[pingyong]

My point is that if a loop

- doesn't terminate, doesn't have side effects -> optimization doesn't matter

- doesn't terminate, has side effects -> optimization isn't valid

- does terminate, doesn't has side effects -> optimization would be valid, but why would such a loop exist? One example that was brought up was generic code, but I'm not entirely convinced yet.

[eru]

Because of interaction with other undefined behaviour (in the body of your loop), you might think you are in a different case than what the compiler thinks.

Also the definition of 'side effect' here is a weird one: reading and writing to variables is not considered a side effect, even though a different thread could change them while your loop is running.