spot/src/tgbaalgos/degen.cc

// -*- coding: utf-8 -*-
// Copyright (C) 2012, 2013, 2014, 2015 Laboratoire de Recherche et
// Développement de l'Epita.
//
// This file is part of Spot, a model checking library.
//
// Spot is free software; you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or
// (at your option) any later version.
//
// Spot is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
// or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
// License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.


#include "degen.hh"
#include "twa/twagraph.hh"
#include "misc/hash.hh"
#include "misc/hashfunc.hh"
#include <deque>
#include <vector>
#include <algorithm>
#include <iterator>
#include "tgbaalgos/sccinfo.hh"
#include "twa/bddprint.hh"

//#define DEGEN_DEBUG

namespace spot
{
  namespace
  {
    // A state in the degenalized automaton corresponds to a state in
    // the TGBA associated to a level.  The level is just an index in
    // the list of acceptance sets.
    typedef std::pair<unsigned, unsigned> degen_state;

    struct degen_state_hash
    {
      size_t
      operator()(const degen_state& s) const
      {
        return wang32_hash(s.first ^ wang32_hash(s.second));
      }
    };

    // Associate the degeneralized state to its number.
    typedef std::unordered_map<degen_state, int, degen_state_hash> ds2num_map;

    // Queue of state to be processed.
    typedef std::deque<degen_state> queue_t;

    // Acceptance set common to all outgoing transitions (of the same
    // SCC -- we do not care about the other) of some state.
    class outgoing_acc
    {
      const_twa_graph_ptr a_;
      typedef std::tuple<acc_cond::mark_t,
			 acc_cond::mark_t,
			 bool> cache_entry;
      std::vector<cache_entry> cache_;
      const scc_info* sm_;

      void fill_cache(unsigned s)
      {
	unsigned s1 = sm_ ? sm_->scc_of(s) : 0;
	acc_cond::mark_t common = a_->acc().all_sets();
        acc_cond::mark_t union_ = 0U;
	bool has_acc_self_loop = false;
	bool seen = false;
	for (auto& t: a_->out(s))
          {
	    // Ignore transitions that leave the SCC of s.
	    unsigned d = t.dst;
	    unsigned s2 = sm_ ? sm_->scc_of(d) : 0;
	    if (s2 != s1)
	      continue;

            common &= t.acc;
            union_ |= t.acc;

	    // an accepting self-loop?
	    has_acc_self_loop |= (t.dst == s) && a_->acc().accepting(t.acc);
	    seen = true;
          }
	if (!seen)
	  common = 0U;
        cache_[s] = std::make_tuple(common, union_, has_acc_self_loop);
      }

    public:
      outgoing_acc(const const_twa_graph_ptr& a, const scc_info* sm):
	a_(a), cache_(a->num_states()), sm_(sm)
      {
	unsigned n = a->num_states();
	for (unsigned s = 0; s < n; ++s)
	  fill_cache(s);
      }

      // Intersection of all outgoing acceptance sets
      acc_cond::mark_t common_acc(unsigned s)
      {
	assert(s < cache_.size());
	return std::get<0>(cache_[s]);
      }

      // Union of all outgoing acceptance sets
      acc_cond::mark_t union_acc(unsigned s)
      {
	assert(s < cache_.size());
	return std::get<1>(cache_[s]);
      }

      // Has an accepting self-loop
      bool has_acc_selfloop(unsigned s)
      {
	assert(s < cache_.size());
	return std::get<2>(cache_[s]);
      }
    };

    // Order of accepting sets (for one SCC)
    class acc_order
    {
      std::vector<unsigned> order_;
      acc_cond::mark_t found_;

    public:
      unsigned
      next_level(int slevel, acc_cond::mark_t set, bool skip_levels)
      {
	// Update the order with any new set we discover
	if (auto newsets = set - found_)
	  {
	    newsets.fill(std::back_inserter(order_));
	    found_ |= newsets;
	  }

        unsigned next = slevel;
        while (next < order_.size() && set.has(order_[next]))
	  {
	    ++next;
	    if (!skip_levels)
	      break;
	  }
        return next;
      }

      void
      print(int scc)
      {
        std::cout << "Order_" << scc << ":\t";
        for (auto i: order_)
	  std::cout << i << ", ";
        std::cout << '\n';
      }
    };

