introduce spot::simplify_acceptance()

Simplify some automata where some marks are identical,
or complementary to another. Fixes #216.

* NEWS: mention the new function.
* spot/twaalgos/cleanacc.cc, spot/twaalgos/cleanacc.hh: Implement
  the function.
* tests/Makefile.am, tests/python/merge.py: Test this implementation.

NEWS

@@ -104,6 +104,10 @@ New in spot 2.3.4.dev (not yet released)
     automaton.  This parameter is defaulted to true, in order to
     keep this modification backward-compatible.
 
+  - The new function spot::simplify_acceptance() is able to perform
+    some simplifications on an acceptance condition, and might lead
+    to the removal of some acceptance sets.
+
   Python:
 
   - The 'spot.gen' package exports the functions from libspotgen.

spot/twaalgos/cleanacc.cc

@@ -73,5 +73,224 @@ namespace spot
                                                      twa::prop_set::all()));
   }
 
+  namespace
+  {
+    twa_graph_ptr merge_identical_marks_here(twa_graph_ptr aut)
+    {
+      // always cleanup before proceeding, otherwise if some mark appears in the
+      // acceptance condition, but not in the automaton the result is undefined.
+      cleanup_acceptance_here(aut, false);
+
+      auto& acc = aut->acc();
+      auto& c = acc.get_acceptance();
+      acc_cond::mark_t used_in_cond = c.used_sets();
+
+      if (!used_in_cond)
+        return aut;
+
+      unsigned num_sets = acc.num_sets();
+      std::vector<acc_cond::mark_t> always_together(num_sets);
+
+      for (unsigned i = 0; i < num_sets; ++i)
+        if (used_in_cond.has(i))
+          always_together[i] = used_in_cond;
+        else
+          always_together[i] = acc_cond::mark_t({i});
+
+      acc_cond::mark_t previous_a = 0U;
+      for (auto& t: aut->edges())
+        {
+          acc_cond::mark_t a = t.acc & used_in_cond;
+          if (a == previous_a)
+            continue;
+          previous_a = a;
+          for (unsigned m: a.sets())
+            {
+              acc_cond::mark_t at = always_together[m];
+              acc_cond::mark_t newm = at & a;
+
+              for (unsigned rem: (at - newm).sets())
+                always_together[rem] -= newm;
+
+              always_together[m] = newm;
+            }
+        }
+
+      acc_cond::mark_t to_remove = 0U;
+      for (unsigned i = 0; i < num_sets; ++i)
+        {
+          auto oldm = always_together[i];
+          if (oldm == acc_cond::mark_t({i}))
+            continue;
+
+          acc_cond::mark_t newm = oldm.lowest();
+          to_remove |= oldm - newm;
+          always_together[i] = newm;
+        }
+      for (auto& t: aut->edges())
+        t.acc -= to_remove;
+
+      // Replace the marks in the acceptance condition
+      auto pos = &c.back();
+      auto end = &c.front();
+      while (pos > end)
+        {
+          switch (pos->sub.op)
+            {
+            case acc_cond::acc_op::And:
+            case acc_cond::acc_op::Or:
+              --pos;
+              break;
+            case acc_cond::acc_op::Fin:
+            case acc_cond::acc_op::Inf:
+            case acc_cond::acc_op::FinNeg:
+            case acc_cond::acc_op::InfNeg:
+              acc_cond::mark_t replace = pos[-1].mark & to_remove;
+              pos[-1].mark -= replace;
+              for (unsigned m: replace.sets())
+                pos[-1].mark |= always_together[m];
+              pos -= 2;
+              break;
+            }
+        }
+      return aut;
+    }
+
+    // Eventually remove complementary marks from the acceptance condition.
+    acc_cond::acc_code remove_compl_rec(const acc_cond::acc_word* pos,
+                                        const std::vector<acc_cond::mark_t>&
+                                                          complement)
+    {
+      auto start = pos - pos->sub.size;
+      switch (pos->sub.op)
+        {
+          case acc_cond::acc_op::And:
+            {
+              --pos;
+              auto res = acc_cond::acc_code::t();
+              acc_cond::mark_t seen_fin = 0U;
+              auto inf = acc_cond::acc_code::inf(0U);
+              do
+                {
+                  auto tmp = remove_compl_rec(pos, complement);
+
+                  if (tmp.back().sub.op == acc_cond::acc_op::Fin
+                      && tmp.front().mark.count() == 1)
+                    seen_fin |= tmp.front().mark;
+
+                  if (tmp.back().sub.op == acc_cond::acc_op::Inf)
+                    {
+                      inf &= std::move(tmp);
+                      pos -= pos->sub.size + 1;
+                      continue;
+                    }
+                  tmp &= std::move(res);
+                  std::swap(tmp, res);
+                  pos -= pos->sub.size + 1;
+                }
+              while (pos > start);
+
+              for (auto m: seen_fin.sets())
+                inf.front().mark -= complement[m];
+
+              res &= inf;
+              return res;
+            }
+          case acc_cond::acc_op::Or:
+            {
+              --pos;
+              auto res = acc_cond::acc_code::f();
+              acc_cond::mark_t seen_inf = 0U;
+              auto fin = acc_cond::acc_code::f();
+              do
+                {
+                  auto tmp = remove_compl_rec(pos, complement);
 
