Question about assumed-rank assumed-type

[wangzpgi]

I have a question about how assumed rank array and assumed type is being used in OpenMPI. I am building openmpi 3.1.3, and I can see that in the configuration step, it checks whether the compiler being used supports dimension(..), type(*), however once it's verified, I don't see this syntax being used anywhere in the source code. Only one place mentions about assumed-rank is "gen-mpi-sizeof.pl" where it does not use this syntax after all. Could you please let me know why this syntax needs to be checked in the configuration step? Thanks.

[jsquyres]

The gen-mpi-sizeof.pl script is used to generate the relevant Fortran bindings for MPI_SIZEOF. The only place that TYPE(*), DIMENSION(..) is mentioned in there is in the comments (saying that if all compilers supported TYPE(*), DIMENSION(..), this script wouldn't be necessary 😄).

Open MPI currently uses "ignore TKR"-style directives for choice buffers, not TYPE(*), DIMENSION(..).

It's on the to-do/someday list to add real support for TYPE(*), DIMENSION(..).

I think we added that configure check when we had an active Fortran person working on the code, and the thought was that TYPE(*),DIMENSION(..) support could have been added in that timeframe. Unfortunately, it didn't happen back then, and has kinda fallen lower on the priority list since then.

[wangzpgi]

Thank you very much for your explanation. Now it makes sense.

[jsquyres]

@wangzpgi Actually, @ggouaillardet literally just updated an old PR as a first foray into supporting this kind of stuff. If you're interested, have a look at #6569.

I would imagine that this stuff would be destined for Open MPI v5.0.x at the earliest -- not the v4.0.x series.

[wangzpgi]

@jsquyres Thanks for your updated information!