    // Accepting order for each SCC
    class scc_orders
    {
      std::map<int, acc_order> orders_;
      bool skip_levels_;

    public:
      scc_orders(bool skip_levels):
	skip_levels_(skip_levels)
      {
      }

      unsigned
      next_level(int scc, int slevel, acc_cond::mark_t set)
      {
        return orders_[scc].next_level(slevel, set, skip_levels_);
      }

      void
      print()
      {
        std::map<int, acc_order>::iterator i;
        for (i = orders_.begin(); i != orders_.end(); i++)
          i->second.print(i->first);
      }
    };

    template<bool want_sba>
    twa_graph_ptr
    degeneralize_aux(const const_twa_graph_ptr& a, bool use_z_lvl,
		     bool use_cust_acc_orders, int use_lvl_cache,
		     bool skip_levels, bool ignaccsl)
    {
      if (!a->acc().is_generalized_buchi())
	throw std::runtime_error
	  ("degeneralize() can only work with generalized Büchi acceptance");

      bool use_scc = use_lvl_cache || use_cust_acc_orders || use_z_lvl;

      bdd_dict_ptr dict = a->get_dict();

      // The result automaton is an SBA.
      auto res = make_twa_graph(dict);
      res->copy_ap_of(a);
      res->set_buchi();
      if (want_sba)
	res->prop_state_based_acc();
      // Preserve determinism, weakness, and stutter-invariance
      res->prop_copy(a, { false, true, true, true });

      // Create an order of acceptance conditions.  Each entry in this
      // vector correspond to an acceptance set.  Each index can
      // be used as a level in degen_state to indicate the next expected
      // acceptance set.  Level order.size() is a special level used to
      // denote accepting states.
      std::vector<unsigned> order;
      {
	// FIXME: revisit this comment once everything compiles again.
	//
	// The order is arbitrary, but it turns out that using push_back
	// instead of push_front often gives better results because
	// acceptance sets at the beginning if the cycle are more often
	// used in the automaton.  (This surprising fact is probably
	// related to the order in which we declare the BDD variables
	// during the translation.)
	unsigned n = a->acc().num_sets();
	for (unsigned i = n; i > 0; --i)
	  order.push_back(i - 1);
      }

      // Initialize scc_orders
      scc_orders orders(skip_levels);

      // and vice-versa.
      ds2num_map ds2num;

      // This map is used to find transitions that go to the same
      // destination with the same acceptance.  The integer key is
      // (dest*2+acc) where dest is the destination state number, and
      // acc is 1 iff the transition is accepting.  The source
      // is always that of the current iteration.
      typedef std::map<int, unsigned> tr_cache_t;
      tr_cache_t tr_cache;

      // Read this early, because it might create a state if the
      // automaton is empty.
      degen_state s(a->get_init_state_number(), 0);

      // State->level cache
      std::vector<std::pair<unsigned, bool>> lvl_cache(a->num_states());

      // Compute SCCs in order to use any optimization.
      scc_info* m = nullptr;
      if (use_scc)
	m = new scc_info(a);

      // Cache for common outgoing acceptances.
      outgoing_acc outgoing(a, m);

      queue_t todo;

      // As a heuristic for building SBA, if the initial state has at
      // least one accepting self-loop, start the degeneralization on
      // the accepting level.
      if (want_sba && !ignaccsl && outgoing.has_acc_selfloop(s.first))
	s.second = order.size();
      // Otherwise, check for acceptance conditions common to all
      // outgoing transitions, and assume we have already seen these and
      // start on the associated level.
      if (s.second == 0)
	{
	  auto set = outgoing.common_acc(s.first);
	  if (use_cust_acc_orders)
	    s.second = orders.next_level(m->initial(), s.second, set);
	  else
	    while (s.second < order.size()
		   && set.has(order[s.second]))
	      {
		++s.second;
		if (!skip_levels)
		  break;
	      }
	  // There is not accepting level for TBA, let reuse level 0.
	  if (!want_sba && s.second == order.size())
	    s.second = 0;
	}

      ds2num[s] = res->new_state();
      todo.push_back(s);

      // If use_lvl_cache is on insert initial state to level cache
      // Level cache stores first encountered level for each state.
      // When entering an SCC first the lvl_cache is checked.
      // If such state exists level from chache is used.
      // If not, a new level (starting with 0) is computed.
      if (use_lvl_cache)
	lvl_cache[s.first] = std::make_pair(s.second, true);

      while (!todo.empty())
	{
	  s = todo.front();
	  todo.pop_front();
	  int src = ds2num[s];
	  unsigned slevel = s.second;

