RFR: 8267968: [PPC64] Use prefixed load and addi instructions for better performance in POWER10 [v3]

[Kazunori Ogata]

On Wed, 9 Jun 2021 12:35:21 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> Kazunori Ogata has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Revert changes for pusing nodes in loadConLNodesTuple and add comments about the node _last points to
>>  - Fix grammatical errors in comments
>
> src/hotspot/cpu/ppc/assembler_ppc.cpp line 364:
> 
>> 362:       // we avoid a buffer overrun in the actual code generation phase.
>> 363:       nop();
>> 364:     }
> 
> Scratch emit should be able to determine the size precisely, not just a pessimistic estimation. Please don't break this design.

@TheRealMDoerr  I understand the design.  However, I'm wondering why the alignment can vary between scratch emit and real emit if the size can be determined precisely.  It is helpful if you could point out some sources of variation.

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PR: https://git.openjdk.java.net/jdk/pull/4267