[llvm-dev] [RFC] Backend for Motorola 6800 series CPU (M68k)

[David Chisnall via llvm-dev]

Hi,

To add to what Renato said:

On 15/11/2020 21:59, Fāng-ruì Sòng via llvm-dev wrote:
> I've looked at a few newer backends in LLVM and I think the policy is
> unclear about how an experimental target is approved and reviewed.

It's generally good form to tag anyone who commented in the mailing list 
threads on any patches, especially people who objected.  If they're 
happy in review, it's probably good to go.

Generally, the bar for being in-tree is fairly low, the bar to being 
removed from the experimental-back-ends list is much higher.  An 
experimental back end is not built by default and is not in any of the 
binary releases.

Experimental back ends provide a probation period for the maintainer 
community.  If bugs are fixed regularly, the back end makes good 
progress, the required infrastructure is maintained, there's engagement 
from the maintainers in reviewing other patches then it's easy to get 
the back end promoted to non-experimental.  If not, then it will 
languish in the experimental state for a while and then eventually be 
removed (this will typically happen much faster if it requires any 
infrastructure in the generic CodeGen logic to support it and is 
imposing a maintenance cost on the rest of the compiler).

It sounds as if there's a fairly active community of m68k enthusiasts 
(I'm assuming that, in spite of the title of this thread, we are talking 
about the 68000, not the 6800), so I expect that the promotion to 
supported back end should go fairly smoothly.

Note that, so far, I've been about the only person reviewing the CSKY 
patches and have very little spare bandwidth to do it at the moment. 
I'd encourage the m68k maintainers to take a look at it and help out as 
good community members.  All of the back ends in LLVM would be better if 
more people reviewed code for back ends other than the one or two that 
they work on.

David