Java doesn't have that many x86 specific optimisations actually. It does some auto-vectorisation, it supports things like AES-NI and other specialised hw instru

Java doesn't have that many x86 specific optimisations actually. It does some auto-vectorisation, it supports things like AES-NI and other specialised hw instructions, but, those are easy to port to ARM. The vast bulk of the effort in modern JVM compiler optimisations is more at the program structural level: removing allocations, merging methods together so they can be optimised as a whole, removing abstraction, and so on. All that stuff is CPU independent.