In this chapter we present a general framework for assignment motion based program transformations that covers all the applications considered in Chapter 6: PDCE, PFCE, PRAE and UPRE. Within this framework the interleaving of admissible assignment motions and eliminations can be investigated in a general setting. Section 7.1 presents the foundation for this framework. The instances of the framework, motion-elimination couples, combine assignment motions with eliminations. As the presence of second order effects requires to apply the component transformations repeatedly, this process raises the following questions of primary interest:
Is the process confluent, i. e. is the final result independent from the application order? Section 7.2 is devoted to this question.
What are the additional costs (compared to the elementary transformations) in terms of computational complexity? This question is addressed in Section 7.3.
Section 7.4 finally considers UPRE as a more ambitious application for reasoning within the framework.
Basic Block Elementary Transformation Program Point Expression Motion Program Path
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