So, generic code with a loop, which, depending on parameters, sometimes has side effects and sometimes doesn't, and in the case that it doesn't have side effect

So, generic code with a loop, which, depending on parameters, sometimes has side effects and sometimes doesn't, and in the case that it doesn't have side effects it is still not easy to recognize if the loop terminates? I suppose that is possible, although I'm having a hard time coming up with any reasonable examples.