Browsing by Subject "General purpose processors"

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    Exploring Instruction Fusion Opportunities in General Purpose Processors
    (IEEE Press, 2023-12-18) Singh, Sawan; Perais, Arthur; Jimborean, Alexandra; Ros, Alberto; Ingeniería y Tecnología de Computadores
    The Complex Instruction Set Computer (CISC) paradigm has led to the introduction of instruction cracking in which an architectural instruction is divided into multiple microarchitectural instructions (μ-ops). However, the dual concept, instruction fusion is also prevalent in modern microarchitectures to maximize resource utilization. In essence, some architectural instructions are too complex to be executed as a unit, so they should be cracked, while others are too simple to waste resources on executing them as a unit, so they should be fused with others. In this paper, we focus on instruction fusion and explore opportunities for fusing additional instructions in a high- performance general purpose pipeline. We show that enabling fusion for common RISC-V idioms improves performance by 7%. Then, we determine experimentally that enabling fusion only for memory instructions achieves 86% of the potential of fusion in this particular case. Finally, we propose the Helios microarchitecture, able to fuse non-consecutive and non-contiguous memory instructions, and discuss microarchitectural changes required to do so efficiently while preserving correctness. Helios allows to fuse an additional 5.5% of dynamic instructions, yielding a 14.2% performance uplift over no fusion (8.2% over baseline fusion).