The way I see it, don’t let your superiors know you’re worried about that kind of stuff because if you’re working for a shitty enough company, they will probably hold that over your head.
Oh, you’re not performing well enough. You don’t want to be fired and homeless, do you?
Don’t know if that’s something they can legally do to you, but I wouldn’t put it past a lot of companies to do that to ensure you don’t leave or do anything they don’t want, like ask for a raise or looking for another job on company time.