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)

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

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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.