Efficient discovery of regular stride patterns in irregular programs and its use in compiler prefetching

Abstract

Irregular data references are difficult to prefetch, as the future memory address of a load instruction is hard to anticipate by a compiler. However, recent studies as well as our experience indicate that some important load instructions in irregular programs contain stride access patterns. Although the load instructions with stride patterns are difficult to identify with static compiler techniques, we developed an efficient profiling method to discover these load instructions. The new profiling method integrates the profiling for stride information and the traditional profiling for edge frequency into a single profiling pass. The integrated profiling pass runs only 17% slower than the frequency profiling alone. The collected stride information helps the compiler to identify load instructions with stride patterns that can be prefetched efficiently and beneficially. We implemented the new profiling and prefetching techniques in a research compiler for Itanium Processor Family (IPF), and obtained significant performance improvement for the SPECINT2000 programs running on Itanium machines. For example, we achieved a 1.59x speedup for 181.mcf, 1.14x for 254.gap, and 1.08x for 197.parser. We also showed that the performance gain is stable across input data sets. These benefits make the new profiling and prefetching techniques suitable for production compilers.