_is_redundant, m.get_basic_family_id());
        expr* c = nullptr, * th = nullptr, * el = nullptr;
        if (!m.is_bool(e) && m.is_ite(e, c, th, el)) {
            app* a = to_app(e);
            sat::bool_var v = si.to_bool_var(c);
            SASSERT(v != sat::null_bool_var);
            expr_ref eq_th(m.mk_eq(a, th), m);
            expr_ref eq_el(m.mk_eq(a, el), m);
            sat::literal lit_th = internalize(eq_th, false, false, m_is_redundant);
            sat::literal lit_el = internalize(eq_el, false, false, m_is_redundant);
            literal lits1[2] = { literal(v, true),  lit_th };
            literal lits2[2] = { literal(v, false), lit_el };
            s().add_clause(2, lits1, st);
            s().add_clause(2, lits2, st);
        }
        else if (m.is_distinct(e)) {
            expr_ref_vector eqs(m);
            unsigned sz = n->num_args();
            for (unsigned i = 0; i < sz; ++i) {
                for (unsigned j = i + 1; j < sz; ++j) {
                    expr_ref eq(m.mk_eq(n->get_arg(i)->get_expr(), n->get_arg(j)->get_expr()), m);
                    eqs.push_back(eq);
                }
            }
            expr_ref fml(m.mk_or(eqs), m);
            sat::literal dist(si.to_bool_var(e), false);
            sat::literal some_eq = si.internalize(fml, m_is_redundant);
            sat::literal lits1[2] = { ~dist, ~some_eq };
            sat::literal lits2[2] = { dist, some_eq };
            s().add_clause(2, lits1, st);
            s().add_clause(2, lits2, st);
        }
    }


    bool solver::is_shared(enode* n) const {
        n = n->get_root();

        if (m.is_ite(n->get_expr()))
            return true;

        theory_id th_id = null_theory_id;
        for (auto p : euf::enode_th_vars(n)) {
            if (th_id == null_theory_id)
                th_id = p.get_id();
            else
                return true;
        }
        if (th_id == null_theory_id)
            return false;

        // the variable is shared if the equivalence class of n
        // contains a parent application.

        for (euf::enode* parent : euf::enode_parents(n)) {
            app* p = to_app(parent->get_expr());
            family_id fid = p->get_family_id();
            if (fid != th_id && fid != m.get_basic_family_id())
                return true;
        }

        // Some theories implement families of theories. Examples:
        // Arrays and Tuples.  For example, array theory is a
        // parametric theory, that is, it implements several theories:
        // (array int int), (array int (array int int)), ...
        //
        // Example:
        //
        // a : (array int int)
        // b : (array int int)
        // x : int
        // y : int
        // v : int
        // w : int
        // A : (array (array int int) int)
        //
        // assert (= b (store a x v))
        // assert (= b (store a y w))
        // assert (not (= x y))
        // assert (not (select A a))
        // assert (not (select A b))
        // check
        //
        // In the example above, 'a' and 'b' are shared variables between
        // the theories of (array int int) and (array (array int int) int).
        // Remark: The inconsistency is not going to be detected if they are
        // not marked as shared.
        return true;
        // TODO
        // return get_theory(th_id)->is_shared(l->get_var());
    }
}