NDLI: What can we gain by unfolding loops?

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What can we gain by unfolding loops?

Content Provider	ACM Digital Library
Author	Song, Litong Kavi, Krishna
Abstract	Loops in programs are the source of many optimizations for improving program performance, particularly on modern high-performance architectures as well as vector and multithreaded systems. Techniques such as loop invariant code motion, loop unrolling and loop peeling have demonstrated their utility in compiler optimizations. However, many of these techniques can only be used in very limited cases when the loops are "well-structured" and easy to analyze. For instance, loop invariant code motion works only when invariant code is inside loops; loop unrolling and loop peeling work effectively when the array references are either constants or affine functions of index variable. It is our contention that there are many opportunities overlooked by limiting the optimizations to "well structured" loops. In many cases, even "badly-structured" loops may be transformed into "well structured" loops. As a case in point, we show how some loop-dependent code can be transformed into loop-independent code by transforming the loops. Our technique described in this paper relies on unfolding the loop for several initial iterations such that more opportunities may be exposed for many other existing compiler optimization techniques such as loop invariant code motion, loop peeling, loop unrolling and so on.
Starting Page	26
Ending Page	33
Page Count	8
File Format	PDF
ISSN	03621340 15581160
DOI	10.1145/967278.967284
Journal	ACM SIGPLAN Notices (SIGP)
Volume Number	39
Issue Number	2
Language	English
Publisher	Association for Computing Machinery (ACM)
Publisher Date	1983-05-01
Publisher Place	New York
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Loop peeling Quasi-index variable Loop unrolling Quasi-invariant variable Loop quasi invariant code motion
Content Type	Text
Resource Type	Article
Subject	Computer Graphics and Computer-Aided Design Software

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