[flang-dev] RFC: LLVM 11 branch

[Steve Scalpone via flang-dev]

No objections to removing the dependencies on pgf90; however, I agree that the existing FC mechanism should preserve the ability to use other compilers to generate code.  Camille Coti post a patch to enable linking with additional libraries, but it's not integrated anywhere that I know of.  David, if you are going to undertake this change, let me know & I'll fwd the email to you.

 - Steve

On 7/8/20, 11:46 AM, "flang-dev on behalf of Hal Finkel via flang-dev" <flang-dev-bounces at lists.llvm.org on behalf of flang-dev at lists.llvm.org> wrote:

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    On 7/8/20 3:58 AM, 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,


    Yes, we should make clear that this is essentially in a developer-only
    mode (excepting any specific tests that we want to ask people to run).


    >   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.


    +1


    >
    > 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.


    +1

    I thought that we had consensus to change this.


    >
    > 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.


    Yes, shared-library builds should work.

    We can also discuss these on Monday's call.

      -Hal


    >
    >
    > Does anyone have any thoughts on this?
    >
    > Thanks
    > David Truby
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    --
    Hal Finkel
    Lead, Compiler Technology and Programming Languages
    Leadership Computing Facility
    Argonne National Laboratory

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