RFR: 8308479: [s390x] Implement alternative fast-locking scheme [v3]

[Amit Kumar]

On Wed, 14 Jun 2023 12:05:44 GMT, Lutz Schmidt <lucy at openjdk.org> wrote:

>> Amit Kumar has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   restore currentHeader after z_nill
>
> src/hotspot/cpu/s390/c1_MacroAssembler_s390.hpp line 54:
> 
>> 52:   // obj     : Must point to the object to lock, contents preserved.
>> 53:   // disp_hdr: Must point to the displaced header location, contents destroyed.
>> 54:   // Z_R0_scratch will be killed as well
> 
> Shouldn't that read 
> `// Z_R1_scratch will be killed as well`
> Such comment should be added to lock_object as well.
> How can `void lock_object()` return anything?

Thanks for all suggestions (and expecting more), I've updated the code.

Please consider looking at the latest changes. :-)

> src/hotspot/cpu/s390/macroAssembler_s390.cpp line 5670:
> 
>> 5668: 
>> 5669:   // Clear lock-bits from hdr (locked state)
>> 5670:   z_xilf(temp, markWord::unlocked_value);
> 
> The markWord values occupy only the rightmost few bits. Therefore, z_xill() will suffice.

we don't have `z_xill()` instruction like `z_nill()` or `z_oill()` :-(

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PR Review Comment: https://git.openjdk.org/jdk/pull/14414#discussion_r1230420685
PR Review Comment: https://git.openjdk.org/jdk/pull/14414#discussion_r1230421679