Add bitblasting fallback to viable::query

(integration between conflict/viable is still messy)

src/math/polysat/conflict.cpp

@@ -182,6 +182,15 @@ namespace polysat {
         SASSERT(s.at_base_level());
         m_level = s.m_level;
         SASSERT(!empty());
+        // TODO: logger().begin_conflict???
+        // TODO: check uses of logger().begin_conflict(). sometimes we call it before adding constraints, sometimes after...
+    }
+
+    void conflict::init_empty() {
+        SASSERT(empty());
+        m_level = s.m_level;
+        SASSERT(!empty());
+        // TODO: logger().begin_conflict???
     }
 
     void conflict::init(signed_constraint c) {
@@ -193,11 +202,13 @@ namespace polysat {
         logger().begin_conflict();
     }
 
+#if 0
     void conflict::set(signed_constraint c) {
         SASSERT(!empty());
         remove_all();
         set_impl(c);
     }
+#endif
 
     void conflict::set_impl(signed_constraint c) {
         if (c.bvalue(s) == l_false) {
@@ -233,6 +244,7 @@ namespace polysat {
     void conflict::init(pvar v, bool by_viable_fallback) {
         LOG("Conflict: viable v" << v);
         SASSERT(empty());
+        SASSERT(!s.is_assigned(v));
         m_level = s.m_level;
         if (by_viable_fallback) {
             logger().begin_conflict(header_with_var("unsat core from viable fallback for v", v));

src/math/polysat/conflict.h

@@ -85,7 +85,7 @@ namespace polysat {
         scoped_ptr<conflict_resolver> m_resolver;
 
         // current conflict core consists of m_literals and m_vars
-        indexed_uint_set m_literals;        // set of boolean literals in the conflict
+        indexed_uint_set m_literals;        // set of boolean literals in the conflict; TODO: why not sat::literal_set
         uint_set m_vars;                    // variable assignments used as premises, shorthand for literals (x := v)
 
         unsigned_vector m_var_occurrences;  // for each variable, the number of constraints in m_literals that contain it
@@ -135,9 +135,13 @@ namespace polysat {
         void init(clause const& cl);
         /** conflict because there is no viable value for the variable v */
         void init(pvar v, bool by_viable_fallback);
+        /** start empty conflict, constraints to be added by caller */
+        void init_empty();   // TODO: remove... rather have all types of conflicts explicitly listed here.
 
+#if 0
         /** replace the current conflict by a single constraint */
         void set(signed_constraint c);
+#endif
 
         bool contains(signed_constraint c) const { SASSERT(c); return contains(c.blit()); }
         bool contains(sat::literal lit) const;

src/math/polysat/solver.cpp

@@ -652,7 +652,7 @@ namespace polysat {
             //       (fail here in debug mode so we notice if we miss some)
             DEBUG_CODE( UNREACHABLE(); );
             m_free_pvars.unassign_var_eh(v);
-            set_conflict(v, false);
+            SASSERT(is_conflict());
             return;
         case find_t::singleton:
             // NOTE: this case may happen legitimately if all other possibilities were excluded by brute force search

src/math/polysat/univariate/univariate_solver.cpp

@@ -26,6 +26,12 @@ Author:
 
 namespace polysat {
 
+    univariate_solver::dep_vector univariate_solver::unsat_core() {
+        dep_vector deps;
+        unsat_core(deps);
+        return deps;
+    }
+
     class univariate_bitblast_solver : public univariate_solver {
         // TODO: does it make sense to share m and bv between different solver instances?
         // TODO: consider pooling solvers to save setup overhead, see if solver/solver_pool.h can be used
@@ -33,6 +39,7 @@ namespace polysat {
         scoped_ptr<bv_util> bv;
         scoped_ptr<solver> s;
         unsigned bit_width;
+        unsigned m_scope_level = 0;
         func_decl_ref x_decl;
         expr_ref x;
         vector<rational> model_cache;
@@ -67,15 +74,22 @@ namespace polysat {
         }
 
         void push() override {
+            m_scope_level++;
             push_cache();
             s->push();
         }
 
         void pop(unsigned n) override {
+            SASSERT(scope_level() >= n);
+            m_scope_level -= n;
             pop_cache();
             s->pop(n);
         }
 
