8331194: NPE in ArrayCreationTree.java with -XX:-UseCompressedOops #20087

JohnTortugo · 2024-07-09T00:06:33Z

Please, review this PR to fix issue in debug information serialization encountered when RAM reduces a Phi for which one of the inputs is an object already scalar replaced.

Details:

Consider class Picture that has two reference fields, first and second of type Point. In a random method in the application an object obj of this class is created, and the fields of this object are initialized such that first is assigned a new object whereas second receives the output of a Phi node merging the object assigned to first and some other allocation. Also, assumes obj is used as debug information in an uncommon_trap and none of these objects escapes. I.e., we have a scenario like this:

Picture obj       = new Picture(); // allocation A
        obj.first = new Point(); // allocation B

Point    p2    = obj.first;
if (<cond>) p2 = new Point(); // allocation C

obj.second = p2;

<trap>

After one iteration of EA+SR, Allocation A will be scalar replaced and debug information in <Trap> adjusted accordingly. The description of field second in the debug information on <Trap> will, however, still involve a Phi node between allocation B and C. In the next iteration of EA+SR the Phi node for field second will be reduced by RAM and debug information will be adjusted accordingly. So far nothing is wrong.

The issue happens because the existing code in Process_OopMap_Node to serialize debug information was missing a check. Simply, the check for setting is_root of an ObjectValue wasn't checking that the ObjectValue might be a description of a field of a scalar replaced object. It was only checking whether ObjectValue was a local, stack or monitor. Consequently, the allocation assigned to obj.first (yes, first) was not being marked as root.

But the issue only manifested if the <trap> was exercised AND the result of <cond> was true. If the result of <cond> was false when the trap was exercised, then no problem would happen. The reason is, when <cond> is true the select method in ObjectMergeValue would flag, correctly, that the allocation inside the if needs to be rematerialized and the other input of the ObjectMergeValue shouldn't be rematerialized because _is_root == false, meaning it's just a candidate for rematerialization.

Fixing the check for setting _is_root solved the problem. The -XX:-UseCompressedOops wasn't directly related to the problem, it just caused DecodeN, EncodeP nodes to not show up in the graph and RAM consider the Phi for reduction.

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Issue

JDK-8331194: NPE in ArrayCreationTree.java with -XX:-UseCompressedOops (Bug - P2)

Reviewers

Vladimir Kozlov (@vnkozlov - Reviewer)

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bridgekeeper · 2024-07-09T00:07:19Z

👋 Welcome back cslucas! 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 · 2024-07-09T00:08:02Z

@JohnTortugo 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:

8331194: NPE in ArrayCreationTree.java with -XX:-UseCompressedOops

Reviewed-by: 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 137 new commits pushed to the master branch:

a60608e: 8334169: Long arguments of attach operation are silently truncated on Windows
59bf3d7: 8336080: Fix -Wzero-as-null-pointer-constant warnings in ClassLoaderStats ctor
88eff4c: 8336421: ciMethod() constructor should use ConditionalMutexLocker(Compile_lock)
c99be35: 8336474: Problemlist compiler/interpreter/Test6833129 on x86_32
419cc46: 8335533: OutOfMemoryError: Metaspace observed again on AIX in test RedefineLeakThrowable.java after JDK-8294960
8feabc8: 8334057: JLinkReproducibleTest.java support receive test.tool.vm.opts
bc7cd42: 8314498: [macos] Transferring File objects to Finder fails
c8a95a7: 8072701: resume001 failed due to ERROR: timeout for waiting for a BreakpintEvent
388fcf0: 8336349: Fix more simple -Wzero-as-null-pointer-constant warnings in C2 code
ab27aca: 8336297: C2: Fix -Wzero-as-null-pointer-constant warnings in derived Node ctors
... and 127 more: https://git.openjdk.org/jdk/compare/77a7078b82fd0cb3cfa13685072f04fdef33758b...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.

