8319777: Zero: Support 8-byte cmpxchg

[shipilev]

Clean backport to improve Zero support.

Additional testing:

• Linux x86_32 Zero, jcstress run
• Large matrix of Zero builds

---

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
• JDK-8319777 needs maintainer approval
• JDK-8320582 needs maintainer approval

Issues

• JDK-8319777: Zero: Support 8-byte cmpxchg (Enhancement - P4 - Approved)
• JDK-8320582: Zero: Misplaced CX8 enablement flag (Bug - P4 - Approved)

Reviewers

• Paul Hohensee (@phohensee - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk21u-dev.git pull/232/head:pull/232
$ git checkout pull/232

Update a local copy of the PR:
$ git checkout pull/232
$ git pull https://git.openjdk.org/jdk21u-dev.git pull/232/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 232

View PR using the GUI difftool:
$ git pr show -t 232

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk21u-dev/pull/232.diff

Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back shade! 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]

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

[shipilev]

/issue add JDK-8320582

[openjdk]

@shipilev
Adding additional issue to issue list: 8320582: Zero: Misplaced CX8 enablement flag.

[shipilev]

/approval request 8319777 Clean backport to improve Zero support. It enables the code that is protected by VMVersion::supports_cx8 flag, but significant chunk of the code is already does 8-byte CASes without consulting this flag. The patch is contained in Zero and gives no risk to Server ports. Zero testing passes. JDK-8320582 is the follow-up for this one.
/approval request 8320582 Clean followup to JDK-8319777. Zero testing passes.

[openjdk]

@shipilev
8319777: The approval request has been created successfully.
8320582: The approval request has been created successfully.

[openjdk]

@shipilev
8319777: The approval request has been updated successfully.
8320582: The approval request has been updated successfully.

[mlbridge]

Webrevs

• 00: Full (54596ccf)

[GoeLin]

/approve yes

[openjdk]

@GoeLin
8319777: The approval request has been approved.
8320582: The approval request has been approved.

[openjdk]

@shipilev 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:

8319777: Zero: Support 8-byte cmpxchg
8320582: Zero: Misplaced CX8 enablement flag

Reviewed-by: phh

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 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.

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

[shipilev]

/integrate

[openjdk]

Going to push as commit 98e6d04.

[openjdk]

@shipilev Pushed as commit 98e6d04.

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