RFR: 8338658: New Object to ObjectMonitor mapping: s390x implementation [v2]

[Martin Doerr]

On Thu, 5 Sep 2024 07:07:55 GMT, Amit Kumar <amitkumar at openjdk.org> wrote:

>> I am often undecided myself. The code as it is now is correct for all displacements. If you omit the else part, you introduce a hidden dependency on the layout of BasicObjectLock and BasicLock. On the other hand, how likely is it that anybody will fundamentally change the layout and thus break the disp12 requirement? Compact or generally valid? **Your choice.**
>
> I guess let's keep it. I mean even if there is need to change the layout, then we have to remove `z_mvghi` and switch back to this implementation again. So maybe better we keep it here and hope for the best ?

`BasicObjectLock` is a very small data structure. 12 bit offsets are more than enough. The actual offsets are 0 :-)

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PR Review Comment: https://git.openjdk.org/jdk/pull/20740#discussion_r1749933492