find_package(MPI)
if(NOT MPI_CXX_FOUND)
  message(FATAL_ERROR "MPI C++ compiler was not found and is required")
endif()
include_directories(${MPI_CXX_INCLUDE_PATH})
set(EXTRA_FLAGS "${EXTRA_FLAGS} ${MPI_CXX_COMPILE_FLAGS}")
# Look for MPI_Reduce_scatter_block (and MPI_Reduce_scatter as sanity check)
set(CMAKE_REQUIRED_FLAGS "${MPI_C_COMPILE_FLAGS} ${MPI_C_LINK_FLAGS}")
set(CMAKE_REQUIRED_INCLUDES ${MPI_C_INCLUDE_PATH})
set(CMAKE_REQUIRED_LIBRARIES ${MPI_C_LIBRARIES})
check_function_exists(MPI_Reduce_scatter ELEM_HAVE_MPI_REDUCE_SCATTER)
if(NOT ELEM_HAVE_MPI_REDUCE_SCATTER)
  message(FATAL_ERROR "Could not find MPI_Reduce_scatter")
endif()
check_function_exists(
  MPI_Reduce_scatter_block ELEM_HAVE_MPI_REDUCE_SCATTER_BLOCK)
check_function_exists(MPI_Iallgather ELEM_HAVE_MPI3_NONBLOCKING_COLLECTIVES)
check_function_exists(MPIX_Iallgather ELEM_HAVE_MPIX_NONBLOCKING_COLLECTIVES)
check_function_exists(MPI_Init_thread ELEM_HAVE_MPI_INIT_THREAD)
check_function_exists(MPI_Query_thread ELEM_HAVE_MPI_QUERY_THREAD)
check_function_exists(MPI_Comm_set_errhandler ELEM_HAVE_MPI_COMM_SET_ERRHANDLER)
check_function_exists(MPI_Type_create_struct ELEM_HAVE_MPI_TYPE_CREATE_STRUCT)
if(NOT ELEM_HAVE_MPI_TYPE_CREATE_STRUCT)
  message(FATAL_ERROR "Could not find MPI_Type_create_struct")
endif()
# Check for MPI_IN_PLACE (essentially MPI2 support)
set(MPI_IN_PLACE_CODE
    "#include \"mpi.h\"
     int main( int argc, char* argv[] )
     {
         MPI_Init( &argc, &argv );
         float a;
         MPI_Allreduce
         ( MPI_IN_PLACE, &a, 1, MPI_FLOAT, MPI_SUM, MPI_COMM_WORLD );
         MPI_Finalize();
         return 0;
     }")
set(MPI_LONG_LONG_CODE
    "#include \"mpi.h\"
     int main( int argc, char* argv[] )
     {
         MPI_Init( &argc, &argv );
         MPI_Datatype lli = MPI_LONG_LONG_INT;
         MPI_Datatype llu = MPI_UNSIGNED_LONG_LONG;
         MPI_Finalize();
         return 0;
     }")
check_c_source_compiles("${MPI_IN_PLACE_CODE}" ELEM_HAVE_MPI_IN_PLACE)
check_c_source_compiles("${MPI_LONG_LONG_CODE}" ELEM_HAVE_MPI_LONG_LONG)
if(ELEM_USE_64BIT_INTS AND NOT ELEM_HAVE_MPI_LONG_LONG)
  message(FATAL_ERROR 
    "Did not detect MPI_LONG_LONG_INT and MPI_UNSIGNED_LONG_LONG")
endif()
# We cannot simply use check_function_exists, since MPI_Comm_f2c is 
# a macro in some MPI implementations
set(MPI_COMM_F2C_CODE
"#include \"mpi.h\"
 int main( int argc, char* argv[] )
 {
     MPI_Init( &argc, &argv );
     MPI_Fint fint;
     MPI_Comm comm = MPI_Comm_f2c( fint );
     MPI_Finalize();
     return 0;
 }")
check_c_source_compiles("${MPI_COMM_F2C_CODE}" ELEM_HAVE_MPI_COMM_F2C)