RFR: Clean up CondCardMark code: remove excess barriers, enable it by default [v2]

[earthling-amzn]

On Thu, 1 Apr 2021 16:07:17 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> We plan to start work on concurrent remembered set scanning very soon. I'm not far enough into it yet to know if we'll need these barriers, but it looks like we might.
>
> Either way, this thing is gone with https://bugs.openjdk.java.net/browse/JDK-8261309 -- and it was needed for CMS. I would prefer to drop it to match upstream, and then reintroduce the barriers iff they are needed.

I agree, thanks for the link and the background on the change.

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PR: https://git.openjdk.java.net/shenandoah/pull/26