Load redundancy removal through instruction reuse

Instruction reuse techniques have been developed to detect and remove redundancy at runtime. By maintaining the execution history of an instruction, reuse techniques detect if a subsequent execution of an instruction will yield the same result as its previous execution, and if this is the case, the result is made available to dependent instructions without executing the instruction. This approach eliminates same instruction redundancy, that is, redundancy across different dynamic instances of the same static instruction. However, the main limitation of existing instruction reuse techniques is that they do not detect or eliminate different instruction redundancy, that is, redundancy across dynamic instances of statically distinct instructions. We present instruction reuse techniques for load redundancy removal that eliminate both same and different instruction redundancy. We first present a study that shows that in addition to significant levels of same instruction redundancy (average of 20%), load instructions also contain high levels (average of 35%) of different instruction redundancy arising at other load or store instructions. We also describe studies that characterize the behavior of the redundancy and develop a hardware implementation guided by this characterization. Our experiments show that our techniques yield IPC improvements of up to 11% and reduces off-chip traffic due to cache misses by as much as 32% for SPECint95 benchmarks