RFR: 8303252: G1: Return early from Full-GC if no regions are selected for compaction. [v5]

[Ivan Walulya]

On Wed, 1 Mar 2023 11:18:37 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

>> Please review this change to return early from full-gc in case no regions have been selected as targets for compaction. 
>> To skip  `phase3_adjust_pointers` and `phase4_do_compaction()`, we need to decouple cleanup work that was piggybacked onto these phases. Thus, the `phase5_` is introduced to do the cleanup.
>> 
>> Testing: Tier 1-3.
>
> Ivan Walulya has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove extra logging

Thanks for the reviews!

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PR: https://git.openjdk.org/jdk/pull/12768