When you have a big system many people rely on you generally try to look for ways to keep their code working - not look for the changes you’re contractually allowed to make.

GCC probably has a better justification than “we are allowed to”.

> GCC probably has a better justification than “we are allowed to”.

Maybe, but I've seen GCC people justify such changes with little more than "it's UB, we can change it, end of story", so I wouldn't assume it.