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openjdk · 2024-07-09T00:08:53Z

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

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mlbridge · 2024-07-09T22:00:33Z

Webrevs

src/hotspot/share/opto/machnode.hpp

src/hotspot/share/opto/output.cpp

test/hotspot/jtreg/compiler/c2/TestReduceAllocationAndNestedScalarized.java

Co-authored-by: Emanuel Peter <emanuel.peter@oracle.com>

eme64 · 2024-07-11T10:34:13Z

@JohnTortugo

This test is intended to "test" a transformation in C2, it won't fail if run in C1, but it won't actually test what's intended for. The flagless option is to make sure that C2 produce an IR graph that will trigger the optimization, same reasoning for all the "CompileCommand" options. I may remove the "vm.bits" part, I included it because of the "-UseCompressedOops".

The flagless requires will just mean that your test is not run if there are flags. So we still rely on the test configuration having some run without additional flags. So your requires seems pointless, especially because your test does not crash without it. Unless your test takes a lot of time and you are trying to conserve runtime.

About flags: I would just have a second run without any flags.

vnkozlov · 2024-07-11T15:38:10Z

You can use -XX:+IgnoreUnrecognizedVMOptions flag instead of require "vm.bits".
Yes, do second run without flags.

I also suggest put test into corresponding directory compiler/escapeAnalysis. compiler/c2 is used for legacy or some C2 general tests.

vnkozlov

The fix looks fine. I have few comments.

src/hotspot/share/opto/machnode.hpp

src/hotspot/share/opto/output.cpp

…ments.

JohnTortugo · 2024-07-11T19:18:09Z

@vnkozlov @eme64 - I moved all tests related to "RAM" to the suggested folder and modified the test, added in this PR, to remove the flags as you suggested.

Please, let me ask more about configuring the test to run without flags. Without the flags, for instance, the CompileCommands, the IR graph will very likely not be in the shape that trigger the problem. Even with the CompileCommands, if some other flags included in the list of flags to run the test, the IR graph may also not be in the shape that will trigger the problem. Why run the test if it doesn't trigger the problem it was intended for? I'm probably missing something here.

vnkozlov

Please, reverse movement of old tests. We need to backport this fix into JDK 23 and for that we need only related test.
You can move them in separate RFE in JDK 24 (current mainline).

vnkozlov · 2024-07-11T19:52:31Z

Why run the test if it doesn't trigger the problem it was intended for? I'm probably missing something here.

We hope to catch other issues with each new test. We are running with variety of flags combinations set by testing environment and a test may fail for different reason. It is all about code shape variations and flags combinations.

JohnTortugo · 2024-07-11T20:00:56Z

Please, reverse movement of old tests. We need to backport this fix into JDK 23 and for that we need only related test. You can move them in separate RFE in JDK 24 (current mainline).

I reverted the move. I had forgot about the backport.

vnkozlov

Good.

test/hotspot/jtreg/compiler/escapeAnalysis/TestReduceAllocationAndNestedScalarized.java

vnkozlov · 2024-07-12T17:53:04Z

I will run testing with latest version. Tobias ran with version 0 and all passed. Since then there were only cosmetic changes but we still need to verify it.

JohnTortugo · 2024-07-12T18:42:49Z

Sounds good. Thank you!

vnkozlov · 2024-07-12T23:29:28Z

My testing passed.

@JohnTortugo, can you check why only 5 tests ran in GHA testing?

JohnTortugo · 2024-07-15T16:19:49Z

@vnkozlov - I'm looking into that and I'll update here.

JohnTortugo · 2024-07-15T19:16:05Z

@vnkozlov - I don't know why some of the checks didn't trigger automatically. It's still under investigation.

I manually triggered them, and they all passed.

JohnTortugo · 2024-07-15T19:16:16Z

/integrate

openjdk · 2024-07-15T19:17:07Z

@JohnTortugo
Your change (at version 8486b4a) is now ready to be sponsored by a Committer.

vnkozlov · 2024-07-15T19:36:18Z

@eme64 I you fine with current version?

test/hotspot/jtreg/compiler/escapeAnalysis/TestReduceAllocationAndNestedScalarized.java

eme64 · 2024-07-16T08:27:30Z

src/hotspot/share/opto/output.cpp

+      continue;
+    }
+
+    ObjectValue* other = (ObjectValue*) sv_for_node_id(objs, n->_idx);


Is the cast here necessary? I see them generally in the file... but not sure why.

