RFR: 8337511: Implement JEP-404: Generational Shenandoah (Experimental) [v3]

[Roman Kennke]

On Fri, 11 Oct 2024 22:00:55 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/c1/shenandoahBarrierSetC1.cpp line 75:
>> 
>>> 73: 
>>> 74:   // Create a mask to test if the marking bit is set.
>>> 75:   // TODO: can we directly test if bit is set?
>> 
>> That comment here is quite justified, IMO. I'm pretty sure that we could test for the flag in a single instruction, instead of doing the and-cmp sequence and even allocating a new register. Unless of course when C1 LIR can't represent it. Have you tried to implement that and failed, and therefore remove the comment?
>
> @shipilev and I looked at this: https://github.com/openjdk/jdk/pull/19180#discussion_r1609666303. The performance change was insignificant.

ok.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21273#discussion_r1799832437