8382489: aarch64: Clean up redundant restore_locals() in TemplateTable::invokeinterface

[zifeihan]

Summary

Remove redundant restore_locals() calls in TemplateTable::invokeinterface() on AArch64 and RISC-V architectures. On x86, this call is necessary because the implementation explicitly uses rlocals (r14) as a temporary register throughout the invokeinterface handler, modifying it in multiple code paths. However, on AArch64 and RISC-V, the locals register (rlocals/xlocals) remains untouched throughout the entire invokeinterface execution, making the restore call redundant.

Problem

In templateTable_aarch64.cpp, the invokeinterface() bytecode handler contains a restore_locals()
call at the notVFinal label that is never needed because no preceding code path modifies the locals register.

Code Flow Analysis

void TemplateTable::invokeinterface(int byte_no) {
  load_resolved_method_entry_interface(...);  // May call call_VM → already restores locals
  prepare_invoke(...);                         // Does NOT use rlocals

  // Forced virtual path
  Label notObjectMethod;
  __ tbz(r3, ...is_forced_virtual_shift, notObjectMethod);
  invokevirtual_helper(rmethod, r2, r3);       // Uses r0, r3, r4 - NOT rlocals
  __ bind(notObjectMethod);

  Label no_such_interface;

  // vfinal path
  Label notVFinal;
  __ tbz(r3, ...is_vfinal_shift, notVFinal);
  __ load_klass(r3, r2);                       // Uses r3, NOT rlocals
  __ check_klass_subtype(r3, r0, r4, subtype); // Uses r3, r4 - NOT rlocals
  __ jump_from_interpreted(...);               // Jumps away, never returns to notVFinal

  // notVFinal path (only reached if NOT vfinal)
  __ bind(notVFinal);
  __ restore_locals();  // ← REDUNDANT: rlocals was never modified!
  __ load_klass(r3, r2);
  ...
}

Testing

• tier1, tier2 tests on linux-aarch64(fastdebug)

• I confirm that I make this contribution in accordance with the OpenJDK Interim AI Policy.

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed (2 reviews required, with at least 1 Reviewer, 1 Author)

Issue

• JDK-8382489: aarch64: Clean up redundant restore_locals() in TemplateTable::invokeinterface (Enhancement - P4)

Reviewers

• Andrew Haley (@theRealAph - Reviewer)
• Fei Yang (@RealFYang - Reviewer)
• Dingli Zhang (@DingliZhang - Committer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/30813/head:pull/30813
$ git checkout pull/30813

Update a local copy of the PR:
$ git checkout pull/30813
$ git pull https://git.openjdk.org/jdk.git pull/30813/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 30813

View PR using the GUI difftool:
$ git pr show -t 30813

Using diff file

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https://git.openjdk.org/jdk/pull/30813.diff

Using Webrev

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[bridgekeeper]

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[openjdk]

@zifeihan 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:

8382489: aarch64: Clean up redundant restore_locals() in TemplateTable::invokeinterface

Reviewed-by: aph, fyang, dzhang

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 33 new commits pushed to the master branch:

• a37fd2b: 8367330: Loosen container detection to include soft limits
• 3dcd365: 8382166: [AOT Cache] CRC was not checked on Code Region
• 7d1ce05: 8382277: Shenandoah: Improve mutator runtime entry points
• ... and 30 more: https://git.openjdk.org/jdk/compare/35b0de3d4d4e8212227af5462fafbd464103f058...master

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[openjdk]

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Webrevs

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[theRealAph]

Looks good, thanks.

[RealFYang]

Looks fine to me.

[DingliZhang]

LGTM, thanks!

[lfoltan]

You appear to have used a generative AI tool to create this PR. This violates the OpenJDK AI Policy (https://openjdk.org/legal/ai). Please close this PR and open a new PR that does not contain any AI-generated content.

[zifeihan]

You appear to have used a generative AI tool to create this PR. This violates the OpenJDK AI Policy (https://openjdk.org/legal/ai). Please close this PR and open a new PR that does not contain any AI-generated content.

Thank you for your suggestion. I used AI to help me write the PR description. I’ve already created a new PR. #30864