@harald sadly, flight recorder isn't of much help. It can tell me what the code is doing when it's slow, but I already know exactly what functions are being called. That function is just slow. What I think happens is that a certain method gets inlined, and when another method gets called 1e9 times, it cannot get inlined because the first one already got inlined first, somehow? Is there a way to inspect the generated machine code? It's crazy it's come to this, but it's the life of a programming language implementation developer I suppose.