[llvm-dev] [RFC] Lanai backend

[Renato Golin via llvm-dev]

On 10 February 2016 at 06:24, Chandler Carruth via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> So regardless of what we do with Lanai, I feel really strongly that we don't
> want to use "have other users" or "can run the code" as the bar for
> supporting platforms.

For a good amount of time only a few selected people had access to
AArch64 but we accepted the back-end anyway, even two of them. The
difference there, IMO, is that we were pretty sure ARM would publish
the specs, docs and make the hardware available at some point. I'm
with Chris in the idea that experimental back-ends are welcome as long
as they don't encumber general development, but to become official it
*must* have *public* buildbots, and the interested parties *must* be
expedite on fixing bugs where no one else has access to the
hardware/emulator.

In a way, the discussion of "can I run it" becomes a problem to the
supporters, not necessarily to everyone else, IFF the back-end is
experimental and could be jettisoned at any time. But once it becomes
official, the toll will be much larger on everyone else. Even the BPF
back-end checks the "can I run" box.

But Chris B. has raised a much more important point, which is the
patents associated with it. We do have a strong patent clause when
contributing code to LLVM:

http://llvm.org/docs/DeveloperPolicy.html#patents

More specifically: "When contributing code, we expect contributors to
notify us of any potential for patent-related trouble with their
changes (including from third parties)."

So, if this back-end has *any* patents that would make cloning it and
creating an alternative emulator or even FPGA hardware, we need to
know beforehand, and "we require that the copyright owner sign an
agreement that allows any other user of LLVM to freely use your
patent".

cheers,
--renato