weak_memory.cpp

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/*******************************************************************\
 
Module: Weak Memory Instrumentation for Threaded Goto Programs
 
Author: Daniel Kroening, Vincent Nimal
 
Date: September 2011
 
\*******************************************************************/
 
 
/*
 * Strategy: we first overapproximate all the read/write sequences of
 * the program executions with a read/write graph. We then detect the
 * pairs potentially dangerous, and to be delayed in some executions
 * of the program. We finally insert the corresponding instrumentations
 * in the program.
 */
 
#include "weak_memory.h"
 
#include <set>
 
#include <util/fresh_symbol.h>
 
#include <goto-programs/remove_skip.h>
 
#include <linking/static_lifetime_init.h>
 
#include <goto-instrument/rw_set.h>
 
#include "shared_buffers.h"
#include "goto2graph.h"
 
void introduce_temporaries(
  value_setst &value_sets,
  symbol_tablet &symbol_table,
  const irep_idt &function_id,
  goto_programt &goto_program,
#ifdef LOCAL_MAY
  const goto_functionst::goto_functiont &goto_function,
#endif
  messaget &message)
{
  namespacet ns(symbol_table);
 
#ifdef LOCAL_MAY
  local_may_aliast local_may(goto_function);
#endif
 
  Forall_goto_program_instructions(i_it, goto_program)
  {
    goto_programt::instructiont &instruction=*i_it;
 
    message.debug() << instruction.source_location() << messaget::eom;
 
    if(instruction.is_goto() ||
       instruction.is_assert() ||
       instruction.is_assume())
    {
      rw_set_loct rw_set(
        ns,
        value_sets,
        function_id,
        i_it
#ifdef LOCAL_MAY
        ,
        local_may
#endif
      ); // NOLINT(whitespace/parens)
      if(rw_set.empty())
        continue;
 
      symbolt &new_symbol = get_fresh_aux_symbol(
        bool_typet(),
        id2string(function_id),
        "$tmp_guard",
        instruction.source_location(),
        ns.lookup(function_id).mode,
        symbol_table);
      new_symbol.is_static_lifetime=true;
      new_symbol.is_thread_local=true;
      new_symbol.value.make_nil();
 
      symbol_exprt symbol_expr=new_symbol.symbol_expr();
 
      goto_programt::instructiont new_i = goto_programt::make_assignment(
        code_assignt(symbol_expr, instruction.condition()),
        instruction.source_location());
 
      // replace guard
      instruction.condition_nonconst() = symbol_expr;
      goto_program.insert_before_swap(i_it, new_i);
 
      i_it++; // step forward
    }
    else if(instruction.is_function_call())
    {
      // nothing
    }
  }
}
 
void weak_memory(
  memory_modelt model,
  value_setst &value_sets,
  goto_modelt &goto_model,
  bool SCC,
  instrumentation_strategyt event_strategy,
  bool no_cfg_kill,
  bool no_dependencies,
  loop_strategyt duplicate_body,
  unsigned input_max_var,
  unsigned input_max_po_trans,
  bool render_po,
  bool render_file,
  bool render_function,
  bool cav11_option,
  bool hide_internals,
  message_handlert &message_handler,
  bool ignore_arrays)
{
  messaget message(message_handler);
 
  // no more used -- dereferences performed in rw_set
  // get rid of pointers
  // remove_pointers(goto_functions, symbol_table, value_sets);
  // add_failed_symbols(symbol_table);
  // message.status() <<"pointers removed"<< messaget::eom;
 
  message.status() << "--------" << messaget::eom;
 
  // all access to shared variables is pushed into assignments
  for(auto &gf_entry : goto_model.goto_functions.function_map)
  {
    if(
      gf_entry.first != INITIALIZE_FUNCTION &&
      gf_entry.first != goto_functionst::entry_point())
    {
      introduce_temporaries(
        value_sets,
        goto_model.symbol_table,
        gf_entry.first,
        gf_entry.second.body,
#ifdef LOCAL_MAY
        gf_entry.second,
#endif
        message);
    }
  }
 
  message.status() << "Temp added" << messaget::eom;
 
  unsigned max_thds = 0;
  instrumentert instrumenter(goto_model, message);
  max_thds=instrumenter.goto2graph_cfg(value_sets, model, no_dependencies,
    duplicate_body);
  message.status()<<"abstraction completed"<<messaget::eom;
 
