On the expressiveness of single-pass instruction sequences

TL;DR

This paper investigates the expressive power of single-pass instruction sequences, demonstrating that finite-state behaviors can be generated without jumps using Boolean registers, and analyzing the limitations when goto instructions are used with label bounds.

Contribution

It shows that all regular threads can be produced by single-pass instruction sequences without jumps if Boolean registers are used, and explores restrictions with goto instructions.

Findings

Regular threads can be generated without jumps using Boolean registers.

Bounded labels limit the expressiveness of goto-based instruction sequences.

Single-pass instruction sequences can model all finite-state behaviors.

Abstract

We perceive programs as single-pass instruction sequences. A single-pass instruction sequence under execution is considered to produce a behaviour to be controlled by some execution environment. Threads as considered in basic thread algebra model such behaviours. We show that all regular threads, i.e. threads that can only be in a finite number of states, can be produced by single-pass instruction sequences without jump instructions if use can be made of Boolean registers. We also show that, in the case where goto instructions are used instead of jump instructions, a bound to the number of labels restricts the expressiveness.