Unsafe.compareAndSetFlatValueAsBytes is slow, due to:

1. Array var handles must specialize and hold layout as a constant for C2
2. Need minimum arrayLayout0 and newSpecialArray C2 intrinsics for hot compareAndSetFlatValueAsBytes

Old:

This issue's purpose is to keep track of a potential performance regression introduced with JDK-8351569 (and discovered while investigating JDK-8343420). JDK-8351569 introduced a new overloaded version of Unsafe::getAndSet that is not intrinsified (which is used by e.g. VarHandle::getAndSet). We should evaluate how much of a performance impact this can have and potentially intrinsify it or make it call the intrinsified version.