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Fix OpenMP on macOS #6114

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merged 3 commits into from
Oct 23, 2024
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cybaol
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@cybaol cybaol commented Aug 24, 2024

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@mvieth
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mvieth commented Aug 25, 2024

Hi, could you explain this a bit, please? Do you know why OpenMP is currently not found on macOS? Shouldn't the FindOpenMP.cmake script handle this? Hardcoding the path /usr/local/opt/libomp/... seems like a bad idea.

By the way, PCL currently has its own FindOpenMP.cmake file, but we are planning to remove that so that CMake's file of the same name is used instead: #6100 I don't know if that changes anything regarding this pull request, I just wanted to mention it.

@valgur
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valgur commented Aug 25, 2024

LightGBM does something similar to support the use of OpenMP via Homebrew: https://github.com/microsoft/LightGBM/blob/v4.5.0/CMakeLists.txt#L161-L183

I would suggest following their approach as it only uses Homebrew as a fallback and does not hard-code any paths.

One other suggestion would be to avoid the use of set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}") in favor of link_libraries(OpenMP::OpenMP_CXX), if possible. The latter makes it easier to provide OpenMP for Clang and AppleClang via a package manager without patching or workarounds. Any non-global linker and include paths cannot be reliably provided via the compiler flags alone.
Specifically, I'm currently working towards getting a better LLVM OpenMP support to Conan and Vcpkg to fill the gap and it would be helpful in that context:

@cybaol
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cybaol commented Sep 20, 2024

libomp is keg-only, which means it was not symlinked into /usr/local,
because it can override GCC headers and result in broken builds.
So must specify manually.

@cybaol cybaol force-pushed the fix-openmp-on-macos branch from 44524c4 to e91faf0 Compare September 20, 2024 15:44
@larshg
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larshg commented Oct 19, 2024

Could we adopt the way they do it from lighthouse - ie https://github.com/microsoft/LightGBM/blob/v4.5.0/CMakeLists.txt#L161-L183.

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larshg commented Oct 20, 2024

Looks good and OpenMp is found again on CIs 👍

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Thank you!

@mvieth mvieth merged commit 56a3172 into PointCloudLibrary:master Oct 23, 2024
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@cybaol cybaol deleted the fix-openmp-on-macos branch October 24, 2024 01:46
@mvieth mvieth added the changelog: fix Meta-information for changelog generation label Nov 19, 2024
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4 participants