counterexample_beautification.cpp

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/*******************************************************************\
 
Module: Counterexample Beautification using Incremental SAT
 
Author: Daniel Kroening, kroening@kroening.com
 
\*******************************************************************/

 
#include "counterexample_beautification.h"
 
#include <util/std_expr.h>
 
#include <solvers/prop/prop_minimize.h>
 
counterexample_beautificationt::counterexample_beautificationt(
  message_handlert &message_handler)
  : log(message_handler)
{
}
 
void counterexample_beautificationt::get_minimization_list(
  prop_convt &prop_conv,
  const symex_target_equationt &equation,
  minimization_listt &minimization_list)
{
  // ignore the ones that are assigned under false guards
 
  for(symex_target_equationt::SSA_stepst::const_iterator it =
        equation.SSA_steps.begin();
      it != equation.SSA_steps.end();
      it++)
  {
    if(
      it->is_assignment() &&
      it->assignment_type == symex_targett::assignment_typet::STATE)
    {
      if(prop_conv.get(it->guard_handle) != false)
      {
        const typet &type = it->ssa_lhs.type();
 
        if(type != bool_typet())
        {
          // we minimize the absolute value, if applicable
          if(
            type.id() == ID_signedbv || type.id() == ID_fixedbv ||
            type.id() == ID_floatbv)
          {
            abs_exprt abs_expr(it->ssa_lhs);
            minimization_list.insert(abs_expr);
          }
          else
            minimization_list.insert(it->ssa_lhs);
        }
      }
    }
 
    // reached failed assertion?
    if(it == failed)
      break;
  }
}
 
symex_target_equationt::SSA_stepst::const_iterator
counterexample_beautificationt::get_failed_property(
  const prop_convt &prop_conv,
  const symex_target_equationt &equation)
{
  // find failed property
 
  for(symex_target_equationt::SSA_stepst::const_iterator it =
        equation.SSA_steps.begin();
      it != equation.SSA_steps.end();
      it++)
  {
    if(
      it->is_assert() && prop_conv.get(it->guard_handle) == true &&
      prop_conv.get(it->cond_handle) == false)
    {
      return it;
    }
  }
 
  UNREACHABLE;
  return equation.SSA_steps.end();
}
 
void counterexample_beautificationt::
operator()(boolbvt &boolbv, const symex_target_equationt &equation)
{
  // find failed property
 
  failed = get_failed_property(boolbv, equation);
 
  // lock the failed assertion
  boolbv.set_to(failed->cond_handle, false);
 
  {
    log.status() << "Beautifying counterexample (guards)" << messaget::eom;
 
    // compute weights for guards
    typedef std::map<literalt, unsigned> guard_countt;
    guard_countt guard_count;
 
    for(symex_target_equationt::SSA_stepst::const_iterator it =
          equation.SSA_steps.begin();
        it != equation.SSA_steps.end();
        it++)
    {
      if(
        it->is_assignment() &&
        it->assignment_type != symex_targett::assignment_typet::HIDDEN)
      {
        literalt l = boolbv.convert(it->guard_handle);
        if(!l.is_constant())
          guard_count[l]++;
      }
 
      // reached failed assertion?
      if(it == failed)
        break;
    }
 
    // give to propositional minimizer
    prop_minimizet prop_minimize{boolbv, log.get_message_handler()};
 
    for(const auto &g : guard_count)
      prop_minimize.objective(g.first, g.second);
 
    // minimize
    prop_minimize();
  }
 
  {
    log.status() << "Beautifying counterexample (values)" << messaget::eom;
 
    // get symbols we care about
    minimization_listt minimization_list;
 
    get_minimization_list(boolbv, equation, minimization_list);
 
    // minimize
    bv_minimizet bv_minimize(boolbv, log.get_message_handler());
    bv_minimize(minimization_list);
  }
}