Iteration Space Slicing and ItsApplication

Program slicing is an analysis that answers questions such as \Which statements might aaect the computation of variable v at statement s?" or \Which statements depend on the value of v computed in statement s?". The answers computed by program slicing are generally a set of statements. We introduce the idea of iteration spacing slicing: we reene program slicing to ask questions such as \Which iterations of which statements might eeect the computation in iterations I of statement s?" or \Which iterations of which statements depend on the value computed by iterations I of statement s?". One application of this general-purpose technique is optimization of interprocessor communication in data-parallel compilers. For example, we can separate a code fragment into 1) those iterations that must be done before a send, 2) those iterations that don't need to be done before a send and don't depend on non-local data and 3), those iterations that depend on non-local data. We examine applications of iteration space slicing to communication optimizations in parallel executions of programs such as stencil computations and block-cyclic Gaussian elimination with partial pivoting. of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for proot or commercial advantage and that copies bear this notice and the full citation on the rst page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior speciic permission and/or a fee. Request permissions from Publications Dept, ACM Inc., fax +1 (212) 869-0481, or [email protected]. Abstract Program slicing is an analysis that answers questions such as \Which statements might aaect the computation of variable v at statement s?" or \Which statements depend on the value of v computed in statement s?". The answers computed by program slicing are generally a set of statements. We introduce the idea of iteration spacing slicing: we reene program slicing to ask questions such as \Which iterations of which statements might eeect the computation in iterations I of statement s?" or \Which iterations of which statements depend on the value computed by iterations I of statement s?". One application of this general-purpose technique is optimization of interprocessor communication in data-parallel compilers. For example, we can separate a code fragment into 1) those iterations that must be …