llvm dev - Feb 2020 - Moving the AVR backend out of experimental

Hi,

There was a thread a few days ago about the expectations for experimental
targets. At the moment, the only experimental target is AVR. It's been in
the tree for a long time now, and generally seems well-behaved.

Should we just make it a normal target?

Nico
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+better dylanmckay address

On Fri, Feb 14, 2020 at 10:58 AM Nico Weber <thakis at chromium.org>
wrote:
> Hi,
>
> There was a thread a few days ago about the expectations for experimental
> targets. At the moment, the only experimental target is AVR. It's been
in
> the tree for a long time now, and generally seems well-behaved.
>
> Should we just make it a normal target?
>
> Nico
>
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What do you see as the pros and cons of making it a stable target?  Does anyone
else have any concerns about doing so?

-Chris
> On Feb 14, 2020, at 7:59 AM, Nico Weber via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> +better dylanmckay address
> 
> On Fri, Feb 14, 2020 at 10:58 AM Nico Weber <thakis at chromium.org
<mailto:thakis at chromium.org>> wrote:
> Hi,
> 
> There was a thread a few days ago about the expectations for experimental
targets. At the moment, the only experimental target is AVR. It's been in
the tree for a long time now, and generally seems well-behaved.
> 
> Should we just make it a normal target?
> 
> Nico
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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On 2/14/20 4:59 PM, Nico Weber via llvm-dev wrote:

Hi,

There was a thread a few days ago about the expectations for experimental
targets. At the moment, the only experimental target is AVR. It's been in
the tree for a long time now, and generally seems well-behaved.

FYI, the VE target is also experimental at this point.

- Simon

Should we just make it a normal target?

Nico

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>
> Should we just make it a normal target?
>
My only remaining reservation here - the generic DebugInfo tests, which
presumably due to an unimplemented 16-bit branch somewhere deep in the
llvm-objdump callstack.

The AVR backend passes virtually all of the LLVM test suite but these when
avr-unknown-unknown is set as the default target. It feels like the
inclusion of ~80 XFAILs for these DebugInfo tests would be the only wart on
the experimental->official code review. I've had a couple long attempts
debugging this one, but have not yet found the source.

Fixing of the DebugInfo tests would make the AVR official backend pitch
much more tenable.

My only concern with AVR is having active mantainers.  It doesn't
seem
> to have had much development in the last 6 months.

This is a fair assessment; throughout the years, the amount of code I as
the code owner directly write definitely follows something like a sine
wave, with the last few months being one of the slower periods due to work
and other personal projects. I value others' thoughts on this topic
stronger than my own though, so I will reserve judgement.

Compared to say, the ARM backend, the AVR backend has much less corporate
backing or resourcing, essentially developed by enthusiasts and those
interested in electronics in their spare time. The arguments for and
against making either backend official or not may or may not be different -
I am not sure what the community thinks.

As of the two months or so, there's been quite a number of patches from
both driveby and newly-active contributors. I suspect at least part of this
will be due to the official deprecation of GCC's AVR backend[1] and
impending removal from the tree. As far as I know, this will make LLVM the
only open-source AVR C/C++ toolchain in active development, and perhaps
more importantly, supporting of newer language standards.

In summary, if the DebugInfo tests were fixed, I think the AVR backend
would be ready to be marked official. I am also interested in any other
thoughts people have about the AVR backend.

Regards,
Dylan

- [1] https://gcc.gnu.org/ml/gcc-patches/2019-09/msg01256.html



On Mon, Feb 17, 2020 at 9:57 PM Simon Moll via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On 2/14/20 4:59 PM, Nico Weber via llvm-dev wrote:
>
>
> Hi,
>
> There was a thread a few days ago about the expectations for experimental
> targets. At the moment, the only experimental target is AVR. It's been
in
> the tree for a long time now, and generally seems well-behaved.
>
> FYI, the VE target is also experimental at this point.
>
> - Simon
>
>
> Should we just make it a normal target?
>
> Nico
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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