The design of a global optimizer

Abstract

We are constructing a compiler for a high level systems and applications programming language. Because the compiler is required to generate efficient object code, a global optimization phase and register allocation phase are an integral part of the design. It was determined that the familiar optimizations of code motion, redundant expression elimination, and dead code removal would be sufficient. The optimizer design was to be based on the most recent applicable theoretical results, yet simple and straightforward to implement. Traditional approaches were considered inadequate because they assume a primitive intermediate code representation (quadruples), elaborate flow graph constructions, and numerous special cases. High level data flow analysis as proposed by Rosen [1,2] provided the framework we sought. Using his approach, the parse tree of the program, with its high level control structures intact, becomes a suitable intermediate representation. Complex statement structures are analyzed quickly in two tree traversals to determine the solutions to data flow problems.