spot/src/ltlvisit/basicreduce.cc

// Copyright (C) 2008, 2009, 2010 Laboratoire de Recherche et
// Développement de l'Epita (LRDE).
// Copyright (C) 2004, 2007 Laboratoire d'Informatique de
// Paris 6 (LIP6), département Systèmes Répartis Coopératifs (SRC),
// Université Pierre et Marie Curie.
//
// 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 2 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 Spot; see the file COPYING.  If not, write to the Free
// Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
// 02111-1307, USA.

#include "basicreduce.hh"
#include "ltlast/visitor.hh"
#include "ltlast/allnodes.hh"
#include <cassert>

namespace spot
{
  namespace ltl
  {
    bool
    is_GF(const formula* f)
    {
      const unop* op = dynamic_cast<const unop*>(f);
      if (op && op->op() == unop::G)
	{
	  const unop* opchild = dynamic_cast<const unop*>(op->child());
	  if (opchild && opchild->op() == unop::F)
	    return true;
	}
      return false;
    }

    bool
    is_FG(const formula* f)
    {
      const unop* op = dynamic_cast<const unop*>(f);
      if (op && op->op() == unop::F)
	{
	  const unop* opchild = dynamic_cast<const unop*>(op->child());
	  if (opchild && opchild->op() == unop::G)
	    return true;
	}
      return false;
    }

    namespace
    {
      class basic_reduce_visitor: public visitor
      {
      public:

	basic_reduce_visitor(){}

	virtual ~basic_reduce_visitor(){}

	formula*
	result() const
	{
	  return result_;
	}

	void
	visit(atomic_prop* ap)
	{
	  formula* f = ap->clone();
	  result_ = f;
	}

	void
	visit(constant* c)
	{
	  result_ = c;
	}

	formula*
	param_case(multop* mo, unop::type op, multop::type op_child)
	{
	  formula* result;
	  multop::vec* res1 = new multop::vec;
	  multop::vec* resGF = new multop::vec;
	  unsigned mos = mo->size();
	  for (unsigned i = 0; i < mos; ++i)
	    if (is_GF(mo->nth(i)))
	      resGF->push_back(mo->nth(i)->clone());
	    else
	      res1->push_back(mo->nth(i)->clone());
	  mo->destroy();
	  multop::vec* res3 = new multop::vec;
	  if (!res1->empty())
	    res3->push_back(unop::instance(op,
					   multop::instance(op_child, res1)));
	  else
	    delete res1;
	  if (!resGF->empty())
	    res3->push_back(multop::instance(op_child, resGF));
	  else
	    delete resGF;
	  result = multop::instance(op_child, res3);
	  return result;
	}

	void
	visit(unop* uo)
	{
	  formula* f = uo->child();
	  result_ = basic_reduce(f);
	  multop* mo = 0;
	  unop* u = 0;
	  binop* bo = 0;
	  switch (uo->op())
	    {
	    case unop::Not:
	      result_ = unop::instance(unop::Not, result_);
	      return;

	    case unop::X:
	      // X(true) = true
	      // X(false) = false
	      if (dynamic_cast<constant*>(result_))
		return;

	      // XGF(f) = GF(f)
	      if (is_GF(result_))
		return;

	      // X(f1 & GF(f2)) = X(f1) & GF(F2)
	      // X(f1 | GF(f2)) = X(f1) | GF(F2)
	      mo = dynamic_cast<multop*>(result_);
	      if (mo)
		{
		  result_ = param_case(mo, unop::X, mo->op());
		  return;
		}

	      result_ = unop::instance(unop::X, result_);
	      return;

	    case unop::F:
	      // F(true) = true
	      // F(false) = false
	      if (dynamic_cast<constant*>(result_))
		return;

	      // FX(a) = XF(a)
	      u = dynamic_cast<unop*>(result_);
	      if (u && u->op() == unop::X)
		{
		  formula* res =
		    unop::instance(unop::X,
				   unop::instance(unop::F,
						  basic_reduce(u->child())));
		  u->destroy();
		  // FXX(a) = XXF(a) ...
		  result_ = basic_reduce(res);
		  res->destroy();
		  return;
		}

