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

[Richard Reingruber]

On Thu, 25 May 2023 16:59:24 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> src/hotspot/cpu/ppc/macroAssembler_ppc.cpp line 2854:
>> 
>>> 2852:     andi_(R0, temp, ObjectMonitor::ANONYMOUS_OWNER);
>>> 2853:     bne(CCR0, anonymous);
>>> 2854:   }
>> 
>> This is surly very rare. Can't we take the slow path, i.e. branch to `failure`?
>
> I had thought that, too. Yes, it is possible. But then I thought they probably added the path for C2 for a reason. Otherwise they would probably not have spent the extra effort for implementing the stub. So, I prefer to have it, too.

Let's see if @rkennke remembers. Roman I wonder why you've implemented the C2HandleAnonOMOwnerStub instead of just taking the slow path into the runtime? @TheRealMDoerr wants to implement the logic inline and I'm actually worried if that will pay off the cost.
Maybe we should add an illegal instruction to see if it's reached. Do you know a benchmark that would be good for such a test?

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PR Review Comment: https://git.openjdk.org/jdk/pull/14069#discussion_r1205898403