[lworld] RFR: 8368875: [lworld] UseParallelGC fails null narrow klass assertion failure

[Frederic Parain]

On Fri, 3 Oct 2025 17:58:31 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Thanks @fparain, I mixed it up when writing it down. I knew that, I promise 😅.  
>> 
>> I think it would be good to introduce an `is_valhalla_concept` (naming may vary) which ORs the larval, inline type, flat array and null free array bit masks into a single mask. That way we can check it in just one call, which is imo easier to read. Thoughts?
>
> Maybe we can consider this as a further enhancement.  If we add valhalla bits (although I think we're out of bits), this would make sense to collect them all.  I think all of this is probably optimized to one load and compare since it's inline.

is_larval_state() is a status that is specific to a particular instance, and cannot be retrieved from another source, and this is why it must be preserved. is_inline_type(), is_flat_array() and is_null_free_array() are all properties than can be retrieved from the K-klass. So I'm not sure why they have been added here.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1655#discussion_r2403116424