[mpiwg-rma] Use of MPI_SHORT_INT, etc with MPI_Accumulate

[Nathan Hjelm]

I have a user who is trying to use MPI_SHORT_INT as the origin and target datatype arguments of MPI_Accumulate. My interpretation of the standard does not allow this type. I am justifying this because of MPI 3-1 § 11.3.4 pp 425:2-8:

Each datatype argument must be a predefined datatype or a derived datatype, where
all basic components are of the same predefined datatype. Both datatype arguments must
be constructed from the same predefined datatype.

MPI_SHORT_INT, MPI_LONG_DOUBLE_INT, etc are not in any of the A.1 tables labeled as "predefined datatypes”. They show up in a separate list of datatypes for reduction functions. Since these datatypes are not “predefined datatypes” and are not composite datatypes of the "same predefined datatype” they are not valid for MPI_Accumulate, MPI_Get_accumulate, etc. Am I wrong in my interpretation?

-Nathan
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