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

Tue Jan 7 15:37:46 PST 2020

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.

 -Hal

Thanks,
  Johannes

On Tue, Jan 7, 2020 at 6:04 AM Peter Waller via llvm-dev <
llvm-dev at lists.llvm.org<mailto: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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--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory
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