RFR: 8372098: Move AccessFlags to InstanceKlass [v5]

[Dean Long]

On Mon, 1 Dec 2025 15:02:50 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> ArrayKlass doesn't set AccessFlags so don't look for them there.  See CR for details.
>> Fixed SA and jvmci.  @iwanowww Can you check that I changed C2 correctly (we talked about this in August).
>> Tested with tier1-4.  5-7 in progress.
>
> 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];

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PR Review Comment: https://git.openjdk.org/jdk/pull/28371#discussion_r2578843984