Improving the operation autonomy of SIMD processing elements by using guarded instructions and pseudo branches

Abstract

This paper presents a novel method for improving the operation autonomy of the processing elements (PE) of SIMD-like machines. By combining guarded instructions and pseudo branches it is possible to achieve higher operation autonomy and higher instruction level parallelism than in previous SIMD/ASIMD architectures. The paper shows that it is feasible to avoid most branches and it is also possible to emulate conditional execution on the processing elements, either by using guarded instructions or by using pseudo branches, thus avoiding unnecessary intervention by the array control unit in data-dependant computations. Pseudo branches are used when it is not possible to use guarded instructions. Additionally, they also support the implementation of complex nested if-then-else constructs, improving the execution of irregular dataparallel applications. The paper also shows that the simplicity of the method allows it to be implemented both in fine-grain and coarse-grain SIMD/ASIMD architectures because it does not require significant additional silicon area. Finally, it is shown that pseudo branches can be used to control the power saving of those processing elements that have instructions nullified.