GHC Weekly News - 10/24/2014

Austin Seipp austin at
Thu Oct 30 16:16:48 UTC 2014

Yes, it is orthogonal to any effort for a NCG for ARMv7 or ARMv8.

Note that ARM is a platform that would particularly benefit from this:
right now, building GHC on ARM is a bit... er, troublesome. There are
a lot of LLVM versions that don't work, or are patched by maintainers
(making it impossible to know what might work or not), or have simply
never been tested depending on the distro. I've had quite my share of
problems trying to get GHC/ARM to build on ARM/Linux, due to all kinds
of incompatibilities or bugs in the code generator for whatever verson
I was using.

I agree that for upstreams (Debian, Fedora, etc) the proposition is a
bit scary perhaps. But I think the significant number of advantages
outweigh the disadvantages quite handily, and as we go forward, I
still think it will be the only truly maintainable solution, at least
in the forseeable future.

I am also of course more than willing to help upstreams adapt to this
(for example, should Debian or Fedora wish to package their own LLVM,
I'd be more than willing to help identify a version that works and we
could give to users).

FWIW, I'm aiming for not requiring any extra patches to LLVM. I'd
prefer using a stable version, and any bugs we find should go
upstream.( GHC requiring extra LLVM patches would be a possibility,
but one of the last things we'd want possibly due to extra

On Thu, Oct 30, 2014 at 5:24 AM, Jens Petersen <juhpetersen at> wrote:
> Thanks for the Weekly News that is really useful info.
> On 25 October 2014 09:00, Austin Seipp <austin at> wrote:
>> Note: this post is available (with full hyperlinks) at
>>  - This past week, a discussion sort of organically started on the
>> `#ghc` IRC channel about the future of the LLVM backend. GHC's backend
>> is buggy, has no control over LLVM versions, and breaks frequently
>> with new versions. This all significantly impacts users, and relegates
>> the backend to a second class citizen. After some discussion, Austin
>> wrote up a proposal for a improved backend, and wrangled several other
>> people to help. The current plan is to try an execute this by GHC
>> 7.12, with the goal of making the LLVM backend Tier 1 for major
>> supported platforms.
> Is this effort orthogonal to NCG for armv7 and armv8?
> I am glad people are thinking about how to address this but
> "we ship and fix a version of LLVM for GHC" sounds a bit scary to me. :)
> Jens


Austin Seipp, Haskell Consultant
Well-Typed LLP,

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