8358334: C2/Shenandoah: incorrect execution with Unsafe

[rwestrel]

21u patch doesn't apply cleanly but only because some code that's
replaced still uses NULL instead of nullptr. Otherwise, patch is
identical to 21u patch.

Tested with hotspot_gc_shenandoah + tier1 with -XX:+UseShenandoahGC

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• JDK-8358334 needs maintainer approval
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8358334: C2/Shenandoah: incorrect execution with Unsafe (Bug - P2 - Requested)

Reviewers

• Paul Hohensee (@phohensee - Reviewer)

Reviewing

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$ git checkout pull/3770

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[bridgekeeper]

👋 Welcome back roland! 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]

⚠️ @rwestrel 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 (74fc45fe)