Abstract

This is an informal note intended for limited distribution. The text will reappear in my dissertation; it appears here for interested parties who don’t want to wait. The explication of the technique is a rough sketch, and assumes you are familiar with my paper “Data-Flow Analysis and Type Recovery in Scheme.” 1 Copy propagation Copy propagation is a standard code improvement technique that is based on data-flow analysis. It is, for example, treated in chapter 10 of the Dragon book. Copy propagation essentially is removing variables that are just redundant copies of other variables. That is, if a reference x+3 to a variable x has only defs of the form x: = y,andy is unchanged along intervening control paths, then we can substitute y for its copy x: y+3. If we can do this with all the references to x, then we can remove the assignment to x completely. In Scheme, copy propagation is handled in some cases by simple We can substitute y for x in:-substitution. (let ((x y))

Citations

4	Useless-variable elimination. Working note #2 - Shivers - 1990
2	Compilation by Program Transformation - Aho, Ullman - 1986
2	A conference-length version of this appears in POPL 89.) David Kranz. ORBIT: An Optimizing Compiler for Scheme. YALEU/DCS/RR-632 - dissertation - 1989
2	A conference-length version of this appears in SIGPLAN 86.) Olin Shivers. Control-flow analysis in Scheme - dissertation, University - 1988
2	Data-flow analysis and type recovery in Scheme - OlinShivers - 1990