Compile Mac OS binary with xCode AND OpenMP

[w-bruns]

This is indeed possible if one installs the dynamic library for OpenMP from Homebrew (information from Dan Grayson). Some tricks are necessary, but we will do it in the long run.

[w-bruns]

See http://antonmenshov.com/2017/09/09/clang-openmp-setup-in-xcode/

Further information by D. Grayson:

..but the secret seems to be to give g++ the pair of options

-Xpreprocessor -fopenmp

and then to link with

-lomp

---

think that's right. Also, you should upgrade to the latest version of the openmp macro file and then apply this diff, which includes
a hack for trying a pair of options.

gallium$ diff -u m4/ax_openmp-2.69.m4 m4/ax_openmp.m4
--- m4/ax_openmp-2.69.m4 2019-08-07 11:53:41.000000000 -0400
+++ m4/ax_openmp.m4 2019-08-07 12:16:18.000000000 -0400
@@ -79,11 +79,12 @@
 #                -xopenmp (Sun), -omp (Tru64),
 #                -qsmp=omp (AIX),
 #                none
-ax_openmp_flags="-fopenmp -openmp -qopenmp -mp -xopenmp -omp -qsmp=omp none"
+ax_openmp_flags="-fopenmp -openmp -qopenmp -mp -xopenmp -omp -qsmp=omp -Xpreprocessor%-fopenmp none"
 if test "x$OPENMP_[]_AC_LANG_PREFIX[]FLAGS" != x; then
   ax_openmp_flags="$OPENMP_[]_AC_LANG_PREFIX[]FLAGS $ax_openmp_flags"
 fi
 for ax_openmp_flag in $ax_openmp_flags; do
+  ax_openmp_flag=`echo $ax_openmp_flag | sed 's/%/ /g'` ;
   case $ax_openmp_flag in
     none) []_AC_LANG_PREFIX[]FLAGS=$save[]_AC_LANG_PREFIX[] ;;
     *) []_AC_LANG_PREFIX[]FLAGS="$save[]_AC_LANG_PREFIX[]FLAGS $ax_openmp_flag" ;;

[mahrud]

By the way, I'm not sure if you're aware but I've made a homebrew "bottle" for Normaliz based on this formula. It's on a separate homebrew tap, so you need an extra step to install it:

brew tap Macaulay2/tap
brew install normaliz

The key for getting it to build with OpenMP is the following flag:

ENV["OPENMP_CXXFLAGS"] = "-Xpreprocessor\ -fopenmp\ -I#{libomp.opt_include} #{libomp.opt_lib}/libomp.dylib"

Other than that, my PR #335 the only fix to get this to work automatically.

[w-bruns]

Very good! Thanks for your support.

I am preparing a list of questions for you.

[w-bruns]

In order to integrate your "bottle" completely the following steps would be necessary:

1. Insertion into the install scripts (install_normaliz.sh in the main directory and in install_scripts_opt for the optional libaries) with the corresponding changes in the manual

2. integration into out GitHub workflow, in particular for the compilation of an almost static binary that we can download as an artifact.

It would also be good if we could include an M1-binary in our distribution. I am not sure where we could compile it. It is unclear to me whether GitHub actions offer M1 support.

[mahrud]

I'm not sure if I follow. In what way would you like to integrate the bottle?

If you'd like, you can create and maintain your own tap on a repository Normaliz/homebrew-tap by following this guide, but the GitHub Workflows on the Macaulay2 tap already build bottles for Normaliz on linux and macOS catalina and big sur (currently GitHub only supports x86_64 actions), so it wouldn't be any different.

If you do decide to create your own tap, you're welcome to copy the formula I created here as the starting point, and I'll switch the dependencies so your tap is used as the source.

You can also try to get Normaliz to be included in the homebrew's core repository (see this guide), which has the benefit of also building bottles for M1 systems, but that might require some additional work.