RFR(M): 8181211: C2: Use profiling data to optimize on/off heap unsafe accesses

[Roland Westrelin]

> Yes, it avoided the profile pollution induced by virtual calls to
> multiple buffer implementations by accessing common state, but at the
> cost of taking a hit on uniformly reading the heap object value from a
> field. So i suspect your patch might be marginally improve things in
> certain cases?

This patch tries to counter balance the performance degradation caused
by 8176506 which itself tries to make the unsafe code robuster. So yeah,
marginal improvements are possible but in case of profile pollution, a
significant performance drop is also possible. How much of a concern is
it for varhandles?

Roland.