ObjectValue* PhaseOutput::sv_for_node_id(GrowableArray<ScopeValue*> *objs, int id) {

Because objs array may contains 3 types of objects: ScopeValue, ObjectValue and ObjectMergeValue.
I would leave this code as it is for this PR but suggest to file followup RFE to clean this up.
Instead of such casts we should use as_ObjectValue() and as_ObjectMergeValue() which have asserts to check type.

Thank you @eme64 , @vnkozlov for reviewing. I created this RFE to remove the unnecessary casts: https://bugs.openjdk.org/browse/JDK-8336495

eme64 · 2024-07-16T11:59:43Z

@vnkozlov @JohnTortugo I'm not familiar enough with this part of the code, just gave some code style and testing suggestions. I was given something else that has higher priority, so maybe some one else can give the VM changes a review?

…nAndNestedScalarized.java Co-authored-by: Emanuel Peter <emanuel.peter@oracle.com>

vnkozlov

Update is good.

JohnTortugo · 2024-07-16T19:59:52Z

/integrate

openjdk · 2024-07-16T20:00:39Z

@JohnTortugo
Your change (at version 9726bd7) is now ready to be sponsored by a Committer.

vnkozlov · 2024-07-16T20:45:23Z

/sponsor

openjdk · 2024-07-16T20:47:45Z

Going to push as commit 005fb67.
Since your change was applied there have been 137 commits pushed to the master branch:

a60608e: 8334169: Long arguments of attach operation are silently truncated on Windows
59bf3d7: 8336080: Fix -Wzero-as-null-pointer-constant warnings in ClassLoaderStats ctor
88eff4c: 8336421: ciMethod() constructor should use ConditionalMutexLocker(Compile_lock)
c99be35: 8336474: Problemlist compiler/interpreter/Test6833129 on x86_32
419cc46: 8335533: OutOfMemoryError: Metaspace observed again on AIX in test RedefineLeakThrowable.java after JDK-8294960
8feabc8: 8334057: JLinkReproducibleTest.java support receive test.tool.vm.opts
bc7cd42: 8314498: [macos] Transferring File objects to Finder fails
c8a95a7: 8072701: resume001 failed due to ERROR: timeout for waiting for a BreakpintEvent
388fcf0: 8336349: Fix more simple -Wzero-as-null-pointer-constant warnings in C2 code
ab27aca: 8336297: C2: Fix -Wzero-as-null-pointer-constant warnings in derived Node ctors
... and 127 more: https://git.openjdk.org/jdk/compare/77a7078b82fd0cb3cfa13685072f04fdef33758b...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-07-16T20:47:53Z

@vnkozlov @JohnTortugo Pushed as commit 005fb67.

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

TobiHartmann · 2024-07-17T05:14:26Z

/backport :jdk23

openjdk · 2024-07-17T05:16:29Z

@TobiHartmann the backport was successfully created on the branch backport-TobiHartmann-005fb67e-jdk23 in my personal fork of openjdk/jdk. To create a pull request with this backport targeting openjdk/jdk:jdk23, just click the following link:

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Hi all,

This pull request contains a backport of commit 005fb67e from the openjdk/jdk repository.

The commit being backported was authored by Cesar Soares Lucas on 16 Jul 2024 and was reviewed by Vladimir Kozlov.

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$ git push https://github.com/openjdk-bots/jdk.git backport-TobiHartmann-005fb67e-jdk23

Fix RAM Nested Scalarized Objects

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Revert moving tests. Another rename.

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8331194: NPE in ArrayCreationTree.java with -XX:-UseCompressedOops #20087

8331194: NPE in ArrayCreationTree.java with -XX:-UseCompressedOops #20087

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8331194: NPE in ArrayCreationTree.java with -XX:-UseCompressedOops #20087

8331194: NPE in ArrayCreationTree.java with -XX:-UseCompressedOops #20087

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