RFR: 8341708: Optimize safepoint poll encoding with smaller poll data offset [v2]

[Aleksey Shipilev]

On Thu, 10 Oct 2024 02:50:47 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Shuffle things around: keep the accessors in JavaThread
>
> src/hotspot/share/runtime/thread.hpp line 140:
> 
>> 138:  protected:
>> 139:   // Poll data is used in generated code for safepoint polls.
>> 140:   SafepointMechanism::ThreadData _poll_data;
> 
> Should this be private and you can add `friend class JavaThread` to this class. Also, the accessor below should be moved to `JavaThread`, too. Comments explaining that it is put here only for offset optimization would be great.

I tried to avoid this kind of coupling between `Thread` and `JavaThread`, but I don't mind go that way as well. This is would also avoid the awkwardness of having `JavaThread::polling_data_*()` accessors all around our code calling essentially the superclass accessor otherwise. See new commit. I am re-running tests now.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21405#discussion_r1795027052