• Install Openmp
• _openmp Macro
• Openmp For Machine Learning

Full support for OpenMP 3.1 and most of OpenMP 4.0 features (except for offloading) are implemented. This implementation relies on the Intel OpenMP API, and should be used along with Intel® OpenMP. Runtime Library that supports that API (available from www.openmprtl.org).

1. This not only is cleaner than the old method, it will also correctly set the library link line differently from the compile line if needed. In CMake 3.12+, this will even support OpenMP on macOS (if the library is available, such as with brew install libomp). However, if you need to support older CMake, the following works on CMake 3.1+.
2. The OpenMP Examples document has been updated to include the new features found in the OpenMP 5.0 Specification. The latest source codes for the examples are also available on GitHub. Tim.lewis 2020-05-14T09:36:29+00:00.

For those impatient, skip to how to enable OpenMP in packages.

OpenMP support in Xcode

Apple has explicitly disabled OpenMP support in compilers that they ship in Xcode: even though clang had OpenMP support for quite a long time now (great thanks to the folks at Intel providing their library as open source!). In fact, the clang compiler in Xcode can generate all the necessary code for OpenMP. It can be tricked into performing its designed function by using -Xclang -fopenmp flags.

The unfortunate part about this is that Apple is not shipping the necesssary libomp.dylib run-time library needed for OpenMP support. To make things worse, the version of the library you need depends on the clang version used, which Apple obfuscates so that it's non-trivial to reverse-engineer it. Fortunately, some clever folks were able to find the traces in Apple's released source so we can build the binaries that correspond to the clang version used. It is sometimes possible to use a more recent version of the runtime than the version of Apple clang.

OpenMP run-time downloads

The follwing are links to libomp OpenMP run-time built from official LLVM release sources using Xcode compilers. They are signed and support macOS 10.13 (High Sierra) and higher. All tar-balls contain the system tree usr/local/lib and usr/local/include so the recommended installation is: The contained set of files is the same in all tar balls: so you can simply remove those to uninstall. Note that any package you compile against libomp.dylib will need that run-time so you have to ship it with your package or have users install it.

Build	Download	SHA1 checksum
LLVM 10.0.0 Xcode 12+	openmp-10.0.0-darwin17-Release.tar.gz (Release) openmp-10.0.0-darwin17-Debug.tar.gz (Debug)	9bf16a64ab747528c5de7005a1ea1a9e318b3cf0 d4508d3f0c2952c3f984393b088e0b4beab33b58
LLVM 9.0.1 Xcode 11.4 and up (Apple clang 1103.x)	openmp-9.0.1-darwin17-Release.tar.gz (Release) openmp-9.0.1-darwin17-Debug.tar.gz (Debug)	e5bd8501a3f957b4babe27b0a266d4fa15dbc23f c4c8491631504fb060f7c25ec14324d02d617d5b
LLVM 8.0.1 Xcode 11.0-11.3.1 (Apple clang 1100.x)	openmp-8.0.1-darwin17-Release.tar.gz (Release) openmp-8.0.1-darwin17-Debug.tar.gz (Debug)	e4612bfcb1bf520bf22844f7db764cadb7577c28 d6c83918b28405d43950d4b864ca8d1687eed4d1
LLVM 7.1.0 Xcode 10.2-10.3 (Apple clang 1001.x)	openmp-7.1.0-darwin17-Release.tar.gz (Release) openmp-7.1.0-darwin17-Debug.tar.gz (Debug)	6891ff6f83f2ed83eeed42160de819b50cf643cd 34456adde62b9a1047f906e1d7f54990a1c15a34

How to enable OpenMP in packages

• Download the libomp run-time corresponding to the Xcode version you use from the links above
• add -Xclang -fopenmp to CPPFLAGS, add -lomp to LIBS

How you do the latter depends on the package, but if the package does not set these environment variables itself, you can try If that doesn't work, please consult the package's documentation, and liaise with its maintainer. It is also possible to add those flags globally by adding the following to ~/.R/Makevars: but be very careful when doing this, always check your ~/.R/Makevars whenever you upgrade R, macOS or Xcode.

Side notes

It may be possible in principle to build static version of the run-time. That can be done via -DLIBOMP_ENABLE_SHARED=OFF, but has not been tested. There is a potential for chaos when more OMP run-times get loaded into one process. Another interesting test would be to try -DLIBOMP_FORTRAN_MODULES=ON and see which versions are compatible with the GNU Fortran used in R. We are intentionally removing the gomp symlink from the binary so that iomp and gomp don't conflict.

License and sources

All sources were obtained directly from the LLVM releases and copies are also available in the src directory (including the build script). See LICENSE.txt in the sources for the corresponding license and https://openmp.llvm.org/ for details on the OpenMP run-time.

Acknowledgements

Thanks to John Clayden, Kevin Ushey and others who contributed to the discussion and testing.

Install Openmp

Trademark notices

_openmp Macro

• The OpenMP name and the OpenMP logo are registered trademarks of the OpenMP Architecture Review Board.
• Intel is a trademark of Intel Corporation in the U.S. and/or other countries.
• Apple, Xcode and macOS are trademarks of Apple Inc., registered in the U.S. and other countries.

Openmp For Machine Learning

Last modified on 2020/05/01 by Simon Urbanek