RFR: 8374145: Remove legacy locking remnants from markWord

[Stefan Karlsson]

On Fri, 19 Dec 2025 14:05:13 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

> There's a bunch of unused code in markWord that used to be used by the removed legacy locking. I propose that we remove it.
> 
> There's a Shenandoah change that should be checked closer. My thinking is:
>  `is_being_inflated`: always returns false
>  `has_displaced_mark_helper`: Only returns true if both these are true:
>    * `!UseCompactObjectTable` - there's an early return for this earlier in the function.
>    * `lockbits == monitor_value` - checked in the if-statement above

Thanks for the reviews!

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PR Review: https://git.openjdk.org/jdk/pull/28927#pullrequestreview-3603327790