Optimization of Generated Code by Means of Attributes: Local elimination of common redundant sub-expressions

Abstract

This paper deals with the application of the notion of semantic attributes (as developped by D.E. KNUTH [1]) to generation of optimized code. Taking local elimination of common sub-expressions as a starting point, it is demonstrated by means of an example that meta-compilation by attributes allows semantic formalization of classical optimization algorithms. A redundancy attribute, R+, is defined to play an optimizing role in connection with redundant common sub-expressions during compilation without having to undergo a special treatment.

Extending these basic ideas the possibility of creating a set of attributes which define various desirable optimizations in algebraic languages is indicated. Thus a certain methodology, at the level of semantic description of a language, may be outlined. In addition such descriptions offer the advantage of being easy to write, clear and rigourous.