8372154: AArch64: Match rule failure with some CompareAndSwap operand shapes

[shipilev]

Fixes the corner case in AArch64 encoding rules that assert in debug and bail out in release.

Additional testing:

• Linux AArch64 server fastdebug, all
• Linux AArch64 server release, 24h jcstress run

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Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8372154 needs maintainer approval

Issue

• JDK-8372154: AArch64: Match rule failure with some CompareAndSwap operand shapes (Bug - P4 - Requested)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk25u-dev.git pull/709/head:pull/709
$ git checkout pull/709

Update a local copy of the PR:
$ git checkout pull/709
$ git pull https://git.openjdk.org/jdk25u-dev.git pull/709/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 709

View PR using the GUI difftool:
$ git pr show -t 709

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk25u-dev/pull/709.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

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[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]

⚠️ @shipilev 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 (82fdc81c)

[shipilev]

/approval request Fixes the corner case in AArch64 encoding rules that assert in debug and bail out in release. Bailing out from C2 compilation would cause performance anomalies. Patch applies cleanly. There are no follow-ups after 8 months in mainline, except the rewrite to use M4 stencils later. Risk is medium-low: touches C2 match rules, but in simple manner, tests pass, no bugtail.

[openjdk]

@shipilev
8372154: The approval request has been created successfully.