[llvm-dev] [RFC] Make Lanai backend non-experimental

Renato Golin via llvm-dev llvm-dev at lists.llvm.org
Mon Jul 25 13:25:40 PDT 2016

Hi Chandler,

I think you have good points. Maybe we could make some hard-lined
rules and others as "nice-to-have".

The biggest problem is the community behind it, outside of LLVM. If
the community is strong, and they care about LLVM support, than we can
keep their back-ends in tree and not have to worry about them.

IIRC, our *only* rule for a long time has been "keep up or give up".
Now, how do we know when a target is good for moving out of
experimental? And what is the meaning of experimental anyway?

Maybe we should separate the discussion from the actual change. So, if
you could comment on the review D22753 about which of the points you'd
consider mandatory and which are nice-to-have, that'd probably be

About the Lanai back-end being official, I have no reservations. But I
was the only one to say anything, so I'll wait for others to have
their say on the review before I put my approval.

Just a few unrelated comments below... :)

On 25 July 2016 at 19:46, Chandler Carruth <chandlerc at google.com> wrote:
> Even for fairly pedestrian backends such as AArch64 and PowerPC, we
> routinely have people ask active developers on those backends to do the
> triaging of issues.

I think that's most for specific environment than anything else.

Really, you can get sub-$100 AArch64 1-day delivery and a *very*
decent open source emulator (QEMU), both system and user level.

> And I don't think any of these backends are bad or should be removed. I
> rather like several of them. =] I just think that sufficient community
> involvement makes the availability of hardware/emulator "nice to have" but
> not essential, and it makes the ISA documentation substantially less
> important.

I also don't think emulators replace the ISA in any way, but I get
what you mean. Being nice-to-have, either one would be better than
nothing, but having both would be really optimal.

Between the two, I'd personally prefer the ISA (if it was correct and
complete) than a simulator. But that's me.


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