On Thu, 12 Feb 2026 14:17:25 GMT, Roberto Castañeda Lozano
<[email protected]> wrote:
> This simple changeset enables the diagnostic flag `PrintFlatArrayLayout` in
> product builds, similarly to other diagnostic flags such as
> `PrintFieldLayout`. This was useful to quickly grasp what arrays are
> flattened when analyzing a benchmark.
>
> before:
>
>
> $ java --enable-preview -XX:+UnlockDiagnosticVMOptions
> -XX:+PrintFlatArrayLayout --version
> openjdk 27-jep401ea2 2026-09-15
> OpenJDK Runtime Environment (build 27-jep401ea2-rocastan.open)
> OpenJDK 64-Bit Server VM (build 27-jep401ea2-rocastan.open, mixed mode)
>
>
> after:
>
>
> $ java --enable-preview -XX:+UnlockDiagnosticVMOptions
> -XX:+PrintFlatArrayLayout --version
> Flat Type Array: [Ljava.lang.Character; {0x0000000095040348}
> - element klass: 'java/lang/Character'
> - layout kind: NULLABLE_ATOMIC_FLAT
> - array properties: DEFAULT (NULLABLE ATOMIC)
> - element size 4 aligned layout size 4
> Flat Type Array: [Ljava.lang.Integer; {0x000000009505d0a0}
> - element klass: 'java/lang/Integer'
> - layout kind: NULLABLE_ATOMIC_FLAT
> - array properties: DEFAULT (NULLABLE ATOMIC)
> - element size 8 aligned layout size 8
> openjdk 27-jep401ea2 2026-09-15
> OpenJDK Runtime Environment (build 27-jep401ea2-rocastan.open)
> OpenJDK 64-Bit Server VM (build 27-jep401ea2-rocastan.open, mixed mode)
>
>
> **Testing**: tier1-3, manually checked that flattened array info is shown on
> a couple of scenarios.
Thanks.
-------------
Marked as reviewed by phubner (Committer).
PR Review:
https://git.openjdk.org/valhalla/pull/2090#pullrequestreview-3791364365
