[lworld] Integrated: 8376813: [lworld] Add print for dummy field reused as null-marker

[Joel Sikström]

On Fri, 30 Jan 2026 15:29:17 GMT, Joel Sikström <jsikstro at openjdk.org> wrote:

> Hello,
> 
> Right now it's not clear that the dummy field that is injected into empty inline klasses can be/is reused for the null-marker when looking at the printed layout from -XX:+PrintInlineLayout. I suggest we enhance this print to indicate if the dummy field has been reused for the null-marker.
> 
> I've tested that the added comment in the print is there when nullability is turned on (default), and not there when turned off (`-XX:-UseNullableValueFlattening -XX:-UseNullableNonAtomicValueFlattening`).
> 
> 
> Before:
> Instance fields:
>  @0 RESERVED 12/-
>  @12 REGULAR 1/1 ".empty" B
> 
> After:
> Instance fields:
>  @0 RESERVED 12/-
>  @12 REGULAR 1/1 ".empty" B (reused as null-marker)
> 
> 
> Testing:
> * GHA
> * Oracle's tier1

This pull request has now been integrated.

Changeset: ff2e2092
Author:    Joel Sikström <jsikstro at openjdk.org>
Committer: Paul Hübner <phubner at openjdk.org>
URL:       https://git.openjdk.org/valhalla/commit/ff2e20922e3c9ca2a206156cdb515dac1adce68c
Stats:     21 lines in 2 files changed: 10 ins; 0 del; 11 mod

8376813: [lworld] Add print for dummy field reused as null-marker

Reviewed-by: fparain, phubner

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PR: https://git.openjdk.org/valhalla/pull/2001