can't move to latest version of llvm on ghc 9.12.2

[Andreas Klebinger]

Looking at https://gitlab.haskell.org/ghc/ghc/-/issues/25011 it seems
the desire was to fail with a proper error when LLVM was not found at all.

To me failing when the llvm version is too new seems like a unintended
side effect of fixing the former.

I agree that simply warning and trying anway is the better default. A
ticket would be appreciated!

Am 01/04/2025 um 19:05 schrieb George Colpitts:
> I was trying to find out if it works but I ran into the problem I
> described. Yes, there were a few years where the latest version didn't
> work but in many years it did. ghc used to give a warning, this is an
> unsupported version but we'll try it anyways. I would like to
> return to that.
>
> In any case I believe ghc dev should test to see if it works and if so
> use it in HEAD. If it doesn't work than we should file a bug and fix
> it. In the past we got a few versions behind llvm. I think we want to
> be on the latest version available for each new release if possible.
> The earlier we look into this the more chance we have to succeed at that.
>
> On Tue, Apr 1, 2025 at 1:27 PM Brandon Allbery <allbery.b at gmail.com>
> wrote:
>
>     Have you demonstrated that it works? IIRC the current behavior is
>     because some LLVM version (16, IIRC) didn't work with GHC (threw
>     errors from opt, I think).
>
>     On Tue, Apr 1, 2025 at 10:49 AM George Colpitts
>     <george.colpitts at gmail.com> wrote:
>
>         llvm 20 is out but unlike in earlier versions of ghc moving to
>         it means you can no longer use llvm:
>
>         compiling:
>
>             ghc -fllvm hello.hs
>             Loaded package environment from
>             /Users/avie/.ghc/aarch64-darwin-9.12.2/environments/default
>             [1 of 2] Compiling Main             ( hello.hs, hello.o )
>             <no location info>: error: [GHC-66599]
>               GHC was not configured with a supported LLVM toolchain
>               Make sure you have installed LLVM between [13 and 20)
>             and reinstall GHC to make -fllvm work
>
>
>         from configure:
>
>             configure: We only support llvm 13 upto 20 (non-inclusive)
>             (found 20.1.1).
>
>
>         Can we move to llvm 20 on HEAD and can we revert to the old
>         behavior on ghc 9.12.3?
>
>         Should I file an ER?
>
>         Thanks
>
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>
>
>
>     --
>     brandon s allbery kf8nh
>     allbery.b at gmail.com
>
>
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