remove_internal_symbols.cpp

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/*******************************************************************\
 
Module: Remove symbols that are internal only
 
Author: Daniel Kroening
 
\*******************************************************************/
 
 
#include "remove_internal_symbols.h"
 
#include <util/c_types.h>
#include <util/config.h>
#include <util/find_symbols.h>
#include <util/message.h>
#include <util/namespace.h>
#include <util/std_types.h>
#include <util/symbol_table_base.h>
 
#include <goto-programs/adjust_float_expressions.h>
 
#include "static_lifetime_init.h"
 
static void get_symbols(
  const namespacet &ns,
  const symbolt &in_symbol,
  find_symbols_sett &dest)
{
  std::vector<const symbolt *> working_set;
 
  working_set.push_back(&in_symbol);
 
  while(!working_set.empty())
  {
    const symbolt *current_symbol_ptr = working_set.back();
    working_set.pop_back();
    const symbolt &symbol = *current_symbol_ptr;
 
    if(!dest.insert(symbol.name).second)
      continue;
 
    find_symbols_sett new_symbols;
 
    find_type_and_expr_symbols(symbol.type, new_symbols);
    find_type_and_expr_symbols(symbol.value, new_symbols);
 
    for(const auto &s : new_symbols)
      working_set.push_back(&ns.lookup(s));
 
    if(symbol.type.id() == ID_code)
    {
      const code_typet &code_type = to_code_type(symbol.type);
      const code_typet::parameterst &parameters = code_type.parameters();
 
      for(const auto &p : parameters)
      {
        const symbolt *s;
        // identifiers for prototypes need not exist
        if(!ns.lookup(p.get_identifier(), s))
          working_set.push_back(s);
      }
 
      // check for contract definitions
      const code_with_contract_typet &maybe_contract =
        to_code_with_contract_type(code_type);
 
      find_symbols_sett new_symbols;
      for(const exprt &a : maybe_contract.c_assigns())
        find_type_and_expr_symbols(a, new_symbols);
      for(const exprt &e : maybe_contract.c_ensures())
        find_type_and_expr_symbols(e, new_symbols);
      for(const exprt &r : maybe_contract.c_requires())
        find_type_and_expr_symbols(r, new_symbols);
 
      for(const auto &s : new_symbols)
      {
        const symbolt *symbol_ptr;
        // identifiers for parameters of prototypes need not exist, and neither
        // does __CPROVER_return_value
        if(!ns.lookup(s, symbol_ptr))
          working_set.push_back(symbol_ptr);
      }
    }
  }
}
 
void remove_internal_symbols(
  symbol_table_baset &symbol_table,
  message_handlert &mh,
  const bool keep_file_local)
{
  remove_internal_symbols(symbol_table, mh, keep_file_local, {});
}
 
void remove_internal_symbols(
  symbol_table_baset &symbol_table,
  message_handlert &mh,
  const bool keep_file_local,
  const std::set<irep_idt> &keep)
{
  namespacet ns(symbol_table);
  find_symbols_sett exported;
  messaget log(mh);
 
  // we retain certain special ones
  find_symbols_sett special;
  special.insert("argc'");
  special.insert("argv'");
  special.insert("envp'");
  special.insert("envp_size'");
  special.insert(CPROVER_PREFIX "memory");
  special.insert(INITIALIZE_FUNCTION);
  special.insert(CPROVER_PREFIX "deallocated");
  special.insert(CPROVER_PREFIX "dead_object");
  special.insert(CPROVER_PREFIX "assignable");
  special.insert(CPROVER_PREFIX "object_upto");
  special.insert(CPROVER_PREFIX "object_from");
  special.insert(CPROVER_PREFIX "object_whole");
  special.insert(CPROVER_PREFIX "freeable");
  special.insert(CPROVER_PREFIX "is_freeable");
  special.insert(CPROVER_PREFIX "was_freed");
  special.insert(rounding_mode_identifier());
  special.insert("__new");
  special.insert("__new_array");
  special.insert("__placement_new");
  special.insert("__placement_new_array");
  special.insert("__delete");
  special.insert("__delete_array");
  // plus any extra symbols we wish to keep
  special.insert(keep.begin(), keep.end());
 
  for(symbol_table_baset::symbolst::const_iterator it =
        symbol_table.symbols.begin();
      it != symbol_table.symbols.end();
      it++)
  {
    // already marked?
    if(exported.find(it->first)!=exported.end())
      continue;
 
    // not marked yet
    const symbolt &symbol=it->second;
 
    if(special.find(symbol.name)!=special.end())
    {
      get_symbols(ns, symbol, exported);
      continue;
    }
 
    bool is_function=symbol.type.id()==ID_code;
    bool is_file_local=symbol.is_file_local;
    bool is_type=symbol.is_type;
    bool has_body=symbol.value.is_not_nil();
    bool has_initializer = symbol.value.is_not_nil();
    bool is_contract = is_function && symbol.is_property;
 
    // __attribute__((constructor)), __attribute__((destructor))
    if(symbol.mode==ID_C && is_function && is_file_local)
    {
      const code_typet &code_type=to_code_type(symbol.type);
      if(code_type.return_type().id()==ID_constructor ||
         code_type.return_type().id()==ID_destructor)
        is_file_local=false;
    }
 
    if(is_type || symbol.is_macro)
    {
      // never EXPORTED by itself
    }
    else if(is_function)
    {
      // body? not local (i.e., "static")?
      if(
        has_body &&
        (!is_file_local ||
         (config.main.has_value() && symbol.base_name == config.main.value())))
      {
        get_symbols(ns, symbol, exported);
      }
      else if(has_body && is_file_local && keep_file_local)
      {
        get_symbols(ns, symbol, exported);
      }
      else if(is_contract)
        get_symbols(ns, symbol, exported);
    }
    else
    {
      // 'extern' symbols are only exported if there
      // is an initializer.
      if((has_initializer || !symbol.is_extern) &&
         !is_file_local)
      {
        get_symbols(ns, symbol, exported);
      }
    }
  }
 
  // remove all that are _not_ exported!
  for(symbol_table_baset::symbolst::const_iterator it =
        symbol_table.symbols.begin();
      it != symbol_table.symbols.end();) // no it++
  {
    if(exported.find(it->first)==exported.end())
    {
      symbol_table_baset::symbolst::const_iterator next = std::next(it);
      log.debug() << "Removing unused symbol " << it->first << messaget::eom;
      symbol_table.erase(it);
      it=next;
    }
    else
    {
      it++;
    }
  }
}