  // collects cycles, directly or by SCCs
  if(input_max_var!=0 || input_max_po_trans!=0)
    instrumenter.set_parameters_collection(input_max_var,
      input_max_po_trans, ignore_arrays);
  else
    instrumenter.set_parameters_collection(max_thds, 0, ignore_arrays);
 
  if(SCC)
  {
    instrumenter.collect_cycles_by_SCCs(model);
    message.status()<<"cycles collected: "<<messaget::eom;
    unsigned interesting_scc = 0;
    unsigned total_cycles = 0;
    for(unsigned i=0; i<instrumenter.num_sccs; i++)
      if(instrumenter.egraph_SCCs[i].size()>=4)
      {
        message.status()<<"SCC #"<<i<<": "
          <<instrumenter.set_of_cycles_per_SCC[interesting_scc++].size()
          <<" cycles found"<<messaget::eom;
        total_cycles += instrumenter
          .set_of_cycles_per_SCC[interesting_scc++].size();
      }
 
    /* if no cycle, no need to instrument */
    if(total_cycles == 0)
    {
      message.status()<<"program safe -- no need to instrument"<<messaget::eom;
      return;
    }
  }
  else
  {
    instrumenter.collect_cycles(model);
    message.status()<<"cycles collected: "<<instrumenter.set_of_cycles.size()
      <<" cycles found"<<messaget::eom;
 
    /* if no cycle, no need to instrument */
    if(instrumenter.set_of_cycles.empty())
    {
      message.status()<<"program safe -- no need to instrument"<<messaget::eom;
      return;
    }
  }
 
  if(!no_cfg_kill)
    instrumenter.cfg_cycles_filter();
 
  // collects instructions to instrument, depending on the strategy selected
  if(event_strategy == my_events)
  {
    const std::set<event_idt> events_set = instrumentert::extract_my_events();
    instrumenter.instrument_my_events(events_set);
  }
  else
    instrumenter.instrument_with_strategy(event_strategy);
 
  // prints outputs
  instrumenter.set_rendering_options(render_po, render_file, render_function);
  instrumenter.print_outputs(model, hide_internals);
 
  // now adds buffers
  shared_bufferst shared_buffers(
    goto_model.symbol_table, max_thds, message);
 
  if(cav11_option)
    shared_buffers.set_cav11(model);
 
  // stores the events to instrument
  shared_buffers.cycles = instrumenter.var_to_instr; // var in the cycles
  shared_buffers.cycles_loc = instrumenter.id2loc; // instrumented places
  shared_buffers.cycles_r_loc = instrumenter.id2cycloc; // places in the cycles
 
  // for reads delays
  shared_buffers.affected_by_delay(value_sets, goto_model.goto_functions);
 
  for(std::set<irep_idt>::iterator it=
    shared_buffers.affected_by_delay_set.begin();
    it!=shared_buffers.affected_by_delay_set.end();
    it++)
    message.debug()<<id2string(*it)<<messaget::eom;
 
  message.status()<<"I instrument:"<<messaget::eom;
  for(std::set<irep_idt>::iterator it=shared_buffers.cycles.begin();
    it!=shared_buffers.cycles.end(); it++)
  {
    typedef std::multimap<irep_idt, source_locationt>::iterator m_itt;
    const std::pair<m_itt, m_itt> ran=
      shared_buffers.cycles_loc.equal_range(*it);
    for(m_itt ran_it=ran.first; ran_it!=ran.second; ran_it++)
      message.result() << (it->empty() ? "fence" : *it) << ", "
                       << ran_it->second << messaget::eom;
  }
 
  shared_bufferst::cfg_visitort visitor(
    shared_buffers, goto_model.symbol_table, goto_model.goto_functions);
  visitor.weak_memory(
    value_sets, goto_model.goto_functions.entry_point(), model);
 
  /* removes potential skips */
  remove_skip(goto_model);
 
  // initialization code for buffers
  shared_buffers.add_initialization_code(goto_model.goto_functions);
 
  // update counters etc.
  goto_model.goto_functions.update();
 
  message.status()<< "Goto-program instrumented" << messaget::eom;
}