I'm skeptical of the claim that this change will "silently break so much existing code". For it to change the behavior of code, the first member would have to be smaller than other members, someone would have to use this construct to initialize union objects, and it would have to affect the behavior. In any case, it's standard for the Fedora, Ubuntu, and Debian developers to go through all the packages and test with new GCC versions before they come out, so that issues are fixed before the new compiler is released.