custom_bitvector_analysis.cpp

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/*******************************************************************\
 
Module: Field-insensitive, location-sensitive bitvector analysis
 
Author: Daniel Kroening, kroening@kroening.com
 
\*******************************************************************/
 
 
#include "custom_bitvector_analysis.h"
 
#include <util/expr_util.h>
#include <util/pointer_expr.h>
#include <util/simplify_expr.h>
#include <util/string_constant.h>
#include <util/xml_irep.h>
 
#include <langapi/language_util.h>
 
#include <iostream>
 
void custom_bitvector_domaint::set_bit(
  const irep_idt &identifier,
  unsigned bit_nr,
  modet mode)
{
  switch(mode)
  {
  case modet::SET_MUST:
    set_bit(must_bits[identifier], bit_nr);
    break;
 
  case modet::CLEAR_MUST:
    clear_bit(must_bits[identifier], bit_nr);
    break;
 
  case modet::SET_MAY:
    set_bit(may_bits[identifier], bit_nr);
    break;
 
  case modet::CLEAR_MAY:
    clear_bit(may_bits[identifier], bit_nr);
    break;
  }
}
 
void custom_bitvector_domaint::set_bit(
  const exprt &lhs,
  unsigned bit_nr,
  modet mode)
{
  irep_idt id=object2id(lhs);
  if(!id.empty())
    set_bit(id, bit_nr, mode);
}
 
irep_idt custom_bitvector_domaint::object2id(const exprt &src)
{
  if(src.id()==ID_symbol)
  {
    return to_symbol_expr(src).get_identifier();
  }
  else if(src.id()==ID_dereference)
  {
    const exprt &op=to_dereference_expr(src).pointer();
 
    if(op.id()==ID_address_of)
    {
      return object2id(to_address_of_expr(op).object());
    }
    else if(op.id()==ID_typecast)
    {
      irep_idt op_id=object2id(to_typecast_expr(op).op());
 
      if(op_id.empty())
        return irep_idt();
      else
        return '*'+id2string(op_id);
    }
    else
    {
      irep_idt op_id=object2id(op);
 
      if(op_id.empty())
        return irep_idt();
      else
        return '*'+id2string(op_id);
    }
  }
  else if(src.id()==ID_member)
  {
    const auto &m=to_member_expr(src);
    const exprt &op=m.compound();
 
    irep_idt op_id=object2id(op);
 
    if(op_id.empty())
      return irep_idt();
    else
      return id2string(op_id)+'.'+
             id2string(m.get_component_name());
  }
  else if(src.id()==ID_typecast)
    return object2id(to_typecast_expr(src).op());
  else
    return irep_idt();
}
 
void custom_bitvector_domaint::assign_lhs(
  const exprt &lhs,
  const vectorst &vectors)
{
  irep_idt id=object2id(lhs);
  if(!id.empty())
    assign_lhs(id, vectors);
}
 
void custom_bitvector_domaint::assign_lhs(
  const irep_idt &identifier,
  const vectorst &vectors)
{
  // we erase blank ones to avoid noise
 
  if(vectors.must_bits==0)
    must_bits.erase(identifier);
  else
    must_bits[identifier]=vectors.must_bits;
 
  if(vectors.may_bits==0)
    may_bits.erase(identifier);
  else
    may_bits[identifier]=vectors.may_bits;
}
 
custom_bitvector_domaint::vectorst
  custom_bitvector_domaint::get_rhs(const irep_idt &identifier) const
{
  vectorst vectors;
 
  bitst::const_iterator may_it=may_bits.find(identifier);
  if(may_it!=may_bits.end())
    vectors.may_bits=may_it->second;
 
  bitst::const_iterator must_it=must_bits.find(identifier);
  if(must_it!=must_bits.end())
    vectors.must_bits=must_it->second;
 
  return vectors;
}
 
custom_bitvector_domaint::vectorst
  custom_bitvector_domaint::get_rhs(const exprt &rhs) const
{
  if(rhs.id()==ID_symbol ||
     rhs.id()==ID_dereference)
  {
    const irep_idt identifier=object2id(rhs);
    return get_rhs(identifier);
  }
  else if(rhs.id()==ID_typecast)
  {
    return get_rhs(to_typecast_expr(rhs).op());
  }
  else if(rhs.id()==ID_if)
  {
    // need to merge both
    vectorst v_true=get_rhs(to_if_expr(rhs).true_case());
    vectorst v_false=get_rhs(to_if_expr(rhs).false_case());
    return merge(v_true, v_false);
  }
 
