libomp 5.0.1 (new formula) #20589

henryiii · 2017-11-13T14:57:19Z

Add OpenMP for Apple Clang. Apple Clang now has support for OpenMP, but
it has been disabled in the driver and is not included with High Sierra.
It can be built and used, though; this formula will build it and
provides hints on the correct usage.

There have been a few other formula in the past, such as clang-omp, that provided
special compilers and other tricks to add OpenMP. This is not like those; this is for
the built-in system Clang. On at least High Sierra, this is now possible due to the fact
that it is based on a version of Clang (4.0) that has OpenMP support; it's just not built and
included by Apple.

This is the message printed by the formula:

On Apple Clang, you need to add several options to use OpenMP's front end
instead of the standard driver option. This usually looks like:
  -Xpreprocessor -fopenmp -lomp

You might need to make sure the lib and include directories are discoverable if /usr/local is not searched:
  -L/usr/local/opt/libomp/lib -I/usr/local/opt/libomp/include

For CMake, the following will flags will cause the OpenMP::OpenMP_CXX target to be set up correctly:
  -DOpenMP_CXX_FLAGS="-Xpreprocessor -fopenmp -I/usr/local/opt/libomp/include" -DOpenMP_CXX_LIB_NAMES="omp" -DOpenMP_omp_LIBRARY=/usr/local/opt/libomp/lib/libomp.a

And, future thoughts:

Support could be added to FindOpenMP for automatic discovery, at least if the OpenMP::* targets are used. I'm investigating a patch for CMake.

Note: Original idea from https://stackoverflow.com/questions/44380459/is-openmp-available-in-high-sierra-llvm/47230419#47230419

Have you followed the guidelines for contributing?
Have you checked that there aren't other open pull requests for the same formula update/change?
Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
Does your build pass brew audit --strict <formula> (after doing brew install <formula>)?

fxcoudert · 2017-11-13T15:47:58Z

I do not think this is a good idea.

It's not supported by Apple (the front-end option is there currently, but they might remove it in the future)
The library version is not matching the compiler version exactly, and the mismatch might be problematic.
We already ship llvm, which includes OpenMP support (GCC does as well, too)

henryiii · 2017-11-13T16:16:37Z

However, building with a completely different compiler can cause problems; for example, using Boost + llvm 5 vs. Boost + Apple llvm 9 vs. Boost + GCC. This does not require a completely different compiler chain.

ilovezfs · 2017-11-13T16:38:15Z

Agreed with @fxcoudert. This duplicates what's available in the llvm formula. It's already possible to use openmp from the llvm formula with Xcode's clang.

Sorry @henryiii! We look forward to your next contribution.

henryiii · 2017-11-13T17:09:16Z

@ilovezfs , how would you do that? Including /usr/local/opt/llvm\@4/lib/clang/4.0.1/include/ causes errors due to the other files in that directory (not omp.h itself). If I manually copy omp.h to the current directory, and use the line:

clang++ -Xpreprocessor -fopenmp simple.cxx -I. -L/usr/local/opt/llvm/lib -lomp

it works.

henryiii · 2017-11-13T20:34:01Z

If anyone needs it, I've moved the PR contents to a Tap, https://github.com/CLIUtils/homebrew-apple. A cmake include file that conditionally adds this if it's installed is in https://github.com/CLIUtils/cmake/blob/master/PatchOpenMPApple.cmake. I'm using it in GooFit successfully. I'll probably write a blog post about it eventually (which I'll link in the Stack Overflow answers above)

ilovezfs · 2018-02-27T09:41:22Z

@henryiii mind updating this for llvm 5? We'd like to experiment with using

depends_on "libomp"

instead of

depends_on "gcc"
fails_with :clang

for formulae that need openmp.

henryiii · 2018-02-27T09:47:57Z

Okay, though keep in mind, the build and linking line is a bit different than GCC. I can make a PR to CMake to help with that in the future.

ilovezfs · 2018-02-27T09:50:18Z

Okay, though keep in mind, the build and linking line is a bit different than GCC. I can make a PR to CMake to help with that in the future.

