RFR: 8365055: G1: Merge Heap Roots phase incorrectly clears young gen remembered set every time [v2]

[Thomas Schatzl]

On Mon, 18 Aug 2025 08:34:34 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

>> Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   * fix comment in verification code
>>   * move that G1Policy member to G1CollectedHeap as it's used to verify stuff in G1CollectedHeap (and not used elsewhere anyway)
>
> src/hotspot/share/gc/g1/g1RemSet.cpp line 1443:
> 
>> 1441:   }
>> 1442: 
>> 1443:   {
> 
> guarding this block with `if (initial_evacuation)`  might be an easier alternative.

I want to eventually move all the special handling for the `young_regions_cset_group` out of `merge_heap_roots` and into the collection set. All this special handling at various places where we do something with the collection set and then do something with the young card set is tiring to review and error prone.
Imo it is better to just make `G1CollectionSet` handle all this.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/26695#discussion_r2290468771