Sorry, we cannot just ignore the dumping issue. We don't want to
waste CPU cycles each startup to regenerate these standard bitmaps.
So the fringe bit patterns need to be initialized at dump time and
dumped together with all the other stuff we prepare at that time.

Ok, I'm not sure about how dumping works, but the patterns that you store are backend specific. Does the dumper take that into account?

Does this proposal resolve the difficulty? If not, please point out
what else is missing.

I just thought that the change decoupled and simplified the code, but I can always add an initialization step to the rif, previous to the definition of the actual bitmaps used by the backend.