8358334: C2/Shenandoah: incorrect execution with Unsafe

[rwestrel]

When a barrier is expanded, some control is picked as a location for
the barrier. The control input of data nodes that depend on that
control are updated so the nodes are after the expanded barrier unless
the barrier itself depends on some of those nodes.

In this particular failure, a raw memoy Store is the input memory to
the barrier. That Store has an anti-dependent Load. All 3 nodes
(barrier, Load and Store) are at the same control. The Store is
an input to the barrier so it stays before the barrier. The Load's
control is updated to be after the barrier which breaks the
anti-dependency. The bug is that the logic that sorts nodes that need
to be before the barrier and those that can be after ignores
anti-dependencies. The fix simply extends that logic to take them into
account.

/cc shenandoah,hotspot-compiler

---

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Issue

• JDK-8358334: C2/Shenandoah: incorrect execution with Unsafe (Bug - P4)

Reviewers

• William Kemper (@earthling-amzn - Reviewer)
• 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:

8358334: C2/Shenandoah: incorrect execution with Unsafe

Reviewed-by: wkemper, shade

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At the time when this comment was updated there had been 129 new commits pushed to the master branch:

• 8f73357: 8358815: Exception event spec has stale reference to catch_klass parameter
• 4291582: 8357382: runtime/cds/appcds/aotClassLinking/BulkLoaderTest.java#aot fails with Xcomp and C1
• ef4cbec: 8358556: Assert when running with -XX:-UseLibmIntrinsic
• ... and 126 more: https://git.openjdk.org/jdk/compare/faf19abd312ac461f9f74035fec61af7d834ffc1...master

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[openjdk]

@rwestrel
The shenandoah label was successfully added.

The hotspot-compiler label was successfully added.

[mlbridge]

Webrevs

• 00: Full (152ac8e0)

[JohnTortugo]

LGTM. Thanks.

[earthling-amzn]

Thank you for this!

[shipilev]

The patch makes sense.

I ran make test TEST=all TEST_VM_OPTS=-XX:+UseShenandoahGC without new failures.

[rwestrel]

@JohnTortugo @earthling-amzn @shipilev thanks for the reviews and testing.

[rwestrel]

/integrate

[openjdk]

Going to push as commit 1fcede0.
Since your change was applied there have been 143 commits pushed to the master branch:

• fae9c7a: 8351661: NMT: VMATree should support separate call-stacks for reserve and commit operations
• dd68829: 8347273: C2: VerifyIterativeGVN for Ideal and Identity
• b85fe02: 8358600: Template-Framework Library: Template for TestFramework test class
• ... and 140 more: https://git.openjdk.org/jdk/compare/faf19abd312ac461f9f74035fec61af7d834ffc1...master

Your commit was automatically rebased without conflicts.

[openjdk]

@rwestrel Pushed as commit 1fcede0.

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