#if 0
	      // F(f1 & GF(f2)) = F(f1) & GF(F2)
	      //
	      // As is, these two formulae are translated into
	      // equivalent Büchi automata so the rewriting is
	      // useless.
	      //
	      // However when taken in a larger formulae such as F(f1
	      // & GF(f2)) | F(a & GF(b)), this rewriting used to
	      // produce (F(f1) & GF(f2)) | (F(a) & GF(b)), missing
	      // the opportunity to apply the F(E1)|F(E2) = F(E1|E2)
	      // rule which really helps the translation. F((f1 &
	      // GF(f2)) | (a & GF(b))) is indeed easier to translate.
	      //
	      // So let's not consider this rewriting rule.
	      mo = dynamic_cast<multop*>(result_);
	      if (mo && mo->op() == multop::And)
		{
		  result_ = param_case(mo, unop::F, multop::And);
		  return;
		}
#endif

	      result_ = unop::instance(unop::F, result_);
	      return;

	    case unop::G:
	      // G(true) = true
	      // G(false) = false
	      if (dynamic_cast<constant*>(result_))
		return;

	      // G(a R b) = G(b)
	      bo = dynamic_cast<binop*>(result_);
	      if (bo && bo->op() == binop::R)
		{
		  result_ = unop::instance(unop::G,
					   basic_reduce(bo->second()));
		  bo->destroy();
		  return;
		}

	      // GX(a) = XG(a)
	      u = dynamic_cast<unop*>(result_);
	      if (u && u->op() == unop::X)
		{
		  formula* res =
		    unop::instance(unop::X,
				   unop::instance(unop::G,
						  basic_reduce(u->child())));
		  u->destroy();
		  // GXX(a) = XXG(a) ...
		  // GXF(a) = XGF(a) = GF(a) ...
		  result_ = basic_reduce(res);
		  res->destroy();
		  return;
		}

	      // G(f1 | GF(f2)) = G(f1) | GF(F2)
	      mo = dynamic_cast<multop*>(result_);
	      if (mo && mo->op() == multop::Or)
		{
		  result_ = param_case(mo, unop::G, multop::Or);
		  return;
		}

	      result_ = unop::instance(unop::G, result_);
	      return;

	    case unop::Finish:
	      result_ = unop::instance(unop::Finish, result_);
	      return;
	    }
	  /* Unreachable code.  */
	  assert(0);
	}

	void
	visit(binop* bo)
	{
	  formula* f1 = bo->first();
	  formula* f2 = bo->second();
	  binop::type op = bo->op();
	  switch (op)
	    {
	    case binop::Xor:
	    case binop::Equiv:
	    case binop::Implies:
	      result_ = binop::instance(bo->op(),
					basic_reduce(f1),
					basic_reduce(f2));
	      return;
	    case binop::W:
	    case binop::M:
	    case binop::U:
	    case binop::R:
	      {
		f1 = basic_reduce(f1);
		f2 = basic_reduce(f2);

		// a W false = Ga
		if (op == binop::W && f2 == constant::false_instance())
		  {
		    result_ = unop::instance(unop::G, f1);
		    return;
		  }
		// a M true = Fa
		if (op == binop::M && f2 == constant::true_instance())
		  {
		    result_ = unop::instance(unop::F, f1);
		    return;
		  }
		// a U false = false
		// a U true = true
		// a R false = false
		// a R true = true
		// a W true = true
		// a M false = false
		if (dynamic_cast<constant*>(f2))
		  {
		    result_ = f2;
		    f1->destroy();
		    return;
		  }

