8382150: Shenandoah: Clean up nmethod entry barrier support

[shipilev]

Additional testing:

• Linux x86_64 server fastdebug, jcstress 8 hour run
• Linux x86_64 server fastdebug, hotspot_gc_shenandoah
• Linux x86_64 server fastdebug, hotspot_gc_shenandoah with -XX:TieredStopAtLevel=1
• Linux x86_64 server fastdebug, all with -XX:+UseShenandoahGC
• Linux AArch64 server fastdebug, all with -XX:+UseShenandoahGC
• Linux x86_64 server fastdebug, all with -XX:+UseShenandoahGC -XX:TieredStopAtLevel=1
• Linux AArch64 server fastdebug, all with -XX:+UseShenandoahGC -XX:TieredStopAtLevel=1

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Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8382150 needs maintainer approval

Issue

• JDK-8382150: Shenandoah: Clean up nmethod entry barrier support (Enhancement - P4 - Requested)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk25u-dev.git pull/720/head:pull/720
$ git checkout pull/720

Update a local copy of the PR:
$ git checkout pull/720
$ git pull https://git.openjdk.org/jdk25u-dev.git pull/720/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 720

View PR using the GUI difftool:
$ git pr show -t 720

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk25u-dev/pull/720.diff

Using Webrev

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[bridgekeeper]

👋 Welcome back shade! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[openjdk]

⚠️ @shipilev This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[shipilev]

/approval request Simplifies Shenandoah code, removes another intermediate GC state, provides cleaner grounds for more fixes. Applies cleanly. Aggressive testing passes. Risk is low: touches production code, but only makes unsafe corner case safer, does not change the core functionality, no bugtail since several months in mainline.

[openjdk]

@shipilev
8382150: The approval request has been created successfully.

[mlbridge]

Webrevs

• 00: Full (a8b440c1)