During itable/vtable initialization, klass->is_shared() is called frequently. Because there's no specialized implementation of Klass::is_shared(), we end up calling MetaspaceObj::is_shared, which walks the list of shared regions.

JDK-8178351 proposes simplifying MetaspaceObj::is_shared() by doing fewer comparisons. However, in the case of Klass, we can actually use a free bit in Klass::_access_flags to indicate whether the Klass is shared, so we can have an even more optimal implementation of Klass::is_shared().