void havoc_loopst::get_modifies(
const loopt &loop,
modifiest &modifies)
{
for(loopt::const_iterator
i_it=loop.begin(); i_it!=loop.end(); i_it++)
{
const goto_programt::instructiont &instruction=**i_it;
if(instruction.is_assign())
{
const exprt &lhs=to_code_assign(instruction.code).lhs();
function_modifies.get_modifies_lhs(local_may_alias, *i_it, lhs, modifies);
}
else if(instruction.is_function_call())
{
const code_function_callt &code_function_call=
to_code_function_call(instruction.code);
const exprt &lhs=code_function_call.lhs();
// return value assignment
if(lhs.is_not_nil())
function_modifies.get_modifies_lhs(
local_may_alias, *i_it, lhs, modifies);
function_modifies(code_function_call.function(), modifies);
}
}
}
goto_programt::targett havoc_loopst::get_loop_exit(const loopt &loop)
{
assert(!loop.empty());
// find the last instruction in the loop
std::map<unsigned, goto_programt::targett> loop_map;
for(loopt::const_iterator l_it=loop.begin();
l_it!=loop.end();
l_it++)
loop_map[(*l_it)->location_number]=*l_it;
// get the one with the highest number
goto_programt::targett last=(--loop_map.end())->second;
return ++last;
}
void havoc_loopst::havoc_loop(
const goto_programt::targett loop_head,
const loopt &loop)
{
assert(!loop.empty());
// first find out what can get changed in the loop
modifiest modifies;
get_modifies(loop, modifies);
// build the havocking code
goto_programt havoc_code;
build_havoc_code(loop_head, modifies, havoc_code);
// Now havoc at the loop head. Use insert_swap to
// preserve jumps to loop head.
goto_function.body.insert_before_swap(loop_head, havoc_code);
// compute the loop exit
goto_programt::targett loop_exit=
get_loop_exit(loop);
// divert all gotos to the loop head to the loop exit
for(loopt::const_iterator
l_it=loop.begin(); l_it!=loop.end(); l_it++)
{
goto_programt::instructiont &instruction=**l_it;
if(instruction.is_goto())
{
for(goto_programt::targetst::iterator
t_it=instruction.targets.begin();
t_it!=instruction.targets.end();
t_it++)
{
if(*t_it==loop_head)
*t_it=loop_exit; // divert
}
}
}
// remove skips
remove_skip(goto_function.body);
}
void k_inductiont::get_modifies(
const loopt &loop,
modifiest &modifies)
{
for(loopt::const_iterator
i_it=loop.begin(); i_it!=loop.end(); i_it++)
{
const goto_programt::instructiont &instruction=**i_it;
if(instruction.is_assign())
{
const exprt &lhs=to_code_assign(instruction.code).lhs();
get_modifies_lhs(*i_it, lhs, modifies);
}
else if(instruction.is_function_call())
{
const exprt &lhs=to_code_function_call(instruction.code).lhs();
get_modifies_lhs(*i_it, lhs, modifies);
}
}
}
void k_inductiont::process_loop(
const goto_programt::targett loop_head,
const loopt &loop)
{
assert(!loop.empty());
// compute the loop exit
goto_programt::targett loop_exit=
get_loop_exit(loop);
if(base_case)
{
// now unwind k times
unwind(goto_function.body, loop_head, loop_exit, k);
// assume the loop condition has become false
goto_programt::instructiont assume(ASSUME);
assume.guard=loop_head->guard;
goto_function.body.insert_before_swap(loop_exit, assume);
}
if(step_case)
{
// step case
// find out what can get changed in the loop
modifiest modifies;
get_modifies(loop, modifies);
// build the havoc-ing code
goto_programt havoc_code;
build_havoc_code(loop_head, modifies, havoc_code);
// unwind to get k+1 copies
std::vector<goto_programt::targett> iteration_points;
unwind(goto_function.body, loop_head, loop_exit, k+1, iteration_points);
// now turn any assertions in iterations 0..k-1 into assumptions
assert(iteration_points.size()==k+1);
assert(k>=1);
goto_programt::targett end=iteration_points[k-1];
std::size_t it_p_count=0;
bool after_it_p=true;
for(goto_programt::targett t=loop_head; t!=end; t++)
{
assert(t!=goto_function.body.instructions.end());
if(t->is_assert()) t->type=ASSUME;
if(t==iteration_points[it_p_count])
{
after_it_p=true;
++it_p_count;
}
else if(t->is_goto() && after_it_p)
{
assert(t==loop_head ||
not_exprt(t->guard)==loop_head->guard);
t->type=ASSUME;
t->targets.clear();
t->guard=not_exprt(t->guard);
after_it_p=false;
}
}
// assume the loop condition has become false
goto_programt::instructiont assume(ASSUME);
assume.guard=to_not_expr(loop_head->guard).op();
goto_function.body.insert_before_swap(loop_exit, assume);
// Now havoc at the loop head. Use insert_swap to
// preserve jumps to loop head.
goto_function.body.insert_before_swap(loop_head, havoc_code);
}
// remove skips
remove_skip(goto_function.body);
}
void k_inductiont::process_loop(
const goto_programt::targett loop_head,
const loopt &loop)
{
assert(!loop.empty());
// save the loop guard
const exprt loop_guard=loop_head->guard;
// compute the loop exit
goto_programt::targett loop_exit=
get_loop_exit(loop);
if(base_case)
{
// now unwind k times
unwind(goto_function.body, loop_head, loop_exit, k);
// assume the loop condition has become false
goto_programt::instructiont assume(ASSUME);
assume.guard=loop_guard;
goto_function.body.insert_before_swap(loop_exit, assume);
}
if(step_case)
{
// step case
// find out what can get changed in the loop
modifiest modifies;
get_modifies(loop, modifies);
// build the havoc-ing code
goto_programt havoc_code;
build_havoc_code(loop_head, modifies, havoc_code);
// unwind to get k+1 copies
std::vector<goto_programt::targett> iteration_points;
unwind(goto_function.body, loop_head, loop_exit, k+1, iteration_points);
// we can remove everything up to the first assertion
for(goto_programt::targett t=loop_head; t!=loop_exit; t++)
{
if(t->is_assert()) break;
t->make_skip();
}
// now turn any assertions in iterations 0..k-1 into assumptions
assert(iteration_points.size()==k+1);
assert(k>=1);
goto_programt::targett end=iteration_points[k-1];
for(goto_programt::targett t=loop_head; t!=end; t++)
{
assert(t!=goto_function.body.instructions.end());
if(t->is_assert()) t->type=ASSUME;
}
// assume the loop condition has become false
goto_programt::instructiont assume(ASSUME);
assume.guard=loop_guard;
goto_function.body.insert_before_swap(loop_exit, assume);
// Now havoc at the loop head. Use insert_swap to
// preserve jumps to loop head.
goto_function.body.insert_before_swap(loop_head, havoc_code);
}
// remove skips
remove_skip(goto_function.body);
}