RFR: 8315884: New Object to ObjectMonitor mapping [v9]

[Axel Boldt-Christmas]

On Tue, 23 Jul 2024 20:21:05 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Only legacy locking uses the displaced header, I believe, which isn't clear in this code at all.  This seems like a fix.  We should probably assert that only legacy locking uses this field as a displaced header.
>
> Update: yes, this code change does assert if you use BasicLock's displaced header for locking modes other than LM_LEGACY.

This is correct. The `displaced_header` in the BasicLock is only used by Legacy. Which is more strongly asserted now.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20067#discussion_r1715299608