Increasing and Detecting Memory Address Congruence

• Published in: PACT: Proceedings of the 2002 International Conference on Parallel Architectures and Compilation Techniques; 22-25 Sept. 2002 pp. 18 - 29
• Main Authors: Larsen, Samuel, Witchel, Emmett, Amarasinghe, Saman P.
• Format: Conference Proceeding
• Language: English
• Published: Washington, DC, USA IEEE Computer Society 22.09.2002
• Series: ACM Conferences
• Subjects: Software and its engineering; Software and its engineering > Software notations and tools; Software and its engineering > Software notations and tools > Compilers
• ISBN: 9780769516202; 0769516203
• DOI: 10.5555/645989.674329

A static memory reference exhibits a unique property when its dynamic memory addresses are congruent with respect to some non-trivial modulus. Extraction of this congruence information at compile-time enables new classes of program optimization. In this paper, we present methods for forcing congruence among the dynamic addresses of a memory reference. We also introduce a compiler algorithm for detecting this property. Our transformations do not require interprocedural analysis and introduce almostno overhead. As a result, they can be incorporated into real compilation systems.On average, our transformations are able to achieve a five-fold increase in the number of congruent memory operations. We are then able to detect 95% of these references. This success is invaluable in providing performance gains in a variety of areas. When congruence information is incorporated into a vectorizing compiler, we can increase the performance of a G4 AltiVec processor up to a factor of two. Using the same methods, we are able to reduce energy consumption in a data cache by as much as 35%.