RFR: 8256999: Add C2 intrinsic for Reference.refersTo and PhantomReference::refersTo

[Erik Österlund]

On Wed, 25 Nov 2020 10:01:15 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> The information that there was a barrier attached, is implicit in the ins_encode block due to it being run at all. In other words, since we matched the mach node to our ZGC access instead of a normal access, we already know that there was barrier data attached, and that we no longer have such barrier data.
>
> Ok, makes sense. What do you think about making `ZLoadBarrierElided = 0` then?

I'm okay with that. I don't have a strong preference.

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PR: https://git.openjdk.java.net/jdk/pull/1425