  return vectorst();
}
 
unsigned custom_bitvector_analysist::get_bit_nr(
  const exprt &string_expr)
{
  if(string_expr.id()==ID_typecast)
    return get_bit_nr(to_typecast_expr(string_expr).op());
  else if(string_expr.id()==ID_address_of)
    return get_bit_nr(to_address_of_expr(string_expr).object());
  else if(string_expr.id()==ID_index)
    return get_bit_nr(to_index_expr(string_expr).array());
  else if(string_expr.id()==ID_string_constant)
    return bits.number(to_string_constant(string_expr).value());
  else
    return bits.number("(unknown)");
}
 
std::set<exprt> custom_bitvector_analysist::aliases(
  const exprt &src,
  locationt loc)
{
  if(src.id()==ID_symbol)
  {
    std::set<exprt> result;
    result.insert(src);
    return result;
  }
  else if(src.id()==ID_dereference)
  {
    exprt pointer=to_dereference_expr(src).pointer();
 
    const std::set<exprt> alias_set =
      local_may_alias_factory(loc).get(loc, pointer);
 
    std::set<exprt> result;
 
    for(const auto &alias : alias_set)
      if(alias.type().id() == ID_pointer)
        result.insert(dereference_exprt(alias));
 
    result.insert(src);
 
    return result;
  }
  else if(src.id()==ID_typecast)
  {
    return aliases(to_typecast_expr(src).op(), loc);
  }
  else
    return std::set<exprt>();
}
 
void custom_bitvector_domaint::assign_struct_rec(
  locationt from,
  const exprt &lhs,
  const exprt &rhs,
  custom_bitvector_analysist &cba,
  const namespacet &ns)
{
  if(lhs.type().id() == ID_struct || lhs.type().id() == ID_struct_tag)
  {
    const struct_typet &struct_type=
      to_struct_type(ns.follow(lhs.type()));
 
    // assign member-by-member
    for(const auto &c : struct_type.components())
    {
      member_exprt lhs_member(lhs, c),
                   rhs_member(rhs, c);
      assign_struct_rec(from, lhs_member, rhs_member, cba, ns);
    }
  }
  else
  {
    // may alias other stuff
    std::set<exprt> lhs_set=cba.aliases(lhs, from);
 
    vectorst rhs_vectors=get_rhs(rhs);
 
    for(const auto &lhs_alias : lhs_set)
    {
      assign_lhs(lhs_alias, rhs_vectors);
    }
 
    // is it a pointer?
    if(lhs.type().id()==ID_pointer)
    {
      dereference_exprt lhs_deref(lhs);
      dereference_exprt rhs_deref(rhs);
      assign_lhs(lhs_deref, get_rhs(rhs_deref));
    }
  }
}
 
void custom_bitvector_domaint::transform(
  const irep_idt &function_from,
  trace_ptrt trace_from,
  const irep_idt &function_to,
  trace_ptrt trace_to,
  ai_baset &ai,
  const namespacet &ns)
{
  locationt from{trace_from->current_location()};
  locationt to{trace_to->current_location()};
 
  // upcast of ai
  custom_bitvector_analysist &cba=
    static_cast<custom_bitvector_analysist &>(ai);
 
  const goto_programt::instructiont &instruction=*from;
 
  switch(instruction.type())
  {
  case ASSIGN:
    assign_struct_rec(
      from, instruction.assign_lhs(), instruction.assign_rhs(), cba, ns);
    break;
 
  case DECL:
    {
      const auto &decl_symbol = instruction.decl_symbol();
      assign_lhs(decl_symbol, vectorst());
 
      // is it a pointer?
      if(decl_symbol.type().id() == ID_pointer)
        assign_lhs(dereference_exprt(decl_symbol), vectorst());
    }
    break;
 
  case DEAD:
    assign_lhs(instruction.dead_symbol(), vectorst());
 
    // is it a pointer?
    if(instruction.dead_symbol().type().id() == ID_pointer)
      assign_lhs(dereference_exprt(instruction.dead_symbol()), vectorst());
    break;
 
  case FUNCTION_CALL:
    {
      const exprt &function = instruction.call_function();
 
      if(function.id()==ID_symbol)
      {
        const irep_idt &identifier=to_symbol_expr(function).get_identifier();
 
        if(
          identifier == CPROVER_PREFIX "set_must" ||
          identifier == CPROVER_PREFIX "clear_must" ||
          identifier == CPROVER_PREFIX "set_may" ||
          identifier == CPROVER_PREFIX "clear_may")
        {
          if(instruction.call_arguments().size() == 2)
          {
            unsigned bit_nr = cba.get_bit_nr(instruction.call_arguments()[1]);
 
