RFR: 8372098: Move AccessFlags to InstanceKlass [v5]

[Coleen Phillimore]

On Mon, 1 Dec 2025 21:48:06 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Added a comment for checking interface guard after array guard.
>
> 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.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28371#discussion_r2578975466