8382277: Shenandoah: Improve mutator runtime entry points

[shipilev]

This is a separate part of Shenandoah LBE work. On some workloads, the LRB-weak path is very hot, and little optimizations are paying off there.

Currently, we call into load_reference_barrier_mutator for strong loads, and to "normal" load_reference_barrier for weak/phantom loads. This means we are risking two things: a) a performance penalty if compiler does not inline through the Decorator value; b) exposing to interaction with JVMTI/JFR that *forwardee_mutator is protecting us from.

Additional testing:

• Performance tests (pending)
• Linux x86_64 server fastdebug, hotspot_gc_shenandoah

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Progress

• Change must not contain extraneous whitespace
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• Change must be properly reviewed (2 reviews required, with at least 1 Reviewer, 1 Author)

Issue

• JDK-8382277: Shenandoah: Improve mutator runtime entry points (Enhancement - P4)

Reviewers

• Roman Kennke (@rkennke - Reviewer) 🔄 Re-review required (review applies to e0edbbe5)
• Kelvin Nilsen (@kdnilsen - Reviewer)

Reviewing

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[bridgekeeper]

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[openjdk]

@shipilev This change is no longer ready for integration - check the PR body for details.

[openjdk]

@shipilev The following labels will be automatically applied to this pull request:

• hotspot-gc
• shenandoah

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing lists. If you would like to change these labels, use the /label pull request command.

[mlbridge]

Webrevs

• 02: Full - Incremental (0f3a5fc9)
• 01: Full - Incremental (e0edbbe5)
• 00: Full (7cabe2ff)

[rkennke]

This is a nice improvement! Just one small question. No need for another review, if you choose to change it.

[kdnilsen]

Thanks for all your work on these barrier improvements.

[openjdk]

The total number of required reviews for this PR has been set to 2 based on the presence of this label: hotspot-gc. This can be overridden with the /reviewers command.