8328107: Shenandoah/C2: TestVerifyLoopOptimizations test failure

[rwestrel]

The failure occurs because a load barrier is expanded on the backedge
of the counted loop. That breaks the expected counted loop shape. The
fix I propose is to replace the CountedLoop with a Loop node when
that happens. We're basically done with optimizations related to
counted loop at this point so this shouldn't make a difference.

/cc hotspot-compiler

---

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Issue

• JDK-8328107: Shenandoah/C2: TestVerifyLoopOptimizations test failure (Bug - P3)

Reviewers

• Aleksey Shipilev (@shipilev - Reviewer)

Reviewing

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[bridgekeeper]

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[openjdk]

@rwestrel This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8328107: Shenandoah/C2: TestVerifyLoopOptimizations test failure

Reviewed-by: shade

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At the time when this comment was updated there had been 346 new commits pushed to the master branch:

• 2a37764: 8333743: Change .jcheck/conf branches property to match valid branches
• 75dc2f8: 8330182: Start of release updates for JDK 24
• 054362a: 8332550: [macos] Voice Over: java.awt.IllegalComponentStateException: component must be showing on the screen to determine its location
• 9b436d0: 8333674: Disable CollectorPolicy.young_min_ergo_vm for PPC64
• 487c477: 8333647: C2 SuperWord: some additional PopulateIndex tests
• d02cb74: 8333270: HandlersOnComplexResetUpdate and HandlersOnComplexUpdate tests fail with "Unexpected reference" if timeoutFactor is less than 1/3
• 02f2404: 8333560: -Xlint:restricted does not work with --release
• 606df44: 8332670: C1 clone intrinsic needs memory barriers
• 33fd6ae: 8333622: ubsan: relocInfo_x86.cpp:101:56: runtime error: pointer index expression with base (-1) overflowed
• 8de5d20: 8332865: ubsan: os::attempt_reserve_memory_between reports overflow
• ... and 336 more: https://git.openjdk.org/jdk/compare/7ce4a13c0a891e606480e138f4025ffa328a18b3...master

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[openjdk]

@rwestrel
The hotspot-compiler label was successfully added.

[mlbridge]

Webrevs

• 00: Full (9d2d06d0)

[shipilev]

This looks reasonable, thanks. Passes all the tests I throw at it.