[arch-dev-public] RFC Final Comment Period: Provide a x86_64_v3 microarchitecture level port

[Allan McRae]

An RFC has now entered Final Comment Period. In 14 days, discussion will
end and the proposal will either be accepted, rejected or withdrawn:

https://gitlab.archlinux.org/archlinux/rfcs/-/merge_requests/2

Please visit the above link for discussion.  (Note much discussion in
that link is relevant for the prior proposal of using x86-64-v2 as a
baseline.)


Summary: Provide a x86_64_v3 microarchitecture level port

Build packages for both --march=x86-64 and --march=x86-64-v3.  Assuming
SSE4 and AVX2 (and others) while compiling will provide greater
out-of-the-box performance in Arch Linux.


Note, the exact implementation of this change is not discussed in the
RFC. I'm of the opinion that RFCs are about ideas, so do not always need
to go into full implementation details.  However, to provide packages
for two architectures we could (1) have packagers build both, (2) bring
in packagers to keep the architectures in sync, (3) have a bot do it
automatically.  I'd guess a combination of 1+2 initially, and add 3 once
we get the signing enclave running. Or 3 could be done with a variant of
the rebuild system where jobs spawn out to available build machines.

Also, we need both gcc-11 and clang-12 to be released to provide support
for the x86-64-v3 variant.  And support for enabling multiple
architectures in pacman needs to be implemented (though we do have a 9
year old patch that did that!).  So this will not happen overnight.