[llvm-dev] Moving the AVR backend out of experimental

Nico Weber via llvm-dev llvm-dev at lists.llvm.org
Fri Mar 13 05:53:45 PDT 2020

To tie things together, Dylan's change to move AVR out of experimental has
landed :)

On Thu, Feb 27, 2020 at 5:09 PM Renato Golin <rengolin at gmail.com> wrote:

> Parachuting here, collating many responses into one, forgive me.
> On Fri, 14 Feb 2020 at 18:58, Nico Weber via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > Pros:
> > - LLVM's release binaries contain AVR support :)
> > - It'd happen to remove the only backend that's currently marked
> experimental, which imho makes the build config easier to understand
> I think well maintained and well behaved backends with real users (no
> matter how many) should be built by default once they fulfilled their
> experimental cooling period successfully.
> > Cons:
> > - Everyone gets to pay the cost for maintaining AVR for cross-cutting
> changes. From the last 3 months, this seems to happen once or twice a
> month. We have a bit over 100 commits/day, so that seems fine.
> > - By default all backends get linked, so all binaries get larger by the
> size of the AVR backend (but people who care probably already have an
> explicit list of enabled targets)
> Those are the costs of every backend, and as they go, AVR seems pretty
> cheap in comparison, so I don't see a problem here.
> > (Tom) My only concern with AVR is having active mantainers.  It doesn't
> seem to have had much development in the last 6 months.
> I agree this may be a sign of potential bit-rot, but as long as it has
> real users and the maintainer is up for fixing the eventual bugs quick
> enough, it's ok to have a slow paced back-end, especially without
> heavy corporate backing.
> For example:
> > (Dylan) I re-ran the test suite with
> '-DLLVM_TARGET_ARCH=avr-unknown-unknown' and now the only errors I get are
> JIT errors related to no JIT compiler enabled for my host machine, x86. It
> seems the few failing generic CodeGen tests have since been fixed, along
> with the ~80 or so DebugInfo tests no doubt fixed by one of Ayke's recent
> changes.
> This looks like an active sub-community to me. The JIT "errors" are
> not really errors. When we turned the ARM backend built by default it
> had no JIT support at all either. Just mark them as ignored in LIT.
> The buildbot (http://lab.llvm.org:8014/builders/llvm-avr-linux) is
> green for quite a while, which is also positive.
> --renato
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