Affine Loop Optimization Based on Modulo Unrolling in Chapel

This paper presents modulo unrolling without unrolling (mod-ulo unrolling WU), a method for message aggregation for parallel loops in message passing programs that use affine ar-ray accesses in Chapel, a Partitioned Global Address Space (PGAS) parallel programming language. Messages incur a non-trivial run time overhead, a significant component of which is independent of the size of the message. Therefore, aggregating messages improves performance. Our optimiza-tion for message aggregation is based on a technique known as modulo unrolling, pioneered by Barua [3], whose purpose was to ensure a statically predictable single tile number for each memory reference for tiled architectures, such as the MIT Raw Machine [18]. Modulo unrolling WU applies to data that is distributed in a cyclic or block-cyclic manner. I