Fixes a wrong answer from MPI_Ireduce when the red_sched_chain()
path was taken (which only happens for np<=4 and mesgsize>=64k).
The way libnbc treats MPI_IN_PLACE is to set sbuf == rbuf, and
whether an algorithm will work cleanly or not after that depends on the
details.
In this case the last steps of the algorithm amounted to
(right neighbor is sending us reduction results from ranks 1..n-1)
recv into rbuf from right neighbor
add the contribution from our sbuf into rbuf
this would be fine in general, but if sbuf==rbuf, that recv overwrites
the sbuf. I changed it to recv into a tmpbuf if MPI_IN_PLACE was used.
Signed-off-by: Geoffrey Paulsen <gpaulsen@us.ibm.com>
045d0c5f4c