Optimizing software data prefetches with rotating registers

Software data prefetching is a well-known technique to improve the performance of programs that suffer many cache misses at several levels of memory hierarchy. However, it has significant overhead in terms of increased code size, additional instructions, and possibly increased memory bus traffic due to redundant prefetches. This paper presents two novel methods to reduce the overhead of software data prefetching and improve the program performance by optimized prefetch scheduling. These methods exploit the availability of rotating registers and predication in architectures such as the Itanium^TM architecture. The methods (I) minimize redundant prefetches, (2) reduce the number of issue slots needed for prefetch instructions, and (3) avoid branch mispredict penalties - all with minimal code size increase. Compared to traditional data prefetching techniques, these methods (i) do not require loop unrolling, (ii) do not require predicate computations and (iii) require fewer machine resources. One of these methods has been implemented in the Intel Production Compiler for the ItaniumTM processor. This technique is compared with traditional approaches for software prefetching and experimental results are presented based on the floating-point benchmark suite of CPU2000