Dynamically accelerating client-side web applications through decoupled execution

The emergence and wide adoption of Web applications have moved the client-side component, often written in JavaScript, to the forefront of computing on the Web. Web application developers try to move more computation to the client side to avoid unnecessary network traffic and make the applications more responsive. Therefore, JavaScript applications are becoming larger and more computation intensive. Trace-based just-in-time compilation have been proposed to address the performance bottleneck in these applications. In this paper, we exploit the extra processing power in multicore systems to further improve the performance of trace-based execution of JavaScript programs. In trace-based engines, a considerable portion of execution time is spent on running guards which are operations inserted in the native code to check if the properties assumed by the compiled code actually hold during execution. We introduce ParaGuard to off-load these guards to another thread, while speculatively executing the main trace. In a manner similar to what happens in current trace-based JITs, if a check fails, ParaGuard aborts the native trace execution and reverts back to interpreting the JavaScript bytecode. We also propose several optimizations including guard branch aggregation and profile-based snapshot elimination to further improve the performance of our technique. We show that ParaGuard can achieve an average of 15% performance improvement over current trace-based compilers using an extra processor on commodity multicore processors.