JuliusC: a practical approach for the analysis of divide-and-conquer algorithms

  • Authors:
  • Paolo D'Alberto;Alexandru Nicolau

  • Affiliations:
  • School of Information and Computer Science, University of California at Irvine;School of Information and Computer Science, University of California at Irvine

  • Venue:
  • LCPC'04 Proceedings of the 17th international conference on Languages and Compilers for High Performance Computing
  • Year:
  • 2004

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Abstract

The development of divide and conquer (D&C) algorithms for matrix computations has led to the widespread use of high- performance scientific applications and libraries. In turn, D&C algorithms can be implemented using loop nests or recursion. Recursion is extremely appealing because it is an intuitive means for the deployment of top-down techniques, which exploit data locality and parallelism naturally. However, recursion has been considered impractical for high-performance codes, mostly because of the inherent overhead of the division process into small subproblems. In this work, we develop techniques to model the behavior of recursive algorithms in a way suitable for use by a compiler in estimating and reducing the division process overheads. We describe these techniques and JuliusC, a (lite) C compiler, which we developed to exploit them. JuliusC unfolds the application call graph (partially) and extracts the relations among function calls. As a final result, it produces a directed acyclic graph (DAG) modeling the function calls concisely. The approach is a combination of compile-time and run-time analysis and both have negligible complexity. We illustrate the applicability of our approach by studying 6 test cases. We present the analysis results and we show how our (optimizing) compiler can use these results to increase the efficiency of the division process between 14 to 20 million times, for our codes.