RFR: 8339960: GenShen: Fix inconsistencies in generational Shenandoah behavior [v2]

[Kelvin Nilsen]

On Mon, 16 Sep 2024 21:51:40 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> This pull request contains a backport of commit 1a7d597d from the openjdk/shenandoah repository.
>> 
>> The commit being backported was authored by Kelvin Nilsen on 13 Sep 2024 and was reviewed by William Kemper.
>
> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove dependency on utilities/checkedCast.hpp

We are planning to problem-list IU tests and deprecate IU mode.

The failure reported by GHA tests with ExceptionInInitializerError is known and has been fixed upstream. The fix is not feasible for backporting to JDK21.  See https://github.com/openjdk/jdk/pull/14404

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PR Comment: https://git.openjdk.org/shenandoah-jdk21u/pull/90#issuecomment-2356487302