Automatic and interactive parallelization
McKinley, Kathryn Stuart
Doctor of Philosophy
The goal of this dissertation is to give programmers the ability to achieve high performance by focusing on developing parallel algorithms, rather than on architecture-specific details. The advantages of this approach also include program portability and legibility. To achieve high performance, we provide automatic compilation techniques that tailor parallel algorithms to shared-memory multiprocessors with local caches and a common bus. In particular, the compiler maps complete applications onto the specifics of a machine, exploiting both parallelism and memory. To optimize complete applications, we develop novel, general algorithms to transform loops that contain arbitrary conditional control flow. In addition, we provide new interprocedural transformations which enable optimization across procedure boundaries. These techniques provide the basis for a robust automatic parallelizing algorithm that is applicable to complete programs. The algorithm for automatic parallel code generation takes into consideration the interaction of parallelism and data locality, as well as the overhead of parallelism. The algorithm is based on a simple cost model that accurately predicts cache line reuse from multiple accesses to the same memory location and from consecutive accesses. The optimizer uses this model to improve data locality. It also uses the model to discover and introduce effective parallelism that complements the benefits of data locality. The optimizer further improves the effectiveness of parallelism by seeking to increase its granularity. Parallelism is introduced only when granularity is sufficient to overcome its associated costs. The algorithm for parallel code generation is shown to be efficient and several of its component algorithms are proven optimal. The efficacy of the optimizer is illustrated with experimental results. In most cases, it is very effective and either achieves or improves the performance of hand-crafted parallel programs. When performance is not satisfactory, we provide an interactive parallel programming tool which combines compiler analysis and algorithms with human expertise.