[CMake] Use of mpi compiler / FINDMPI.cmake

[Olivier Pierard]

Dear all,

I'm a little bit confused with the use of findmpi.cmake.  Does anyone
has an example of its usage (for compilation, not yet for running) ?

Since we have two mpi implementations (mpich and openmpi-ib), I set the
compiler as indicated in the preamble of the module and the library to
not found:
  set(MPI_COMPILER ${MPI_ROOT}/bin/mpicxx)
  set(MPI_LIBRARY MPI_LIBRARY-NOTFOUND)
  find_package(MPI)

Cache variables are well set for MPI but not for MPIEXEC (but I don't
care for the moment, it's in a non-standard location):
 MPIEXEC                          MPIEXEC-NOTFOUND
 MPIEXEC_MAX_NUMPROCS             2
 MPIEXEC_NUMPROC_FLAG             -np
 MPIEXEC_POSTFLAGS
 MPIEXEC_PREFLAGS
 MPI_COMPILE_FLAGS
 MPI_EXTRA_LIBRARY               
/softs/openmpi-ib/1.2.8-1/64/gcc/4.1.2/lib64/libmpi.so;/softs/openmpi
 MPI_INCLUDE_PATH                
/softs/openmpi-ib/1.2.8-1/64/gcc/4.1.2/include
 MPI_LIBRARY                     
/softs/openmpi-ib/1.2.8-1/64/gcc/4.1.2/lib64/libmpi_cxx.so
 MPI_LINK_FLAGS                   -Wl,-rpath
-Wl,/softs/openmpi-ib/1.2.8-1/64/gcc/4.1.2/lib64 -Wl,--exp

Now, what do I have to do with these variables ?
More precisely, how can I force the use of the MPI_COMPILER ?  Do I have
to set the CMAKE_CXX_COMPILER to MPI_COMPILER value ?  If yes, how can I
force it because it is initially set to /usr/bin/c++ (I've a cache
option to switch on/off sequential/parallel mode) and it seems
impossible to modify CMAKE_CXX_COMPILER once the variable is set (by the
way, when is it exectly initialized, with enable_language ?).  If that's
the way, I imagine I've to append MPI_LIBRARY, MPI_COMPILE_FLAGS,
MPI_LINK_FLAGS,... to default flags, include dirs,...

Thank you very much for your help,

-- 
Olivier Pierard

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