Executing an allgather operation on a parallel computer that includes a plurality of compute nodes where the compute nodes are organized into at least one operational group of compute nodes for collective parallel operations of the parallel computer, and each compute node in the operational group is assigned a unique rank. In such a parallel computer, executing an allgather operation may include configuring on each compute node in an operational group of compute nodes a memory buffer with contribution data for an allreduce operation at a rank-dependent position in each memory buffer and zeros in all other positions in each memory buffer and executing on the compute nodes in the operational group, with the entire contents of each memory buffer, an allreduce operation with a bitwise OR function.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with Government support under Contract No. B519700 awarded by the Department of Energy. The Government has certain rights in this invention.