The speedup I found on C2 is 2.547 / 1.719 ~= 1.5, the OP's speedup (also on C2) was 0.71 s / 0.38 s ~= 1.9. Not the same factor, but not above 2 either. The benchmark is quite small, so the overhead of setting up the parallel computation might matter. The JDK version might matter as well.

> Graal was competitive with C2's code for mono- and bimorphic scenarios for a much larger number of input functions. I don't recall the exact number, but I believe it was around 25.

If we are talking about a call like Arrays.setAll(array, function) and you have one or two candidates for function, then you are mono- or bimorphic. If you have 25 candidates for function, you are highly polymorphic. I don't understand what you mean by a mono- or bimorphic scenario with up to 25 candidates.

Performance will usually decrease as you transition from a call site with few candidates to one with many candidates. I agree that a factor of 15x looks steep, but it's hard to say more without context. The inliners (Community and Enterprise use different ones) are constantly being tweaked, though that's not my area of expertise. It's very possible that this behaves differently than it did more than a year ago.

If you have a concrete JMH benchmark you can link to and are willing to post to the GraalVM Slack (see signup link from https://www.graalvm.org/community/), that would be great. Alternatively, you could drop me a line at <first . last at oracle dot com>, and I could have a look at a benchmark, without promising anything.