Compile-Time Silent-Store Elimination for Energy Efficiency: an Analytic Evaluation for Non-Volatile Cache Memory

International audienceEnergy-efficiency has become very critical in modern high-performance and embedded systems. In on-chip systems, memory consumes an important part of energy. Emerging non-volatile memory (NVM) technologies, such as Spin-Transfer Torque RAM (STT-RAM), offer power saving opportunities , while they suffer from high write latency. In this paper, we propose a fast evaluation of NVM integration at cache level, together with a compile-time approach for mitigating the penalty incurred by the high write latency of STT-RAM. We implement a code optimization in LLVM for reducing so-called silent stores, i.e., store instruction instances that write to memory values that were already present there. This makes our optimization portable over any architecture supporting LLVM. Then, we assess the possible benefit of such an optimization on the Rodinia benchmark suite through an analytic approach based on parameters extracted from the literature devoted to NVMs. This makes it possible to rapidly analyze the impact of NVMs on memory energy consumption. Reported results show up to 42% energy gain when considering STT-RAM caches