[obi1kenobi]

(Post author here.) Agreed with the parent comment. To restate the same thing in another way in the hope of avoiding confusion:

It isn't a bug in the compiler if the compiler is non-deterministic in the presence of UB. Such behavior does not violate any guarantee provided by the compiler or language spec.

In fact, it's still not a bug if the compiler is non-deterministic, full stop. Many (most?) compilers have non-deterministic behavior due to a variety of factors. To get a sense of what's involved in getting determinism, look up some articles on why it's difficult to get reproducible builds working. It's a lot harder than it might seem at first.

[gpderetta]

Determinism is a QoI issue. It is an important QoI feature though and I think most compilers meant for production use at least strive to implement it. I guess things like parallel, distributed compilation make it quite hard.