add simplifiation pass

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/sat/sat_aig_cuts.cpp

@@ -18,6 +18,7 @@
 #include "util/trace.h"
 #include "sat/sat_aig_cuts.h"
 #include "sat/sat_solver.h"
+#include "sat/sat_lut_finder.h"
 
 namespace sat {
         
@@ -762,6 +763,34 @@ namespace sat {
         cut2def(on_clause, c, literal(v, true));
     }
 
+    /**
+     * simplify a set of cuts by removing don't cares.
+     */
+    void aig_cuts::simplify() {        
+        uint64_t masks[7];
+        for (unsigned i = 0; i <= 6; ++i) {
+            masks[i] = cut::effect_mask(i);
+        }
+        unsigned dont_cares = 0;
+        for (cut_set & cs : m_cuts) {
+            for (cut const& c : cs) {
+                uint64_t t = c.table();
+                for (unsigned i = 0; i < std::min(6u, c.size()); ++i) {
+                    uint64_t diff = masks[i] & (t ^ (t >> (1ull << i)));
+                    if (diff == 0ull) {
+                        cut d(c);
+                        d.remove_elem(i);
+                        cs.insert(m_on_cut_add, m_on_cut_del, d);
+                        cs.evict(m_on_cut_del, c);
+                        ++dont_cares;
+                        break;
+                    }
+                }
+            }
+        }
+        IF_VERBOSE(0, verbose_stream() << "#don't cares " << dont_cares << "\n");
+    }
+
     struct aig_cuts::validator {
         aig_cuts& t;
         params_ref p;

src/sat/sat_aig_cuts.h

@@ -227,6 +227,8 @@ namespace sat {
 
         cut_eval simulate(unsigned num_rounds);
 
+        void simplify();
+
         std::ostream& display(std::ostream& out) const;
 
     };

src/sat/sat_config.cpp

@@ -107,6 +107,7 @@ namespace sat {
         m_cut_delay         = p.cut_delay();
         m_cut_lut           = p.cut_lut();
         m_cut_xor           = p.cut_xor();
+        m_cut_dont_cares    = p.cut_dont_cares();
         m_lookahead_simplify = p.lookahead_simplify();
         m_lookahead_double = p.lookahead_double();
         m_lookahead_simplify_bca = p.lookahead_simplify_bca();

src/sat/sat_config.h

@@ -124,6 +124,7 @@ namespace sat {
         unsigned           m_cut_delay;
         bool               m_cut_lut;
         bool               m_cut_xor;
+        bool               m_cut_dont_cares;
         bool               m_anf_simplify;
         unsigned           m_anf_delay;
         bool               m_anf_exlin;

src/sat/sat_cut_simplifier.cpp

@@ -192,6 +192,7 @@ namespace sat {
             m_aig_cuts.add_node(head, ite_op, 3, args);
             m_stats.m_xites++;
         };
+
         aig_finder af(s);
         af.set(on_and);
         af.set(on_ite);
@@ -231,13 +232,15 @@ namespace sat {
             xf.set(on_xor);
             xf(clauses);
         }
+
+        std::function<void(uint64_t, bool_var_vector const&, bool_var)> on_lut = 
+            [&,this](uint64_t lut, bool_var_vector const& vars, bool_var v) {
+            m_stats.m_xluts++;
+            // m_aig_cuts.add_cut(v, lut, vars);
+            m_aig_cuts.add_node(v, lut, vars.size(), vars.c_ptr());
+        };
+
         if (s.m_config.m_cut_lut) {
-            std::function<void(uint64_t, bool_var_vector const&, bool_var)> on_lut = 
-                [&,this](uint64_t lut, bool_var_vector const& vars, bool_var v) {
-                m_stats.m_xluts++;
-                // m_aig_cuts.add_cut(v, lut, vars);
-                m_aig_cuts.add_node(v, lut, vars.size(), vars.c_ptr());
-            };
             lut_finder lf(s);
             lf.set(on_lut);
             lf(clauses);
@@ -567,11 +570,12 @@ namespace sat {
     }
 
     void cut_simplifier::add_dont_cares(vector<cut_set> const& cuts) {
-        if (!m_config.m_enable_dont_cares) 
+        if (!s.m_config.m_cut_dont_cares) 
             return;
         cuts2bins(cuts);
         bins2dont_cares();
         dont_cares2cuts(cuts);        
+        m_aig_cuts.simplify();
     }
 
     /**

src/sat/sat_cutset.cpp

@@ -89,6 +89,15 @@ namespace sat {
         m_cuts[m_size++] = c; 
     }
 
+    void cut_set::evict(on_update_t& on_del, cut const& c) {
+        for (unsigned i = 0; i < m_size; ++i) {
+            if (m_cuts[i] == c) {
+                evict(on_del, i);
+                break;
+            }
+        }
+    }
+
     void cut_set::evict(on_update_t& on_del, unsigned idx) {
         if (m_var != UINT_MAX && on_del) on_del(m_var, m_cuts[idx]); 
         m_cuts[idx] = m_cuts[--m_size]; 
@@ -166,6 +175,56 @@ namespace sat {
         return true;
     }
 
