Add aarch64 support to the SH2 dynarec

[dsx724]

Right now, the SH2 dynarec (used for Sega 32X) only works for the following platforms:

• Intel x86 (32bit / 64bit)
• ARM v7 (32bit)

Every other architecture right now has to fall back on an interpreter core which is not fast enough for many low powered Aarch64 SoCs, including the one on the Nintendo Switch.

This bounty is for the purpose of adding an Aarch64 dynarec backend as well to the existing SH2 dynarec. Perfomance needs to be comparable or better than the existing dynarecs.

https://www.bountysource.com/issues/64126757-missing-feature-ifdef-__aarch64__-in-cpu-sh2-compiler-c

Bounty has been started and starts at $50.

Edited by: twinaphex

[dmiller423]

They are what 20mhz? The interpreter must be terribly slow...
This is odd since the instructions are 16b like thumb and a jump table / [] func *'s caches well compressed.
Theoretically even on bad performance 2x of them should only take ~400-500mhz to emulate...

Also isn't ARMv8 capable of running 32b arm code?

[andres-asm]

ARMv8 can, switch, or at least libnx can't.
Even if it could that doesn't make the bounty irrelevant. AARC64 SoCs are becoming common and there are gonna be slow SoCs, fast SoCs, bad SoCs, good SoCs.

[dmiller423]

I don't have a ton of time, but given enough interest, perhaps I could add an aarch64 emitter to the dynarec in reicast and add it to picodrive as well.

[dsx724]

How much time would you estimate such a project would take?

[dmiller423]

A full aarch64 emitter to satisfy reicast would take a few weeks, updating the recompiler and testing would take several more per target. Prob ~ 2-3mo

[irixxxx]

Would this be satisfactory: https://github.com/irixxxx/picodrive

[m4xw]

@irixxxx I will check it out and try it on the Switch, if it's satisfactory and you want the bounty, sure go claim afterwards.
Will probably be a few days since I have a lot of stuff to do IRL.

[Panderner]

Current state of aarch64 dynarec?

[hizzlekizzle]

no change

[Panderner]

Any updates for this?

[hizzlekizzle]

Nope. No change.

[irixxxx]

With current core It should be enabled on all build targets with aarch64 architecture. Any feedback?

[m4xw]

It doesn't seem to be enabled for Switch (libnx)?
I would expect a crash since it would need support for dual bases in the emitter (different rx and rw buffers) but it runs as usual.
Should be fairly simple to add support tho if its now in the repo.