8256046: Shenandoah: Mix-in NULL_PTR in non-strong ShLRBNode's type

[rkennke]

Testing found this problem (very rare/hard to reproduce):

# Internal Error (d:/a/jdk/jdk/jdk/src/hotspot/cpu/x86/macroAssembler_x86.cpp:880), pid=6160, tid=5828
# fatal error: DEBUG MESSAGE: unexpected null in intrinsic

I believe this may be caused by non-strong LRB reporting a non-NULL type by passing-through its input's type, even though it may actually return NULL on non-NULL inputs. If this serves as input to an intrinsic, it may lead to elimination of surrounding null-check, and thus end up passing a NULL to the intrinsic even thought it should not.

Testing:

• hotspot_gc_shenandoah
• tier1+Shenandoah
• tier2+Shenandoah

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Testing

	Linux x64	Linux x86	Windows x64	macOS x64
Build	✔️ (5/5 passed)	✔️ (2/2 passed)	✔️ (2/2 passed)	✔️ (2/2 passed)
Test (tier1)	✔️ (9/9 passed)	✔️ (9/9 passed)	⏳ (3/9 running)	❌ (1/9 failed)

Failed test task

• macOS x64 (hs/tier1 common)

Issue

• JDK-8256046: Shenandoah: Mix-in NULL_PTR in non-strong ShLRBNode's type

Reviewers

• Roland Westrelin (@rwestrel - Reviewer) ⚠️ Review applies to 6fbeabb
• Aleksey Shipilev (@shipilev - Reviewer)

Download

$ git fetch https://git.openjdk.java.net/jdk pull/1120/head:pull/1120
$ git checkout pull/1120

[bridgekeeper]

👋 Welcome back rkennke! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

@rkennke The following labels will be automatically applied to this pull request:

• hotspot-gc
• shenandoah

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[openjdk]

@rkennke 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:

8256046: Shenandoah: Mix-in NULL_PTR in non-strong ShLRBNode's type

Reviewed-by: roland, shade

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 18 new commits pushed to the master branch:

• a1d4b9f: 8256009: Remove src/hotspot/share/adlc/Test/i486.ad
• 3455fa9: 8256050: JVM crashes with -XX:+PrintDeoptimizationDetails
• e6df13e: 8256054: C2: Floating-point min/max operations on vectors intermittently produce wrong results for NaN values
• 52805f5: 8256048: Incomplete gitignore setting for netbeans project
• 9d07259: 8255598: [PPC64] assert(Universe::heap()->is_in(result)) failed: object not in heap
• e281b13: 8255011: [TESTBUG] compiler/codecache/stress/UnexpectedDeoptimizationAllTest.java timed out
• c601849: 8256038: G1: Improve comment about mark word handling of displaced mark words
• a38dd53: 8256040: Shenandoah: Allow NULL referent in ShenandoahReferenceProcessor::should_discover()
• 01567b5: 8256036: Shenandoah: MethodHandles adapters section overflows after JDK-8255762
• 4bc065c: 8255782: Turn UseTLAB and ResizeTLAB from product_pd to product, defaulting to "true"
• ... and 8 more: https://git.openjdk.java.net/jdk/compare/d99e1f6c296c23b8714fc94fe4f3c7bece000f9c...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.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[mlbridge]

Webrevs

• 02: Full - Incremental (8350d33)
• 01: Full - Incremental (d98ea79)
• 00: Full (6fbeabb)

[shipilev]

Thanks. Looks fine to me.

[rkennke]

/integrate

[openjdk]

@rkennke Since your change was applied there have been 18 commits pushed to the master branch:

• a1d4b9f: 8256009: Remove src/hotspot/share/adlc/Test/i486.ad
• 3455fa9: 8256050: JVM crashes with -XX:+PrintDeoptimizationDetails
• e6df13e: 8256054: C2: Floating-point min/max operations on vectors intermittently produce wrong results for NaN values
• 52805f5: 8256048: Incomplete gitignore setting for netbeans project
• 9d07259: 8255598: [PPC64] assert(Universe::heap()->is_in(result)) failed: object not in heap
• e281b13: 8255011: [TESTBUG] compiler/codecache/stress/UnexpectedDeoptimizationAllTest.java timed out
• c601849: 8256038: G1: Improve comment about mark word handling of displaced mark words
• a38dd53: 8256040: Shenandoah: Allow NULL referent in ShenandoahReferenceProcessor::should_discover()
• 01567b5: 8256036: Shenandoah: MethodHandles adapters section overflows after JDK-8255762
• 4bc065c: 8255782: Turn UseTLAB and ResizeTLAB from product_pd to product, defaulting to "true"
• ... and 8 more: https://git.openjdk.java.net/jdk/compare/d99e1f6c296c23b8714fc94fe4f3c7bece000f9c...master

Your commit was automatically rebased without conflicts.

Pushed as commit 97d6e4a.

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