one awesome trick the jit does is in the case of child classes with virtual functions, if there is only one child class used in a run, it can remove the virtual-ness and inline the function used.
so, for example, one place you would see this is if you have distributions, and eg class Distribution has a virtual member function like deviance or some such. However, for a given run of your code, you only ever use one distribution. Also say that the loop that uses the deviance is hot enough that you can see the slowdown from the vtable and the function call. The java jit will inline the deviance function for the distribution you use (assuming the method is small enough, which it often is). The only way to get this behavior in c++ is to lift the decision out of the hot loop and generate one function for each distribution. I've done this and seen noticeable performance gains (10-15% on hours/days long runtimes), but it does not make the code nice to work with.
one awesome trick the jit does is in the case of child classes with virtual functions, if there is only one child class used in a run, it can remove the virtual-ness and inline the function used.
so, for example, one place you would see this is if you have distributions, and eg class Distribution has a virtual member function like deviance or some such. However, for a given run of your code, you only ever use one distribution. Also say that the loop that uses the deviance is hot enough that you can see the slowdown from the vtable and the function call. The java jit will inline the deviance function for the distribution you use (assuming the method is small enough, which it often is). The only way to get this behavior in c++ is to lift the decision out of the hot loop and generate one function for each distribution. I've done this and seen noticeable performance gains (10-15% on hours/days long runtimes), but it does not make the code nice to work with.