[CMake] New, improved FindMPI.cmake

[Alexander Neundorf]

On Thursday 06 March 2008, Doug Gregor wrote:
> The FindMPI module that ships with CMake is rather rudimentary. It
> identifies some variants of MPICH and MPICH2, but leaves users of
> other MPI implementations (Open MPI, LAM-MPI, MS-MPI, etc.) to their
> own devices. It also doesn't account for other compile and link flags
> needed to link against some MPIs. So, I've rewritten it.
>
> The attached FindMPI.cmake module uses a completely different approach
> to detecting the MPI implementation. It starts by looking for the MPI
> compiler driver, which is provided by most MPI implementations to help
> build MPI programs. It then queries the MPI driver to determine what
> flags it uses, based on the various command-line parameters common
> drivers provide (e.g., -showme:compile, -showme, -show), and parses
> those command lines into compile flags, include paths, link flags,
> link libraries, and libraries. If there is no MPI compiler driver, it
> falls back to doing what the current FindMPI module does, probing for
> specific MPICH variants.
>
> This new FindMPI sets quite a few more variables, since it detects
> more information. Of particular note is MPI_LIBRARIES, which will
> store all of the libraries that MPI programs need to link against. In
> the old FindMPI, we only had MPI_LIBRARY and, optionally,
> MPI_EXTRA_LIBRARY, but there is no reason to make this arbitrary
> division. Still, this new FindMPI module still sets MPI_LIBRARY and
> MPI_EXTRA_LIBRARY, for the sake of backward compatibility. See the top
> of the module file for information about the variables this module
> sets.
>
> There are two known issues:
>   1) Microsoft's MPI (MS-MPI) has different directories for 32-bit vs.
> 64-bit libraries. How do we know whether we're building in 64-bit mode
> to select among the two?
>   2) FindMPI.cmake has changed a little on the CMake trunk, but I
> haven't yet incorporated those changes.

Please put this in the bug tracker so it doesn't get lost.

Alex