RFR: 8334060: Implementation of Late Barrier Expansion for G1 [v17]

[Roberto Castañeda Lozano]

On Fri, 6 Sep 2024 21:33:42 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Roberto Castañeda Lozano has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   s390 port : late barrier expansion
>
> src/hotspot/cpu/x86/gc/g1/g1BarrierSetAssembler_x86.cpp line 176:
> 
>> 174:   __ jcc(Assembler::zero, runtime);                           // jump to runtime if index == 0 (full buffer)
>> 175:   // The buffer is not full, store value into it.
>> 176:   __ subptr(temp, wordSize);                                  // temp := next index
> 
> Instead of 
> 
>   __ testptr(temp, temp);
>   __ jcc(Assembler::zero, runtime);
>   __ subptr(temp, wordSize);
> 
> it seems like this might be better
> 
>   __ subptr(temp, wordSize);
>   __ jcc(Assembler::below, runtime);
> 
> I think the code in the PR matches what the early expansion generates, so I think a change here
> can be deferred to a followup.

Good point, thanks! I made a note for follow-up work.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19746#discussion_r1750088920