[flang-dev] RFC: LLVM 11 branch

Hal Finkel via flang-dev flang-dev at lists.llvm.org
Wed Jul 8 11:46:22 PDT 2020

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.


> 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.


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.


> 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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