llvm dev - Nov 2021 - PowerPC LLVM support much appreciated

I am sorry about the delay, somehow I lost this email in my inbox.

While I certainly sympathize with enthusiast developers working on obsolete
systems and doing some pretty cool hacking, I agree that the goals of an
actively developed back end and an enthusiast-maintained back end are
rather different.

Any code for Darwin PPC in the upstream back end is a burden for new
development on actively supported platforms such as Linux, AIX and FreeBSD.
Similarly, all the new code added for those actively supported platforms as
well as new hardware is a burden for enthusiast developers looking to
maintain support for obsolete platforms. As such, I believe that
coexistence in the same codebase provides little benefit while causing a
fair bit of friction. I would suggest that an out-of-tree back end for
Darwin PPC would reduce this friction.

While I understand there are definite disadvantages to keeping code
out-of-tree due to interface/API changes, I think that these changes are
less frequent than the daily interactions that developers for active
platforms would have with code that is specific to Darwin PPC.

Nemanja

On Mon, Oct 25, 2021 at 2:38 PM Andrew Chiw <andrew.work0 at gmail.com>
wrote:
> There is a sizable Mac PowerPC community that also thinks that if Rust is
> on m68k, then it should also be on Darwin PPC, seeing that it's already
on
> Darwin and PPC Linux.
>
> Although speaking with Iain, it doesn't sound like it's actually a
trivial
> matter.
>
> I think the problem is that nobody showed up to defend Rust on PPC Darwin
> back then (and by extension, Go on PowerPC in a similar GitHub issue)
> because the cultures are so different. On one side you have devs working
> deep in large companies and using mailing lists and on the other side you
> have users on Macrumors/Discord who have no idea how to voice their opinion
> at crucial times like this.
>
> If someone could onboard me to the scope of this problem in an efficient
> way, I'd be happy to maintain and also provide docs to make it easy for
> other devs to jump in and help maintain. Because the main problem here is
> it's difficult to know what needs to be done, not enough people
understand
> systems programming at a low level to keep things alive for old systems
> like this. As you know there are so many web devs these days on JS and the
> like.
>
> I also think it would be interesting to create an economy to incentivize
> enthusiast development for obsolete platforms. For example, F at H's
points
> system gets people contributing even though they have no monetary value.
> And there are Patreons for people like Hector Marcan and Rene Rebe. I just
> think that it should be possible to incentivize and organize an entire
> community, not just individuals.
>
> But all this will come after a successful port of Rust over...
>
> On Mon, 25 Oct 2021, 13:10 John Paul Adrian Glaubitz, <
> glaubitz at physik.fu-berlin.de> wrote:
>
>> Hi Nemanja!
>>
>> On 10/25/21 11:27, Nemanja Ivanovic wrote:
>> > Bringing back support for Darwin/PowerPC is of course possible,
but such
>> > undertakings are not free. Aside from the effort to bring it back,
>> there is
>> > the effort of maintaining that support as the PowerPC back end
>> continues to
>> > be developed for supported platforms (Linux, AIX, FreeBSD). So in
order
>> to
>> > consider bringing it back, we would really need to understand the
use
>> case
>> > - now and in the future.
>>
>> I understand. But since both PowerPC and Darwin support are still
there,
>> I would
>> assume that the changes in question aren't big at all. I just had a
quick
>> look
>> and it looks like the majority of changes affects removing tests
specific
>> to
>> Darwin/PowerPC [1] and some minor removal in the AsmPrinter code [2].
>>
>> I'm not a strong proponent of Darwin but I think those changes are
>> relatively small.
>>
>> Adrian
>>
>> > [1]
>>
https://github.com/llvm/llvm-project/commit/7c80f98b69a6a9ad027a3f4bfda073958141d977
>> > [2]
>>
https://github.com/llvm/llvm-project/commit/ebd26cc8c434f40fe8079ee823e7657b5138769f
>>
>> --
>>  .''`.  John Paul Adrian Glaubitz
>> : :' :  Debian Developer - glaubitz at debian.org
>> `. `'   Freie Universitaet Berlin - glaubitz at physik.fu-berlin.de
>>   `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913
>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20211110/6adac965/attachment.html>

Hello!

On 11/10/21 14:47, Nemanja Ivanovic wrote:
> While I certainly sympathize with enthusiast developers working on obsolete
> systems and doing some pretty cool hacking, I agree that the goals of an
> actively developed back end and an enthusiast-maintained back end are
> rather different.
> 
> Any code for Darwin PPC in the upstream back end is a burden for new
> development on actively supported platforms such as Linux, AIX and FreeBSD.
> Similarly, all the new code added for those actively supported platforms as
> well as new hardware is a burden for enthusiast developers looking to
> maintain support for obsolete platforms. As such, I believe that
> coexistence in the same codebase provides little benefit while causing a
> fair bit of friction. I would suggest that an out-of-tree back end for
> Darwin PPC would reduce this friction.
I fully understand the reasoning and I absolutely agree with you. However, the
the actual changes required to get LLVM to build on Darwin/PPC seem to be rather
minimal, given when we ignore the additional tests which is why I don't
think
that Darwin/PPC would actually be such a maintenance burden.

It would be different if there was no support for either Darwin or PPC at all,
but
that's not the case. It's more a question of tying to pieces of string
together
which are already there.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz at debian.org
`. `'   Freie Universitaet Berlin - glaubitz at physik.fu-berlin.de
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913