8223923: C2: Missing interference with mismatched unsafe accesses

[iwanowww]

Memory effects of mixed or mismatched unsafe accesses aren't properly tracked, so every problematic access is wrapped into a pair of MemBarCPUOrder nodes to isolate it from the rest of the memory graph. But MemNode::can_see_stored_value() unconditionally steps over MemBarCPUOrder and exposes problematic MergeMem nodes.

Proposed fix forbids stepping over MemBarCPUOrder nodes when looking for an earlier store into the same location.

Alternatively, a new kind of barrier could be introduced specifically for isolation purposes, but I didn't spot any issues during performance testing with the current patch to justify more complex solution.

Testing: hs-tier1 - hs-tier6, performance testing.

---

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Issue

• JDK-8223923: C2: Missing interference with mismatched unsafe accesses

Reviewers

• Tobias Hartmann (@TobiHartmann - Reviewer)

Reviewing

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[mlbridge]

Webrevs

• 00: Full (8c8bd180)

[TobiHartmann]

That looks reasonable to me.

[openjdk]

@iwanowww 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:

8223923: C2: Missing interference with mismatched unsafe accesses

Reviewed-by: thartmann

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At the time when this comment was updated there had been 12 new commits pushed to the master branch:

• 5189047: 8272558: IR Test Framework README misses some flags
• ec63957: 8272398: Update DockerTestUtils.buildJdkDockerImage()
• 14623cd: 8270835: regression after JDK-8261006
• fe72197: 8272551: mark hotspot runtime/modules tests which ignore external VM flags
• 05d64da: 8272291: mark hotspot runtime/logging tests which ignore external VM flags
• a68b5b9: 8272369: java/io/File/GetXSpace.java failed with "RuntimeException: java.nio.file.NoSuchFileException: /run/user/0"
• a199ebc: 8272581: sun/security/pkcs11/Provider/MultipleLogins.sh fails after JDK-8266182
• 1cbf41a: 8225083: Remove Google certificate that is expiring in December 2021
• cf64c3e: 8272326: java/util/Random/RandomTestMoments.java had two Gaussian fails
• 2ed7b70: 8272521: Remove unused PSPromotionManager::_claimed_stack_breadth
• ... and 2 more: https://git.openjdk.java.net/jdk/compare/0e3fde6c3c2f5c05777b79ff5eb1188014269b0f...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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[iwanowww]

Thanks for the review, Tobias.

/integrate

[openjdk]

Going to push as commit 86add21.
Since your change was applied there have been 38 commits pushed to the master branch:

• c701f6e: 8272739: Misformatted error message in EventHandlerCreator
• fb1dfc6: 8267185: Add string deduplication support to ParallelGC
• d874e96: 8271579: G1: Move copy before CAS in do_copy_to_survivor_space
• 92bde67: 8271946: Cleanup leftovers in Space and subclasses
• db9834f: 8258951: java/net/httpclient/HandshakeFailureTest.java failed with "RuntimeException: Not found expected SSLHandshakeException in java.io.IOException"
• a81e5e9: 8272654: Mark word accesses should not use Access API
• 4bd37c3: 8272708: [Test]: Cleanup: test/jdk/security/infra/java/security/cert/CertPathValidator/certification/BuypassCA.java no longer needs ocspEnabled
• ddcd851: 8272602: [macos] not all KEY_PRESSED events sent when control modifier is used
• d007be0: 8272700: [macos] Build failure with Xcode 13.0 after JDK-8264848
• f4be211: 8270041: Consolidate oopDesc::cas_forward_to() and oopDesc::forward_to_atomic()
• ... and 28 more: https://git.openjdk.java.net/jdk/compare/0e3fde6c3c2f5c05777b79ff5eb1188014269b0f...master

Your commit was automatically rebased without conflicts.

[openjdk]

@iwanowww Pushed as commit 86add21.

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