The correct way of building MPI program using Cmake

[Last update on Feb 18, 2018]

Many posts on this topic appear outdated. Modern cmake is centered around target-specific configurations. A correct way of building MPI program with cmake (version 3.10.2 for instance) would be:

find_package(MPI REQUIRED)
add_executable(my_mpi_bin src1.cpp src2.cpp)
target_include_directories(my_mpi_bin PRIVATE ${MPI_CXX_INCLUDE_PATH} src1.h src2.h)
target_compile_options(my_mpi_bin PRIVATE ${MPI_CXX_COMPILE_FLAGS} my_compile_flags)
target_link_libraries(my_mpi_bin ${MPI_CXX_LIBRARIES} ${MPI_CXX_LINK_FLAGS} my_link_flags)

If the MPI implementation (MPICH-3.2 for instance) is installed at certain location that cmake is unable to find automatically, explicitly specify the path. For example:

cmake \
-DMPI_CXX_COMPILER=/usr/local/mpich-install/bin/mpicxx \
-DMPI_C_COMPILER=/usr/local/mpich-install/bin/mpicc \
-DMPIEXEC_EXECUTABLE=/usr/local/mpich-install/bin/mpiexec.hydra

MPI_CXX_COMPILER and MPI_C_COMPILER are merely MPI wrappers. They are not the actual compiler/linker. To specify a certain compiler/linker:

cmake \
-DCMAKE_CXX_COMPILER=/usr/local/bin/g++-6.4.0 \
-DCMAKE_C_COMPILER=/usr/local/bin/gcc-6.4.0 \
-DMPI_CXX_COMPILER=/usr/local/mpich-install/bin/mpicxx \
-DMPI_C_COMPILER=/usr/local/mpich-install/bin/mpicc \
-DMPIEXEC_EXECUTABLE=/usr/local/mpich-install/bin/mpiexec.hydra

*Never ever specify CMAKE_CXX_COMPILER and CMAKE_CXX_COMPILER by hardcoding them in the cmake script. This is such a common anti-pattern.

To create a test for the MPI program:

add_test(NAME my_mpi_test
         COMMAND ${MPIEXEC_EXECUTABLE}
         ${MPIEXEC_NUMPROC_FLAG}
         ${MPIEXEC_MAX_NUMPROCS}
         ${MPIEXEC_PREFLAGS}
         ${CMAKE_CURRENT_BINARY_DIR}/my_mpi_bin
         ${MPIEXEC_POSTFLAGS}
         my_arg_1 my_arg_2 ...)

*Prior to cmake 3.10.2, use MPIEXEC instead of MPIEXEC_EXECUTABLE.

What phrase is considered toxic but may apply now? — GG EZ

Reference:
https://cmake.org/cmake/help/v3.9/module/FindMPI.html
http://www.urbandictionary.com/define.php?term=ggez

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