RFR: 8322383: G1: Only preserve marks on objects that are actually moved [v3]

[Thomas Schatzl]

On Fri, 12 Jan 2024 12:02:37 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> The G1 full-GC preserves marks during marking, for all live objects in compaction region. However, not all live objects do actually move. In particular, the start of a compaction chain may have a sediment of all-live objects which would not move, and thus don't need to have their marks preserved.
>> The problem can easily be solved by preserving marks during forwarding. That also seems a more natural place to do that.
>> 
>> Testing:
>>  - [x] hotspot_gc
>>  - [x] tier1
>>  - [ ] tier2
>
> Roman Kennke has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Cleanup
>  - Move forwarded-predicate into G1

Marked as reviewed by tschatzl (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/17159#pullrequestreview-1821993066