[Bug c/59850] Support sparse-style pointer address spaces (type attributes)

["tromey at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59850

--- Comment #21 from Tom Tromey <tromey at gcc dot gnu.org> ---
(In reply to Tom Tromey from comment #20)

> BTW if you want to try it out I have a branch:
> https://github.com/tromey/gcc/tree/add-sparse-attributes

This still needs a bit of work.
I rebased it to be more patchlike and wrote some ChangeLog
entries, but I still need to verify that all the behavior
is correct (I forgot a lot of state...) and also write the
documentation.

That said, recently I've been wondering whether this could
be better done as a plugin.  I started down the road of
simply patching gcc due, I think, to the designated_init
attribute, which can't really be done as a plugin.
But it seems that perhaps noderef/force/address_space could
be; and perhaps also bitwise and nocast.

In the "pro" column, as a plugin it could be maintained elsewhere.
That might be interesting.

In the "con" column, it's a pain if multiple projects want to
use these checks.  Then it's just one more thing to fetch.

I'm curious to hear your thoughts on the subject.