Pip Cet <pipcet@protonmail.com> writes:

> My understanding is it is safe to access an entire union at once, as the
> old code did, and that GCC concluded based on the undefined behavior
> elsewhere that the only possible union members were those with the holes
> in the right place.

BTW, if so, how do you explain this reproducer?  At no point in the
code's execution is hold_quit ever read or written to.