Addressing Mode and Bit Extensions to the Thumb-2 Instruction Set Architecture

Abstract

Thumb-2 is the most recent instruction set architecture for ARM processors which are one of the most widely used embedded processors. In this paper, two extensions are proposed to improve the performance of the Thumb-2 instruction set architecture, which are addressing mode extensions and sign/zero extensions combined with data processing instructions. To speed up access to an element of an aggregated data, the proposed approach first introduces three new addressing modes for load and store instructions. They are register-plus-immediate offset addressing mode, negative register offset addressing mode, and post-increment register offset addressing mode. Register-plus-immediate offset addressing mode permits two offsets and negative register offset allows offset to be a negative value of a register content. Post-increment register offset mode automatically modifies the offset address after the memory operation. The second is the sign/zero extension combined with a data processing instruction which allows the result of a data processing operation to be sign/zero extended to accelerate a type conversion. Several least frequently used instructions are reduced to provide the encoding space for the new extensions. Experiments show that the proposed approach improves performance by an average of 8.6% when compared to the Thumb-2 instruction set architecture.