+                  if (tmp.back().sub.op == acc_cond::acc_op::Inf
+                      && tmp.front().mark.count() == 1)
+                    seen_inf |= tmp.front().mark;
+
+                  if (tmp.back().sub.op == acc_cond::acc_op::Fin)
+                    {
+                      fin |= std::move(tmp);
+                      pos -= pos->sub.size + 1;
+                      continue;
+                    }
+                  tmp |= std::move(res);
+                  std::swap(tmp, res);
+                  pos -= pos->sub.size + 1;
+                }
+              while (pos > start);
+
+              for (auto m: seen_inf.sets())
+                fin.front().mark -= complement[m];
+
+              res |= fin;
+              return res;
+            }
+          case acc_cond::acc_op::Fin:
+            return acc_cond::acc_code::fin(pos[-1].mark);
+          case acc_cond::acc_op::Inf:
+            return acc_cond::acc_code::inf(pos[-1].mark);
+          case acc_cond::acc_op::FinNeg:
+          case acc_cond::acc_op::InfNeg:
+            SPOT_UNREACHABLE();
+        };
+        SPOT_UNREACHABLE();
+        return {};
+    }
+
+    // Always cleanup_acceptance_here with stripping after calling this function
+    // As complementary marks might be simplified in the acceptance condition.
+    twa_graph_ptr simplify_complementary_marks_here(twa_graph_ptr aut)
+    {
+      auto& acc = aut->acc();
+      auto c = acc.get_acceptance();
+      acc_cond::mark_t used_in_cond = c.used_sets();
+      if (!used_in_cond)
+        return aut;
+
+      unsigned num_sets = acc.num_sets();
+      std::vector<acc_cond::mark_t> complement(num_sets);
+
+
+      for (unsigned i = 0; i < num_sets; ++i)
+        if (used_in_cond.has(i))
+          complement[i] = used_in_cond - acc_cond::mark_t({i});
+
+      acc_cond::mark_t previous_a = 0U;
+      for (auto& t: aut->edges())
+        {
+          if (t.acc == previous_a)
+            continue;
+          previous_a = t.acc;
+          for (unsigned m: used_in_cond.sets())
+            {
+              if (t.acc.has(m))
+                complement[m] -= t.acc;
+              else
+                complement[m] &= t.acc;
+            }
+        }
+      aut->set_acceptance(num_sets,
+                          remove_compl_rec(&acc.get_acceptance().back(),
+                                           complement));
+      return aut;
+    }
+  }
+
+  twa_graph_ptr simplify_acceptance_here(twa_graph_ptr aut)
+  {
+    cleanup_acceptance_here(aut, false);
+    merge_identical_marks_here(aut);
+    simplify_complementary_marks_here(aut);
+    cleanup_acceptance_here(aut, true);
+
+    return aut;
+  }
+
+  twa_graph_ptr simplify_acceptance(const_twa_graph_ptr aut)
+  {
+    return simplify_acceptance_here(make_twa_graph(aut, twa::prop_set::all()));
+  }
 }

spot/twaalgos/cleanacc.hh

@@ -34,4 +34,17 @@ namespace spot
   /// \brief Remove useless acceptance sets
   SPOT_API twa_graph_ptr
   cleanup_acceptance(const_twa_graph_ptr aut);
+
+  /// \brief Simplify an acceptance condition
+  ///
+  /// Remove useless acceptance sets.
+  /// Merge identical sets.
+  /// If some sets are complement to each other, might result in the
+  /// simplification of some clause in the acceptance condition.
+  SPOT_API twa_graph_ptr
+  simplify_acceptance_here(twa_graph_ptr aut);
+
+  /// \brief Simplify an acceptance condition
+  SPOT_API twa_graph_ptr
+  simplify_acceptance(const_twa_graph_ptr aut);
 }

tests/Makefile.am

@@ -348,6 +348,7 @@ TESTS_python = \
   python/ltlf.py \
   python/ltlparse.py \
   python/ltlsimple.py \
+  python/merge.py \
   python/minato.py \
   python/misc-ec.py \
   python/optionmap.py \