8353341: C2: removal of a Mod[DF]Node crashes when the node is already dead

[marc-chevalier]

If the Mod[DF]Node has no control projection when it's being removed (because its result is unused), extract_projections will fail an assert. So, let's skip the removal.

But that should happen only when the nodes are already unreachable (control input being transitively top). At the end of the day, the node should be dropped. because of that, so there is no rush, and let dead node deletion do the job.

On the reduced reproducer, the crash is not common (even with -XX:RepeatCompilation=300, it might need more than a run to reproduce). So I've tried my fix on multiple thousands repeat compilations (by 300 packs) without a crash, and without having the modulo node alive at the end.

For instance, that's what happen on the reproducer. Quickly, some big sub-graph is dead, but nodes stay a while in the graph:

Then:

And eventually, everything is removed, so the control projection is removed, and extract_projections doesn't like it.

Thanks,
Marc

---

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Issue

• JDK-8353341: C2: removal of a Mod[DF]Node crashes when the node is already dead (Bug - P3)

Reviewers

• Tobias Hartmann (@TobiHartmann - Reviewer)
• Christian Hagedorn (@chhagedorn - Reviewer)

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[openjdk]

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

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

8353341: C2: removal of a Mod[DF]Node crashes when the node is already dead

Reviewed-by: thartmann, chagedorn

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At the time when this comment was updated there had been 40 new commits pushed to the master branch:

• bd74922: 8338675: javac shouldn't silently change .jar files on the classpath
• 8d3d1d4: 8353058: [PPC64] Some IR framework tests are failing after JDK-8352595
• b01026a: 8353325: Rewrite appcds/methodHandles test cases to use CDSAppTester
• e2e1598: 8353584: [BACKOUT] DaCapo xalan performance with -XX:+UseObjectMonitorTable
• 814730e: 8352645: Add tool support to check order of includes
• d435362: 8353479: jcmd with streaming output breaks intendation
• 130b0cd: 8353217: Build libsleef on macos-aarch64
• 209e72d: 8353234: Refactor XMLSecurityPropertyManager
• cc870d4: 8352088: Call of com.sun.jdi.ThreadReference.threadGroups() can lock up target VM
• d979bd8: 8344671: Few JFR streaming tests fail with application not alive error on MacOS 15
• ... and 30 more: https://git.openjdk.org/jdk/compare/aff5aa72bbf4ecea614339483581093a67efa265...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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[TobiHartmann]

Looks good to me!

[mlbridge]

Webrevs

• 02: Full - Incremental (48bd2037)
• 01: Full - Incremental (f1f0b93b)
• 00: Full (2a347bc0)

[chhagedorn]

Looks good!

[marc-chevalier]

I've fixed everything, ready for next round.

[chhagedorn]

Thanks for the updates, looks good!

[TobiHartmann]

Looks good to me too.

[marc-chevalier]

/integrate

Thanks @chhagedorn and @TobiHartmann!

[openjdk]

@marc-chevalier
Your change (at version 48bd203) is now ready to be sponsored by a Committer.

[chhagedorn]

/sponsor

[openjdk]

Going to push as commit 00a038e.
Since your change was applied there have been 40 commits pushed to the master branch:

• bd74922: 8338675: javac shouldn't silently change .jar files on the classpath
• 8d3d1d4: 8353058: [PPC64] Some IR framework tests are failing after JDK-8352595
• b01026a: 8353325: Rewrite appcds/methodHandles test cases to use CDSAppTester
• e2e1598: 8353584: [BACKOUT] DaCapo xalan performance with -XX:+UseObjectMonitorTable
• 814730e: 8352645: Add tool support to check order of includes
• d435362: 8353479: jcmd with streaming output breaks intendation
• 130b0cd: 8353217: Build libsleef on macos-aarch64
• 209e72d: 8353234: Refactor XMLSecurityPropertyManager
• cc870d4: 8352088: Call of com.sun.jdi.ThreadReference.threadGroups() can lock up target VM
• d979bd8: 8344671: Few JFR streaming tests fail with application not alive error on MacOS 15
• ... and 30 more: https://git.openjdk.org/jdk/compare/aff5aa72bbf4ecea614339483581093a67efa265...master

Your commit was automatically rebased without conflicts.

[openjdk]

@chhagedorn @marc-chevalier Pushed as commit 00a038e.

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