	  // If we have a state on the last level, it should be accepting.
	  bool is_acc = slevel == order.size();
	  // On the accepting level, start again from level 0.
	  if (want_sba && is_acc)
	    slevel = 0;

	  // Check SCC for state s
	  int s_scc = -1;
	  if (use_scc)
	    s_scc = m->scc_of(s.first);

	  for (auto& i: a->out(s.first))
	    {
	      degen_state d(i.dst, 0);

	      // Check whether the target SCC is accepting
	      bool is_scc_acc;
	      int scc;
	      if (use_scc)
		{
		  scc = m->scc_of(d.first);
		  is_scc_acc = m->is_accepting_scc(scc);
		}
	      else
		{
		  // If we have no SCC information, treat all SCCs as
		  // accepting.
		  scc = -1;
		  is_scc_acc = true;
		}

	      // The old level is slevel.  What should be the new one?
	      auto acc = i.acc;
	      auto otheracc = outgoing.common_acc(d.first);

	      if (want_sba && is_acc)
		{
		  // Ignore the last expected acceptance set (the value of
		  // prev below) if it is common to all other outgoing
		  // transitions (of the current state) AND if it is not
		  // used by any outgoing transition of the destination
		  // state.
		  //
		  // 1) It's correct to do that, because this acceptance
		  //    set is common to other outgoing transitions.
		  //    Therefore if we make a cycle to this state we
		  //    will eventually see that acceptance set thanks
		  //    to the "pulling" of the common acceptance sets
		  //    of the destination state (d.first).
		  //
		  // 2) It's also desirable because it makes the
		  //    degeneralization idempotent (up to a renaming
		  //    of states).  Consider the following automaton
		  //    where 1 is initial and => marks accepting
		  //    transitions: 1=>1, 1=>2, 2->2, 2->1. This is
		  //    already an SBA, with 1 as accepting state.
		  //    However if you try degeralize it without
		  //    ignoring *prev, you'll get two copies of state
		  //    2, depending on whether we reach it using 1=>2
		  //    or from 2->2.  If this example was not clear,
		  //    play with the "degenid.test" test case.
		  //
		  // 3) Ignoring all common acceptance sets would also
		  //    be correct, but it would make the
		  //    degeneralization produce larger automata in some
		  //    cases.  The current condition to ignore only one
		  //    acceptance set if is this not used by the next
		  //    state is a heuristic that is compatible with
		  //    point 2) above while not causing more states to
		  //    be generated in our benchmark of 188 formulae
		  //    from the literature.
		  if (!order.empty())
		    {
		      unsigned prev = order.size() - 1;
		      auto common = outgoing.common_acc(s.first);
		      if (common.has(order[prev]))
			{
			  auto u = outgoing.union_acc(d.first);
			  if (!u.has(order[prev]))
			    acc -= a->acc().mark(order[prev]);
			}
		    }
		}
	      // A transition in the SLEVEL acceptance set should
	      // be directed to the next acceptance set.  If the
	      // current transition is also in the next acceptance
	      // set, then go to the one after, etc.
	      //
	      // See Denis Oddoux's PhD thesis for a nice
	      // explanation (in French).
	      // @PhDThesis{    oddoux.03.phd,
	      //   author     = {Denis Oddoux},
	      //   title      = {Utilisation des automates alternants pour un
	      //                model-checking efficace des logiques
	      //                temporelles lin{\'e}aires.},
	      //   school     = {Universit{\'e}e Paris 7},
	      //   year       = {2003},
	      //   address= {Paris, France},
	      //   month      = {December}
	      // }
	      if (is_scc_acc)
		{
		  // If lvl_cache is used and switching SCCs, use level
		  // from cache
		  if (use_lvl_cache && s_scc != scc
		      && lvl_cache[d.first].second)
		    {
		      d.second = lvl_cache[d.first].first;
		    }
		  else
		    {
		      // Complete (or replace) the acceptance sets of
		      // this link with the acceptance sets common to
		      // all transitions leaving the destination state.
		      if (s_scc == scc)
			acc |= otheracc;
		      else
			acc = otheracc;

