RFR: 8371284: GenShen: Avoid unnecessary card marking [v4]

[Nityanand Rai]

On Wed, 19 Nov 2025 22:16:39 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> Nityanand Rai has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   remove UseCondCardMark chnages, to decouple issues fixed
>
> src/hotspot/share/gc/shenandoah/shenandoahBarrierSet.inline.hpp line 199:
> 
>> 197:   }
>> 198:   T heap_oop = RawAccess<>::oop_load(field);
>> 199:   if (CompressedOops::is_null(heap_oop)) {
> 
> For completeness, add a comment:
> 
>  // Null reference store

Added

> src/hotspot/share/gc/shenandoah/shenandoahBarrierSet.inline.hpp line 204:
> 
>> 202:   oop obj = CompressedOops::decode_not_null(heap_oop);
>> 203:   if (!_heap->is_in_young(obj)) {
>> 204:     // Young object -> old field stores do not require card mark.
> 
> As worded, this comment is wrong (or at least confusing). May be rephrase to:
> 
> 
> // Not an old->young reference store

Updated

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PR Review Comment: https://git.openjdk.org/jdk/pull/28204#discussion_r2543863775
PR Review Comment: https://git.openjdk.org/jdk/pull/28204#discussion_r2543864179