Comment by fuhsnn

If you are taking notes, add `-fzero-init-padding-bits=all` to the list, without this flag, GCC 15 onwards will not zero-initialize a full union if you wrote pre-C23 style ={0} and the largest member is not the first one. `-ftrivial-auto-var-init` cannot help this case. https://godbolt.org/z/7zKccfnea