RFR: 8254320: Shenandoah: C2 native LRB should activate for non-cset objects [v2]

[Aleksey Shipilev]

On Fri, 9 Oct 2020 17:04:26 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> In C2 native-LRB, we don't call the slow-path when the reference is not in cset. However, it may need to return NULL
>> for non-cset objects too, in order to prevent accidental ressurrection of referenced object.
>
> Roman Kennke has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev
> excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since
> the last revision:
>  - Merge remote-tracking branch 'upstream/master' into 8254320
>  - 8254320: Shenandoah: C2 native LRB should activate for non-cset objects

A minor documentation nit. Otherwise is fine.

src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp line 1345:

> 1343:     // Wires !in_cset(obj) to slot 2 of region and phis
> 1344:     Node* not_cset_ctrl = NULL;
> 1345:     if (!lrb->is_native()) {

I think it deserves a comment why LRB-native is special.

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Marked as reviewed by shade (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/580