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

Chris Lattner via llvm-dev llvm-dev at lists.llvm.org
Mon Jul 25 16:08:49 PDT 2016

On Jul 25, 2016, at 4:02 PM, Sean Silva via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> I'm sure it is theoretically possible for me to acquire such a system and test on it, but the amount of time and energy it would take make it a practical impossibility.
> 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've never seen this be a problem in practice, and I'm not convinced that it is something we should actually require to have an upstream backend.
> As I mentioned in the original thread "[llvm-dev] [RFC] Lanai backend", it seems to me that the "can I run the code coming out of the backend?" property is more about enabling LLVM's users to do interesting things with the backend, rather than about LLVM's internal maintenance.
> http://lists.llvm.org/pipermail/llvm-dev/2016-February/095214.html <http://lists.llvm.org/pipermail/llvm-dev/2016-February/095214.html>
> I'm not sure how that affects the decision.

MHO, but I almost completely disagree with you.  I agree that the question comes down to asking how much benefit to the community there is to merging the backend, balances vs how much cost there is (your "internal maintenance" point).

It is unquestionably easier for a contributor to land their backend in-tree than to maintain it out-of-tree.  This is because landing it in tree shifts the maintenance burden from the *contributor* to the *community*.  If there is low value to the community, then this is a "bad deal” for the project as a whole, since there is only so much attention to go around.

> My gut (and I'm actually not sure if I exactly consider this a pro or a con personally) is that is sounds Stallman-esque to require backends to answer "yes" to "can I run the code coming out of the backend?". If you squint it is sort of like an anti-tivoization requirement, which would be a very ironic requirement for a BSD-licensed project.

This seems like some weird FUD or mud slinging argument, I’m not sure what to make of it.

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