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8312749: Generational ZGC: Tests crash with assert(index == 0 || is_power_of_2(index)) #15288

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@robcasloz robcasloz commented Aug 15, 2023

This changeset ensures that the array copy stub underlying the intrinsic implementation of Object.clone only copies its (double-word aligned) payload, excluding the remaining object alignment padding words, when a non-default ObjectAlignmentInBytes value is used. This prevents the specialized ZGC stubs for Object[] array copy from processing undefined object alignment padding words as valid object pointers. For further details about the specific failure, see initial analysis by Erik Österlund and Stefan Karlsson and comments in the regression test included in this changeset.

As a side-benefit, the changeset simplifies the array size computation logic in GraphKit::new_array() by decoupling computation of header size and alignment padding size.

Testing

Functionality
  • tier1-3 (windows-x64, linux-x64, linux-aarch64, macosx-x64, and macosx-aarch64)
  • tier4-5 (windows-x64, linux-x64, linux-aarch64, macosx-x64, and macosx-aarch64; ZGC-specific tests only)
  • tier6-9 (linux-x64; ZGC-specific tests only)
  • tier1-3, and a few custom examples, applying JDK-8139457 (under review) on top of this changeset
Performance

Tested performance on the following set of OpenJDK micro-benchmarks, on linux-x64 (for both G1 and ZGC, using different ObjectAlignmentInBytes values):

  • openjdk.bench.java.lang.ArrayClone.byteClone
  • openjdk.bench.java.lang.ArrayClone.intClone
  • openjdk.bench.java.lang.ArrayFiddle.simple_clone
  • openjdk.bench.java.lang.Clone.cloneLarge
  • openjdk.bench.java.lang.Clone.cloneThreeDifferent

No significant regression was observed.


Progress

  • Change must be properly reviewed (1 review required, with at least 1 Reviewer)
  • Change must not contain extraneous whitespace
  • Commit message must refer to an issue

Issue

  • JDK-8312749: Generational ZGC: Tests crash with assert(index == 0 || is_power_of_2(index)) (Bug - P3)

Reviewers

Contributors

  • Stefan Karlsson <stefank@openjdk.org>
  • Erik Österlund <eosterlund@openjdk.org>

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/15288/head:pull/15288
$ git checkout pull/15288

Update a local copy of the PR:
$ git checkout pull/15288
$ git pull https://git.openjdk.org/jdk.git pull/15288/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 15288

View PR using the GUI difftool:
$ git pr show -t 15288

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/15288.diff

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bridgekeeper bot commented Aug 15, 2023

👋 Welcome back rcastanedalo! 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.

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/contributor add @stefank

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/contributor add @fisk

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openjdk bot commented Aug 15, 2023

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Contributor Stefan Karlsson <stefank@openjdk.org> successfully added.

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openjdk bot commented Aug 15, 2023

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Contributor Erik Österlund <eosterlund@openjdk.org> successfully added.

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openjdk bot commented Aug 15, 2023

@robcasloz The following label will be automatically applied to this pull request:

  • hotspot

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

@openjdk openjdk bot added the hotspot hotspot-dev@openjdk.org label Aug 15, 2023
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/label add hotspot-compiler

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/label add hotspot-gc

@openjdk openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Aug 17, 2023
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The hotspot-compiler label was successfully added.

@openjdk openjdk bot added the hotspot-gc hotspot-gc-dev@openjdk.org label Aug 17, 2023
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The hotspot-gc label was successfully added.

@robcasloz robcasloz marked this pull request as ready for review August 17, 2023 12:38
@openjdk openjdk bot added the rfr Pull request is ready for review label Aug 17, 2023
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Webrevs

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Looks good to me!

src/hotspot/share/gc/shared/c2/barrierSetC2.cpp Outdated Show resolved Hide resolved
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openjdk bot commented Aug 21, 2023

@robcasloz 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:

8312749: Generational ZGC: Tests crash with assert(index == 0 || is_power_of_2(index))

Co-authored-by: Stefan Karlsson <stefank@openjdk.org>
Co-authored-by: Erik Österlund <eosterlund@openjdk.org>
Reviewed-by: thartmann, ayang, kvn

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 271 new commits pushed to the master branch:

