conf-openblas does not build on macos ARM due to unsupported '-fopenmp'

[nilsbecker]

this is the error i get:

#=== ERROR while compiling conf-openblas.0.2.2 ================================#
# context     2.3.0 | macos/arm64 | ocaml-option-flambda.1 ocaml-option-no-flat-float-array.1 ocaml-variants.5.3.0+options | https://opam.ocaml.org#717e57b54bb7da8f42974d56f9408e807e4a154f
# path        ~/.opam/53/.opam-switch/build/conf-openblas.0.2.2
# command     ~/.opam/opam-init/hooks/sandbox.sh build sh -exc cc $CFLAGS $(PKG_CONFIG_PATH="$(brew --prefix openblas)/lib/pkgconfig:$PKG_CONFIG_PATH" pkg-config --cflags openblas) test.c $(PKG_CONFIG_PATH="$(brew --prefix openblas)/lib/pkgconfig:$PKG_CONFIG_PATH" pkg-config --libs openblas)
# exit-code   1
# env-file    ~/.opam/log/conf-openblas-84329-72df6a.env
# output-file ~/.opam/log/conf-openblas-84329-72df6a.out
### output ###
# +++ brew --prefix openblas
# ++ PKG_CONFIG_PATH=/opt/homebrew/opt/openblas/lib/pkgconfig:/opt/homebrew/opt/openblas/lib/pkgconfig:/opt/X11/lib/pkgconfig:/usr/X11/lib/pkgconfig
# ++ pkg-config --cflags openblas
# +++ brew --prefix openblas
# ++ PKG_CONFIG_PATH=/opt/homebrew/opt/openblas/lib/pkgconfig:/opt/homebrew/opt/openblas/lib/pkgconfig:/opt/X11/lib/pkgconfig:/usr/X11/lib/pkgconfig
# ++ pkg-config --libs openblas
# + cc -I/opt/homebrew/Cellar/openblas/0.3.29/include -fopenmp test.c -L/opt/homebrew/Cellar/openblas/0.3.29/lib -lopenblas
# clang: error: unsupported option '-fopenmp'
# clang: error: unsupported option '-fopenmp'

apparently this comes up in other places too, and https://thelinuxnotes.com/index.php/resolving-clang-error-unsupported-option-fopenmp-on-macos/ suggests installing a different llvm than shipped with the os. i'm hoping there is a simpler solution?

[nilsbecker]

any insights? for all i can tell, currently openblas and therefore owl are not installable on macos