[llvm-dev] [RFC] Lanai backend

Chris Lattner via llvm-dev
Tue, 09 Feb 2016 22:37:18 -0000

> 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