Register assignment in tree-structured programs

Abstract

Much complex decision-making is performed routinely by the software of a computer system. It is appropriate to study more thoroughly the performance of this built-in decision-making, because it can strongly influence the efficiency of the entire system. One objective of compilers is to produce a reasonably efficient machine-language version of a user's program. Traditionally, one of the best opportunities for improving the compiler-produced machine-language program has been in devising efficient policies for assigning quantities to the computer's registers. The programs of interest here involve flow of control which can be represented by a tree structure. The problem of assigning index registers in such programs is formulated as a (nonserial) dynamic-programming problem. Following the resulting recursion equations leads to a policy which the compiler could follow to minimize costs. The policy decisions specify those steps in the program where particular quantities should be loaded or stored into registers. An example involving a branching program is solved by this method.