            // initialize to make Visual Studio happy
            modet mode = modet::SET_MUST;
 
            if(identifier == CPROVER_PREFIX "set_must")
              mode=modet::SET_MUST;
            else if(identifier == CPROVER_PREFIX "clear_must")
              mode=modet::CLEAR_MUST;
            else if(identifier == CPROVER_PREFIX "set_may")
              mode=modet::SET_MAY;
            else if(identifier == CPROVER_PREFIX "clear_may")
              mode=modet::CLEAR_MAY;
            else
              UNREACHABLE;
 
            exprt lhs = instruction.call_arguments()[0];
 
            if(lhs.type().id()==ID_pointer)
            {
              if(
                lhs.is_constant() &&
                is_null_pointer(to_constant_expr(lhs))) // NULL means all
              {
                if(mode==modet::CLEAR_MAY)
                {
                  for(auto &bit : may_bits)
                    clear_bit(bit.second, bit_nr);
 
                  // erase blank ones
                  erase_blank_vectors(may_bits);
                }
                else if(mode==modet::CLEAR_MUST)
                {
                  for(auto &bit : must_bits)
                    clear_bit(bit.second, bit_nr);
 
                  // erase blank ones
                  erase_blank_vectors(must_bits);
                }
              }
              else
              {
                dereference_exprt deref(lhs);
 
                // may alias other stuff
                std::set<exprt> lhs_set=cba.aliases(deref, from);
 
                for(const auto &l : lhs_set)
                {
                  set_bit(l, bit_nr, mode);
                }
              }
            }
          }
        }
        else if(identifier=="memcpy" ||
                identifier=="memmove")
        {
          if(instruction.call_arguments().size() == 3)
          {
            // we copy all tracked bits from op1 to op0
            // we do not consider any bits attached to the size op2
            dereference_exprt lhs_deref(instruction.call_arguments()[0]);
            dereference_exprt rhs_deref(instruction.call_arguments()[1]);
 
            assign_struct_rec(from, lhs_deref, rhs_deref, cba, ns);
          }
        }
        else
        {
          // only if there is an actual call, i.e., we have a body
          if(function_from != function_to)
          {
            const code_typet &code_type=
              to_code_type(ns.lookup(identifier).type);
 
            code_function_callt::argumentst::const_iterator arg_it =
              instruction.call_arguments().begin();
            for(const auto &param : code_type.parameters())
            {
              const irep_idt &p_identifier=param.get_identifier();
              if(p_identifier.empty())
                continue;
 
              // there may be a mismatch in the number of arguments
              if(arg_it == instruction.call_arguments().end())
                break;
 
              // assignments arguments -> parameters
              symbol_exprt p=ns.lookup(p_identifier).symbol_expr();
              // may alias other stuff
              std::set<exprt> lhs_set=cba.aliases(p, from);
 
              vectorst rhs_vectors=get_rhs(*arg_it);
 
              for(const auto &lhs : lhs_set)
              {
                assign_lhs(lhs, rhs_vectors);
              }
 
              // is it a pointer?
              if(p.type().id()==ID_pointer)
              {
                dereference_exprt lhs_deref(p);
                dereference_exprt rhs_deref(*arg_it);
                assign_lhs(lhs_deref, get_rhs(rhs_deref));
              }
 
              ++arg_it;
            }
          }
        }
      }
    }
    break;
 
  case OTHER:
    {
      const auto &code = instruction.get_other();
      const irep_idt &statement = code.get_statement();
 
      if(
        statement == ID_set_may || statement == ID_set_must ||
        statement == ID_clear_may || statement == ID_clear_must)
      {
        DATA_INVARIANT(
          code.operands().size() == 2, "set/clear_may/must has two operands");
 
        unsigned bit_nr = cba.get_bit_nr(code.op1());
 
        // initialize to make Visual Studio happy
        modet mode = modet::SET_MUST;
 
        if(statement == ID_set_must)
          mode=modet::SET_MUST;
        else if(statement == ID_clear_must)
          mode=modet::CLEAR_MUST;
        else if(statement == ID_set_may)
          mode=modet::SET_MAY;
        else if(statement == ID_clear_may)
          mode=modet::CLEAR_MAY;
        else
          UNREACHABLE;
 
        exprt lhs = code.op0();
 
        if(lhs.type().id()==ID_pointer)
        {
          if(
            lhs.is_constant() &&
            is_null_pointer(to_constant_expr(lhs))) // NULL means all
          {
            if(mode==modet::CLEAR_MAY)
            {
              for(bitst::iterator b_it=may_bits.begin();
                  b_it!=may_bits.end();
                  b_it++)
                clear_bit(b_it->second, bit_nr);
 
