A register window scheduling method for prolog

Abstract

This paper describes a windowed register file management technique for Prolog that we call “SORWT'’ (Splittable Overlapped Register Window Technique). This scheme is implemented in our Prolog system. Two pointers, the CWP (Current Window Pointer) and TWP (Top Window Pointer), are used with the register file so that the environment, choice point and arguments can be stored in register windows. This greatly reduces the number of memory accesses and procedure call/return overhead. This paper describes in detail how Warren instructions can be implemented in a windowed register file system. A mapping function between register windows and memory window areas and register file overflow/underflow handling algorithms are also presented. In addition, to cope with argument overflow problems in a window, the concept of extended windows is proposed.

Thirty benchmark programs are used to study the following effects: performance issue of SORW versus conventional stacked register windows; optimal register file and window sizes; argument overflow rate; and the efficiency of extended windows.