RFR: 8271579: G1: Move copy before CAS in do_copy_to_survivor_space [v2]

[Thomas Schatzl]

On Thu, 5 Aug 2021 12:41:50 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> Propose to move copy before CAS in do_copy_to_survivor_space, as we found this will improve G1 performance. Specjbb shows 3.7% in critical on aarch64, no change in max.
>> 
>> After this change copy_to_survivor in G1 is also aligned with PS's copy_to_survivor.
>
> Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:
> 
>   simplify mark/age adjust

We are currently trying to reproduce these improvements on aarch64 and x64.

Also, please revert the change to the age calculation and file this separately. I think I remember the reason for incrementing the age the way it is done is/was that it is supposed to avoid some forced reloads of the mark word which may or may not be important. Either way it is completely unrelated to this change.

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PR: https://git.openjdk.java.net/jdk/pull/4983