Towards a Systematic, Pragmatic and Architecture-Aware Program Optimization Process for Complex Processors

Because processor architectures are increasingly complex, it is increasingly difficult to embed accurate machine models within compilers. As a result, compiler efficiency tends to decrease. Currently, the trend is on top-down approaches: static compilers are progressively augmented with information from the architecture as in profile-based, iterative or dynamic compilation techniques. However, for the moment, fairly elementary architectural information is used. In this article, we adopt a bottom-up approach to the architecture complexity issue: we assume we know everything about the behavior of the program on the architecture. We present a manual but systematic process for optimizing a program on a complex processor architecture using extensive dynamic analysis, and we find that a small set of run-time information is sufficient to drive an efficient process. We have experimentally observed on an Alpha 21264 that this approach can yield significant performance improvement on Spec benchmarks, beyond peak Spec. We are currently using this approach for optimizing customer applications.