		// X(a) U X(b) = X(a U b)
		// X(a) R X(b) = X(a R b)
		// X(a) W X(b) = X(a W b)
		// X(a) M X(b) = X(a M b)
		unop* fu1 = dynamic_cast<unop*>(f1);
		unop* fu2 = dynamic_cast<unop*>(f2);
		if (fu1 && fu2
		    && fu1->op() == unop::X
		    && fu2->op() == unop::X)
		  {
		    formula* ftmp = binop::instance(op,
						    basic_reduce(fu1->child()),
						    basic_reduce(fu2->child()));
		    result_ = unop::instance(unop::X, basic_reduce(ftmp));
		    f1->destroy();
		    f2->destroy();
		    ftmp->destroy();
		    return;
		  }

		if (op == binop::U || op == binop::W)
		  {
		    // a U Ga = Ga
		    // a W Ga = Ga
		    if (fu2 && fu2->op() == unop::G && fu2->child() == f1)
		      {
			result_ = f2;
			f1->destroy();
			return;
		      }

		    // a U (b | G(a)) = a W b
		    // a W (b | G(a)) = a W b
		    multop* fm2 = dynamic_cast<multop*>(f2);
		    if (fm2 && fm2->op() == multop::Or)
		      {
			int s = fm2->size();
			for (int i = 0; i < s; ++i)
			  {
			    unop* c = dynamic_cast<unop*>(fm2->nth(i));
			    if (c && c->op() == unop::G && c->child() == f1)
			      {
				multop::vec* v = new multop::vec;
				v->reserve(s - 1);
				int j;
				for (j = 0; j < i; ++j)
				  v->push_back(fm2->nth(j)->clone());
				// skip j=i
				for (++j; j < s; ++j)
				  v->push_back(fm2->nth(j)->clone());
				result_ =
				  binop::instance(binop::W, f1,
						  multop::instance(multop::Or,
								   v));
				f2->destroy();
				return;
			      }
			  }
		      }
		  }
		else if (op == binop::M || op == binop::R)
		  {
		    // a R Fa = Fa
		    // a M Fa = Fa
		    if (fu2 && fu2->op() == unop::F && fu2->child() == f1)
		      {
			result_ = f2;
			f1->destroy();
			return;
		      }

		    // a R (b & F(a)) = a M b
		    // a M (b & F(a)) = a M b
		    multop* fm2 = dynamic_cast<multop*>(f2);
		    if (fm2 && fm2->op() == multop::And)
		      {
			int s = fm2->size();
			for (int i = 0; i < s; ++i)
			  {
			    unop* c = dynamic_cast<unop*>(fm2->nth(i));
			    if (c && c->op() == unop::F && c->child() == f1)
			      {
				multop::vec* v = new multop::vec;
				v->reserve(s - 1);
				int j;
				for (j = 0; j < i; ++j)
				  v->push_back(fm2->nth(j)->clone());
				// skip j=i
				for (++j; j < s; ++j)
				  v->push_back(fm2->nth(j)->clone());
				result_ =
				  binop::instance(binop::M, f1,
						  multop::instance(multop::And,
								   v));
				f2->destroy();
				return;
			      }
			  }
		      }
		  }

		result_ = binop::instance(op, f1, f2);
		return;
	      }
	    }
	  /* Unreachable code.  */
	  assert(0);
	}

	void
	visit(automatop*)
	{
	  assert(0);
	}

	void
	visit(multop* mo)
	{
	  multop::type op = mo->op();
	  unsigned mos = mo->size();
	  multop::vec* res = new multop::vec;

	  multop::vec* tmpX = new multop::vec;
	  multop::vec* tmpU = new multop::vec;
	  multop::vec* tmpR = new multop::vec;
	  multop::vec* tmpFG = new multop::vec;
	  multop::vec* tmpF = new multop::vec;
	  multop::vec* tmpGF = new multop::vec;
	  multop::vec* tmpG = new multop::vec;

	  multop::vec* tmpOther = new multop::vec;

	  for (unsigned i = 0; i < mos; ++i)
	    res->push_back(basic_reduce(mo->nth(i)));

	  switch (op)
	    {
	    case multop::And:

