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

[Quan Anh Mai]

On Wed, 26 Apr 2023 08:12:41 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove unnecessary comments
>
> src/hotspot/cpu/x86/c2_CodeStubs_x86.cpp line 81:
> 
>> 79:   // C2CodeStubList::emit() will throw an assertion and report the actual size that
>> 80:   // is needed.
>> 81:   return 33;
> 
> This should be 36 with `ASSERT` and 21 without. If you are sure that `JavaThread::lock_stack_top_offset()` or `OM_OFFSET_NO_MONITOR_VALUE_TAG(owner)` fits within an `int8_t` then it reduces 3 bytes for each usage.

This stub has 2 instructions, and it seems not really uncommon, is it worth it to have a stub here?

> src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp line 781:
> 
>> 779: #ifdef _LP64
>> 780:       C2HandleAnonOMOwnerStub* stub = new (Compile::current()->comp_arena()) C2HandleAnonOMOwnerStub(tmpReg, boxReg);
>> 781:       Compile::current()->output()->add_stub(stub);
> 
> This should be added only if we are really emitting the code (i.e. not emitting into a scratch buffer to measure the node size)

Also, I think this `if (LockingMode == LM_LIGHTWEIGHT)` block should be moved out of the enclosing if block, we are checking for inflation here, it seems logical to separate the inflation path out.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/10907#discussion_r1177570766
PR Review Comment: https://git.openjdk.org/jdk/pull/10907#discussion_r1177304198