[lworld] RFR: 8341757: Field layout computation allowing atomic and nullable flattening

[Coleen Phillimore]

On Mon, 21 Oct 2024 14:04:21 GMT, Dan Heidinga <heidinga at openjdk.org> wrote:

>> Initial implementation of fields layouts in order to support heap flattening with JEP 401 model.
>> The patch includes the generation of two new flat fields layouts: atomic and nullable.
>> The patch also includes the support in the interpreter (through the access API) to access the new layouts while respecting the new semantic (on x86_64 and aarch64).
>> Some areas do not support the new layouts yet, like JITs, Unsafe and arrays.
>> 
>> There's no automatic tests yet, but considering the impact those new layouts will have on the JVM, the priority was to make this code available to all developers as soon as possible. Automatic tests will be added in a following CR.
>> 
>> Fred
>
> src/hotspot/share/classfile/classFileParser.cpp line 1566:
> 
>> 1564:     _temp_field_info->adr_at(idx)->set_index(idx);
>> 1565:     _static_oop_count++;
>> 1566:     // Inject static ".reset" field
> 
> I think we should rename this field to be something like `null_examplar` or `null_reset`.  
> Suggestion:
> 
>     // Inject static ".null_examplar" field.  This is the same as the `.default field but will never have its null-channel set to non-zero.

null_exemplar I like that!

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1275#discussion_r1809361337