	      for (multop::vec::iterator i = res->begin(); i != res->end(); i++)
		{
		  // An iteration of the loop may zero some later elements
		  // of the vector to mark them as redundant.  Skip them.
		  if (!*i)
		    continue;
		  unop* uo = dynamic_cast<unop*>(*i);
		  binop* bo = dynamic_cast<binop*>(*i);
		  if (uo)
		    {
		      if (uo->op() == unop::X)
			{
			  // Xa & Xb = X(a & b)
			  tmpX->push_back(uo->child()->clone());
			}
		      else if (is_FG(*i))
			{
			  // FG(a) & FG(b) = FG(a & b)
			  unop* uo2 = dynamic_cast<unop*>(uo->child());
			  tmpFG->push_back(uo2->child()->clone());
			}
		      else if (uo->op() == unop::G)
			{
			  // G(a) & G(b) = G(a & b)
			  tmpG->push_back(uo->child()->clone());
			}
		      else if (uo->op() == unop::F)
			{
			  // F(a) & (a R b) = a M b
			  // F(a) & (a M b) = a M b
			  // F(a) & (b W a) = b U a
			  // F(a) & (b U a) = b U a
			  formula* a = uo->child();
			  bool rewritten = false;
			  for (multop::vec::iterator j = i;
			       j != res->end(); ++j)
			    {
			      if (!*j)
				continue;
			      binop* b = dynamic_cast<binop*>(*j);
			      if (b && (b->op() == binop::R
					|| b->op() == binop::M)
				  && b->first() == a)
				{
				  binop* r =
				    binop::instance(binop::M,
						    a->clone(),
						    b->second()->clone());
				  tmpOther->push_back(r);
				  (*j)->destroy();
				  *j = 0;
				  rewritten = true;
				}
			      else if (b && (b->op() == binop::W
					     || b->op() == binop::U)
				       && b->second() == a)
				{
				  binop* r =
				    binop::instance(binop::U,
						    b->first()->clone(),
						    a->clone());
				  tmpOther->push_back(r);
				  (*j)->destroy();
				  *j = 0;
				  rewritten = true;
				}
			    }
			  if (!rewritten)
			    tmpOther->push_back(uo->clone());
			}
		      else
			{
			  tmpOther->push_back((*i)->clone());
			}
		    }
		  else if (bo)
		    {
		      if (bo->op() == binop::U || bo->op() == binop::W)
			{
			  // (a U b) & (c U b) = (a & c) U b
			  // (a U b) & (c W b) = (a & c) U b
			  // (a W b) & (c W b) = (a & c) W b
			  bool weak = true;
			  formula* ftmp = dynamic_cast<binop*>(*i)->second();
			  multop::vec* right = new multop::vec;
			  for (multop::vec::iterator j = i; j != res->end();
			       j++)
			    {
			      if (!*j)
				continue;
			      // (a U b) & Fb = a U b.
			      // (a W b) & Fb = a U b.
			      unop* uo2 = dynamic_cast<unop*>(*j);
			      if (uo2 && uo2->op() == unop::F
				  && uo2->child() == ftmp)
				{
				  (*j)->destroy();
				  *j = 0;
				  weak = false;
				}
			      binop* bo2 = dynamic_cast<binop*>(*j);
			      if (bo2 && (bo2->op() == binop::U
					  || bo2->op() == binop::W)
				  && ftmp == bo2->second())
				{
				  if (bo2->op() == binop::U)
				    weak = false;
				  right->push_back(bo2->first()->clone());
				  if (j != i)
				    {
				      (*j)->destroy();
				      *j = 0;
				    }
				}
			    }
			  tmpU
			    ->push_back(binop::instance(weak ?
							binop::W : binop::U,
							multop::
							instance(multop::
								 And, right),
							ftmp->clone()));
			}
		      else if (bo->op() == binop::R || bo->op() == binop::M)
			{
			  // (a R b) & (a R c) = a R (b & c)
			  // (a R b) & (a M c) = a M (b & c)
			  bool weak = true;
			  formula* ftmp = dynamic_cast<binop*>(*i)->first();
			  multop::vec* right = new multop::vec;
			  for (multop::vec::iterator j = i; j != res->end();
			       j++)
			    {
			      if (!*j)
				continue;
			      // (a R b) & Fa = a M b.
			      // (a M b) & Fa = a M b.
			      unop* uo2 = dynamic_cast<unop*>(*j);
			      if (uo2 && uo2->op() == unop::F
				  && uo2->child() == ftmp)
				{
				  (*j)->destroy();
				  *j = 0;
				  weak = false;
				}
			      binop* bo2 = dynamic_cast<binop*>(*j);
			      if (bo2 && (bo2->op() == binop::R
					  || bo2->op() == binop::M)
				  && ftmp == bo2->first())
				{
				  if (bo2->op() == binop::M)
				    weak = false;
				  right->push_back(bo2->second()->clone());
				  if (j != i)
				    {
				      (*j)->destroy();
				      *j = 0;
				    }
				}
			    }
			  tmpR
			    ->push_back(binop::instance(weak ?
							binop::R : binop::M,
							ftmp->clone(),
							multop::
							instance(multop::And,
								 right)));
			}
		      else
			{
			  tmpOther->push_back((*i)->clone());
			}
		    }
		  else
		    {
		      tmpOther->push_back((*i)->clone());
		    }
		  (*i)->destroy();
		}
	      break;

