RFR: 8276927: [PPC64] Port shenandoahgc to linux on ppc64le

[Martin Doerr]

On Wed, 10 Nov 2021 09:00:04 GMT, Niklas Radomski <nradomski at openjdk.org> wrote:

> Port the Shenandoah garbage collector (JDK-8241457)[https://bugs.openjdk.java.net/browse/JDK-8241457] to linux on ppc64le.

Nice work! Looks correct.
For others: Note that this change already contains feedback from my offline review.

src/hotspot/cpu/ppc/gc/shenandoah/shenandoahBarrierSetAssembler_ppc.cpp line 74:

> 72:   // IU barriers are also employed to avoid resurrection of weak references,
> 73:   // even if Shenandoah does not operate in incremental update mode.
> 74:   if (ShenandoahIUBarrier || ShenandoahSATBBarrier) {

Sharing the code for IU and SATB sounds like a good idea, but one needs to be careful. `ShenandoahBarrierSetC1::iu_barrier` only works with `ShenandoahIUBarrier`, so this trick can't be used in C1.
It's a bit confusing, but I'm ok with this version. At least, I don't have any better suggestion at the moment.

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Marked as reviewed by mdoerr (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6325