[flang-dev] RFC: LLVM 11 branch

Alastair McKinstry via flang-dev flang-dev at lists.llvm.org
Wed Jul 8 12:29:47 PDT 2020


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
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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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