Silent stores for free

Abstract

Silent store instructions write values that exactly match the values that are already stored at the memory address that is being written. A recent study reveals that significant benefits can be gained by detecting and removing such stores from a program's execution. This paper studies the problem of detecting silent stores and shows that an average of 31% and 50% of silent stores can be detected for very low implementation cost, by exploiting temporal and spatial locality in a processor's load and store queues. We also show that over 83% of all silent stores can be detected using idle cache read access ports. Furthermore, we show that processors that use standard error-correction codes to protect data caches from transient errors can be modified only slightly to detect 100% of silent stores that hit in the cache. Finally, we show that silent store detection via these methods can result in a 11% harmonic mean performance improvement in a two-level store-through on-chip cache hierarchy that is based on a real microprocessor design.