8383810: Shenandoah: Simplify native CAS barriers

[shipilev]

In Shenandoah LBE, we have switched to a more succinct way to deal with concurrent evacuation false negatives in atomics: do the fix up early on, thus avoiding any need for CAS retry logic.

We should start transplanting that to native and C1 CAS variants as well. This one handles the architecture-agnostic native side. We cannot easily switch C1 parts until LBE separates the high-performance C2 implementation. This simplifies CAS barriers quite a bit, makes them easier to reason about, and also potentially gives a performance improvement, as we ditch the loops and fix up the heap as we go.

Additional testing:

• Linux x86_64 server fastdebug, hotspot_gc_shenandoah

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Issue

• JDK-8383810: Shenandoah: Simplify native CAS barriers (Enhancement - P4)

Reviewers

• Roman Kennke (@rkennke - Reviewer)
• Xiaolong Peng (@pengxiaolong - Committer)

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8383810: Shenandoah: Simplify native CAS barriers

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At the time when this comment was updated there had been 24 new commits pushed to the master branch:

• 70f20f9: 8383770: Remove flags from AOTCodeCache::Config already covered by cpu features
• 91933ed: 8381862: Refactor remaining TestNG tests under jdk/net/ExtendedSocketOption to use JUnit
• 1be2fc4: 8383243: Make objcopy configurable to compress debug info
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[rkennke]

Looks good to me. Thank you!

[pengxiaolong]

Thanks for the work to simplify this!

Upgrading Unsafe CAS to strong access seems reasonable to maintain integrity.