8309953: Strengthen and optimize oopDesc age methods

[rgithubli]

https://bugs.openjdk.org/browse/JDK-8309953

A clean backport. An minor optimization for oopDesc age.

tier 1 passed locally. The logic is simple - store the mark() value into a var so we don't read it twice. The original commit is in tip for almost 2 years. Low risk.

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Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8309953 needs maintainer approval

Issue

• JDK-8309953: Strengthen and optimize oopDesc age methods (Enhancement - P4 - Requested)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk21u-dev.git pull/1950/head:pull/1950
$ git checkout pull/1950

Update a local copy of the PR:
$ git checkout pull/1950
$ git pull https://git.openjdk.org/jdk21u-dev.git pull/1950/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 1950

View PR using the GUI difftool:
$ git pr show -t 1950

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Download this PR as a diff file:
https://git.openjdk.org/jdk21u-dev/pull/1950.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back rgithubli! 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 change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

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

[openjdk]

⚠️ @rgithubli 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 (34fbdc94)

[rgithubli]

/approval request for backport of 4a5475ce0492fc02019b0f89b50601c388c63e21.

Minor gc perf improvement when it's on a hot path: See the benchmark in comment: openjdk/jdk#14456 (comment)

The backport applies cleanly. Tested with tier 1. In mainline for 2 years. The risk is low.

[openjdk]

@rgithubli
8309953: The approval request has been created successfully.