		      // If use_z_lvl is on, start with level zero 0 when
		      // swhitching SCCs
		      unsigned next = (!use_z_lvl || s_scc == scc) ? slevel : 0;

		      // If using custom acc orders, get next level
		      // for this scc
		      if (use_cust_acc_orders)
			{
			  d.second = orders.next_level(scc, next, acc);
			}
		      // Else compute level according the global acc order
		      else
			{
			  // As a heuristic, if we enter the SCC on a
			  // state that has at least one accepting
			  // self-loop, start the degeneralization on
			  // the accepting level.
			  if (s_scc != scc
			      && !ignaccsl
			      && outgoing.has_acc_selfloop(d.first))
			    {
			      d.second = order.size();
			    }
			  else
			    {
			      // Consider both the current acceptance
			      // sets, and the acceptance sets common to
			      // the outgoing transitions of the
			      // destination state.  But don't do
			      // that if the state is accepting and we
			      // are not skipping levels.
			      if (skip_levels || !is_acc)
				while (next < order.size()
				       && acc.has(order[next]))
				  {
				    ++next;
				    if (!skip_levels)
				      break;
				  }
			      d.second = next;
			    }
			}
		    }
		}

	      // In case we are building a TBA is_acc has to be
	      // set differently for each transition, and
	      // we do not need to stay use final level.
	      if (!want_sba)
		{
		  is_acc = d.second == order.size();
		  if (is_acc)	// The transition is accepting
		    {
		      d.second = 0; // Make it go to the first level.
		      // Skip levels as much as possible.
		      if (!a->acc().accepting(acc) && !skip_levels)
			{
			  if (use_cust_acc_orders)
			    {
			      d.second = orders.next_level(scc, d.second, acc);
			    }
			  else
			    {
			      while (d.second < order.size() &&
				     acc.has(order[d.second]))
				++d.second;
			    }
			}
		    }
		}

	      // Have we already seen this destination?
	      int dest;
	      ds2num_map::const_iterator di = ds2num.find(d);
	      if (di != ds2num.end())
		{
		  dest = di->second;
		}
	      else
		{
		  dest = res->new_state();
		  ds2num[d] = dest;
		  todo.push_back(d);
		  // Insert new state to cache

		  if (use_lvl_cache)
		    {
		      auto lvl = d.second;
		      if (lvl_cache[d.first].second)
			{
			  if (use_lvl_cache == 3)
			    lvl = std::max(lvl_cache[d.first].first, lvl);
			  else if (use_lvl_cache == 2)
			    lvl = std::min(lvl_cache[d.first].first, lvl);
			}
		      lvl_cache[d.first] = std::make_pair(lvl, true);
		    }
		}

	      unsigned& t = tr_cache[dest * 2 + is_acc];

	      if (t == 0)	// Create transition.
		t = res->new_acc_transition(src, dest, i.cond, is_acc);
	      else		// Update existing transition.
		res->trans_data(t).cond |= i.cond;
	    }
	  tr_cache.clear();
	}

#ifdef DEGEN_DEBUG
      std::cout << "Orig. order:  \t";
      for (auto i: order)
	{
	  std::cout << i << ", ";
	}
      std::cout << '\n';
      orders.print();
#endif

      delete m;

      res->merge_transitions();
      return res;
    }
  }

  twa_graph_ptr
  degeneralize(const const_twa_graph_ptr& a,
	       bool use_z_lvl, bool use_cust_acc_orders,
               int use_lvl_cache, bool skip_levels, bool ignaccsl)
  {
    // If this already a degeneralized digraph, there is nothing we
    // can improve.
    if (a->is_sba())
      return std::const_pointer_cast<twa_graph>(a);

    return degeneralize_aux<true>(a, use_z_lvl, use_cust_acc_orders,
				  use_lvl_cache, skip_levels, ignaccsl);
  }

  twa_graph_ptr
  degeneralize_tba(const const_twa_graph_ptr& a,
		   bool use_z_lvl, bool use_cust_acc_orders,
		   int use_lvl_cache, bool skip_levels, bool ignaccsl)
  {
    // If this already a degeneralized digraph, there is nothing we
    // can improve.
    if (a->acc().is_buchi())
      return std::const_pointer_cast<twa_graph>(a);

    return degeneralize_aux<false>(a, use_z_lvl, use_cust_acc_orders,
				   use_lvl_cache, skip_levels, ignaccsl);
  }
}