Speculative-aware execution

Abstract

In this paper a new architecture, Speculative-Aware Execution (SAE) is presented that employs speculative-awareness as a means of mitigating the drawbacks of speculative execution which are: useless work (uses speculative values so it produces incorrect results or is done on the wrong path) and redundant work (produces results previously obtained). In order to achieve this, SAE tries to partition the dynamic instruction stream into two disjoint parallel threads: A speculative thread that is partially speculative-aware (p-thread) as it records its speculative state and uses it to avoid useless work (using speculative values) but have no account for its control-flow violations; and a fully speculativeaware thread (f-thread) that has full record of p-thread's speculations, and so can steer p-thread away from incorrect control-flow paths and can accurately identify p-thread's correct work and avoid it, otherwise it would be redundant. By eliminating useless and redundant works, SAE outperforms existing architectures that share similar high-level microarchitecture while incurring only minor hardware additions/changes. Detailed experimental results confirm that SAE indeed reduces the number of useless and redundant computations. We also report an average performance improvement of 18% for the SPEC_INT2000 benchmarks.