Generating Communication for Array Statement: Design, Implementation, and Evaluation

Array statements as included in Fortran 90 or High Performance Fortran (HPF) are a wellaccepted way to specify data parallelism in programs. When generating code for such a data parallel program for a private memory parallel system, the compiler must determine when array elements must be moved from one processor to another. This paper describes a practical method to compute the set of array elements that are to be moved; it covers all the distributions that are included in HPF: block, cyclic, and block-cyclic. This method is the foundation for an efficient protocol for modern private memory parallel systems: for each block of data to be sent, the sender processor computes the local address in the receiver’s address space, and the address is then transmitted together with the data. This strategy increases the communication load but reduces the overhead on the receiving processor. We implemented this optimization in an experimental Fortran compiler, and this paper reports an empirical evaluation on a 64-node private memory iWarp system, using a number of different distributions. Running head: Communication for Array Statements