+        unsigned scope_level() override {
+            return m_scope_level;
+        }
+
         expr* mk_numeral(rational const& r) const {
             return bv->mk_numeral(r, bit_width);
         }
@@ -198,8 +212,8 @@ namespace polysat {
             return s->check_sat();
         }
 
-        dep_vector unsat_core() override {
-            dep_vector deps;
+        void unsat_core(dep_vector& deps) override {
+            deps.reset();
             expr_ref_vector core(m);
             s->get_unsat_core(core);
             for (expr* a : core) {
@@ -207,7 +221,6 @@ namespace polysat {
                 deps.push_back(dep);
             }
             SASSERT(deps.size() > 0);
-            return deps;
         }
 
         rational model() override {

src/math/polysat/univariate/univariate_solver.h

@@ -39,13 +39,15 @@ namespace polysat {
 
         virtual void push() = 0;
         virtual void pop(unsigned n) = 0;
+        virtual unsigned scope_level() = 0;
 
         virtual lbool check() = 0;
 
         /**
          * Precondition: check() returned l_false
          */
-        virtual dep_vector unsat_core() = 0;
+        dep_vector unsat_core();
+        virtual void unsat_core(dep_vector& out_deps) = 0;
 
         /**
          * Precondition: check() returned l_true

src/math/polysat/viable.cpp

@@ -23,6 +23,10 @@ TODO: improve management of the fallback univariate solvers:
       - incrementally add/remove constraints
       - set resource limit of univariate solver
 
+TODO: plan to fix the FI "pumping":
+    1. simple looping detection and bitblasting fallback.
+    2. intervals at multiple bit widths
+
 --*/
 
 
@@ -33,6 +37,8 @@ TODO: improve management of the fallback univariate solvers:
 
 namespace polysat {
 
+    using namespace viable_query;
+
     struct inf_fi : public inference {
         viable& v;
         pvar var;
@@ -137,7 +143,7 @@ namespace polysat {
                 prop = true;
                 break;
             case find_t::empty:
-                s.set_conflict(v, false);
+                SASSERT(s.is_conflict());
                 return true;
             default:
                 break;
@@ -543,15 +549,22 @@ namespace polysat {
         return refine_viable(v, val);
     }
 
+    lbool viable::min_viable(pvar v, rational& lo) {
+        return query<query_t::min_viable>(v, lo);
+    }
 
-    rational viable::min_viable(pvar v) {
-        refined:
-        rational lo(0);
-        auto* e = m_units[v];
+    lbool viable::max_viable(pvar v, rational& hi) {
+        return query<query_t::max_viable>(v, hi);
+    }
+
+    bool viable::query_min(pvar v, rational& lo) {
+        // TODO: should be able to deal with UNSAT case; since also min_viable has to deal with it due to fallback solver
+        lo = 0;
+        entry* e = m_units[v];
         if (!e && !refine_viable(v, lo))
-            goto refined;
+            return false;
         if (!e)
-            return lo;
+            return true;
         entry* first = e;
         entry* last = first->prev();
         if (last->interval.currently_contains(lo))
@@ -564,19 +577,19 @@ namespace polysat {
         }
         while (e != first);
         if (!refine_viable(v, lo))
-            goto refined;
+            return false;
         SASSERT(is_viable(v, lo));
-        return lo;
+        return true;
     }
 
-    rational viable::max_viable(pvar v) {
-        refined:
-        rational hi = s.var2pdd(v).max_value();
+    bool viable::query_max(pvar v, rational& hi) {
+        // TODO: should be able to deal with UNSAT case; since also max_viable has to deal with it due to fallback solver
+        hi = s.var2pdd(v).max_value();
         auto* e = m_units[v];
         if (!e && !refine_viable(v, hi))
-            goto refined;
+            return false;
         if (!e)
-            return hi;
+            return true;
         entry* last = e->prev();
         e = last;
         do {
@@ -587,17 +600,13 @@ namespace polysat {
         }
         while (e != last);
         if (!refine_viable(v, hi))
-            goto refined;
+            return false;
         SASSERT(is_viable(v, hi));
-        return hi;
+        return true;
     }
 
