[llvm-dev] Flang landing in the monorepo - next Monday!

Tue Jan 7 17:47:44 PST 2020

On Tue, Jan 7, 2020 at 5:29 PM Eric Christopher <echristo at gmail.com> wrote:

> Hi Hal,
>
> On Tue, Jan 7, 2020 at 3:38 PM Finkel, Hal J. via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>>
>> On 1/7/20 4:38 PM, Doerfert, Johannes via llvm-dev wrote:
>>
>> On 01/07, David Blaikie via llvm-dev wrote:
>>
>> Hey Peter - would you be able to link to/describe the history on this
>> process/decision. I can find one old thread where this was first proposed (http://lists.llvm.org/pipermail/llvm-dev/2019-February/130497.html ) with
>> some general positive responses and a lot of questions.
>>
>> I see there's a flang-dev list, though I'm not sure where code review is
>> happening (is there flang-commits or equivalent?) as there's not much
>> chatter on the mailing list that I can see.
>>
>> There is a flang-commits. We have everything set up to use Phabricator
>> as MLIR did.
>>
>>
>> & I'm a bit concerned about flang, already a project with no LLVM API
>> usage, it seems, and a community that doesn't currently look like it has
>> much overlap with the LLVM developer community (a very rough glance at
>> flang-dev participants, but I could be wrong - the LLVM community is large,
>> to be sure) - I'm concerned that this might create a not very well
>> integrated community, as we saw in the past with lldb, for instance.
>>
>> I think I mentioned this before but some people are waiting for the move
>> to be able to actually participate in the Flang development. So the
>> current github contributions do not necessarily reflect the LLVM
>> developers that will be involved.
>>
>>
>> I'll add to this that a number of us who have been involved with LLVM for
>> a long time are involved in guiding the Flang project. While it's certainly
>> true that a few of the people working hard on Flang are new to the LLVM
>> community, there is a reasonable overlap with the existing LLVM community
>> in the overall effort.
>>
>>
>> On flang-dev [0] we have long term LLVM developers and people that join
>> the LLVM developers community with the merge of Flang but even those
>> already actively participated at the LLVM-Dev!
>>
>> The API usage is a valid concern, among others, which will require code
>> changes in the near future.
>>
>> [0] http://lists.llvm.org/pipermail/flang-dev/2019-December/author.html
>>
>>
>> The other thing that I'll add here is that the existing Flang development
>> has been broad and not deep - the development started with the lexical
>> analysis (and preprocessor), then the semantic analysis, and so on. It is
>> only very recently that any work on actual code generation has begun, and
>> there, the initial focus has been on targeting LLVM via MLIR. I'm not
>> saying that there aren't more places to use LLVM APIs (e.g., filesystem
>> abstractions, ADT, etc.) -- there are -- but that's something we're
>> planning to improve over time.
>>
>> At a high level, however, the whole point of this Flang project is
>> produce an LLVM-community-integrated Fortran frontend for LLVM. The current
>> developers of the project, which is a growing community, are committed to
>> realizing that outcome and are open to feedback on code structure, API
>> usage, and other aspects of integrating with the rest of the LLVM project.
>>
> I added you to the original thread when I was replying because I knew you
> were around this effort, it might be nice to see if you can respond to the
> other thread too.
>
> A lot of my concerns are echoed by David here and I have additional
> concerns as well. I don't think the project is ready for inclusion into the
> main llvm tree as I don't see the point right now. There's nothing llvm
> about it.
>
>
To elaborate a bit because this almost assuredly comes off poorly (and I
apologize):

I am in favor of having a flang front end in tree. I have concerns about
the design of flang versus other front ends, the lack of llvm based library
use, and a number of other things that I tried to enumerate in previous
emails. I don't know if anything has changed and the responses I got back
originally were "we're going to do it anyway" so it didn't leave much room
for engagement.

Thanks.

-eric

> -eric
>
>
>>  -Hal
>>
>>
>> Thanks,
>>   Johannes
>>
>>
>> On Tue, Jan 7, 2020 at 6:04 AM Peter Waller via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>
>>
>> Hi All,
>>
>> As discussed before Christmas, this is a reminder that we intend to
>> merge flang on the 13th January (next Monday) before the llvm-10 branch.
>> At the moment I'm proposing to do it at 10am GMT. I can be flexible on
>> this point if it requires close coordination with anyone in another
>> timezone, just let me know.
>>
>> Previous discussion was in [llvm-dev] Flang landing in the monorepo<http://lists.llvm.org/pipermail/llvm-dev/2019-December/137661.html> <http://lists.llvm.org/pipermail/llvm-dev/2019-December/137661.html>.
>>
>> The current plan of action is summarized at<https://github.com/flang-compiler/f18/issues/876> <https://github.com/flang-compiler/f18/issues/876>.
>>
>> The result will look a lot like the recent MLIR merge from 24th Dec:<https://github.com/llvm/llvm-project/commits/0f0d0ed1c78> <https://github.com/llvm/llvm-project/commits/0f0d0ed1c78>, commit
>> 0f0d0ed1c78 in the llvm-project monorepo.
>>
>> Once it is done I'll mail the list. If you want to coordinate with me,
>> please get in touch.
>>
>> Regards,
>>
>> - Peter
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>> _______________________________________________
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>>
>> --
>> Hal Finkel
>> Lead, Compiler Technology and Programming Languages
>> Leadership Computing Facility
>> Argonne National Laboratory
>>
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>
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