Support the RISC-V Vector extension

[rmader]

Slowly the first RISC-V consumer boards appear on the market - I just came across a test (german) of the SiFive Freedom U740 where successfully people ran Gnome-Shell on such a board.

In order to have decent performance on this architecture we'll need SIMD fast paths using Vector extension.

P.S.: I don't plan to get such a board right now, but wanted to have a tracker issue in case I or somebody else gets their hands on it.

[ebassi]

I don't plan on writing RISC-V support either. It's not that I don't enjoy having "tracker" issues, but if somebody plans to work on this stuff, they can work on this stuff regardless of an issue being available—and chances are that they won't even link to this issue.

[rmader]

Right - my idea was to spread the link in places with people who already have the board and might consider contributing such code, such as https://discourse.ubuntu.com/t/installing-ubuntu-21-04-on-the-hifive-unmatched/22456/23

[stalkerg]

I tried vectors in qemu + fedora and it works, but I can't say anything else. RISC-V vectors it's not a SIMD (SIMD extensions is still under discussion) and easily migrating NEON to such things will be difficult.