void termination_baset::find_required_steps(
const goto_tracet &goto_trace,
goto_tracet::stepst::const_iterator &loop_begin,
required_stepst &required_steps,
const std::string &prefix) const
{
find_symbols_sett required_symbols;
unsigned before=0, after=1;
// initialize: find all (potential) loop exits and
// remember the symbols in them
for(goto_tracet::stepst::const_iterator it1=loop_begin;
it1!=goto_trace.steps.end();
it1++)
{
if(it1->pc->is_goto() &&
it1->pc->function==loop_begin->pc->function)
{
bool found_next=false, found_target=false;
goto_programt::const_targett next=it1->pc; next++;
goto_programt::const_targett target=it1->pc->targets.front();
for(goto_tracet::stepst::const_iterator it2=loop_begin;
it2!=goto_trace.steps.end();
it2++)
{
if(it1!=it2)
{
if(it2->pc==next)
found_next=true;
else if(it2->pc==target)
found_target=true;
}
}
if(!found_target || !found_next)
{
exprt temp=it1->cond_expr;
remove_ssa_ids(temp);
find_symbols(temp, required_symbols);
}
}
}
#if 0
std::cout << "INITIAL SYMBOLS: ";
for(find_symbols_sett::const_iterator it=required_symbols.begin();
it!=required_symbols.end();
it++)
std::cout << *it << ", ";
std::cout << std::endl;
#endif
// get the fixpoint
while(before!=after)
{
before=required_symbols.size();
for(goto_tracet::stepst::const_iterator step=loop_begin;
step!=goto_trace.steps.end();
step++)
{
find_symbols_sett intersection;
if(step->is_assignment())
{
exprt lhs, rhs;
const codet &code=to_code(step->pc->code);
if(code.get_statement()==ID_assign)
{
const code_assignt &acode=to_code_assign(step->pc->code);
lhs=acode.lhs();
rhs=acode.rhs();
}
else if(code.get_statement()==ID_function_call)
{
const code_function_callt fcode=to_code_function_call(step->pc->code);
lhs=fcode.lhs();
rhs=fcode.op2();
}
else
throw "Unexpected assign statement";
if(lhs.id()==ID_symbol &&
has_prefix(lhs.get_string(ID_identifier), prefix))
{
// if we depend on the RHS syms, we also need the pre-symbol
find_symbols_sett rhs_sym;
find_symbols(rhs, rhs_sym);
if(intersects(rhs_sym, required_symbols))
{
find_symbols(lhs, required_symbols);
required_steps.insert(&(*step));
}
}
else
{
find_symbols_sett lhs_sym;
if(lhs.id()==ID_index)
find_symbols(lhs.op0(), lhs_sym); // we're not modifying the index
else
find_symbols(lhs, lhs_sym);
if(intersects(lhs_sym, required_symbols))
{
find_symbols(rhs, required_symbols);
required_steps.insert(&(*step));
}
}
}
else if(step->is_assume())
{
find_symbols_sett syms;
find_symbols(step->pc->guard, syms);
if(intersects(syms, required_symbols))
{
required_symbols.insert(syms.begin(), syms.end());
required_steps.insert(&(*step));
}
}
}
after=required_symbols.size();
#if 0
std::cout << "REQUIRED SYMBOLS: ";
for(find_symbols_sett::const_iterator it=required_symbols.begin();
it!=required_symbols.end();
it++)
std::cout << *it << ", ";
std::cout << std::endl;
#endif
}
}