+    /**
+     * \brief create the masks
+     * i = 0: 101010101010101
+     * i = 1: 1100110011001100
+     * i = 2: 1111000011110000
+     * i = 3: 111111110000000011111111
+     */
+
+    uint64_t cut::effect_mask(unsigned i) {
+        SASSERT(i <= 6);
+        uint64_t m = 0;
+        if (i == 6) {
+            m = ~((uint64_t)0);
+        }
+        else {
+            m = (1ull << (1u << i)) - 1;   // i = 0: m = 1
+            unsigned w = 1u << (i + 1);    // i = 0: w = 2
+            while (w < 64) {
+                m |= (m << w);             // i = 0: m = 1 + 4
+                w *= 2;
+            }
+        }
+        return m;
+    }
+
+    /**
+       remove element from cut as it is deemed a don't care
+     */
+    void cut::remove_elem(unsigned i) {
+        for (unsigned j = i + 1; j < m_size; ++j) {
+            m_elems[j-1] = m_elems[j]; 
+        }
+        --m_size;
+        uint64_t m = effect_mask(i);
+        uint64_t t = 0;
+        for (unsigned j = 0, offset = 0; j < 64; ++j) {
+            if (0 != (m & (1ull << j))) {
+                t |= ((m_table >> j) & 1u) << offset;
+                ++offset;
+            }
+        }
+        m_table = t;
+        m_dont_care = 0;
+        unsigned f = 0;
+        for (unsigned e : *this) {
+            f |= (1u << (e & 0x1F));
+        }
+        m_filter = f;
+    }
+
     /**
        sat-sweep evaluation. Given 64 bits worth of possible values per variable, 
        find possible values for function table encoded by cut.

src/sat/sat_cutset.h

@@ -160,6 +160,10 @@ namespace sat {
             return true;
         }
 
+        void remove_elem(unsigned i);
+
+        static uint64_t effect_mask(unsigned i);
+
         std::ostream& display(std::ostream& out) const;
 
         static std::ostream& display_table(std::ostream& out, unsigned num_input, uint64_t table);
@@ -196,6 +200,7 @@ namespace sat {
             std::swap(m_cuts, other.m_cuts); 
         }
         void evict(on_update_t& on_del, unsigned idx);
+        void evict(on_update_t& on_del, cut const& c);
 
         std::ostream& display(std::ostream& out) const;
     };

src/sat/sat_lut_finder.cpp

@@ -32,7 +32,9 @@ namespace sat {
         // max_size = 6 -> 64 bits
         SASSERT(sizeof(m_combination)*8 >= (1ull << static_cast<uint64_t>(max_size)));
         init_clause_filter();
-        for (unsigned i = 0; i <= 6; ++i) init_mask(i);
+        for (unsigned i = 0; i <= 6; ++i) {
+            m_masks[i] = cut::effect_mask(i);
+        }
         m_var_position.resize(s.num_vars());
         for (clause* cp : clauses) {
             cp->unmark_used();
@@ -203,31 +205,6 @@ namespace sat {
         return false;
     }
 
-    /**
-     * \brief create the masks
-     * i = 0: 101010101010101
-     * i = 1: 1100110011001100
-     * i = 2: 1111000011110000
-     * i = 3: 111111110000000011111111
-     */
-
-    void lut_finder::init_mask(unsigned i) {
-        SASSERT(i <= 6);
-        uint64_t m = 0;
-        if (i == 6) {
-            m = ~((uint64_t)0);
-        }
-        else {
-            m = (1ull << (1u << i)) - 1;   // i = 0: m = 1
-            unsigned w = 1u << (i + 1);    // i = 0: w = 2
-            while (w < 64) {
-                m |= (m << w);             // i = 0: m = 1 + 4
-                w *= 2;
-            }
-        }
-        m_masks[i] = m;
-    }
-
     /**
      * \brief check if all output combinations for variable i are defined.
      */

src/sat/sat_lut_finder.h

@@ -61,7 +61,6 @@ namespace sat {
         bool extract_lut(literal l1, literal l2);
         bool extract_lut(clause& c2);
         bool update_combinations(unsigned mask);
-        void init_mask(unsigned i);
         void init_clause_filter();
         void init_clause_filter(clause_vector& clauses);
         unsigned get_clause_filter(clause const& c);
@@ -75,5 +74,6 @@ namespace sat {
 
         unsigned max_lut_size() const { return m_max_lut_size; }
         void operator()(clause_vector& clauses);        
+
     };
 }

src/sat/sat_params.pyg

@@ -77,6 +77,7 @@ def_module_params('sat',
 	                  ('cut.delay', UINT, 2, 'delay cut simplification by in-processing round'),
                           ('cut.lut',   BOOL, False, 'extract luts from clauses for cut simplification'),
                           ('cut.xor',   BOOL, False, 'extract xors from clauses for cut simplification'),
+                          ('cut.dont_cares', BOOL, True, 'integrate dont cares with cuts'),
                           ('lookahead.cube.cutoff', SYMBOL, 'depth', 'cutoff type used to create lookahead cubes: depth, freevars, psat, adaptive_freevars, adaptive_psat'),
                           # - depth: the maximal cutoff is fixed to the value of lookahead.cube.depth.
                           #          So if the value is 10, at most 1024 cubes will be generated of length 10.