Right I think we need some superenv (see https://github.com/Homebrew/brew/tree/master/Library/Homebrew/shims/super) support for it. It would be really nice to be able to have

depends_on "libomp"

"just work"

henryiii · 2018-02-27T09:58:16Z

Done.

ilovezfs · 2018-02-27T09:59:58Z

@henryiii thanks! Have you been able to figure out what the minimum Xcode for this magic to work is?

ilovezfs · 2018-02-27T10:19:21Z

@henryiii the test block seems to pass even if I remove the -Xpreprocessor -fopenmp. It would be great if you could make the test do something that actually fails if that isn't passed.

henryiii · 2018-02-27T10:21:03Z

Okay, will fix that in a minute. Working on adding a travis test on multiple versions of XCode (running, unfortunately it seems, that test block...)

henryiii · 2018-02-27T10:43:16Z

Is there something obvious missing from the test block? I can get that to fail or pass manually, just not when it's part of the formula; then it always passes.

ilovezfs · 2018-02-27T10:45:11Z

I would think the test should fail if the -Xpreprocessor -fopenmp is not passed.

henryiii · 2018-02-27T10:46:25Z

Oh, I thought the rest ran when install ran. Nevermind, I now have a test that fails properly if those parts are removed. I'll commit it in a second.

ilovezfs · 2018-02-27T10:47:35Z

Ah, I see. Yeah you have to manually run brew test --verbose --debug foo

henryiii · 2018-02-27T13:24:55Z

@ilovezfs , it works with XCode 7+, from a simple test. XCode 6 fails. See https://travis-ci.org/henryiii/test_omp . (Build is still finishing for XCode 6, but it will eventually fail)

Is it better to have the caveat print -L$(brew --prefix libomp)/lib -I$(brew --prefix libomp)/include or the actual expanded value of the path (as it does now)? (For me, the unexpanded line is incorrect because I use fish shell)

ilovezfs · 2018-02-27T13:28:52Z

It should use #{opt_lib} and #{opt_include}.

Also, I think we want

depends_on :macos => :yosemite

since that's the minimum version for Xcode 7.

ilovezfs · 2018-02-27T13:45:03Z

Formula/libomp.rb

+      -L#{opt_lib} -I#{opt_include}
+
+    For CMake, the following will flags will cause the OpenMP::OpenMP_CXX target to be set up correctly:
+      -DOpenMP_CXX_FLAGS="-Xpreprocessor -fopenmp -I#{opt_include}" -DOpenMP_CXX_LIB_NAMES="omp" -DOpenMP_omp_LIBRARY=#{opt_lib}/libomp.a


I think by default we'd want to suggest the dylib not the .a

That's a typo, I don't think it even makes a .a.

Fixed. (Actually, this one does make .a and .dylib; the one I had in my tap only made the dylib)

Add OpenMP for Apple Clang. Apple Clang now has support for OpenMP, but it has been disabled in the driver and is not included with High Sierra. It can be built and used, though; this formula will build it and provides hints on the correct usage.

henryiii · 2018-02-28T14:14:07Z

What about adding the bottles? I can see the hashes from Jenkins, should I copy and paste them in?

ilovezfs · 2018-02-28T14:14:58Z

@henryiii no that is handled automatically by brew pull

henryiii · 2018-02-28T14:15:43Z

Oh, okay, thanks. Wasn't sure how that was setup.

ilovezfs · 2018-02-28T14:17:08Z

If you're curious https://github.com/Homebrew/brew/blob/master/Library/Homebrew/dev-cmd/pull.rb#L19-L20

ilovezfs · 2018-02-28T14:20:50Z

Thanks for your first contribution to Homebrew, @henryiii! Without people like you submitting PRs we couldn't run this project. You rock!

henryiii · 2018-03-01T11:58:00Z

I've got a patch I'm working on for CMake's FindOpenMP: https://gitlab.kitware.com/cmake/cmake/merge_requests/1812

ilovezfs closed this Nov 13, 2017

ilovezfs reopened this Feb 27, 2018

ilovezfs mentioned this pull request Feb 27, 2018

Add macOS libs ahead of brewed llvm libs in lib search path Homebrew/brew#3840

Merged

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MikeMcQuaid changed the title ~~libomp 4.0.1 (new formula)~~ libomp 5.0.1 (new formula) Feb 27, 2018

ilovezfs reviewed Feb 27, 2018

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fxcoudert approved these changes Feb 28, 2018

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ilovezfs force-pushed the libomp branch from d5b3d8f to b43e185 Compare February 28, 2018 14:12

ilovezfs approved these changes Feb 28, 2018

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libomp 5.0.1 (new formula)

b43e185

Add OpenMP for Apple Clang. Apple Clang now has support for OpenMP, but it has been disabled in the driver and is not included with High Sierra. It can be built and used, though; this formula will build it and provides hints on the correct usage.

ilovezfs added the new formula PR adds a new formula to Homebrew/homebrew-core label Feb 28, 2018

ilovezfs added the ready to merge PR can be merged once CI is green label Feb 28, 2018

ilovezfs closed this in 3c6486f Feb 28, 2018

henryiii deleted the libomp branch February 28, 2018 19:47

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libomp 5.0.1 (new formula) #20589

libomp 5.0.1 (new formula) #20589

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libomp 5.0.1 (new formula) #20589

libomp 5.0.1 (new formula) #20589

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