8254314: Shenandoah: null checks in c2 should not skip over native load barrier

[rwestrel]

C2 optimizes (CmpP (LoadBarrier o) NULL) as (CmpP o NULL). The ative
load barrier is not guaranteed to return a non null oop when passed a
non null oop so this optimization could lead to a crash.

/cc shenandoah,hotspot-compiler

---

Progress

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Testing

	Linux x64	Windows x64	macOS x64
Build	❌ (2/5 failed)	✔️ (2/2 passed)	✔️ (2/2 passed)
Build / test	✔️ (0/0 passed)
Test (tier1)		✔️ (9/9 passed)	✔️ (9/9 passed)

Failed test tasks

• Linux x64 (build hotspot minimal)
• Linux x64 (build hotspot zero)

Issue

• JDK-8254314: Shenandoah: null checks in c2 should not skip over native load barrier

Reviewers

• Roman Kennke (@rkennke - Reviewer)

Download

$ git fetch https://git.openjdk.java.net/jdk pull/576/head:pull/576
$ git checkout pull/576

[bridgekeeper]

👋 Welcome back roland! 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]

@rwestrel
The shenandoah label was successfully added.

The hotspot-compiler label was successfully added.

[rkennke]

It looks good to me! While this doesn't seem to reproduce with normal native-barriers yet, it's been a major headache in the ongoing work on concurrent weak reference processing, and I don't see why normal native-barriers wouldn't be affected by it. We've probably been lucky so far.

[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:

8254314: Shenandoah: null checks in c2 should not skip over native load barrier

Reviewed-by: rkennke

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 6 new commits pushed to the master branch:

• 2bbf8a2: 8245543: Cgroups: Incorrect detection logic on some systems (still reproducible)
• aaa0a2a: 8254297: Zero and Minimal VMs are broken with undeclared identifier 'DerivedPointerTable' after JDK-8253180
• 7e80c98: 8254261: fix javadocs in jdk.test.lib.Utils
• d4b5dfd: 8253857: Shenandoah: Bugs in ShenandoahEvacOOMHandler related code
• e9c1905: 8253740: [PPC64] Minor interpreter cleanup
• b1448da: 8253900: SA: wrong size computation when JVM was built without AOT

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
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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[mlbridge]

Webrevs

• 00: Full (11a6202)

[rwestrel]

/integrate

[openjdk]

@rwestrel Since your change was applied there have been 21 commits pushed to the master branch:

• c73a0ff: 8252105: Parallel heap inspection for ZCollectedHeap
• 45b09a3: 8253833: mutexLocker assert_locked_or_safepoint should not access VMThread state from non-VM-thread
• 77c7762: 8254353: Remove unused non-product flags
• d3069ac: 8254362: x86_32 builds fail after JDK-8253180
• 25001c5: 8254352: 3 compiler tests failed with "assert(allocates2(pc)) failed: not in CodeBuffer memory"
• d43f141: 8254351: Minimal VM build fails with undeclared identifier 'MaxVectorSize' after JDK-8252847
• cc52358: 8254335: logging/logStream.hpp includes memory/resourceArea.hpp but doesn't need it
• 4b5ac3a: 8252847: Optimize primitive arrayCopy stubs using AVX-512 masked instructions
• ec41046: 8254348: Build fails when cds is disabled after JDK-8247536
• e4469d2: 8247536: Support for pre-generated java.lang.invoke classes in CDS static archive
• ... and 11 more: https://git.openjdk.java.net/jdk/compare/2bc8bc572233b4bb59554f2da064d8feef23635a...master

Your commit was automatically rebased without conflicts.

Pushed as commit a2bb4c6.

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