[flang-dev] RFC: LLVM 11 branch

Alastair McKinstry via flang-dev flang-dev at lists.llvm.org
Thu Jul 9 08:08:46 PDT 2020

On 09/07/2020 11:31, David Truby via flang-dev wrote:
> Hi Alastair,
> The current flang in the debian repos is the old flang found at
> https://github.com/flang-compiler/flang, which I think will support
> LLVM 11 at some point (although I'm not the right person to ask about
> this).

Thanks.  Is there any timeline or roadmap for the "legacy flang" compiler ?

> This discussion is about the new LLVM-integrated flang, which will be a
> developer only release in LLVM 11 and not really useful to include in
> the Debian repositories as it will still be reliant on other fortran
> compilers to generate code.
> As a result it's probably more useful to include the flang-
> compiler/flang project in the next Debian release I think.
> Perhaps someone else can comment more on that though?
> David
> On Wed, 2020-07-08 at 20:29 +0100, Alastair McKinstry via flang-dev
> wrote:
>> Hi
>> I'm the maintainer of  flang in Debian/Ubuntu.
>> Is flang on LLVM 11 likely to be in usable state for early next year
>> (Q1)?
>> flang shipped in the last stable release of Debian (20181126) built
>> against LLVM-7.
>> Now LLVM-7 is removed from Bullseye, the upcoming release, but LLVM
>> 11
>> is likely to be included.
>> Could flang with LLVM-11 be built to use gfortran or flang itself
>> instead of pgfortran ?
>> Best regards
>> Alastair McKinstry
>> On 08/07/2020 09:58, David Truby via flang-dev wrote:
>>> Hi all,
>>> The LLVM 11 branch is happening soon so we should have a discussion
>>> about what we want Flang to look like in that branch.
>>> tldr; I see a couple of issues currently that we should discuss for
>>> the
>>> release:
>>> * Flang defaults to calling a proprietary compiler (pgfortran)
>>> * Flang enables Werror by default
>>> * Shared library builds don't work
>>> Does anyone else see any other things we should consider that I
>>> haven't
>>> listed here?
>>> To elaborate on my issues list:
>>> I think it's reasonable for us to leave flang in the release,
>>> rather
>>> than for example removing it, and add info in the Release Notes
>>> about
>>> the state of Flang (e.g. that it fully parses and semantically
>>> analyses
>>> Fortran 2018 code but then calls out to another compiler to build
>>> it).
>>> The biggest issue I see with this is that currently flang defaults
>>> to
>>> calling out to a proprietary compiler that many people in an open
>>> source community like LLVM are unlikely to have installed. I would
>>> propose that we either add a CMake flag to select the default
>>> compiler
>>> to call out to, or that we rely on the existing mechanism of
>>> defining
>>> FC, but that either way we should default to gfortran if no other
>>> compiler is specified. That way we would be calling out to a
>>> compiler
>>> that almost anyone interested in Fortran is likely to have
>>> installed,
>>> and if not it is at least easily available.
>>> The other major issue I forsee is that we currently enable Werror
>>> by
>>> default in flang. This is likely to break the release for people
>>> building it with as-yet-unreleased compilers, with downstream
>>> proprietary compilers we haven't tested with, or other unforseen
>>> circumstances. I think there are too many potential issues for
>>> Werror
>>> by default to go into a release version of LLVM.
>>> Shared library builds also don't currently work due to a circular
>>> dependency between two libraries. I think it's farily
>>> uncontroversial
>>> to say that this should be fixed, and I am happy to start working
>>> on it
>>> personally.
>>> Does anyone have any thoughts on this?
>>> Thanks
>>> David Truby
>>> _______________________________________________
>>> flang-dev mailing list
>>> flang-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/flang-dev
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Alastair McKinstry, email: alastair at sceal.ie, matrix: @alastair:sceal.ie, phone: 087-6847928
Green Party Councillor, Galway County Council

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