void interval_domaint::assume_rec(
const exprt &cond,
bool negation)
{
if(cond.id()==ID_lt || cond.id()==ID_le ||
cond.id()==ID_gt || cond.id()==ID_ge ||
cond.id()==ID_equal || cond.id()==ID_notequal)
{
assert(cond.operands().size()==2);
if(negation) // !x<y ---> x>=y
{
if(cond.id()==ID_lt)
assume_rec(cond.op0(), ID_ge, cond.op1());
else if(cond.id()==ID_le)
assume_rec(cond.op0(), ID_gt, cond.op1());
else if(cond.id()==ID_gt)
assume_rec(cond.op0(), ID_le, cond.op1());
else if(cond.id()==ID_ge)
assume_rec(cond.op0(), ID_lt, cond.op1());
else if(cond.id()==ID_equal)
assume_rec(cond.op0(), ID_notequal, cond.op1());
else if(cond.id()==ID_notequal)
assume_rec(cond.op0(), ID_equal, cond.op1());
}
else
assume_rec(cond.op0(), cond.id(), cond.op1());
}
else if(cond.id()==ID_not)
{
assume_rec(to_not_expr(cond).op(), !negation);
}
else if(cond.id()==ID_and)
{
if(!negation)
forall_operands(it, cond)
assume_rec(*it, false);
}
else if(cond.id()==ID_or)
{
if(negation)
forall_operands(it, cond)
assume_rec(*it, true);
}
}
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);
}