https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67650
--- Comment #31 from Vincent <vincent.lextrait at gmail dot com> --- It turns out we might be in front of two bugs actually. With 8.1 I have a new diagnosis for this 67650 bug (definition missing at compile time, not just at link edition time), but I do have other parts of my old code where 8.1 is now reporting missing definitions, and the definitions are there (definitions are shown in the error message from 8.1 itself). And no virtuals are involved there at all. So either the old bug is now much more extensive, or there are two bugs now in the same general "area".
