RFR: 8310680: GenShen: In-place region promotions may fail [v3]

[Y. Srinivas Ramakrishna]

On Fri, 23 Jun 2023 21:08:54 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> There are a few small changes here:
>> * In `op-update-refs-final`, only active regions are aged.
>> * In `op-final-roots`, a region's age may be reset outside of an aging cycle.
>> * When the field used to save `top` before promotion is set, it indicates the region has been chosen for in-place-promotion.
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Assert that promotion conditions hold, rather than rechecking

LGTM except for the second assert that was moved from the test into the assert.

It would be good if the condition for promote-in-place were extracted into a method to avoid inconsistency of use in different places, but I am not sure how that can be done easily or if it's overkill to do so, since the condition is tested and then we set a sentinel that signals that condition for the later step.

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Marked as reviewed by ysr (Committer).

PR Review: https://git.openjdk.org/shenandoah/pull/290#pullrequestreview-1496074064