RFR: 8291555: Implement alternative fast-locking scheme [v62]

[Daniel D. Daugherty]

On Wed, 26 Apr 2023 10:43:48 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp line 701:
>> 
>>> 699:   // ZFlag == 0 count in slow path
>>> 700:   jccb(Assembler::notZero, NO_COUNT); // jump if ZFlag == 0
>>> 701: 
>> 
>> `DONE_LABEL` is conditionally jumped into from a lot of places, the only path it is reached without known `ZF` seems to be `LM_LEGAGY` fall-through. Maybe refactor a little to eliminate this block.
>
> I intentionally have not changed the existing paths to make it absolutely clear that the old behaviour is not changed. I'd  rather make any changes to the stack-locking in a separate follow-up.

Thanks for minimizing changes to the old/legacy code.

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PR Review Comment: https://git.openjdk.org/jdk/pull/10907#discussion_r1178113575