The practical reality appears to be that compilers use the loose interpretation of UB and that every compiler that works hard to optimise things as much as possible takes advantage of that as much as it can.

I am very much sympathetic to the people who really wish that wasn't the case, and I appreciate the logic of arguments like this one that in theory it shouldn't be the case, but in practice, it is the case, and has been for some years now.

So it goes.