[RESOLVED] unsupported option '-fopenmp' on Mac OS X about lightgbm HOT 30 CLOSED

@Clovel after installing gcc --without-multilib try to run gcc specific version compiler:
gcc-7 -fopenmp hello_par.c -o hello_par

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Compiling LightGBM with gcc-6 on OSX works:

brew install cmake gcc
cmake -DCMAKE_CXX_COMPILER=g++-6 CMakeLists.txt
make

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brew install gcc --without-multilib

It generated this error:
Error: invalid option: --without-multilib

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By the way, non-Apple LLVM on macOS works just fine, as well. Just use brew install llvm (that'll get 5.0, with OpenMP), and set up the environment for the compiler in /usr/local/opt/llvm.
In Sierra, with Apple Clang based on 3.9, and High Sierra, with Apple Clang based on 4.0, the OpenMP library is disabled on the built-in compiler. (even though the -fopenmp-targets option slipped through!)

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Hi !

I'm trying to install gcc --without-multilib too, but the option seems to have disappeared from brew. The command given by @guolinke does'n work any more.

BTW, im on High Sierra, 10.13.1.

Any luck that you guys have a solution ?

Thanks,
Clovel

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@bartleusink Thank you!
For me it finally worked.

If anybody's interested: I had to additionally link brew to gcc so that g++-6 is in path.

sudo chown -R $USER /usr/local/
brew link --overwrite gcc

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@Clovel
I can't install with option of "--without-multilib" either.
But it's funny that, after I changed " gcc -fopenmp ...... " to " gcc-7 -fopenmp ......", it doesn't return clang error and works!
@piotrek1543 Thank you!

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After installing gcc with
brew install gcc
You can run brew install gcc again and it will show its version.
After that, use
gcc-x -fopenmp file_name.c -o file_name
Replacing the "x" for the version shown in the terminal, using only the first number.

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@Yorko Hi. I tried doing the brew link --overwrite gcc and got this error
Error: No such keg: /usr/local/Cellar/gcc

do you know why?

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@piotrek1543 THANK YOU! Only solution after fighting for hours.

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try with only -openmp...

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Try compiling your .c file using gcc-6

gcc-6 hello.c -o hello -fopenmp

The above command worked for me in my OSX-10.15.2(Catalina) machine after binging with this problem for days

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Actually, It is not tested on OSX now. Will fix soon

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Maybe it'll work with Clang updated, I'll try.

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hi, @Yorko , we currently doesn't have clear plan to support OSX (but it should have). However, this issue is caused by that OpenMP is needed by lightGBM for building, please refer to https://clang-omp.github.io/ for the instuctions

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I'll close this issue first, please feel free to reopen if the problem still there after installing OpenMP properly.

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On mac os sierra, installing OpenMPI with with homebrew and following instructions still resulted in same error. Installing using C++11 mode and with C++ MPI bindings (these were flags for the homebrew recipe) did not fix the error.

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hi @sooheon , i'm not quite sure that you are confusing openMP with openMPI(or just an typo) which doesn't needed by lightGBM by default.
since I don't have an sierra , I'm not quite sure that apple clang has openMP supported on sierra. the 10.11 OSX has the clang version accord to ~3.7, and openMP was default supported since 3.8.

if you using gcc as your default compiler on sierra. the build should succeed.

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Thank you I was indeed confusing OpenMPI and OpenMP

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@bartleusink , thanks for your sharing

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Same problem as BeatricGR! Any ideas?

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@BeatriceGR @ktorimaru
Use following command to install gcc in osx:

brew install gcc --without-multilib

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Please have a look at :
https://stackoverflow.com/a/50313990/3465857

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Can anyone solve my issue:
clang: error: unsupported option '-fopenmp'

I am totally new to terminal and want to use openmp but I am getting above error; I copied and run all the above commands (as mentioned above) but the problem persists. Currently, I am using high Sierra 10.13.6.

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@itzzmeanmol , we're testing compiler with Clang.

would you give a shot of the latest instruction doc

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So in cmakelist we should set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -openmp -std=c++17")?

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@Yassunaga it works but why does specifying the version helps lol

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@yinhaosen because calling gcc defaults to clang on macOS. You need to call GNU gcc

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Hi,

I have the same problem:

clang: error: unsupported option '-fopenmp'

If I do
brew install gcc:
gcc 9.2.0 is already installed, it's just not linked

gcc-9 -o omp_hello -fopenmp omp_hello.c

-bash: gcc-9: command not found

so
brew link gcc
but

Linking /usr/local/Cellar/gcc/9.2.0... 
Error: Could not symlink bin/gfortran
Target /usr/local/bin/gfortran
already exists. You may want to remove it:
  rm '/usr/local/bin/gfortran'

To force the link and overwrite all conflicting files:
  brew link --overwrite gcc

To list all files that would be deleted:
  brew link --overwrite --dry-run gcc

But I need to use Fortran as well! Could you help me??
Kind regards,
Nico

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After trying to run with gcc-9 I'm getting the following message:

Undefined symbols for architecture x86_64: "std::ios_base::Init::Init()", referenced from: __static_initialization_and_destruction_0(int, int) in cczeen3H.o "std::ios_base::Init::~Init()", referenced from: __static_initialization_and_destruction_0(int, int) in cczeen3H.o "std::cout", referenced from: _main in cczeen3H.o "std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)", referenced from: _main in cczeen3H.o ld: symbol(s) not found for architecture x86_64 collect2: error: ld returned 1 exit status

What can I do to try and run with the -fopenmp?

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