  • 2624324: 8219567: Name of first parameter of RandomAccessFile(String,String) is inconsistent
  • 8e4240c: 8314850: SharedRuntime::handle_wrong_method() gets called too often when resolving Continuation.enter
  • d9fc6b6: 8314759: VirtualThread.parkNanos timeout adjustment when pinned should be replaced
  • acaab6f: 8306040: HttpResponseInputStream.available() returns 1 on empty stream
  • 76b9011: 8314656: GHA: No need for Debian ports keyring installation after JDK-8313701
  • e36620d: 8314554: Debian/Ubuntu should not link OpenJDK with --as-needed link option
  • 97b94cb: 8314883: Java_java_util_prefs_FileSystemPreferences_lockFile0 write result errno in missing case
  • 75e19e0: 8314819: [JVMCI] HotSpotJVMCIRuntime.lookupType throws unexpected ClassNotFoundException
  • c418933: 8313530: VM build without C2 fails after JDK-8312579
  • de0e46c: 8303815: Improve Metaspace test speed
  • ... and 261 more: https://git.openjdk.org/jdk/compare/ec2f38fd389dc51dc4d8925e037a8bf2e64a3722...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.

@openjdk openjdk bot added the ready Pull request is ready to be integrated label Aug 21, 2023
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If I understand it correctly, much of the diff is to ensure that ArrayCopyNode::make (in BarrierSetC2::clone) gets the correct value for the length arg, calculated as align_up(array-length * elem-size, word-size) / word-size.

I wonder if it's possible to pass the actual array length (#slots) as length and move the merge-bytes-to-words-copying optimization to a lower level, e.g. inside conjoint_jbytes. Ofc, BarrierSetC2::clone_at_expansion and its derived siblings need to be adjusted accordingly, e.g. to use the actual elem-type.

(Preexisting: having ArrayCopyNode to cover both array and instance cloning hinders the readability, IMO.)

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Thanks for reviewing, Tobias!

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Looks good.

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Looks good.

Thanks for reviewing, Vladimir!

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If I understand it correctly, much of the diff is to ensure that ArrayCopyNode::make (in BarrierSetC2::clone) gets the correct value for the length arg, calculated as align_up(array-length * elem-size, word-size) / word-size.

I wonder if it's possible to pass the actual array length (#slots) as length and move the merge-bytes-to-words-copying optimization to a lower level, e.g. inside conjoint_jbytes. Ofc, BarrierSetC2::clone_at_expansion and its derived siblings need to be adjusted accordingly, e.g. to use the actual elem-type.

(Preexisting: having ArrayCopyNode to cover both array and instance cloning hinders the readability, IMO.)

Thanks for looking at this, Albert! I agree that the code could benefit from some clean-up, and postponing the merge-bytes-to-words-copying optimization to at least BarrierSetC2::clone_at_expansion() is worth exploring. However, your suggested refactoring would not be trivial, so I suggest to integrate this fix as-is and address the simplification in a separate RFE. Please let me know if you agree, and, if so, I will create a separate RFE for your suggestion.

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I suggest to integrate this fix as-is and address the simplification in a separate RFE

Sounds reasonable.

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Sounds reasonable.

Thanks, Albert! I created JDK-8314994 to capture your suggestions, please feel free to edit/extend the description if needed to reflect better your idea.

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/integrate

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openjdk bot commented Aug 25, 2023

Going to push as commit 002b594.
Since your change was applied there have been 272 commits pushed to the master branch:

  • d024059: 8314951: VM build without C2 still fails after JDK-8313530
  • 2624324: 8219567: Name of first parameter of RandomAccessFile(String,String) is inconsistent
  • 8e4240c: 8314850: SharedRuntime::handle_wrong_method() gets called too often when resolving Continuation.enter
  • d9fc6b6: 8314759: VirtualThread.parkNanos timeout adjustment when pinned should be replaced
  • acaab6f: 8306040: HttpResponseInputStream.available() returns 1 on empty stream
  • 76b9011: 8314656: GHA: No need for Debian ports keyring installation after JDK-8313701
  • e36620d: 8314554: Debian/Ubuntu should not link OpenJDK with --as-needed link option
  • 97b94cb: 8314883: Java_java_util_prefs_FileSystemPreferences_lockFile0 write result errno in missing case
  • 75e19e0: 8314819: [JVMCI] HotSpotJVMCIRuntime.lookupType throws unexpected ClassNotFoundException
  • c418933: 8313530: VM build without C2 fails after JDK-8312579
  • ... and 262 more: https://git.openjdk.org/jdk/compare/ec2f38fd389dc51dc4d8925e037a8bf2e64a3722...master

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Aug 25, 2023
@openjdk openjdk bot closed this Aug 25, 2023
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Aug 25, 2023
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@robcasloz Pushed as commit 002b594.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

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