JavaScript is a sequential programming language, and Thread-Level Speculation has been proposed to dynamically extract parallelism in order to take advantage of parallel hardware. In previous work, we have showed significant speed-ups with a simple on/off speculation heuristic. In this paper, we propose and evaluate three heuristics for dynamically adapt the speculation: a 2-bit heuristic, an exponential heuristic, and a combination of these two. Our results show that the combined heuristic is able to both increase the number of successful speculations and decrease the execution time for 15 popular web applications.
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