Compiling C code with openmp using clang-cl

Question

I am trying to compile C code in Visual Studio using Clang-Cl (via llvm-vs2014 in the platform toolset) with openmp code. When I enable openmp with /openmp I get a warning in clang-cl.exe that it was not used during compilation and my test code confirms that openmp is not working.

In addition I've tried Clang 3.7 with Microsoft CodeGen but it doesn't appear to support openmp yet (as verified by code).

Switching to Visual Studio 2015 allows the code to work but my default code (without any openmp) runs 50% slower.

Is there some way of getting openmp to work with the llvm-vs2014 platform toolset? Should I be using something outside of visual studio to get this to work?

I've switched to using mingw - w64 for all my Windows C code — Jimbo
– Jimbo, Commented May 13, 2018 at 15:12
The answer I posted at stackoverflow.com/a/68378031/7268445 may help you / some future reader out. — Bart
– Bart, Commented Jul 14, 2021 at 12:27

Matthias · Accepted Answer · 2016-12-05 15:46:59Z

1

You can use:

clang -Xclang -fopenmp -l .\libiomp5md.lib

(note, though, that this is not officially supported by Microsoft)

Obviously, you have to have a copy of OpenMP runtime library. You can get and build it from https://www.openmprtl.org/.

Alternatively, you can build clang compiler along with OpenMP RTL yourself, from http://clang.llvm.org/.

edited Dec 5, 2016 at 15:46

Matthias

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answered May 31, 2016 at 11:49

Andrey Bokhanko

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4 Comments

Regis Portalez Over a year ago

please provide a prebuilt runtime.

Andrey Bokhanko Over a year ago

Pre-built OpenMP runtime is included in clang Windows/Linux/FreeBSD binaries: llvm.org/releases/download.html

Regis Portalez Over a year ago

indeed. This is true since version 3.8. Could you add that in the answer please and i delete my downvote.

Royi Over a year ago

They have it in 5.0.2 but they stopped in 6.0.0 (Which doesn't include OpenMP). Is there a way to enable OpenMP with clang-cl.exe?

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