-    // template <viable::query_t mode>
-    find_t viable::query(query_t mode, pvar v, rational& lo, rational& hi) {
-        SASSERT(mode == query_t::find_viable);  // other modes are TODO
-
-        auto const& max_value = s.var2pdd(v).max_value();
-
+    template <query_t mode>
+    lbool viable::query(pvar v, typename query_result<mode>::result_t& result) {
         // max number of interval refinements before falling back to the univariate solver
         unsigned const refinement_budget = 1000;
         unsigned refinements = refinement_budget;
@@ -606,25 +615,152 @@ namespace polysat {
 
         if (!refinements) {
             LOG("Refinement budget exhausted! Fall back to univariate solver.");
-            return find_t::resource_out;
+            return query_fallback<mode>(v, result);
         }
 
         refinements--;
 
+        if constexpr (mode == query_t::find_viable) {
+            lbool res = query_find(v, result.first, result.second);
+            if (res == l_undef)
+                goto refined;
+            return res;
+        }
+
+        if constexpr (mode == query_t::min_viable) {
+            if (!query_min(v, result))
+                goto refined;
+            return l_true;
+        }
+
+        if constexpr (mode == query_t::max_viable) {
+            if (!query_max(v, result))
+                goto refined;
+            return l_true;
+        }
+
+        if constexpr (mode == query_t::has_viable) {
+            NOT_IMPLEMENTED_YET();
+            return l_undef;
+        }
+
+        UNREACHABLE();
+        return l_undef;
+    }
+
+    template <query_t mode>
+    lbool viable::query_fallback(pvar v, typename query_result<mode>::result_t& result) {
+        unsigned const bit_width = s.size(v);
+        univariate_solver* us = s.m_viable_fallback.usolver(bit_width);
+        sat::literal_set added;
+
+        // First step: only query the looping constraints and see if they alone are already UNSAT.
+        // The constraints which caused the refinement loop will be reached from m_units.
+        entry const* first = m_units[v];
+        entry const* e = first;
+        do {
+            entry const* origin = e;
+            while (origin->refined)
+                origin = origin->refined;
+            signed_constraint const c = origin->src;
+            sat::literal const lit = c.blit();
+            if (!added.contains(lit)) {
+                added.insert(lit);
+                c.add_to_univariate_solver(s, *us, lit.to_uint());
+            }
+            e = e->next();
+        }
+        while (e != first);
+
+        switch (us->check()) {
+        case l_false:
+            set_fallback_conflict(v, *us);
+            return l_false;
+        case l_true:
+            // At this point we don't know much because we did not add all relevant constraints
+            break;
+        default:
+            // resource limit
+            return l_undef;
+        }
+
+        // Second step: looping constraints aren't UNSAT, so add the remaining relevant constraints
+        auto const& cs = s.m_viable_fallback.m_constraints[v];
+        for (unsigned i = cs.size(); i-- > 0; ) {
+            sat::literal const lit = cs[i].blit();
+            if (added.contains(lit))
+                continue;
+            added.insert(lit);
+            cs[i].add_to_univariate_solver(s, *us, lit.to_uint());
+        }
+
+        switch (us->check()) {
+        case l_false:
+            set_fallback_conflict(v, *us);
+            return l_false;
+        case l_true:
+            // pass solver to mode-specific query
+            break;
+        default:
+            // resource limit
+            return l_undef;
+        }
+
+        if constexpr (mode == query_t::find_viable)
+            return query_find_fallback(v, *us, result.first, result.second);
+
+        if constexpr (mode == query_t::min_viable)
+            return query_min_fallback(v, *us, result);
+
+        if constexpr (mode == query_t::max_viable)
+            return query_max_fallback(v, *us, result);
+
+        if constexpr (mode == query_t::has_viable) {
+            NOT_IMPLEMENTED_YET();
+            return l_undef;
+        }
+
+        UNREACHABLE();
+        return l_undef;
+    }
+
+    lbool viable::query_find_fallback(pvar v, univariate_solver& us, rational& lo, rational& hi) {
+        if (!us.find_min(lo))
+            return l_undef;
+        if (!us.find_max(hi))
+            return l_undef;
+        return l_true;
+    }
+
+    lbool viable::query_min_fallback(pvar v, univariate_solver& us, rational& lo) {
+        return us.find_min(lo) ? l_true : l_undef;
+    }
+
+    lbool viable::query_max_fallback(pvar v, univariate_solver& us, rational& hi) {
+        return us.find_max(hi) ? l_true : l_undef;
+    }
+
+    lbool viable::query_find(pvar v, rational& lo, rational& hi) {
+        auto const& max_value = s.var2pdd(v).max_value();
+        lbool const refined = l_undef;
+
         // After a refinement, any of the existing entries may have been replaced
         // (if it is subsumed by the new entry created during refinement).
         // For this reason, we start chasing the intervals from the start again.
         lo = 0;
+        hi = max_value;
 
