Analysis of the conditional skip instructions of the HP precision architecture

The HP-PA instruction set allows any arithmetic instruction to conditionally skip the following instruction based on the result of the arithmetic calculation. We have isolated this architectural feature and measured its performance benefit on a set of SPEC benchmark programs. Results indicate that adding the ability to skip to arithmetic instructions yields only a marginal performance benefit (less than 0.3%) for floating point intensive programs. For integer programs, however, the average benefit is between 0.6 and 2.8%. Most of this benefit comes from using arithmetic nullification with the COMICLR and COMCLR instructions. Our results assume a scalar processor, and therefore provide a lower bound on the performance benefit for more aggressive implementations.