8371284: GenShen: Avoid unnecessary card marking

[nityarai08]

Exclude young-young, old-old and honor UseCondCardMark in dirty card marking.

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Progress

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• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8371284: GenShen: Avoid unnecessary card marking (Enhancement - P4)

Reviewing

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$ git fetch https://git.openjdk.org/jdk.git pull/28204/head:pull/28204
$ git checkout pull/28204

Update a local copy of the PR:
$ git checkout pull/28204
$ git pull https://git.openjdk.org/jdk.git pull/28204/head

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$ git pr checkout 28204

View PR using the GUI difftool:
$ git pr show -t 28204

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https://git.openjdk.org/jdk/pull/28204.diff

Using Webrev

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[bridgekeeper]

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[openjdk]

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[openjdk]

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• hotspot-gc
• shenandoah

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[mlbridge]

Webrevs

• 01: Full - Incremental (59f7a0d0)
• 00: Full (09ad25ab)

[earthling-amzn]

Let's make sure we don't mark cards for null objects.