[lworld] RFR: 8376813: [lworld] Add print for dummy field reused as null-marker [v2]

[Joel Sikström]

On Mon, 2 Feb 2026 10:55:14 GMT, Paul Hübner <phubner at openjdk.org> wrote:

> Thanks for the changes, this makes debugging and developing a lot easier. One thing that came to mind is that we have a bunch of flat array specific printing logic in e.g. `FlatArrayKlass::oop_print_value_on`. As a possible extension, would we ever want to convey such information in the array itself, rather than the field? For example when debug-printing the human-version of the array header to indicate the null marker is reused as the dummy field (when applicable)?

I'm not entirely sure of how arrays work so I'd need to spend some time on figuring that out before giving a better answer. When trying to understand emtpy InlineKlasses, it wasn't immediately clear to me that the empty dummy-field was reused as the null-marker, so I'd say anything we can do to convey that more clearly is something we'd want to do.

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PR Comment: https://git.openjdk.org/valhalla/pull/2001#issuecomment-3845927992