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

Paul Sandoz paul.sandoz at oracle.com
Thu Jun 1 21:03:10 UTC 2017

> On 1 Jun 2017, at 09:01, Roland Westrelin <rwestrel at redhat.com> wrote:
>> 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?

It was a nice property that VarHandles avoided the profile pollution of mixed memory buffer usage but that was not the primary reason for the feature. So i would say mildly concerned :-) and robust unsafe access is far more important.

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