(Cmake, Trilinos)clang: error: unsupported option '-fopenmp' - cmake

Question

platform:macOS 11.1
when I tried to configure Trilinos, I met a problem and I can not handle it.
The following command is used to compile Trilinos:
#!/bin/bash
rm -rf CMakeCache.txt
rm -rf CMakeFiles
rm -rf CMakeCache.txt
cmake \
-D CMAKE_INSTALL_PREFIX:PATH=/Users/weiqiangguo/Downloads/Trilinos/build \
-D CMAKE_BUILD_TYPE=Release \
-D BUILD_SHARED_LIBS:BOOL=ON \
\
-D TPL_ENABLE_MPI:BOOL=ON \
-D TPL_ENABLE_BLAS:BOOL=ON \
-D TPL_ENABLE_LAPACK:BOOL=ON \
-D TPL_ENABLE_Pthread:BOOL=ON \
-D TPL_ENABLE_HWLOC:BOOL=ON \
-D TPL_ENABLE_HDF5:BOOL=ON \
-D TPL_ENABLE_SCALAPACK:BOOL=ON \
-D TPL_ENABLE_SuperLU:BOOL=ON \
-D TPL_ENABLE_SuperLUDist:BOOL=ON \
-D TPL_ENABLE_METIS:BOOL=ON \
-D TPL_ENABLE_ParMETIS:BOOL=ON \
\
-D ML_ENABLE_SuperLU:BOOL=OFF \
\
-D CMAKE_C_COMPILER:STRING="mpicc" \
-D CMAKE_CXX_COMPILER:FILEPATH=/usr/local/bin/mpicxx \
-D CMAKE_Fortran_COMPILER:STRING="mpif90" \
-D CMAKE_CXX_FLAGS:STRING="-O3 -g -fopenmp" \
\
-D TPL_SCALAPACK_LIBRARIES='/usr/local/lib/libscalapack.dylib' \
\
-D Teuchos_ENABLE_COMPLEX=ON \
\
-D Trilinos_ENABLE_ALL_PACKAGES:BOOL=OFF \
-D Trilinos_ENABLE_ALL_OPTIONAL_PACKAGES:BOOL=OFF \
-D Trilinos_ENABLE_ML:BOOL=ON \
-D Trilinos_ENABLE_Belos:BOOL=ON \
-D Trilinos_ENABLE_Epetra:BOOL=ON \
-D Trilinos_ENABLE_EpetraExt:BOOL=ON \
-D Trilinos_ENABLE_Ifpack:BOOL=ON \
-D Trilinos_ENABLE_Amesos:BOOL=ON \
-D Trilinos_ENABLE_Anasazi:BOOL=ON \
-D Trilinos_ENABLE_NOX:BOOL=ON \
-D Trilinos_ENABLE_Teko:BOOL=ON \
-D Trilinos_ENABLE_Galeri:BOOL=ON \
-D Trilinos_ENABLE_OpenMP:BOOL=OFF \
-D Trilinos_ENABLE_PyTrilinos:BOOL=ON \
\
-D MPI_BASE_DIR:FILEPATH="/usr/local/Cellar/open-mpi" \
-D PYTHON_EXECUTABLE:FILEPATH="/usr/bin/python3" \
-D SuperLU_LIBRARY_DIRS:FILEPATH="/usr/local/lib" \
-D SuperLU_INCLUDE_DIRS:FILEPATH="/usr/local/include" \
-D SuperLUDist_LIBRARY_DIRS:FILEPATH="/usr/local/lib" \
-D SuperLUDist_INCLUDE_DIRS:FILEPATH="/usr/local/include" \
../
The error information is shown below:
Probing the environment ...
-- USE_XSDK_DEFAULTS='FALSE'
-- BUILD_SHARED_LIBS='ON'
-- CMAKE_BUILD_TYPE='Release'
-- MPI_BASE_DIR='/usr/local/Cellar/open-mpi'
-- MPI_BIN_DIR='/usr/local/Cellar/open-mpi/bin'
-- MPI_USE_COMPILER_WRAPPERS='ON'
-- Leaving current CMAKE_C_COMPILER=mpicc since it is already set!
-- Leaving current CMAKE_CXX_COMPILER=/usr/local/bin/mpicxx since it is already set!
-- Leaving current CMAKE_Fortran_COMPILER=mpif90 since it is already set!
-- MPI_EXEC='/usr/local/bin/mpiexec'
-- The C compiler identification is AppleClang 12.0.0.12000032
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/local/bin/mpicc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- CMAKE_C_COMPILER_ID='AppleClang'
-- CMAKE_C_COMPILER_VERSION='12.0.0.12000032'
-- The CXX compiler identification is AppleClang 12.0.0.12000032
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - failed
-- Check for working CXX compiler: /usr/local/bin/mpicxx
-- Check for working CXX compiler: /usr/local/bin/mpicxx - broken
CMake Error at /Applications/CMake.app/Contents/share/cmake-3.20/Modules/CMakeTestCXXCompiler.cmake:59 (message):
The C++ compiler
"/usr/local/bin/mpicxx"
is not able to compile a simple test program.
It fails with the following output:
Change Dir: /Users/weiqiangguo/Downloads/Trilinos/build/CMakeFiles/CMakeTmp
Run Build Command(s):/usr/bin/make -f Makefile cmTC_690b0/fast && /Library/Developer/CommandLineTools/usr/bin/make -f CMakeFiles/cmTC_690b0.dir/build.make CMakeFiles/cmTC_690b0.dir/build
Building CXX object CMakeFiles/cmTC_690b0.dir/testCXXCompiler.cxx.o
/usr/local/bin/mpicxx -O3 -g -fopenmp -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX11.1.sdk -std=gnu++14 -MD -MT CMakeFiles/cmTC_690b0.dir/testCXXCompiler.cxx.o -MF CMakeFiles/cmTC_690b0.dir/testCXXCompiler.cxx.o.d -o CMakeFiles/cmTC_690b0.dir/testCXXCompiler.cxx.o -c /Users/weiqiangguo/Downloads/Trilinos/build/CMakeFiles/CMakeTmp/testCXXCompiler.cxx
clang: error: unsupported option '-fopenmp'
make[1]: *** [CMakeFiles/cmTC_690b0.dir/testCXXCompiler.cxx.o] Error 1
make: *** [cmTC_690b0/fast] Error 2
CMake will not be able to correctly generate this project.
I really don't know how to fix it. I also tried to set gcc complier as homebrew gcc instead of clang.
Could anyone help me with this?

Answer 1

Xcode toolchains have no support for OpenMP.
There is no technical reason other than that they want you to use the Apple specific APIs instead (which are obviously not equivalent).
To use OpenMP, you can use LLVM Clang/libc++/libopenmp which you should be able to install through Homebrew:
brew install --with-toolchain llvm
or build from source yourself.