[flang-dev] [EXTERNAL] RFC: LLVM 11 branch

[McCormick, Pat via flang-dev]

Somewhere I have a version of the “dummy” driver that allows you to specify the target compiler to hand off to.  I can try and track that code down (as I recall it was pretty simple patch as it used an environment variable).   It should be quick to fix in the latest code base and we could potentially also consider making it a CMake settings/parameter if that is an easier (more user friendly) path for use cases we have across the community.

Thoughts?

—Pat

On Jul 8, 2020, at 4:54 PM, Steve Scalpone via flang-dev <flang-dev at lists.llvm.org<mailto:flang-dev at lists.llvm.org>> wrote:

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<mailto:flang-dev-bounces at lists.llvm.org> on behalf of flang-dev at lists.llvm.org<mailto:flang-dev at lists.llvm.org>> wrote:

   External email: Use caution opening links or attachments


   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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