Flow-Sensitive Loop-Variant Variable Classification in Linear Time

  • Authors:
  • Yixin Shou;Robert Engelen;Johnnie Birch

  • Affiliations:
  • Florida State University, Tallahassee, FL 32306;Florida State University, Tallahassee, FL 32306;University of Texas at San Antonio, San Antonio, TX 78249

  • Venue:
  • Languages and Compilers for Parallel Computing
  • Year:
  • 2007

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Abstract

This paper presents an efficient algorithm for classifying generalized induction variables and more complicated flow-sensitive loop-variant variables that have arbitrary conditional update patterns along multiple paths in a loop nest. Variables are recognized and translated into closed-form functions, such as linear, polynomial, geometric, wrap-around, periodic, and mixer functions. The remaining flow-sensitive variables (those that have no closed forms) are bounded by tight bounding functions on their value sequences by bounds derived from our extensions of the Chains of Recurrences (CR#) algebra. The classification algorithm has a linear worst-case execution time in the size of the SSA region of a loop nest. Classification coverage and performance results for the SPEC2000 benchmarks are given and compared to other methods.