8382490: RISC-V: 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_riscv.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 xlocals

  // Forced virtual path
  Label notObjectMethod;
  __ test_bit(t0, x13, ...is_forced_virtual_shift);
  __ beqz(t0, notObjectMethod);
  invokevirtual_helper(xmethod, x12, x13);     // Uses x10, x13, x14 - NOT xlocals
  __ bind(notObjectMethod);

  Label no_such_interface;

  // vfinal path
  Label notVFinal;
  __ test_bit(t0, x13, ...is_vfinal_shift);
  __ beqz(t0, notVFinal);
  __ load_klass(x13, x12);                     // Uses x13, NOT xlocals
  __ check_klass_subtype(x13, x10, x14, subtype); // Uses x13, x14 - NOT xlocals
  __ jump_from_interpreted(xmethod);           // Jumps away, never returns to notVFinal

  // notVFinal path (only reached if NOT vfinal)
  __ bind(notVFinal);
  __ restore_locals();  // ← REDUNDANT: xlocals was never modified!
  __ load_klass(x13, x12);
  ...
}

Testing

• tier1 tests on SOPHON SG2042 (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-8382490: RISC-V: Clean up redundant restore_locals() in TemplateTable::invokeinterface (Enhancement - P4)

Reviewers

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

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/30814/head:pull/30814
$ git checkout pull/30814

Update a local copy of the PR:
$ git checkout pull/30814
$ git pull https://git.openjdk.org/jdk.git pull/30814/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 30814

View PR using the GUI difftool:
$ git pr show -t 30814

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/30814.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back gcao! 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]

@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:

8382490: RISC-V: Clean up redundant restore_locals() in TemplateTable::invokeinterface

Reviewed-by: 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

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.

As you do not have Committer status in this project an existing Committer must agree to sponsor your change. Possible candidates are the reviewers of this PR (@RealFYang, @DingliZhang) but any other Committer may sponsor as well.

➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

[openjdk]

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

• hotspot

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

[openjdk]

The total number of required reviews for this PR has been set to 2 based on the presence of this label: hotspot. This can be overridden with the /reviewers command.

[RealFYang]

Looks good. Thanks.

[mlbridge]

Webrevs

• 00: Full (43cacbc0)

[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.