RFR: JDK-8260372: [PPC64] Add support for JDK-8210498 and JDK-8222841 [v3]

[Goetz Lindenmaier]

On Mon, 8 Feb 2021 23:57:10 GMT, Niklas Radomski <github.com+9200663+Quaffel at openjdk.org> wrote:

>> Introduces support for _nmethod entry barriers_ and _c2i entry barriers_ on the ppc platform. Those are required to enable concurrent class unloading for compatible garbage collectors, such as Shenandoah or zGC.
>> 
>> _This is a preparational change for the Shenandoah GC port to ppc. As such, it introduces features that the current version doesn't make use of, but that are required for the upcoming change. This way, the scope of the upcoming change is limited to Shenandoah-specific functionality; making its review a little easier._
>
> Niklas Radomski has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Use toc offset in c2i entry barrier
>  - Update comments

Hi,
I'm not that deep in this code, but looking at other platforms this looks good.
Thanks for porting this!
Feel free to fix the comment or push as-is ... if this is possible with this tooling :)

src/hotspot/cpu/ppc/gc/shared/barrierSetAssembler_ppc.cpp line 184:

> 182:   __ bne(CCR0, skip_barrier);
> 183: 
> 184:   // Class loader is weak. Determine whether the holder still alive.

'is' in comment missing:   ... whether the holder _is_ still alive.

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Marked as reviewed by goetz (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2432