         auto* e = m_units[v];
         if (!e && !refine_viable(v, lo))
-            goto refined;
-        if (!e && !refine_viable(v, rational::one()))
-            goto refined;
+            return refined;
+        if (!e && !refine_viable(v, hi))
+            return refined;
         if (!e)
-            return find_t::multiple;
-        if (e->interval.is_full())
-            return find_t::empty;
+            return l_true;
+        if (e->interval.is_full()) {
+            set_interval_conflict(v);
+            return l_false;
+        }
 
         entry* first = e;
         entry* last = first->prev();
@@ -635,10 +771,10 @@ namespace polysat {
             last->interval.hi_val() < max_value) {
             lo = last->interval.hi_val();
             if (!refine_viable(v, lo))
-                goto refined;
+                return refined;
             if (!refine_viable(v, max_value))
-                goto refined;
-            return find_t::multiple;
+                return refined;
+            return l_true;
         }
 
         // find lower bound
@@ -652,8 +788,10 @@ namespace polysat {
         }
         while (e != first);
 
-        if (e->interval.currently_contains(lo))
-            return find_t::empty;
+        if (e->interval.currently_contains(lo)) {
+            set_interval_conflict(v);
+            return l_false;
+        }
 
         // find upper bound
         hi = max_value;
@@ -666,83 +804,59 @@ namespace polysat {
         }
         while (e != last);
         if (!refine_viable(v, lo))
-            goto refined;
+            return refined;
         if (!refine_viable(v, hi))
-            goto refined;
+            return refined;
+        return l_true;
+    }
 
-        if (lo == hi)
-            return find_t::singleton;
-        else
-            return find_t::multiple;
+    lbool viable::find_viable(pvar v, rational& lo, rational& hi) {
+        std::pair<rational&, rational&> args{lo, hi};
+        return query<query_t::find_viable>(v, args);
     }
 
     find_t viable::find_viable(pvar v, rational& lo) {
-#if 1
         rational hi;
-        // return query<query_t::find_viable>(v, lo, hi);
-        return query(query_t::find_viable, v, lo, hi);
-#else
-        refined:
-        lo = 0;
-        auto* e = m_units[v];
-        if (!e && !refine_viable(v, lo))
-            goto refined;
-        if (!e && !refine_viable(v, rational::one()))
-            goto refined;
-        if (!e)
-            return find_t::multiple;
-        if (e->interval.is_full())
+        switch (find_viable(v, lo, hi)) {
+        case l_true:
+            return (lo == hi) ? find_t::singleton : find_t::multiple;
+        case l_false:
             return find_t::empty;
-
-        entry* first = e;
-        entry* last = first->prev();
-
-        // quick check: last interval does not wrap around
-        // and has space for 2 unassigned values.
-        auto& max_value = s.var2pdd(v).max_value();
-        if (last->interval.lo_val() < last->interval.hi_val() &&
-            last->interval.hi_val() < max_value) {
-            lo = last->interval.hi_val();
-            if (!refine_viable(v, lo))
-                goto refined;
-            if (!refine_viable(v, max_value))
-                goto refined;
-            return find_t::multiple;
+        default:
+            return find_t::resource_out;
         }
+    }
 
