In practice, PGO with C/C++ gets most of the really valuable low-hanging fruit, provided the test cases aren't too far off from a typical workload. Also, the J

In practice, PGO with C/C++ gets most of the really valuable low-hanging fruit, provided the test cases aren't too far off from a typical workload. Also, the JVM JIT needs a steady-state workload to make good guesses about it's optimizations - if it JITs a bunch of methods and then the load changes such that the optimizations no longer apply (loops iterate differently, inlined methods don't get called as much), the JVM's runtime optimization can be foiled. JITting a very heterogenous program can trick the JVM into finding a local-minimum in native performance (which I guess is still a lot better than actually interpreting java byte code).