	    case multop::Or:

	      for (multop::vec::iterator i = res->begin(); i != res->end(); i++)
		{
		  if (!*i)
		    continue;
		  unop* uo = dynamic_cast<unop*>(*i);
		  binop* bo = dynamic_cast<binop*>(*i);
		  if (uo)
		    {
		      if (uo->op() == unop::X)
			{
			  // Xa | Xb = X(a | b)
			  tmpX->push_back(uo->child()->clone());
			}
		      else if (is_GF(*i))
			{
			  // GF(a) | GF(b) = GF(a | b)
			  unop* uo2 = dynamic_cast<unop*>(uo->child());
			  tmpGF->push_back(uo2->child()->clone());
			}
		      else if (uo->op() == unop::F)
			{
			  // F(a) | F(b) = F(a | b)
			  tmpF->push_back(uo->child()->clone());
			}
		      else if (uo->op() == unop::G)
			{
			  // G(a) | (a U b) = a W b
			  // G(a) | (a W b) = a W b
			  formula* a = uo->child();
			  bool rewritten = false;
			  for (multop::vec::iterator j = i;
			       j != res->end(); ++j)
			    {
			      if (!*j)
				continue;
			      binop* b = dynamic_cast<binop*>(*j);
			      if (b && (b->op() == binop::U
					|| b->op() == binop::W)
				  && b->first() == a)
				{
				  binop* r =
				    binop::instance(binop::W,
						    a->clone(),
						    b->second()->clone());
				  tmpOther->push_back(r);
				  (*j)->destroy();
				  *j = 0;
				  rewritten = true;
				}
			    }
			  if (!rewritten)
			    tmpOther->push_back(uo->clone());
			}
		      else
			{
			  tmpOther->push_back((*i)->clone());
			}
		    }
		  else if (bo)
		    {
		      if (bo->op() == binop::U || bo->op() == binop::W)
			{
			  // (a U b) | (a U c) = a U (b | c)
			  // (a W b) | (a U c) = a W (b | c)
			  bool weak = false;
			  formula* ftmp = bo->first();
			  multop::vec* right = new multop::vec;
			  for (multop::vec::iterator j = i; j != res->end();
			       j++)
			    {
			      if (!*j)
				continue;
			      // (a U b) | Ga = a W b.
			      // (a W b) | Ga = a W b.
			      unop* uo2 = dynamic_cast<unop*>(*j);
			      if (uo2 && uo2->op() == unop::G
				  && uo2->child() == ftmp)
				{
				  (*j)->destroy();
				  *j = 0;
				  weak = true;
				}
			      binop* bo2 = dynamic_cast<binop*>(*j);
			      if (bo2 && (bo2->op() == binop::U ||
					  bo2->op() == binop::W)
				  && ftmp == bo2->first())
				{
				  if (bo2->op() == binop::W)
				    weak = true;
				  right->push_back(bo2->second()->clone());
				  if (j != i)
				    {
				      (*j)->destroy();
				      *j = 0;
				    }
				}
			    }
			  tmpU->push_back(binop::instance(weak ?
							  binop::W : binop::U,
							  ftmp->clone(),
							  multop::
							  instance(multop::Or,
								   right)));
			}
		      else if (bo->op() == binop::R || bo->op() == binop::M)
			{
			  // (a R b) | (c R b) = (a | c) R b
			  // (a R b) | (c M b) = (a | c) R b
			  // (a M b) | (c M b) = (a | c) M b
			  bool weak = false;
			  formula* ftmp = dynamic_cast<binop*>(*i)->second();
			  multop::vec* right = new multop::vec;
			  for (multop::vec::iterator j = i; j != res->end();
			       j++)
			    {
			      if (!*j)
				continue;
			      // (a R b) | Gb = a R b.
			      // (a M b) | Gb = a R b.
			      unop* uo2 = dynamic_cast<unop*>(*j);
			      if (uo2 && uo2->op() == unop::G
				  && uo2->child() == ftmp)
				{
				  (*j)->destroy();
				  *j = 0;
				  weak = true;
				}
			      binop* bo2 = dynamic_cast<binop*>(*j);
			      if (bo2 && (bo2->op() == binop::R
					  || bo2->op() == binop::M)
				  && ftmp == bo2->second())
				{
				  if (bo2->op() == binop::R)
				    weak = true;
				  right->push_back(bo2->first()->clone());
				  if (j != i)
				    {
				      (*j)->destroy();
				      *j = 0;
				    }
				}
			    }
			  tmpR
			    ->push_back(binop::instance(weak ?
							binop::R : binop::M,
							multop::
							instance(multop::Or,
								 right),
							ftmp->clone()));
			}
		      else
			{
			  tmpOther->push_back((*i)->clone());
			}
		    }
		  else
		    {
		      tmpOther->push_back((*i)->clone());
		    }
		  (*i)->destroy();
		}

