[llvm-dev] [RFC] Lanai backend

Daniel Berlin via llvm-dev
Tue, 09 Feb 2016 22:53:01 -0000

My random view:
If the team is going to contribute more generally (IE do more than maintain
the backend), it could be a net win for the community.
Otherwise, ...


On Tue, Feb 9, 2016 at 2:37 PM, Chris Lattner via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
> > On Feb 9, 2016, at 9:40 AM, Jacques Pienaar via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > Hi all,
> >
> > We would like to contribute a new backend for the Lanai processor
> (derived from the processor described in [1]).
>
> Hi Jacques,
>
> We generally have a low bar for accepting new “experimental” backends, but
> I think that this is the first proposal to add a target for a hardware that
> general LLVM contributors can’t have access to.  As such, we’ll have to
> figure out as a community whether this makes sense.
>
> Here are the tradeoffs I see of accepting the backend:
>
> 1) I imagine that there is a big win for you, not having to merge with
> mainline.  Maintaining an out of tree backend is a pain :-)
>
> 2) For the community, this is probably a net loss since changes to common
> codegen could would be required to update your backend, but no one else in
> the community would benefit from the target being in mainline.
>
> 3) There is probably a small but non-zero benefit to keeping your team
> working directly on mainline, since you’re more likely to do ancillary work
> in ToT.  If your development is in mainline, this work is most likely to go
> into llvm.org instead of into your local branch.
>
> 4) There could be an educational benefit of having the backend,
> particularly if it has unique challenges to overcome.
>
>
> What do others think about this?  I know that several organizations have
> not even bothered proposing internal-only targets for inclusion in
> llvm.org, since they would effectively be contributing dead code that the
> community would have to maintain.
>
> -Chris
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