RFR: 8271579: G1: Move copy before CAS in do_copy_to_survivor_space [v4]

[Hamlin Li]

On Tue, 17 Aug 2021 01:45:51 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:
> 
>   Closes JDK-8272070: simplify age calculation

Thanks Thomas, I just saw Albert has been a reviewer too. 
Congratulation @albertnetymk

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