Loop fission is a process normally applied by a compiler to loops to make them faster. The idea is to split larger loop bodies which perform several distinct tasks into separate loops, in the hope that the individual loops can be optimised more effectively in isolation. As far as I’m aware, C2, Hotspot’s JIT compiler, doesn’t do this so you have to do it yourself. I came across a couple of cases where this was profitable recently, and this post uses these as examples.