[YZF]

I'd be interested in seeing the code. I guess my perspective is that with C++ or C getting something to run fast is a process. The first naive implementation will run pretty fast with a good compiler but then you whip out the profiler and look at the generated assembly. It's not just the language it's also the tooling. As an example, you might find that to make good utilization of SSE you want to process multiple matrices concurrently. You may arrange your input data such that you can quickly load the corner element of 4 matrices into an SSE register. You may further rearrange things so that you hide the latency of certain instructions. A good compiler can do some of that for you but the biggest thing is having visibility and being able to exert control at this level. This is often an order of magnitude difference in performance.

Now with a VM you can't really do that. Even if you could for a given implementation of the VM you might get terrible performance somewhere else. The run anywhere VM approach means you're giving up the ability to fine tune things and there's really no way around that. All you can do is try to minimize the impact and I guess JIT is one way. It's certainly true it's a lot faster than it used to be but presumably there are some sweet spots, patterns the JIT is very good at, and some less than sweet spots, patterns where it's not, and your visibility and ability to engineer things is reduced...