8304880: [PPC64] VerifyOops code in C1 doesn't work with ZGC

[TheRealMDoerr]

I suggest to remove this code for the following reasons:

• It doesn't work with ZGC (oop needs to go through load barrier, see JBS issue).
• It generates too much code. Loading oops is quite common and the oop verification code is quite lengthy.
• Other platforms don't have it, either.

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Issue

• JDK-8304880: [PPC64] VerifyOops code in C1 doesn't work with ZGC

Reviewers

• Aleksey Shipilev (@shipilev - Reviewer)

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[openjdk]

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

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[mlbridge]

Webrevs

• 00: Full (0b37c1d2)

[TheRealMDoerr]

/label add hotspot-gc

[openjdk]

@TheRealMDoerr
The hotspot-gc label was successfully added.

[shipilev]

So this check_oop happens too early after the load, right?

There are also VerifyOops blocks for stores in the same file, would you like to handle those as well? These oops should be okay with most GCs, but the point about the code size stands. Other platforms do not have the checks on those paths too, AFAICS.

[TheRealMDoerr]

So this check_oop happens too early after the load, right?

Correct, it is placed between the raw load and the load barrier.

There are also VerifyOops blocks for stores in the same file, would you like to handle those as well? These oops should be okay with most GCs, but the point about the code size stands. Other platforms do not have the checks on those paths too, AFAICS.

The store cases are ok with all GCs because we only write valid oops into the heap. Stores seem to be a less frequent than loads. So, the impact on size is smaller. But we could discuss the removal. Other platforms don't have them.

[shipilev]

The store cases are ok with all GCs because we only write valid oops into the heap. Stores seem to be a less frequent than loads. So, the impact on size is smaller. But we could discuss the removal. Other platforms don't have them.

I see no reason to leave them. Your call.

[openjdk]

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

8304880: [PPC64] VerifyOops code in C1 doesn't work with ZGC

Reviewed-by: shade

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At the time when this comment was updated there had been 5 new commits pushed to the master branch:

• 9764948: 8273986: JEditorPane HTML Demo - Accessibility issues
• 5727610: 8304353: Add lib-test tier1 testing in GHA
• d8ba227: 8304069: ClassFileParser has ad-hoc hashtables
• 9a8a60f: 8304833: (fc) Remove dead code in sun.nio.ch.FileChannelImpl::implCloseChannel
• f96aee7: 8291154: Create a non static nested class without enclosing class throws VerifyError

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[TheRealMDoerr]

Thanks for the review!
Hmm, it may be beneficial in some bug chasing scenario if we can ensure that C1 doesn't write any broken oops. I think I had implemented the checking code for that a long time ago. On the other side, we didn't need it for quite some time. Maybe someone else has an opinion about it.

[TheRealMDoerr]

17u is also affected. I keep this PR to fix only the ZGC issue without further cleanup. In addition, the store part may be interesting for testing generational ZGC.
/integrate

[openjdk]

Going to push as commit 695683b.
Since your change was applied there have been 42 commits pushed to the master branch:

• 83ce65e: 8305004: add @SPEC tags to langtools modules
• 32ef452: 8304884: Update Bytecodes data to be mostly compile time constants
• 927e674: 8300977: Retire java.io.ExpiringCache
• c90699e: 8304989: unnecessary dash in @param gives double-dash in docs
• 395a4ce: 8304591: (fs) UnixPath.stringValue need not be volatile
• 60640a2: 8300979: Lazily initialize (byte, char)arr in java.io.DataInputStream
• cddaf68: 8304962: sun/net/www/http/KeepAliveCache/B5045306.java: java.lang.RuntimeException: Failed: Initial Keep Alive Connection is not being reused
• a06f461: 8303214: Typo in java.util.Collections#synchronizedNavigableMap javadoc
• 7987ad4: 8304412: Serial: Refactor old generation cards update after Full GC
• 3c4cd50: 8304963: HttpServer closes connection after processing HEAD after JDK-7026262
• ... and 32 more: https://git.openjdk.org/jdk/compare/4ec720db9f1fedb5da96e70d1a8c5da5e773a5a7...master

Your commit was automatically rebased without conflicts.

[openjdk]

@TheRealMDoerr Pushed as commit 695683b.

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