RFR: 8372098: Move AccessFlags to InstanceKlass [v5]

[Dean Long]

On Mon, 1 Dec 2025 22:48:05 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> src/hotspot/share/oops/instanceKlass.hpp line 237:
>> 
>>> 235: 
>>> 236:   // State is set either at parse time or while executing, atomically to not disturb other state
>>> 237:   InstanceKlassFlags _misc_flags;
>> 
>> It looks like the size of these 3 fields, _reference_type, _access_flags, and _misc_flags, will take 8 bytes because of alignment/padding, but if _reference_type was moved to the end of InstanceKlassFlags and the order reversed, it could be reduced to 6 bytes, leaving 2 for future expansion:
>> 
>> InstanceKlassFlags _misc_flags; // contains _reference_type
>> AccessFlags        _access_flags;
>> char _reserved[2];
>
> ClassState is a u1 so that fills the u2 gap with reference_type.  So I don't think moving reference type will help.

You're right, I missed that.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28371#discussion_r2579576187