Design and evaluation of compact ISA extensions

The modern embedded market massively relies on RISC processors. The code density of such processors directly affects memory usage, an expensive resource. Solutions to mitigate this issue include code compression techniques and ISAs extensions with reduced instructions bit-width, such as Thumb2 and MicroMIPS. This paper proposes a 16-bit extension to the SPARC processor, the SPARC16. Additionally, we provide the first methodology for generating 16-bit ISAs and evaluate compression among different 16-bit extensions. SPARC16 programs can achieve better compression ratios than other extensions, attaining results as low as 67%. Moreover, SPARC16 reduces cache miss rates up to 9%, requiring smaller caches than SPARC processors to achieve the same performance; a cache size reduction that can reach a factor of 16.