RFR: 8303968: Serial: Use more precise liveness info in Young GC reference processing [v2]

[Kim Barrett]

On Sun, 26 Mar 2023 17:53:22 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Simple refactoring around Young-GC keep-alive-closure.
>> 
>> (I went for the static-local-var approach, as other solutions that I am aware of would expose the is-alive-closure in the header.)
>> 
>> Test: tier1-3
>
> Albert Mingkun Yang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:
> 
>  - review
>  - s1-ref-is-alive

I like the changes to IsAliveClosure::do_oop_work, but I don't like the introduction of
the _is_alive_closure non-local variable of class type with the associated introduction
of the init function.  Also, this is contrary to the style-guide, which says "Avoid non-local
variables with non-constexpr initialization."  Any other comments I might make are
heavily impacted by this.

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Changes requested by kbarrett (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/12975#pullrequestreview-1360258229