IBM will talk about a performance bonus but you will not see anything worth calling a bonus as an engineer. Even sales people who have sales incentives have complained about not getting the full amount they were promised after they met ridiculously high targets.
But why stop at bonuses....raises over the years have been low and are pretty rare. The idea (per IBM speak) has been to give a low percentage of employees a "reasonable" size raise rather than give most people an "insultingly small" raise.....but in reality BOTH of these situations annoy/frustrate employees.
If you really want to come to IBM, take the opportunity now to negotiate at decent initial BASE salary. If you are not happy with the starting BASE SALARY, do not bother accepting the job.