Dynamic recompilation and profile-guided optimisations for a .NET JIT compiler

The paper describes the design and implementation of an adaptive recompilation framework for Rotor, a shared source implementation of the common language infrastructure (CLI) that can increase program performance through intelligent recompilation decisions and optimisations based on the program´s past behaviour. Our extensions to Rotor include a low overhead run-time-stack based sampling profiler that identifies program hotspots. At the first level of optimisation, the compiler uses a fast yet effective linear scan algorithm for register allocation. Hot methods can be instrumented to collect basic-block, edge and call-graph profile information. Profile-guided optimisations driven by online profile information are used to further optimise heavily executed methods at the second level of recompilation. An evaluation of the framework using a set of test programs shows that performance can improve by a maximum of 42.3% and by 9% on average. Our results also show that the overheads of collecting accurate profile information through instrumentation to an extent outweigh the benefits of profile-guided optimisations in our implementation, suggesting the need for implementing techniques that can reduce such overheads. A flexible and extensible framework design implies that additional profiling and optimisation techniques can easily be incorporated to further improve performance.