8389905: Shenandoah: SBSA::card_table uses own temp registers that clobber obj

[shipilev]

Fixes a clobbering bug in Shenandoah card table barriers.

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-8389905 needs maintainer approval

Issue

• JDK-8389905: Shenandoah: SBSA::card_table uses own temp registers that clobber obj (Bug - P2 - Requested)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk25u-dev.git pull/729/head:pull/729
$ git checkout pull/729

Update a local copy of the PR:
$ git checkout pull/729
$ git pull https://git.openjdk.org/jdk25u-dev.git pull/729/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 729

View PR using the GUI difftool:
$ git pr show -t 729

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk25u-dev/pull/729.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

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[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.

[mlbridge]

Webrevs

• 00: Full (6e60d9f6)

[shipilev]

/approval request Fixes a clobbering bug in Shenandoah card table barriers. Readily manifested with Valhalla, but the bug is actually generic. Patch is relatively new, but the fix is straightforward. Applies cleanly, aggressive testing passes. Risk is medium-low: affects production paths, confined to Generational Shenandoah, was in mainline for 10+ days without issues; backporting it provides a firmer testing ground for other changes in barrier set.

[openjdk]

@shipilev
8389905: The approval request has been created successfully.