[llvm-dev] Proposal: Make the VE target official

[Simon Moll via llvm-dev]

Hi Renato,

On Mon, 2021-11-08 at 10:09 +0000, Renato Golin wrote:
> On Wed, 3 Nov 2021 at 12:52, Simon Moll <Simon.Moll at emea.nec.com>
> wrote:
> > We propose the switch from 'experimental' backend status to
> > 'official',
> > 
> 
> 
> Hi Simon,
> 
> The VE community seems to have adopted all requirements laid out in
> the new targets' document[1], so I guess it's just a matter of
> ironing out the transition.
> 
> > * The staging builder (clang-ve-ninja) [2].  This builder builds
> > and
> >   checks LLVM+Clang and compiler-rt. The functional compiler-rt
> > tests
> >   run C code on a VE device.
> > 
> 
> 
> This bot seems red for a long time. One of the ideas that reflect a
> target to be stable is that its buildbot is "mostly" green throughout
> the warmup period (and hopefully just before moving out of
> experimental).
If you look at the build logs of clang-ve-ninja, you will see that the
"check all" tests for LLVM+Clang have been passing for a while.
What's failing is compiler-rt and we have a patch for that.

> 
> > * D113093 [3] has the changes to make all compiler-rt tests pass on
> > VE.
> >   Remaining failures are due to denormal support, alignment
> >   requirements and subtle differences in syscalls.
> > 
> 
> 
> Will this make the bots green? It's ok to disable tests that fail for
> known reasons (or are irrelevant), but we shouldn't disable tests
> just to make the bots green to promote the target.
Yes, the compiler-rt tests are failing for well understood reasons
(documented in the patch - check-all on LLVM+Clang is green). The patch
will make compiler-rt pass on VE by accounting for those (no denorm
support, syscall differences).
We explicitly include compiler-rt testing (even though it is failing)
to have LLVM-compiled code running on the VE in CI.. this is not
something we'd do for slick optics.

> 
> > * The downstream reference implementation (LLVM-VE [4]).  This
> > includes
> >   compiler-rt,libcxxabi,libcxx and openmp target offloading and
> > will
> > be
> >   the basis for upstreaming.
> > 
> 
> 
> I looked at the branch and it seems to have a single merged patch
> that is not only huge, but has a lot of style changes to unrelated
> code (ex. clang-tools-extra).
> 
> It would be much simpler if you had a branch with the changes that
> you want to upstream into separated patches rebase onto LLVM's main
> branch.
The github repo is for reference only. If you look at our upstream
patch history, you will see that we submit small patches with tests and
follow the review protocol.

> 
> cheers,
> --renato
> 

Thanks,
Simon