CRPC-TR98745						July 1998

Title: Loop Fusion in High Performance Fortran

Authors: Gerald Roth and Ken Kennedy

Submitted July 1998; Appears in the Proceedings of the 1998 ACM
International Conference on Supercomputing, July 1998, Melbourne,
Australia

Abstract:
In this paper we investigate a unique problem associated with fusing loops
within a High Performance Fortran (HPF) program. In particular, we discuss
the issue of performing loop fusion in an HPF compiler when compiling
Fortran90 array assignment statements for execution on a
distributed-memory machine. During compilation of an HPF program,
Fortran90 array assignment statements must be scalarized into loop nests.
We show how a certain class of these loop nests, when fused, can cause
problems for the compiler's distributed-memory code generator. We then
present an algorithm which not only prevents the fusion of these loops,
but also increases the amount of useful fusion that can be performed.

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Gerald Roth
jerry.roth@eng.sun.com
Sun Microsystems

Ken Kennedy
ken@cs.rice.edu
Department of Computer Science
Rice University