8370039: GenShen: array copy SATB barrier improvements

[earthling-amzn]

When an array copy happens concurrently with old and young marking, Shenandoah's generational mode walks over the array twice. This is unnecessary and increases the workload for marking threads. It also has been unconditionally enqueuing old references during a young mark. This is also unnecessary and also increases marking workload. Finally, the barrier went through a somewhat complicated decision process based on affiliation of the region where the array resides. However, the barrier must consider the affiliation of objects that are pointed at by array elements.

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• JDK-8370039: GenShen: array copy SATB barrier improvements (Enhancement - P4)

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