              // erase blank ones
              erase_blank_vectors(may_bits);
            }
            else if(mode==modet::CLEAR_MUST)
            {
              for(bitst::iterator b_it=must_bits.begin();
                  b_it!=must_bits.end();
                  b_it++)
                clear_bit(b_it->second, bit_nr);
 
              // erase blank ones
              erase_blank_vectors(must_bits);
            }
          }
          else
          {
            dereference_exprt deref(lhs);
 
            // may alias other stuff
            std::set<exprt> lhs_set=cba.aliases(deref, from);
 
            for(const auto &l : lhs_set)
            {
              set_bit(l, bit_nr, mode);
            }
          }
        }
      }
    }
    break;
 
  case GOTO:
    if(has_get_must_or_may(instruction.condition()))
    {
      exprt guard = instruction.condition();
 
      // Comparing iterators is safe as the target must be within the same list
      // of instructions because this is a GOTO.
      if(to!=from->get_target())
        guard = boolean_negate(guard);
 
      const exprt result2 = simplify_expr(eval(guard, cba), ns);
 
      if(result2.is_false())
        make_bottom();
    }
    break;
 
  case CATCH:
  case THROW:
    DATA_INVARIANT(false, "Exceptions must be removed before analysis");
    break;
  case SET_RETURN_VALUE:
    DATA_INVARIANT(false, "SET_RETURN_VALUE must be removed before analysis");
    break;
  case ATOMIC_BEGIN: // Ignoring is a valid over-approximation
  case ATOMIC_END:   // Ignoring is a valid over-approximation
  case END_FUNCTION: // No action required
  case LOCATION:     // No action required
  case START_THREAD: // Require a concurrent analysis at higher level
  case END_THREAD:   // Require a concurrent analysis at higher level
  case SKIP:         // No action required
  case ASSERT:       // No action required
  case ASSUME:       // Ignoring is a valid over-approximation
    break;
  case INCOMPLETE_GOTO:
  case NO_INSTRUCTION_TYPE:
    DATA_INVARIANT(false, "Only complete instructions can be analyzed");
    break;
  }
}
 
void custom_bitvector_domaint::output(
  std::ostream &out,
  const ai_baset &ai,
  const namespacet &) const
{
  if(has_values.is_known())
  {
    out << has_values.to_string() << '\n';
    return;
  }
 
  const custom_bitvector_analysist &cba=
    static_cast<const custom_bitvector_analysist &>(ai);
 
  for(const auto &bit : may_bits)
  {
    out << bit.first << " MAY:";
    bit_vectort b=bit.second;
 
    for(unsigned i=0; b!=0; i++, b>>=1)
      if(b&1)
      {
        INVARIANT(i < cba.bits.size(), "inconsistent bit widths");
        out << ' '
            << cba.bits[i];
      }
 
    out << '\n';
  }
 
  for(const auto &bit : must_bits)
  {
    out << bit.first << " MUST:";
    bit_vectort b=bit.second;
 
    for(unsigned i=0; b!=0; i++, b>>=1)
      if(b&1)
      {
        INVARIANT(i < cba.bits.size(), "inconsistent bit widths");
        out << ' '
            << cba.bits[i];
      }
 
    out << '\n';
  }
}
 
bool custom_bitvector_domaint::merge(
  const custom_bitvector_domaint &b,
  trace_ptrt,
  trace_ptrt)
{
  bool changed=has_values.is_false();
  has_values=tvt::unknown();
 
  // first do MAY
  bitst::iterator it=may_bits.begin();
  for(const auto &bit : b.may_bits)
  {
    while(it!=may_bits.end() && it->first<bit.first)
      ++it;
    if(it==may_bits.end() || bit.first<it->first)
    {
      may_bits.insert(it, bit);
      changed=true;
    }
    else if(it!=may_bits.end())
    {
      bit_vectort &a_bits=it->second;
      bit_vectort old=a_bits;
      a_bits|=bit.second;
      if(old!=a_bits)
        changed=true;
 
      ++it;
    }
  }
 
  // now do MUST
  it=must_bits.begin();
  for(auto &bit : b.must_bits)
  {
    while(it!=must_bits.end() && it->first<bit.first)
    {
      it=must_bits.erase(it);
      changed=true;
    }
    if(it==must_bits.end() || bit.first<it->first)
    {
      must_bits.insert(it, bit);
      changed=true;
    }
    else if(it!=must_bits.end())
    {
      bit_vectort &a_bits=it->second;
      bit_vectort old=a_bits;
      a_bits&=bit.second;
      if(old!=a_bits)
        changed=true;
 
