RFR: 8365191: Cleanup after removing LockingMode related code

[Fredrik Bredberg]

On Tue, 23 Sep 2025 17:26:36 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> This is a general cleanup after removing `LockingMode` related code.
>> It's a sub-task of [JDK-8344261](https://bugs.openjdk.org/browse/JDK-8344261).
>> It includes:
>> - Removing asserts that are no longer necessary, since we removed legacy locking and monitor locking.
>> - Removing or rewriting comments, arguments or functions that are related to displaced headers.
>> - Remove "always true" parameter from `MonitorExitStub`.
>> - Re-type/name metadata in `BasicLock`.
>> 
>> Tier1-5 passes okay on supported platforms.
>> 
>> All other platforms (arm, ppc, riscv and s390) has been sanity checked using Qemu.
>
> src/hotspot/share/runtime/vmStructs.cpp line 685:
> 
>> 683:   volatile_nonstatic_field(ObjectMonitor,      _owner,                                        int64_t)                               \
>> 684:   volatile_nonstatic_field(ObjectMonitor,      _next_om,                                      ObjectMonitor*)                        \
>> 685:   volatile_nonstatic_field(BasicLock,          _monitor,                                      ObjectMonitor*)                        \
> 
> Since nothing now refers to this, you can delete it from vmStructs.

According to @mur47x111, they still need this line for their fast locking implementation.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27448#discussion_r2375512919