oooooh.
Is there a list somewhere of all the functions that have had such special treatment?
(look for "java_lang_Math" for instance)
But otherwise, assembly overrides for hot paths in execution targets that support them aren’t actually a big secret, just that they’re rarely visible. Think Go has a lot of processed architecture specific assembly for some functions, especially crypto iirc.
Many are implemented in the in-memory intermediate SSA (?) representation the JVM uses for its JIT, so they essentially get compiled down to assembly at the same time as the surrounding bytecode.
Some are implemented as jumps to various native methods, which in turn might be implemented in C++ or assembly. Most intrinsics are available on most platforms: only some of the hand-coded assembly versions are less likely to have wide support.