Monotonic evolution: an alternative to induction variable substitution for dependence analysis

  • Authors:
  • Peng Wu;Albert Cohen;Jay Hoeflinger;David Padua

  • Affiliations:
  • Department of Computer Science, University of Illinois, Urbana, IL;A3 Project, INRIA Rocquencourt, 78153 Le Chesnay, France;KAI Software, Intel Americas, Inc., Champaign, IL;Department of Computer Science, University of Illinois, Urbana, IL

  • Venue:
  • ICS '01 Proceedings of the 15th international conference on Supercomputing
  • Year:
  • 2001

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Abstract

We present a new approach to dependence testing in the presence of induction variables. Instead of looking for closed form expressions, our method computes monotonic evolution which captures the direction in which the value of a variable changes. This information is then used in the dependence test to help determine whether array references are dependence-free. Under this scheme, closed form computation and induction variable substitution can be delayed until after the dependence test and be performed on-demand. To improve computative efficiency, we also propose an optimized (non-iterative) data-flow algorithm to compute evolution. Experimental results show that dependence tests based on evolution information matches the accuracy of that based on closed-form computation (implemented in Polaris), and when no closed form expressions can be calculated, our method is more accurate than that of Polaris.