RFR: 8291555: Implement alternative fast-locking scheme [v71]

[Roman Kennke]

On Thu, 4 May 2023 19:32:23 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Address @dholmes-ora's review comments
>
> src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp line 666:
> 
>> 664:   // Invariant: tmpReg == 0.  tmpReg is EAX which is the implicit cmpxchg comparand.
>> 665:   lock();
>> 666:   cmpxchgptr(scrReg, Address(boxReg, OM_OFFSET_NO_MONITOR_VALUE_TAG(owner)));
> 
> Sigh... I had liked the fact that we took care of these old "TODO" items
> in this code. It's true that these changes were in violation of our "try not
> to change stack-lock" mantra. I did run the v66 changes thru Mach5
> Tier[1-8] testing in "stack-locking is default" mode so your changes
> were well tested.

Let's re-do those changes in a follow-up, ok?

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PR Review Comment: https://git.openjdk.org/jdk/pull/10907#discussion_r1185498799