8387192: [lworld] Review comment drop for core libs

[liach]

1. weakCompareAndSetReferenceXxx in Unsafe were delegating to wrong methods
2. Replace use of 0 for reference layout with Unsafe.NON_FLAT_LAYOUT
3. Replace use of 31 - Integer.numberOfLeadingZeros(ascale) with numberOfTrailingZeros
4. Remove null check for VarHandle getting from NR fields (parity with ArrayVarHandle and DirectMethodHandle), add missing null check for flat value var handles
5. Remove the weird directives and old flags of RecursiveValueClass

Thanks to @JornVernee and @AlanBateman for spotting these issues.

---

• 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 (1 review required, with at least 1 Committer)

Issue

• JDK-8387192: [lworld] Review comment drop for core libs (Bug - P4)

Reviewers

• Jorn Vernee (@JornVernee - no project role)
• Vicente Romero (@vicente-romero-oracle - Committer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/valhalla.git pull/2576/head:pull/2576
$ git checkout pull/2576

Update a local copy of the PR:
$ git checkout pull/2576
$ git pull https://git.openjdk.org/valhalla.git pull/2576/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 2576

View PR using the GUI difftool:
$ git pr show -t 2576

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/valhalla/pull/2576.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

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

[openjdk]

@liach 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:

8387192: [lworld] Review comment drop for core libs

Reviewed-by: jvernee, vromero

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 4 new commits pushed to the lworld branch:

• 42fc9c9: 8386999: [lworld] C2: assert(is_dead_loop_safe()) failed: shouldn't be cleared yet
• 4542f1d: 8386787: [lworld] compiler/valhalla/inlinetypes/TestValueConstruction.java#StressIncrementalInliningDontInlineMyAbstractInit timed out
• e614970: 8386995: [lworld] Duplicate value classes are a preview feature warning
• ... and 1 more: https://git.openjdk.org/valhalla/compare/441b428aefd1905882cccb357826eb0801ece031...lworld

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 lworld branch, type /integrate in a new comment.

[mlbridge]

Webrevs

• 01: Full - Incremental (da5be85d)
• 00: Full (7e41acd7)

[viktorklang-ora]

LGTM (after comments being handled)

[JornVernee]

Just for my understanding: why is it okay to remove this?

[liach]

The VM and low level libraries ensure null restricted fields never carry null upon write (with strict field initialization). The checks upon read are thus redundant. DirectMethodHandle getters and ArrayVarHandle both have no null check when they read values out of a null-restricted structure. So I think we don't need to be extra cautious here, too.

[vicente-romero-oracle]

looks sensible to me

[liach]

Thanks for the reviews!

/integrate

[openjdk]

Going to push as commit 59019cf.
Since your change was applied there have been 4 commits pushed to the lworld branch:

• 42fc9c9: 8386999: [lworld] C2: assert(is_dead_loop_safe()) failed: shouldn't be cleared yet
• 4542f1d: 8386787: [lworld] compiler/valhalla/inlinetypes/TestValueConstruction.java#StressIncrementalInliningDontInlineMyAbstractInit timed out
• e614970: 8386995: [lworld] Duplicate value classes are a preview feature warning
• ... and 1 more: https://git.openjdk.org/valhalla/compare/441b428aefd1905882cccb357826eb0801ece031...lworld

Your commit was automatically rebased without conflicts.

[openjdk]

@liach Pushed as commit 59019cf.

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