-        // find lower bound
-        if (last->interval.currently_contains(lo))
-            lo = last->interval.hi_val();
-        do {
-            if (!e->interval.currently_contains(lo))
-                break;
-            lo = e->interval.hi_val();
-            e = e->next();
+    void viable::set_fallback_conflict(pvar v, univariate_solver& us) {
+        SASSERT(!s.is_assigned(v));
+        conflict& core = s.m_conflict;
+        core.init_empty();
+        core.logger().begin_conflict(); //header_with_var("unsat core from viable fallback for v", v));  // TODO: begin_conflict before or after adding constraints?
+        // The conflict is the unsat core of the univariate solver,
+        // and the current assignment (under which the constraints are univariate in v)
+        // TODO:
+        // - currently we add variables directly, which is sound:
+        //      e.g.:   v^2 + w^2 == 0;   w := 1
+        // - but we could use side constraints on the coefficients instead (coefficients when viewed as polynomial over v):
+        //      e.g.:   v^2 + w^2 == 0;   w^2 == 1
+        for (unsigned dep : us.unsat_core()) {
+            sat::literal lit = sat::to_literal(dep);
+            signed_constraint c = s.lit2cnstr(lit);
+            core.insert(c);
+            core.insert_vars(c);
         }
-        while (e != first);
+        SASSERT(!core.vars().contains(v));
+        core.add_lemma("viable unsat core", core.build_lemma());
+        core.revert_pvar(v);  // at this point, v is not assigned
+    }
 
-        if (e->interval.currently_contains(lo))
-            return find_t::empty;
-
-        // find upper bound
-        rational hi = max_value;
-        e = last;
-        do {
-            if (!e->interval.currently_contains(hi))
-                break;
-            hi = e->interval.lo_val() - 1;
-            e = e->prev();
-        }
-        while (e != last);
-        if (!refine_viable(v, lo))
-            goto refined;
-        if (!refine_viable(v, hi))
-            goto refined;
-        if (lo == hi)
-            return find_t::singleton;
-        else
-            return find_t::multiple;
-#endif
+    void viable::set_interval_conflict(pvar v) {
+        SASSERT(!s.is_assigned(v));
+        conflict& core = s.m_conflict;
+        core.init_empty();
+        core.logger().begin_conflict(); //header_with_var("forbidden interval lemma for v", v));
+        VERIFY(resolve(v, core));   // TODO: merge?
+        core.revert_pvar(v);  // at this point, v is not assigned
     }
 
     bool viable::resolve(pvar v, conflict& core) {
@@ -960,6 +1074,7 @@ namespace polysat {
             m_usolver.insert(bit_width, mk_solver(bit_width));
             us = m_usolver[bit_width].get();
         }
+        SASSERT_EQ(us->scope_level(), 0);
 
         // push once on the empty solver so we can reset it before the next use
         us->push();

src/math/polysat/viable.h

@@ -25,6 +25,7 @@ Author:
 #include "math/polysat/conflict.h"
 #include "math/polysat/constraint.h"
 #include "math/polysat/forbidden_intervals.h"
+#include <optional>
 
 namespace polysat {
 
@@ -39,6 +40,34 @@ namespace polysat {
         resource_out,
     };
 
+    namespace viable_query {
+        enum class query_t {
+            has_viable,  // currently only used internally in resolve_viable
+            min_viable,  // currently unused
+            max_viable,  // currently unused
+            find_viable,
+        };
+
+        template <query_t mode>
+        struct query_result {
+        };
+
+        template <>
+        struct query_result<query_t::min_viable> {
+            using result_t = rational;
+        };
+
+        template <>
+        struct query_result<query_t::max_viable> {
+            using result_t = rational;
+        };
+
+        template <>
+        struct query_result<query_t::find_viable> {
+            using result_t = std::pair<rational&, rational&>;
+        };
+    }
+
     std::ostream& operator<<(std::ostream& out, find_t x);
 
     class viable {
@@ -76,15 +105,38 @@ namespace polysat {
 
         void propagate(pvar v, rational const& val);
 
-        enum class query_t {
-            has_viable,  // currently only used internally in resolve_viable
-            min_viable,  // currently unused
-            max_viable,  // currently unused
-            find_viable,
-        };
+        // return true if done, false if refined
+        bool query_min(pvar v, rational& out_lo);
 
