RFR: 8286829: Shenandoah: fix Shenandoah Loom support [v3]

[Zhengyu Gu]

On Wed, 1 Jun 2022 13:00:13 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Hmm... somehow, my comments gone missing.
>> 
>> Yes, I am award of it, but could not find a better place, any suggestions are welcome.
>> 
>> ZGC takes the similar hit [here](https://github.com/openjdk/jdk/blob/master/src/hotspot/share/gc/z/zMark.cpp#L289).
>> 
>> Let's get this in for correctness and work on optimizing it in followup CR.
>> 
>> Thanks.
>
> Both `obj->is_instance()` and `obj->is_stackChunk()` in `relativize_stack_chunk` checks the same Klass::_kind field, so I would be surprised if you would be able to find a perf regression here. We checked the marking times before and  after adding relativize_stack_chunk, and couldn't see any difference.

Thanks for your insights, @stefank

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PR: https://git.openjdk.java.net/jdk/pull/8924