8286451: C2: assert(nb == 1) failed: only when the head is not shared

[rwestrel]

nb counts the number of loops that share a single head. The assert
that fires is in code that handles the case of a self loop (a loop
composed of a single block). There can be a self loop and multiple
loops that share a head: the assert makes little sense and I propose
to simply remove it.

I think there's another issue with this code: in the case of a self
loop and multiple loops that share a head, the self loop can be any of
the loop for which the head is cloned not only the one that's passed
as argument to ciTypeFlow::clone_loop_head(). As a consequence, I
moved the logic for self loops in the loop that's applied to all loops
that share the loop head.

---

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Issue

• JDK-8286451: C2: assert(nb == 1) failed: only when the head is not shared

Reviewers

• Tobias Hartmann (@TobiHartmann - Reviewer) ⚠️ Review applies to 7ece2dc2
• Christian Hagedorn (@chhagedorn - Reviewer)

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[mlbridge]

Webrevs

• 01: Full - Incremental (f3943fc7)
• 00: Full (7ece2dc2)

[TobiHartmann]

Looks reasonable to me. I submitted testing and will report back once it passed.

[openjdk]

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

8286451: C2: assert(nb == 1) failed: only when the head is not shared

Reviewed-by: thartmann, chagedorn

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At the time when this comment was updated there had been 78 new commits pushed to the master branch:

• 062db59: 8286206: Missing cases for RECORD
• ee4a6c2: 8287799: JFR: Less noisy platform threads with jfr print
• 1499e5e: 8273573: [macos12] ActionListenerCalledTwiceTest.java fails on macOS 12
• 2f62f15: 8287808: javac generates illegal class file for pattern matching switch with records
• 905bcbe: 8286571: java source launcher from a minimal jdk image containing jdk.compiler fails with --enable-preview option
• 8d28734: 8287741: Fix of JDK-8287107 (unused cgv1 freezer controller) was incomplete
• f1dd559: 8287896: PropertiesTest.sh fail on msys2
• 4fe0ca9: 8287860: Revise usage of volatile in j.u.Locale
• bde7a7a: 8287236: Reorganize AST related to pattern matching for switch
• 2d8c649: 8287663: Add a regression test for JDK-8287073
• ... and 68 more: https://git.openjdk.java.net/jdk/compare/5acac2238fdc4ffe6ef290456e01cc559d811557...master

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[chhagedorn]

Looks good!

nb counts the number of loops that share a single head

Maybe you also want to rename the variable to make it more clear what it counts.

[chhagedorn]

Could be converted to @run driver TestSharedLoopHead instead.

[rwestrel]

Right but the test needs -XX:-BackgroundCompilation

[rwestrel]

Looks good!

Thanks for the review.

nb counts the number of loops that share a single head

Maybe you also want to rename the variable to make it more clear what it counts.

Done.

[chhagedorn]

That looks good, thanks for doing the updates!

[TobiHartmann]

All tests passed.

[rwestrel]

@chhagedorn @TobiHartmann thanks for the reviews

[rwestrel]

/integrate

[openjdk]

Going to push as commit bf0e625.
Since your change was applied there have been 101 commits pushed to the master branch:

• 0960ecc: 8287700: C2 Crash running eclipse benchmark from Dacapo
• 590337e: 8286625: C2 fails with assert(!n->is_Store() && !n->is_LoadStore()) failed: no node with a side effect
• 4662e06: 8277307: Pre shared key sent under both session_ticket and pre_shared_key extensions
• 7df48f9: 8287353: Use snippet tag instead of pre tag in Javadoc of InterruptedException
• 32dd1ee: 8287967: Update golden test files after JDK-8287886
• 45f1b72: 8287697: Limit auto vectorization to 32-byte vector on Cascade Lake
• 39ec58b: 8287886: Further terminology updates to match JLS
• 68c5957: 8287869: -XX:+AutoCreateSharedArchive doesn't work when JDK build is switched
• bf439f8: 8287876: The recently de-problemlisted TestTitledBorderLeak test is unstable
• b7a34f7: 8287927: ProblemList java/awt/GraphicsDevice/DisplayModes/UnknownRefrshRateTest.java on macosx-aarch64
• ... and 91 more: https://git.openjdk.java.net/jdk/compare/5acac2238fdc4ffe6ef290456e01cc559d811557...master

Your commit was automatically rebased without conflicts.

[openjdk]

@rwestrel Pushed as commit bf0e625.

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