Lazy code motion

  • Authors:
  • Jens Knoop;Oliver Rüthing;Bernhard Steffen

  • Affiliations:
  • FernUniversität Hagen;University of Dortmund;University of Dortmund

  • Venue:
  • ACM SIGPLAN Notices - Best of PLDI 1979-1999
  • Year:
  • 2004

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Abstract

We present a bit-vector algorithm for the optimal and economical placement of computations within flow graphs, which is as efficient as standard uni-directional analyses. The point of our algorithm is the decomposition of the bi-directional structure of the known placement algorithms into a sequence of a backward and a forward analysis, which directly implies the efficiency result. Moreover, the new compositional structure opens the algorithm for modification: two further uni-directional analysis components exclude any unnecessary code motion. This laziness of our algorithm minimizes the register pressure, which has drastic effects on the run-time behaviour of the optimized programs in practice, where an economical use of registers is essential.