[CMake] FindMPI

[Zaak Beekman]

Thanks for the additional pointers Chuck! I am aware that it is preferred
practice to pass the actual compilers rather than the wrappers as FC etc.
but per Brad's advice I think Damian had setup the OpenCoarrays CMake build
system to accept FC=mpif90 etc. and I'm in the process of migrating to the
more normal FC=gfortran etc. approach but I don't want users who use the
old method to get caught out. I'll try setting MPI_{C,etc.}_COMPILER
(rather than MPI_HOME) before calling `find_package(MPI)` and see if that
works as well as setting MPI_HOME does.

Thanks for the tips!

On Mon, Nov 28, 2016 at 10:02 AM Chuck Atkins <chuck.atkins at kitware.com>
wrote:

> Hi Zaak,
>
> When using CMake, it's generally best to use the actual compiler rather
> than any compiler wrappers (with Cray being the exception).  Given that,
> set the CC, CXX, and FC environment variables to the actual compilers you
> want to use and then the MPI_{C,CXX,Fortan}_COMPILER CMake variables the
> MPI wrappers.  FindMPI will then interrogate the MPI wrappers to extract
> the appropriate include and link options.
>
> ----------
> Chuck Atkins
> Staff R&D Engineer, Scientific Computing
> Kitware, Inc.
>
>
> On Mon, Nov 28, 2016 at 9:58 AM, Chuck Atkins <chuck.atkins at kitware.com>
> wrote:
>
> Pass the following CMake options at configure time:
>
> -DMPI_C_COMPILER=/path/to/mpicc
> -DMPI_CXX_COMPILER=/path/to/mpiCC
> -DMPI_Fortran_COMPILER=/path/to/mpif90
>
> ----------
> Chuck Atkins
> Staff R&D Engineer, Scientific Computing
> Kitware, Inc.
>
>
> On Wed, Nov 23, 2016 at 6:05 PM, Zaak Beekman <zbeekman at gmail.com> wrote:
>
> Hi,
>
> I want to be able to pass FC=mpif90 (or FC=$(which mpif90)) and CC=mpicc
> etc. OR also be able to pass a compiler and use FindMPI to add link,
> compile and include flags. I'm encountering an issue when my MPI
> implementation is not on my PATH, I want CMake to be able to look in an
> additional location (our build script can download and build MPICH and by
> default installs it in user space) and also resolve where mpif90 is coming
> from and look there too.
>
> Whats the correct way to pass HINTS or PATHS to FindMPI? i.e., how do I
> specify additional locations to search?
>
> Using `find_package` with HINTS and PATHS means that it doesn't use
> FindMPI. I also tried setting CMAKE_SYSTEM PREFIX_PATH, but I think that's
> a cache variable set early, so it's not having an effect.
>
> It would be great if FindMPI used the realpath of mpif90 etc when passed
> as $FC.
>
> TIA
>
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