-        // template <query_t mode>
-        find_t query(query_t mode, pvar v, rational& out_lo, rational& out_hi);
+        // return true if done, false if refined
+        bool query_max(pvar v, rational& out_hi);
+
+        // return true if done, false if resource out
+        lbool query_min_fallback(pvar v, univariate_solver& us, rational& out_lo);
+        lbool query_max_fallback(pvar v, univariate_solver& us, rational& out_hi);
+
+        // return resource_out if refined
+        lbool query_find(pvar v, rational& out_lo, rational& out_hi);
+        lbool query_find_fallback(pvar v, univariate_solver& us, rational& out_lo, rational& out_hi);
+
+        /**
+         * Interval query with bounded refinement and fallback to bitblasting.
+         * @return l_true on success, l_false on conflict, l_undef on resource limit
+         */
+        template <viable_query::query_t mode>
+        lbool query(pvar v, typename viable_query::query_result<mode>::result_t& out_result);
+
+        /**
+         * @return l_true on success, l_false on conflict, l_undef on resource limit
+         */
+        template <viable_query::query_t mode>
+        lbool query_fallback(pvar v, typename viable_query::query_result<mode>::result_t& out_result);
+
+        /** Set viable conflict due to interval cover */
+        void set_interval_conflict(pvar v);
+
+        /** Set viable conflict due to fallback solver */
+        void set_fallback_conflict(pvar v, univariate_solver& us);
 
     public:
         viable(solver& s);
@@ -122,17 +174,29 @@ namespace polysat {
          */
         bool is_viable(pvar v, rational const& val);
 
-        /*
-         * Extract min and max viable values for v
+        /**
+         * Extract min viable value for v.
+         * @return l_true on success, l_false on conflict, l_undef on resource limit
          */
-        rational min_viable(pvar v);
-        rational max_viable(pvar v);
+        lbool min_viable(pvar v, rational& out_lo);
+
+        /**
+         * Extract max viable value for v.
+         * @return l_true on success, l_false on conflict, l_undef on resource limit
+         */
+        lbool max_viable(pvar v, rational& out_hi);
 
         /**
          * Find a next viable value for variable.
          */
         find_t find_viable(pvar v, rational& out_val);
 
+        /**
+         * Find a next viable value for variable by determining currently viable lower and upper bounds.
+         * @return l_true on success, l_false on conflict, l_undef on resource limit
+         */
+        lbool find_viable(pvar v, rational& out_lo, rational& out_hi);
+
         /**
          * Retrieve the unsat core for v,
          * and add the forbidden interval lemma for v (which eliminates v from the unsat core).
@@ -251,6 +315,8 @@ namespace polysat {
     }
 
     class viable_fallback {
+        friend class viable;
+
         solver& s;
 
         scoped_ptr<univariate_solver_factory>   m_usolver_factory;

src/test/viable.cpp

@@ -38,16 +38,19 @@ namespace polysat {
         auto c = s.ule(x + 3, x + 5);
         s.v.intersect(xv, c);
         std::cout << s.v << "\n";
-        std::cout << "min-max " << s.v.min_viable(xv) << " " << s.v.max_viable(xv) << "\n";
+        std::cout << "min " << s.v.min_viable(xv, val) << " " << val << "\n";
+        std::cout << "max " << s.v.max_viable(xv, val) << " " << val << "\n";
         s.v.intersect(xv, s.ule(x, 2));
         std::cout << s.v << "\n";
         s.v.intersect(xv, s.ule(1, x));
         std::cout << s.v << "\n";
-        std::cout << "min-max " << s.v.min_viable(xv) << " " << s.v.max_viable(xv) << "\n";
+        std::cout << "min " << s.v.min_viable(xv, val) << " " << val << "\n";
+        std::cout << "max " << s.v.max_viable(xv, val) << " " << val << "\n";
         s.v.intersect(xv, s.ule(x, 3));
         std::cout << s.v << "\n";
         std::cout << s.v.find_viable(xv, val) << " " << val << "\n";        
-        std::cout << "min-max " << s.v.min_viable(xv) << " " << s.v.max_viable(xv) << "\n";
+        std::cout << "min " << s.v.min_viable(xv, val) << " " << val << "\n";
+        std::cout << "max " << s.v.max_viable(xv, val) << " " << val << "\n";
         s.v.intersect(xv, s.ule(3, x));
         std::cout << s.v << "\n";
         std::cout << s.v.find_viable(xv, val) << " " << val << "\n";