      ++it;
    }
  }
 
  // erase blank ones
  erase_blank_vectors(may_bits);
  erase_blank_vectors(must_bits);
 
  return changed;
}
 
void custom_bitvector_domaint::erase_blank_vectors(bitst &bits)
{
  for(bitst::iterator a_it=bits.begin();
      a_it!=bits.end();
     ) // no a_it++
  {
    if(a_it->second==0)
      a_it=bits.erase(a_it);
    else
      a_it++;
  }
}
 
bool custom_bitvector_domaint::has_get_must_or_may(const exprt &src)
{
  if(src.id() == ID_get_must || src.id() == ID_get_may)
    return true;
 
  for(const auto &op : src.operands())
  {
    if(has_get_must_or_may(op))
      return true;
  }
 
  return false;
}
 
exprt custom_bitvector_domaint::eval(
  const exprt &src,
  custom_bitvector_analysist &custom_bitvector_analysis) const
{
  if(src.id() == ID_get_must || src.id() == ID_get_may)
  {
    if(src.operands().size()==2)
    {
      unsigned bit_nr =
        custom_bitvector_analysis.get_bit_nr(to_binary_expr(src).op1());
 
      exprt pointer = to_binary_expr(src).op0();
 
      if(pointer.type().id()!=ID_pointer)
        return src;
 
      if(
        pointer.is_constant() &&
        is_null_pointer(to_constant_expr(pointer))) // NULL means all
      {
        if(src.id() == ID_get_may)
        {
          for(const auto &bit : may_bits)
            if(get_bit(bit.second, bit_nr))
              return true_exprt();
 
          return false_exprt();
        }
        else if(src.id() == ID_get_must)
        {
          return false_exprt();
        }
        else
          return src;
      }
      else
      {
        custom_bitvector_domaint::vectorst v=
          get_rhs(dereference_exprt(pointer));
 
        bool value=false;
 
        if(src.id() == ID_get_must)
          value=get_bit(v.must_bits, bit_nr);
        else if(src.id() == ID_get_may)
          value=get_bit(v.may_bits, bit_nr);
 
        if(value)
          return true_exprt();
        else
          return false_exprt();
      }
    }
    else
      return src;
  }
  else
  {
    exprt tmp=src;
    Forall_operands(it, tmp)
      *it=eval(*it, custom_bitvector_analysis);
 
    return tmp;
  }
}
 
void custom_bitvector_analysist::instrument(goto_functionst &)
{
}
 
void custom_bitvector_analysist::check(
  const goto_modelt &goto_model,
  bool use_xml,
  std::ostream &out)
{
  unsigned pass=0, fail=0, unknown=0;
 
  for(const auto &gf_entry : goto_model.goto_functions.function_map)
  {
    if(!gf_entry.second.body.has_assertion())
      continue;
 
    // TODO this is a hard-coded hack
    if(gf_entry.first == "__actual_thread_spawn")
      continue;
 
    if(!use_xml)
      out << "******** Function " << gf_entry.first << '\n';
 
    forall_goto_program_instructions(i_it, gf_entry.second.body)
    {
      exprt result;
      irep_idt description;
 
      if(i_it->is_assert())
      {
        if(!custom_bitvector_domaint::has_get_must_or_may(i_it->condition()))
        {
          continue;
        }
 
        if(operator[](i_it).has_values.is_false())
          continue;
 
        exprt tmp = eval(i_it->condition(), i_it);
        const namespacet ns(goto_model.symbol_table);
        result = simplify_expr(std::move(tmp), ns);
 
        description = i_it->source_location().get_comment();
      }
      else
        continue;
 
      if(use_xml)
      {
        out << "<result status=\"";
        if(result.is_true())
          out << "SUCCESS";
        else if(result.is_false())
          out << "FAILURE";
        else
          out << "UNKNOWN";
        out << "\">\n";
        out << xml(i_it->source_location());
        out << "<description>"
            << description
            << "</description>\n";
        out << "</result>\n\n";
      }
      else
      {
        out << i_it->source_location();
        if(!description.empty())
          out << ", " << description;
        out << ": ";
        const namespacet ns(goto_model.symbol_table);
        out << from_expr(ns, gf_entry.first, result);
        out << '\n';
      }
 
      if(result.is_true())
        pass++;
      else if(result.is_false())
        fail++;
      else
        unknown++;
    }
 
    if(!use_xml)
      out << '\n';
  }
 
  if(!use_xml)
    out << "SUMMARY: " << pass << " pass, " << fail << " fail, "
        << unknown << " unknown\n";
}