8357822: C2: Multiple string optimization tests are no longer testing string concatenation optimizations

[danielogh]

This PR updates a few tests to reintroduce testing of string concatenation optimizations since a few bugs have recently been identified in this area.

Selection criteria: performed a text search on the test suite and identified tests for string concatenations or string optimizations that are not currently compiled with -XDstringConcat=inline and are not using StringBuilders explicitly.

Testing: T1-4.

Extra testing: ran the tests manually with -XX:+PrintOptimizeStringConcat and verified that the tests are exercising string optimizations after the fix.

---

Progress

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Issue

• JDK-8357822: C2: Multiple string optimization tests are no longer testing string concatenation optimizations (Bug - P4)

Reviewers

• Emanuel Peter (@eme64 - Reviewer) Review applies to 731667f4
• Roberto Castañeda Lozano (@robcasloz - Reviewer)

Reviewing

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[bridgekeeper]

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[openjdk]

@danielogh 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:

8357822: C2: Multiple string optimization tests are no longer testing string concatenation optimizations

Reviewed-by: rcastanedalo, epeter

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At the time when this comment was updated there had been 110 new commits pushed to the master branch:

• af87035: 8355746: Start of release updates for JDK 26
• c59e44a: 8357914: TestEmptyBootstrapMethodsAttr.java fails when run with TEST_THREAD_FACTORY=Virtual
• 23f1d4f: 8337666: AArch64: SHA3 GPR intrinsic
• ... and 107 more: https://git.openjdk.org/jdk/compare/83cb0c6de5988de526545d0926c2c6ef60efc1c7...master

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.

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[openjdk]

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

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[mlbridge]

Webrevs

• 01: Full - Incremental (7fd8568a)
• 00: Full (731667f4)

[eme64]

@danielogh Thanks for looking into this and finding more tests!

Looks reasonable to me. I'm not super familiar with string optimizations, so it would be good if a second reviewer knew a little more. But it looks at least like a good step in the right direction from what I can see :)

[robcasloz]

Do we need to add a second run at all to this test case? As far as I can see, all concat* test cases use explicit string builders and already exercise C2's string concatenation optimizations.

[danielogh]

Thanks for checking! I reverted the change to this test as on a second look the benefits of adding the new configuration to it are modest and out of scope.

[robcasloz]

Thanks!

[danielogh]

Thanks for the reviews and suggestions!

[danielogh]

/integrate

[openjdk]

Going to push as commit 6c616c7.
Since your change was applied there have been 128 commits pushed to the master branch:

• e94ad55: 8342639: Global operator new in adlc has wrong exception spec
• d735255: 8345414: Google CAInterop test failures
• d024f58: 8358809: Improve link to stdin.encoding from java.lang.IO
• ... and 125 more: https://git.openjdk.org/jdk/compare/83cb0c6de5988de526545d0926c2c6ef60efc1c7...master

Your commit was automatically rebased without conflicts.

[openjdk]

@danielogh Pushed as commit 6c616c7.

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