Thanks Zubin. I found a small problem; hopefully it is unique to me:

 % ghc --version
The Glorious Glasgow Haskell Compilation System, version 9.12.2.20251110
% ghc -O2 -fllvm prob214ff.hs
Loaded package environment from /Users/gcolpitts/.ghc/aarch64-darwin-9.12.2.20251110/environments/default
[1 of 2] Compiling Main             ( prob214ff.hs, prob214ff.o ) [Missing object file]
<no location info>: warning: [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 ensure -fllvm works

<no location info>: error:
    Warning: Couldn't figure out LLVM version!
             Make sure you have installed LLVM between [13 and 20)

Failed to detect LLVM version!
Make sure LLVM is installed correctly.
We will try though...
<no location info>: error: LLVM Optimiser: could not execute: 

Although llvm 21 is not supported my understanding is that it is supposed to try as it says above. I do have llvm installed:

 opt --version
Homebrew LLVM version 21.1.5
  Optimized build.
  Default target: arm64-apple-darwin25.1.0
  Host CPU: apple-m4
(base) gcolpitts@Mac haskell %

Plus configure also thinks I have it installed:

checking for llc... llc
checking llc version (21.1.5) is between 13 and 20... no
configure: We only support llvm 13 upto 20 (non-inclusive) (found 21.1.5).
checking for opt-19... no
checking for opt-19.0... no
checking for opt19... no
checking for opt-18... no
checking for opt-18.0... no
checking for opt18... no
checking for opt-17... no
checking for opt-17.0... no
checking for opt17... no
checking for opt-16... no
checking for opt-16.0... no
checking for opt16... no
checking for opt-15... no
checking for opt-15.0... no
checking for opt15... no
checking for opt-14... no
checking for opt-14.0... no
checking for opt14... no
checking for opt-13... no
checking for opt-13.0... no
checking for opt13... no
checking for opt... opt
checking opt version (21.1.5) is between 13 and 20... no
configure: We only support llvm 13 upto 20 (non-inclusive) 
checking for llc... llc
checking llc version (21.1.5) is between 13 and 20... no
configure: We only support llvm 13 upto 20 (non-inclusive) (found 21.1.5).
checking for opt-19... no
checking for opt-19.0... no
checking for opt19... no
checking for opt-18... no
checking for opt-18.0... no
checking for opt18... no
checking for opt-17... no
checking for opt-17.0... no
checking for opt17... no
checking for opt-16... no
checking for opt-16.0... no
checking for opt16... no
checking for opt-15... no
checking for opt-15.0... no
checking for opt15... no
checking for opt-14... no
checking for opt-14.0... no
checking for opt14... no
checking for opt-13... no
checking for opt-13.0... no
checking for opt13... no
checking for opt... opt
checking opt version (21.1.5) is between 13 and 20... no
configure: We only support llvm 13 upto 20 (non-inclusive) (found 21.1.5).

Suggestions?

Thanks
George


On Tue, Nov 11, 2025 at 4:02 AM Zubin Duggal <zubin@well-typed.com> wrote:
The GHC developers are very pleased to announce the availability
of the second release candidate for GHC 9.12.3. Binary distributions, source
distributions, and documentation are available at [downloads.haskell.org][] and
via [GHCup](https://www.haskell.org/ghcup/).

GHC 9.12.3 is a bug-fix release fixing several issues of a variety of
severities and scopes. A full accounting of these fixes can be found in the
[release notes][]. As always, GHC's release status, including planned future
releases, can be found on the GHC Wiki [status][].

This release candidate will have a two-week testing period. If all goes well
the final release will be available the week of 24 November 2025.

The changes from the first release candidate are

* Fix a regression resulting in a panic with empty cases (#26442, #25960).
* Fix for a potential segfault in the bytecode interpreter (#23210).
* Fix for a regression with tabs not being allowed in string gaps (#26415).
* Fix for a crash with the non-moving GC (#26204).
* A rework of how internal symbols used by the code-generator are handled to
   adapt to changes in the Apple toolchain, enabling this release to bootstrap on
   macOS 26 Tahoe (#26166).

GHC development is sponsored by:

  * [Juspay](https://juspay.com/)
  * [QBayLogic](https://qbaylogic.com/)
  * [Channable](https://www.channable.com/)
  * [Haskell Foundation](https://haskell.foundation/)
  * [Serokell](https://serokell.io/)
  * [Well-Typed](https://well-typed.com/)
  * [Tweag](https://www.tweag.io/)
  * [Dotcom-Monitor](https://www.dotcom-monitor.com/)
  * [LoadView](https://www.loadview-testing.com/)
  * [Web Hosting Buddy](https://webhostingbuddy.com/)
  * [Find My Electric](https://www.findmyelectric.com/)
  * [Standard Chartered](https://www.sc.com)
  * [UpCloud](https://upcloud.com)

We would like to that these sponsors and other anonymous contributors
whose on-going financial and in-kind support has facilitated GHC maintenance
and release management over the years. Finally, this release would not have
been possible without the hundreds of open-source contributors whose work
comprise this release.

As always, do give this release a try and open a [ticket][] if you see
anything amiss.

[release notes]: https://gitlab.haskell.org/ghc/ghc/-/blob/ghc-9.12/docs/users_guide/9.12.3-notes.rst?ref_type=heads&plain=1
[status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status
[downloads.haskell.org]: https://downloads.haskell.org/ghc/9.12.3-rc2
[ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new
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