On Wed, 17 Dec 2025 11:18:51 GMT, Paul Hübner <[email protected]> wrote:
>> Sub-classes of `InstanceKlass` can't have C++ fields because they would end
>> up overlayed on top of the vtable and other dynamically sized sections of
>> the `InstanceKlass` object.
>>
>> To handle that the `InlineKlass` has a companion class named
>> `InlineKlassFixedBlock`, which lists all the member fields that belongs to
>> the InlineKlass, and an instance of that gets stamped into the `InlineKlass`
>> object after the parts that are provided by the `InstanceKlass`.
>>
>> I propose a few changes:
>>
>> 1) Move `InlineKlassFixedBlock` away from instanceKlass.hpp and place it
>> inside inlineKlass.hpp instead.
>>
>> 2) Nest `InlineKlassFixedBlock` it inside `InlineKlass`. It's only
>> `InlineKlass `(and the compilers) that touch these fields, so it doesn't
>> have to be a public, top-level class.
>>
>> 3) Rename it from `InlineKlassFixedBlock` to `InlineKlass::Members`. I think
>> that "fixed block" term is unclear and doesn't help the reader understand
>> its role in the `InlineKlass`. Hopefully, the name `Members` is a clearer.
>>
>> WDYT?
>
> src/hotspot/share/oops/inlineKlass.hpp line 90:
>
>> 88:
>> 89: Members& members() {
>> 90: assert(_adr_inline_klass_members != 0, "Should have been
>> initialized");
>
> Nitpick: `nullptr` for clarity as that's what we initialize it as?
Of course! Thanks. This is left-overs from an earlier prototype, where I only
saved the offset to the Members. That removes the need for CDS to patch this
address, but it adds extra instructions to the compiler, so I skipped that.
-------------
PR Review Comment:
https://git.openjdk.org/valhalla/pull/1812#discussion_r2626951939
