Efficient and safe-for-space closure conversion

Abstract

Modern compilers often implement function calls (or returns) in two steps: first, a “closure” environment is properly installed to provide access for free variables in the target program fragment; second, the control is transferred to the target by a “jump with arguments (for results).” Closure conversion—which decides where and how to represent closures at runtime—is a crucial step in the compilation of functional languages. This paper presents a new algorithm that exploits the use of compile-time control and data-flow information to optimize funtion calls. By extensive closure sharing and allocation by 36% and memory fetches for local and global variables by 43%; and improves the already efficient code generated by an earlier version of the Standard ML of New Jersey compiler by about 17% on a DECstation 5000. Moreover, unlike most other approaches, our new closure-allocation scheme the strong safe-for-space-complexity rule, thus achieving good asymptotic space usage.