	      break;
	    }

	  res->clear();
	  delete res;


	  if (tmpX && !tmpX->empty())
	    tmpOther->push_back(unop::instance(unop::X,
					       multop::instance(mo->op(),
								tmpX)));
	  else
	    delete tmpX;

	  if (!tmpF->empty())
	    tmpOther->push_back(unop::instance(unop::F,
					       multop::instance(mo->op(),
								tmpF)));
	  else
	    delete tmpF;

	  if (!tmpG->empty())
	    tmpOther->push_back(unop::instance(unop::G,
					       multop::instance(mo->op(),
								tmpG)));
	  else
	    delete tmpG;

	  if (!tmpU->empty())
	    tmpOther->push_back(multop::instance(mo->op(), tmpU));
	  else
	    delete tmpU;

	  if (!tmpR->empty())
	    tmpOther->push_back(multop::instance(mo->op(), tmpR));
	  else
	    delete tmpR;

	  if (!tmpGF->empty())
	    {
	      formula* ftmp
		= unop::instance(unop::G,
				 unop::instance(unop::F,
						multop::instance(mo->op(),
								 tmpGF)));
	      tmpOther->push_back(ftmp);
	    }
	  else
	    delete tmpGF;


	  if (!tmpFG->empty())
	    {
	      formula* ftmp = 0;
	      if (mo->op() == multop::And)
		ftmp
		  = unop::instance(unop::F,
				   unop::instance(unop::G,
						  multop::instance(mo->op(),
								   tmpFG)));
	      else
		ftmp
		  = unop::instance(unop::F,
				   multop::instance(mo->op(), tmpFG));
	      tmpOther->push_back(ftmp);
	    }
	  else
	    delete tmpFG;


	  result_ = multop::instance(op, tmpOther);

	  return;
	}

      protected:
	formula* result_;
      };
    }

    formula*
    basic_reduce(const formula* f)
    {
      basic_reduce_visitor v;
      const_cast<formula*>(f)->accept(v);
      return v.result();
    }

  }
}