8267726: ZGC: array_copy_requires_gc_barriers too strict #4230

neliasso · 2021-05-27T19:59:59Z

I found some cases where an arraycopy clone is eliminated with G1 but not with ZGC. This is probably something that wasn't updated fully after the transition to late gc barrier insertion.

During parse and optimizaton phases array_copy_requires_gc_barriers should return false for clones of oop-arrays. Clone of oop-arrays should be treated the same way as clones of primitive-arrays. During optimization phase - only clones of instances should return true - and that's because they can't be reduced to a raw bulk copy, Clones of instances must either become deconstructed into field copies, or be handled in a special call.

During expansion array_copy_requires_gc_barriers must return true - because we must use a copy with barriers.

To fix this I had to add an extra field to array_copy_requires_gc_barriers to be able to handle instance clones separately. I will follow up with a cleanup. The intersection of arraycopy-kinds and array_copy_requires_gc_barriers-method is the source of much unnecessary complexity.

Please review,
Best regards,
Nils Eliasson

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JDK-8267726: ZGC: array_copy_requires_gc_barriers too strict

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Tobias Hartmann (@TobiHartmann - Reviewer)
Vladimir Ivanov (@iwanowww - Reviewer)

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bridgekeeper · 2021-05-27T20:01:12Z

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openjdk · 2021-05-27T20:04:15Z

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neliasso · 2021-05-28T09:11:56Z

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neliasso · 2021-05-28T09:58:42Z

Moved to hotspot-compiler

TobiHartmann

Looks good to me. Please file a cleanup RFE and link it to this bug. Also, this might be a good candidate for adding a regression test once the IR verification framework is there.

openjdk · 2021-06-01T07:09:05Z

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8267726: ZGC: array_copy_requires_gc_barriers too strict

Reviewed-by: thartmann, vlivanov

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At the time when this comment was updated there had been 139 new commits pushed to the master branch:

d47a77d: 8267773: PhaseStringOpts::int_stringSize doesn't handle min_jint correctly
496fb90: 8267969: Add vectorized implementation for VectorMask.eq()
1cea6ca: 8260360: IGV: Short name of combined nodes is hidden by background color
7530c00: 8266559: XPathEvaluationResult.XPathResultType.NODESET maps to incorrect type
b98e52a: 8267570: The comment of the class JavacParser is not appropriate
379376f: 8265130: Make ConstantDesc class hierarchy sealed
00c7aee: 8267861: Update SourceVersion with new language features in 16 and 17
cb7128b: 8266950: Remove vestigial support for non-strict floating-point execution
8624cb5: 8266530: HotSpot changes for JEP 306
0ae4ceb: 8244146: javac changes for JEP 306
... and 129 more: https://git.openjdk.java.net/jdk/compare/ee2651b9e5a9ab468b4be73d43b8f643e9e92042...master

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neliasso · 2021-06-01T08:58:35Z

I filed RFE https://bugs.openjdk.java.net/browse/JDK-8268020

Yes - all the arraycopy and clone tests should be ported to IR verification. I might do that as a part of the RFE.

Thanks for the review Tobias!

iwanowww

Looks good.

neliasso · 2021-06-02T09:01:25Z

Thanks for the reviews, Tobias and Vladimir.

/integrate

neliasso · 2021-06-02T09:01:40Z

Thanks for the reviews, Tobias and Vladimir.

openjdk · 2021-06-02T09:03:58Z

@neliasso Since your change was applied there have been 139 commits pushed to the master branch:

d47a77d: 8267773: PhaseStringOpts::int_stringSize doesn't handle min_jint correctly
496fb90: 8267969: Add vectorized implementation for VectorMask.eq()
1cea6ca: 8260360: IGV: Short name of combined nodes is hidden by background color
7530c00: 8266559: XPathEvaluationResult.XPathResultType.NODESET maps to incorrect type
b98e52a: 8267570: The comment of the class JavacParser is not appropriate
379376f: 8265130: Make ConstantDesc class hierarchy sealed
00c7aee: 8267861: Update SourceVersion with new language features in 16 and 17
cb7128b: 8266950: Remove vestigial support for non-strict floating-point execution
8624cb5: 8266530: HotSpot changes for JEP 306
0ae4ceb: 8244146: javac changes for JEP 306
... and 129 more: https://git.openjdk.java.net/jdk/compare/ee2651b9e5a9ab468b4be73d43b8f643e9e92042...master

Your commit was automatically rebased without conflicts.

Pushed as commit bba3728.

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Nils Eliasson added 3 commits May 25, 2021 20:46

Fix barrier requirement

e55f283

adapt opt

71e0aa3

Fix array_copy_requires_gc_barriers

19b1427

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neliasso marked this pull request as ready for review May 28, 2021 09:11

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TobiHartmann approved these changes Jun 1, 2021

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iwanowww approved these changes Jun 2, 2021

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openjdk bot added integrated Pull request has been integrated and removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jun 2, 2021

8267726: ZGC: array_copy_requires_gc_barriers too strict #4230

8267726: ZGC: array_copy_requires_gc_barriers too strict #4230

neliasso commented May 27, 2021 •

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8267726: ZGC: array_copy_requires_gc_barriers too strict #4230

8267726: ZGC: array_copy_requires_gc_barriers too strict #4230

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neliasso commented May 27, 2021 • edited by openjdk bot

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