8348411: C2: Remove the control input of LoadKlassNode and LoadNKlassNode #23274

merykitty · 2025-01-23T17:22:02Z

Hi,

This patch removes the control input of LoadKlassNode and LoadNKlassNode. They can only have a control input if created inside Parse::array_store_check(), the reason given is:

// We are allowed to use the constant type only if cast succeeded

But this seems incorrect, the load from the constant type can be done regardless, and it will be constant-folded. This patch only makes that more formal and cleanup LoadKlassNode::can_remove_control.

Please take a look and leave your reviews, thanks a lot.

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JDK-8348411: C2: Remove the control input of LoadKlassNode and LoadNKlassNode (Enhancement - P4)

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Vladimir Ivanov (@iwanowww - Reviewer)
Emanuel Peter (@eme64 - Reviewer)

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bridgekeeper · 2025-01-23T17:23:08Z

👋 Welcome back qamai! 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 · 2025-01-23T17:24:18Z

@merykitty 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:

8348411: C2: Remove the control input of LoadKlassNode and LoadNKlassNode

Reviewed-by: vlivanov, epeter

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At the time when this comment was updated there had been no new commits pushed to the master branch. If another commit should be pushed before you perform the /integrate command, your PR will be automatically rebased. If you prefer to avoid any potential automatic rebasing, please check the documentation for the /integrate command for further details.

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openjdk · 2025-01-23T17:25:16Z

@merykitty The following labels will be automatically applied to this pull request:

graal
hotspot-compiler

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

mlbridge · 2025-01-23T17:28:26Z

Webrevs

src/hotspot/share/opto/parseHelper.cpp

iwanowww · 2025-01-28T20:56:30Z

src/hotspot/share/opto/parseHelper.cpp

-      && !too_many_traps(Deoptimization::Reason_array_check)
-      && !tak->klass_is_exact()
+  if (MonomorphicArrayCheck && !too_many_traps(Deoptimization::Reason_array_check) && !tak->klass_is_exact()
      && tak != TypeInstKlassPtr::OBJECT) {


I'd also turn tak != TypeInstKlassPtr::OBJECT into tak->isa_aryklassptr() to stress the intention.
(Please, keep the original formatting here.)

Done, I assume you meant the formatting of the comment below, right?

No, I referred to the original shape of the condition (1 check per line). IMO it is easier to follow.

iwanowww

Looks good (w/ minor cleanup suggestions).

Testing (hs-tier1 - hs-tier4) results are clean.

src/hotspot/share/opto/parseHelper.cpp

iwanowww · 2025-01-30T16:38:19Z

src/hotspot/share/opto/parseHelper.cpp

-      && !too_many_traps(Deoptimization::Reason_array_check)
-      && !tak->klass_is_exact()
+  if (MonomorphicArrayCheck && !too_many_traps(Deoptimization::Reason_array_check) && !tak->klass_is_exact()
      && tak != TypeInstKlassPtr::OBJECT) {


No, I referred to the original shape of the condition (1 check per line). IMO it is easier to follow.

merykitty · 2025-01-30T17:06:38Z

@iwanowww Thanks a lot for your reviews and testing, I hope I have addressed all of your concerns.

eme64

Nice cleanup.
Though it looks like you are doing more than remove the ctrl input. I don't know the code very well, so I have some questions ;)

eme64 · 2025-02-04T18:39:32Z

src/hotspot/share/opto/parseHelper.cpp

+  if (MonomorphicArrayCheck &&
+      !too_many_traps(Deoptimization::Reason_array_check) &&
+      !tak->klass_is_exact() &&
+      tak->isa_aryklassptr()) {


Looks like an implicit nullptr check. Not allowed by code style ;)

Can you quickly explain this change from tak != TypeInstKlassPtr::OBJECT so I don't need to investigate myself, please?

Looks like an implicit nullptr check. Not allowed by code style ;)

But the verb here is isa and we use these as a bool a lot, though :/

Can you quickly explain this change from tak != TypeInstKlassPtr::OBJECT so I don't need to investigate myself, please?

The bottom type of an array can be either Object or an array of some kind, so tak != TypeInstKlassPtr::OBJECT is the same as tak->isa_aryklassptr().

Ah great, thanks for the explanation!

eme64 · 2025-02-04T18:43:04Z

src/hotspot/share/opto/parseHelper.cpp

      //
      // See issue JDK-8057622 for details.

-    always_see_exact_class = true;


Why is it ok to remove this?
If this branch is not taken, it used to be false, and would lead to something different below...

The only use of this is to decide if we need to attach a control input to the LoadKlass. As the control input is not needed, this can be removed.

Got it, thanks!

eme64

Looks good, thanks for the explanations!

I see we did not yet run internal tests for the last commit, though it is only formatting, so most most likely ok.

But the state of the code is also 2 weeks old, so it would be good if you merged and launched testing again before integration, just in case ;)

merykitty · 2025-02-06T19:12:26Z

@eme64 I have merged the change with master, could you help me initiate the testing process, please? Thanks very much.

eme64 · 2025-02-07T07:04:19Z

@merykitty Testing launched!

eme64 · 2025-02-07T16:37:37Z

@merykitty Testing is all passing!

merykitty · 2025-02-08T04:19:43Z

Thanks a lot for your reviews and testing!
/integrate

openjdk · 2025-02-08T04:20:48Z

Going to push as commit e9278de.
Since your change was applied there have been 17 commits pushed to the master branch:

5395ffa: 8327378: XMLStreamReader throws EOFException instead of XMLStreamException
1ed9ef1: 8349559: Compiler interface doesn't need to store protection domain
f0ea38b: 8349509: [macos] Clean up macOS dead code in jpackage
7f6c687: 8349374: [JVMCI] concurrent use of HotSpotSpeculationLog can crash
bd9b24c: 8349512: Duplicate PermittedSubclasses entries with doclint enabled
b40f8ee: 8337251: C1: Improve Class.isInstance intrinsic
88a8483: 8349121: SSLParameters.setApplicationProtocols() ALPN example could be clarified
fb847bb: 8349493: Replace sun.util.locale.ParseStatus usage with java.text.ParsePosition
7cd5cb2: 8349532: Refactor ./util/Pem/encoding.sh to run in java
86cec4e: 8343782: G1: Use one G1CardSet instance for multiple old gen regions
... and 7 more: https://git.openjdk.org/jdk/compare/ed8945a68a67dd51a7cfa332905941afccc12b36...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-02-08T04:20:57Z

@merykitty Pushed as commit e9278de.

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

remove control input of LoadKlassNode

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openjdk bot added the rfr Pull request is ready for review label Jan 23, 2025

openjdk bot added graal graal-dev@openjdk.org hotspot-compiler hotspot-compiler-dev@openjdk.org labels Jan 23, 2025

iwanowww reviewed Jan 23, 2025

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src/hotspot/share/opto/parseHelper.cpp Show resolved Hide resolved

remove always_see_exact_class

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clearer intention, revert formatting, add assert

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format

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eme64 suggested changes Feb 4, 2025

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Merge branch 'master' into loadklassctrl

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8348411: C2: Remove the control input of LoadKlassNode and LoadNKlassNode #23274

8348411: C2: Remove the control input of LoadKlassNode and LoadNKlassNode #23274

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