[lworld] RFR: 8374800: [lworld] Add a NULLABLE_NON_ATOMIC_FLAT layout [v2]

[Frederic Parain]

On Wed, 14 Jan 2026 20:14:40 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> src/hotspot/share/oops/inlineKlass.hpp line 95:
>> 
>>> 93:     int _null_free_atomic_size_in_bytes;     // size and alignment requirement for a null-free atomic layout, -1 if no atomic flat layout is possible
>>> 94:     int _nullable_atomic_size_in_bytes;   // size and alignment requirement for a nullable layout (always atomic), -1 if no nullable flat layout is possible
>>> 95:     int _nullable_non_atomic_size_in_bytes; // size and alignment requirement for a nullable non-atomic layout, -1 if not available
>> 
>> Here is something that I'm confused about.  Does an InlineKlass have multiple possible layouts and sizes depending on the container?  Is that why the InlineKlass needs to save all these size non-static data members?
>
> Can you align the // s please?

> Here is something that I'm confused about. Does an InlineKlass have multiple possible layouts and sizes depending on the container? Is that why the InlineKlass needs to save all these size non-static data members?

An InlineKlass supports a set of layout according to its own characteristics (number of fields, atomicity, etc.).
When computing the layout of a container with a value field, the JVM looks at the characteristics of the field (static, final , strict, null-free, etc.) and the layouts available for this InlineKlass and selects the best one that satisfies all requirements.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1407#discussion_r2698655768