8365570: C2 fails assert(false) failed: Unexpected node in SuperWord truncation: CastII

[TobiHartmann]

Hi all,

This pull request contains a backport of commit 775f48de from the openjdk/jdk repository.

The commit being backported was authored by Jasmine Karthikeyan on 9 Jan 2026 and was reviewed by Christian Hagedorn, Tobias Hartmann and Emanuel Peter.

Thanks!

---

Progress

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

Issue

• JDK-8365570: C2 fails assert(false) failed: Unexpected node in SuperWord truncation: CastII (Bug - P3)

Reviewers

• Benoît Maillard (@benoitmaillard - Committer)
• Emanuel Peter (@eme64 - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/29134/head:pull/29134
$ git checkout pull/29134

Update a local copy of the PR:
$ git checkout pull/29134
$ git pull https://git.openjdk.org/jdk.git pull/29134/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 29134

View PR using the GUI difftool:
$ git pr show -t 29134

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/29134.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back thartmann! A progress list of the required criteria for merging this PR into jdk26 will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

@TobiHartmann 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:

8365570: C2 fails assert(false) failed: Unexpected node in SuperWord truncation: CastII

Reviewed-by: bmaillard, epeter

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 1 new commit pushed to the jdk26 branch:

• e0f1c3a: 8351889: C2 crash: assertion failed: Base pointers must match (addp 344)

Please see this link for an up-to-date comparison between the source branch of this pull request and the jdk26 branch.
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 jdk26 branch, type /integrate in a new comment.

[openjdk]

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

[openjdk]

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

• hotspot-compiler

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.

[mlbridge]

Webrevs

• 00: Full (2b3c9fa5)

[benoitmaillard]

Looks good to me!

[eme64]

Thanks for the backport :)

[TobiHartmann]

Thanks for the reviews, Benoît and Emanuel!

[TobiHartmann]

/integrate

[openjdk]

Going to push as commit 10d97c5.
Since your change was applied there has been 1 commit pushed to the jdk26 branch:

• e0f1c3a: 8351889: C2 crash: assertion failed: Base pointers must match (addp 344)

Your commit was automatically rebased without conflicts.

[openjdk]

@TobiHartmann Pushed as commit 10d97c5.

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