8374755: ML-KEM's 12-bit decompression can be simplified on aarch64

[stooke]

I would like to backport JDK-8374755 to JDK25 as part of Post Quantum Cryptography support. While this is a performance enhancement, I feel that PQC needs to be as performant as possible to encourage adoption.

This is also for Oracle parity.

This is a clean, low-risk backport.

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Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8374755 needs maintainer approval

Issue

• JDK-8374755: ML-KEM's 12-bit decompression can be simplified on aarch64 (Bug - P4 - Approved)

Reviewers

• Andrew Haley (@theRealAph - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk25u-dev.git pull/645/head:pull/645
$ git checkout pull/645

Update a local copy of the PR:
$ git checkout pull/645
$ git pull https://git.openjdk.org/jdk25u-dev.git pull/645/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 645

View PR using the GUI difftool:
$ git pr show -t 645

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk25u-dev/pull/645.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back stooke! 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]

@stooke 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:

8374755: ML-KEM's 12-bit decompression can be simplified on aarch64

Reviewed-by: aph

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 5 new commits pushed to the master branch:

• b0d5b7d: 8352565: Add native method implementation of Reference.get()
• 7ec1d5f: 8377991: TestLimitsUpdating.java fails with runtime exception even after JDK-8370492 is fixed
• 3b47a4e: 8368520: TLS 1.3 KeyUpdate fails with SunPKCS11 provider
• ... and 2 more: https://git.openjdk.org/jdk25u-dev/compare/b84eb0571a714266c17833782bd4701f94bb3542...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.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[openjdk]

⚠️ @stooke This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[mlbridge]

Webrevs

• 00: Full (f5be6245)