init solve_eqs

src/ast/simplifiers/solve_eqs.cpp

@@ -0,0 +1,116 @@
+/*++
+Copyright (c) 2022 Microsoft Corporation
+
+Module Name:
+
+    solve_eqs.cpp
+
+Abstract:
+
+    simplifier for solving equations
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2022-11-2.
+
+--*/
+
+
+
+#include "ast/simplifiers/solve_eqs.h"
+
+
+namespace euf {
+
+
+    void solve_eqs::init() {
+
+    }
+
+    // initialize graph that maps variable ids to next ids
+    void solve_eqs::extract_dep_graph(dep_eq_vector& eqs) {
+        m_var2id.reset();
+        m_id2var.reset();
+        m_next.reset();
+        unsigned sz = 0;
+        for (auto const& [v, t, d] : eqs)
+            sz = std::max(sz, v->get_id());
+        m_var2id.resize(sz + 1, UINT_MAX);
+        for (auto const& [v, t, d] : eqs) {
+            if (is_var(v))
+                continue;
+            m_var2id[v->get_id()] = m_id2var.size();
+            m_id2var.push_back(v);
+        }
+        m_next.resize(m_id2var.size());
+
+        for (auto const& [v, t, d] : eqs)
+            m_next[var2id(v)].push_back(t);
+    }
+
+    void solve_eqs::add_subst(app* v, expr* term) {
+
+    }
+
+    /**
+    * Build a substitution while assigning levels to terms.
+    * The substitution is well-formed when variables are replaced with terms whose
+    * Free variables have higher levels.
+    */
+    void solve_eqs::extract_subst() {
+        m_var2level.reset();
+        m_var2level.resize(m_id2var.size(), UINT_MAX);
+        auto is_explored = [&](unsigned id) {
+            return m_var2level[id] != UINT_MAX;
+        };
+        auto is_safe = [&](unsigned lvl, expr* t) {
+            for (auto* e : subterms::all(expr_ref(t, m)))
+                if (is_var(e) && m_var2level[var2id(e)] < lvl)
+                    return false;
+        };
+
+        unsigned init_level = UINT_MAX;
+        for (unsigned id = 0; id < m_id2var.size(); ++id) {
+            if (is_explored(id))
+                continue;
+            // initialize current level to have enough room to assign different levels to all variables.
+            init_level -= m_id2var.size() + 1;
+            unsigned curr_level = init_level;
+            todo.push_back(id);
+            while (!todo.empty()) {
+                unsigned j = todo.back();
+                todo.pop_back();
+                if (is_explored(j))
+                    continue;
+                m_var2level[id] = curr_level++;
+                for (expr* t : m_next[j]) {
+                    if (!is_safe(curr_level, t))
+                        continue;
+                    add_subst(m_id2var[j], t);
+                    for (auto* e : subterms::all(expr_ref(t, m))) 
+                        if (is_var(e) && !is_explored(var2id(e))) 
+                            todo.push_back(var2id(e));   
+                    break;
+                }
+            }            
+        }
+    }
+
+    void solve_eqs::extract_subst(dep_eq_vector& eqs, dep_eq_vector& subst) {
+
+    }
+
+    void solve_eqs::apply_subst() {
+
+    }
+    
+    void solve_eqs::reduce() {
+        init();
+        dep_eq_vector eqs, subst;
+        get_eqs(eqs);
+        extract_subst(eqs, subst);
+        apply_subst();
+        advance_qhead(m_fmls.size());
+    }
+
+}