RFR: 8308469: [PPC64] Implement alternative fast-locking scheme [v2]

[Martin Doerr]

On Fri, 26 May 2023 10:25:35 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

>> Ok, you are right! The anon case would just branch to the exit (zero flag would readily be un-set by the test, right?). The normal case would fall-through. This sounds like a useful simplification, and should not affect performance. I'll probably do that in x86_64 and aarch64, feel free to also simplify the PPC version.
>
> Correct that's what I meant. I was just not sure if there is a reason not to do that but have a dedicated C2HandleAnonOMOwnerStub to handle that case.

I think we don't even need to check the `ANONYMOUS_OWNER` bit because that case is also handled by

  cmpd(flag, temp, R16_thread);
  bne(flag, failure);

If `temp` has the `ANONYMOUS_OWNER` set it's unequal to the current thread and we jump to failure with CR0 NE.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14069#discussion_r1206577670