openblas: use `cmake` and depend on `libomp`

[ywwry66]

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---

Related to #209091, #129648, #129100. Upstream has added support for buiding with libomp through https://github.com/OpenMathLib/OpenBLAS/pull/5180, where one can also find multiple issues linked from downstream repositories that are caused by Homebrew's handling of OpenMP for OpenBLAS.

This change requires dependents of OpenBLAS also switched to libomp. For gromacs, cp2k and fftw, the switch seems relatively straightforward. However, I am not sure how to go about dynare. Currently, dynare is directly linked to libgomp and it also pulls in libomp through suite-sparse.

[ywwry66]

fatal error: posix_spawnp: Argument list too long

[ywwry66]

The failures on macOS 15-arm64 can be reproduced on my Sequoia macbook with the current OpenBLAS bottle, so they are not related to this PR.

1. arpack: Minitest::Assertion: Expected /reached/ to match " ** On entry to DLASCL parameter number 4 had an illegal value\n ** On entry to DLASCL parameter number 4 had an illegal value\n \n Error with _naupd, info = -9999\n Check the documentation of _naupd\n \n". (https://github.com/opencollab/arpack-ng/issues/469)
2. ~mlpack: /opt/homebrew/include/cereal/types/tuple.hpp:98:41: error: a template argument list is expected after a name prefixed by the template keyword [-Wmissing-template-arg-list-after-template-kw] (https://github.com/USCiLab/cereal/pull/835)~

~There is an error I didn't see before:~

• ~shtools: make: *** [run-fortran-tests-no-timing] Error 137 (GH Runner out of memory? Cannot reproduce locally.)~

[ywwry66]

Should switching to libomp for dependents be done in this same PR or in separate PRs?

[ywwry66]

fftw's makefile does not support libomp directly, and its cmake system is not feature complete, e.g., no mpi support. Changes to cmake were not very well received upstream. So I am not sure how to proceed here. Ping @carlocab and @cho-m for suggestions.

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[ywwry66]

Keep the PR open for now.

[github-actions[bot]]

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[chenrui333]

probably worth a rebase after https://github.com/Homebrew/homebrew-core/pull/224410

[dimpase]

fftw's makefile does not support libomp directly, and its cmake system is not feature complete, e.g., no mpi support. Changes to cmake were not very well received upstream. So I am not sure how to proceed here. Ping @carlocab and @cho-m for suggestions.

can you post more about fftw issue?

[github-actions[bot]]

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[dimpase]

ping?

[cho-m]

fftw's makefile does not support libomp directly, and its cmake system is not feature complete, e.g., no mpi support. Changes to cmake were not very well received upstream. So I am not sure how to proceed here. Ping @carlocab and @cho-m for suggestions.

You could try autotools workaround of setting flags manually, e.g. maybe via OPENMP_CFLAGS and LIBS? https://github.com/FFTW/fftw3/blob/master/m4/ax_openmp.m4#L24-L25

I can't guarantee binary works as expected; however, these types of workarounds are common in other formulae, e.g.

https://github.com/Homebrew/homebrew-core/blob/03e68e13043c68af740de499f37074c0d680b576/Formula/f/fastme.rb#L35-L36

https://github.com/Homebrew/homebrew-core/blob/03e68e13043c68af740de499f37074c0d680b576/Formula/i/imagemagick.rb#L92-L94

[cho-m]

Added some workarounds for dependents. Not ideal though, e.g.

• fftw will overlink to libomp. Shouldn't impact functionality and loading overhead should be minor but would be better to only have the _omp dylibs linked
• dynare needs some patching to build as Meson doesn't allow using GCC with OpenMP. And dynare cannot be built with LLVM/Clang due to https://github.com/llvm/llvm-project/issues/33025

---

Would likely need further testing to make sure the OpenMP support is actually functional.

[cho-m]

Will need to rebase for gromacs. Also will split out some unrelated changes to make easier to review.

[ywwry66]

Just a word of caution: the OpenBLAS upstream is considering reverting the change that has added and streamlined OpenMP customization enabled by cmake's built-in module (ref. https://github.com/OpenMathLib/OpenBLAS/pull/5413). If that is merged, it will also invalidate this PR, at least in its current form.

[cho-m]

A Makefile workaround could be:

# Workaround to use OpenMP with Apple Clang
if ENV.compiler == :clang
  inreplace "Makefile.system", "+= -fopenmp", "+= -Xpreprocessor -fopenmp"
  inreplace "Makefile.install" do |s|
    s.gsub! ":= -fopenmp", ":= -Xpreprocessor -fopenmp"
    s.gsub! "+= -lgomp", "+= -L#{Formula["libomp"].opt_lib} -lomp"
  end
end

Can't comment if this functionally behaves as expected. But at least no mixed linkage

❯ brew linkage openblas
System libraries:
  /usr/lib/libSystem.B.dylib
Homebrew libraries:
  /opt/homebrew/opt/gcc/lib/gcc/current/libgfortran.5.dylib (gcc)
  /opt/homebrew/opt/gcc/lib/gcc/current/libquadmath.0.dylib (gcc)
  /opt/homebrew/opt/libomp/lib/libomp.dylib (libomp)

❯ PKG_CONFIG_PATH=/opt/homebrew/opt/openblas/lib/pkgconfig pkgconf --cflags openblas
-I/opt/homebrew/Cellar/openblas/0.3.30/include -Xpreprocessor -fopenmp

❯ PKG_CONFIG_PATH=/opt/homebrew/opt/openblas/lib/pkgconfig pkgconf --libs openblas
-L/opt/homebrew/Cellar/openblas/0.3.30/lib -lopenblas

❯ PKG_CONFIG_PATH=/opt/homebrew/opt/openblas/lib/pkgconfig pkgconf --libs --static openblas
-L/opt/homebrew/Cellar/openblas/0.3.30/lib -lopenblas -lpthread -lgfortran -lpthread -lgfortran -L/opt/homebrew/opt/libomp/lib -lomp

[cho-m]

Experimenting with Makefile alternative in

• #236492

[ywwry66]

I am trying to keep the upstream cmake improvements from being reverted so hopefully we don't need the Makefile alternative.

BTW, does the arrayfire test failure on Linux X86_64 need to be addressed?

[cho-m]

BTW, does the arrayfire test failure on Linux X86_64 need to be addressed?

• already fixed #235676

---

Also noting that I will be updating openblas test in separate PR to run cpp_thread_test to verify OpenMP is still functional:

• #236505

[github-actions[bot]]

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[dimpase]

is it still being worked on?

[cho-m]

is it still being worked on?

We first need confirmation that upstream won't revert CMake changes.

Afterward will need to decide if the odd quirks this can introduce are worth the change.

[p-linnane]

We can revisit this once upstream makes a decision.