8310299: C2: 8275201 broke constant folding of array store check in some cases

[rwestrel]

Before 8275201, loading the element klass of an array returned:

TypeKlassPtr::make(tkls->ptr(), elem, 0/*offset*/);

that is exact if the array type is exact. I changed it to:

tkls->is_aryklassptr()->elem();

When the array type is exact (newly allocated array for instance) but
the element class has subclasses, this doesn't return an exact class
(so the logic is different from the one that was there before). That
affects array store checks that no longer constant fold.

---

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Issue

• JDK-8310299: C2: 8275201 broke constant folding of array store check in some cases (Bug - P3)

Reviewers

• Tobias Hartmann (@TobiHartmann - Reviewer)
• Vladimir Kozlov (@vnkozlov - Reviewer)

Reviewing

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[openjdk]

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[mlbridge]

Webrevs

• 00: Full (f4e3f1bb)

[TobiHartmann]

Looks good to me.

[openjdk]

@rwestrel 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:

8310299: C2: 8275201 broke constant folding of array store check in some cases

Reviewed-by: thartmann, kvn

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 151 new commits pushed to the master branch:

• 7fffdb5: 8310405: Linker.Option.firstVariadicArg should specify which index values are valid
• b6c789f: 8309140: ResourceHashtable failed "assert(~(_allocation_t[0] | allocation_mask) == (uintptr_t)this) failed: lost resource object"
• 9f98136: 6956385: URLConnection.getLastModified() leaks file handles for jar:file and file: URLs
• 46e4ee1: 8310974: NMT: Arena diffs miss the scale
• f17bfee: 8311034: Fix typo in javac man page
• 2ccdd29: 8299825: Move StdoutLog and StderrLog to LogConfiguration
• e3f18af: 8311007: jdk/jfr/tool/TestView.java can't find event
• 08c51f2: 8310920: Fix -Wconversion warnings in command line flags
• c2e9485: 8310921: Fix -Wconversion warnings from GenerateOopMap
• ef71c32: 8310110: Shenandoah: Trace page sizes
• ... and 141 more: https://git.openjdk.org/jdk/compare/a45f92961bd0dd603daad8149da4a976d60425f9...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.

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

[sviswa7]

@rwestrel Thanks a lot for this fix. It fully recovers the performance drop that we have been observing since JDK 19.

[vnkozlov]

Good.

[rwestrel]

@TobiHartmann @vnkozlov thanks for the reviews
@sviswa7 thanks for running some testing with the patch

[rwestrel]

/integrate

[openjdk]

Going to push as commit be64d3a.
Since your change was applied there have been 165 commits pushed to the master branch:

• b2eae16: 8295191: IR framework timeout options expect ms instead of s
• af319d9: 8311064: Windows builds fail without precompiled headers after JDK-8310728
• cbf418a: 8311020: Typo cleanup in Classfile API
• f4b900b: 8310902: (fc) FileChannel.transferXXX async close and interrupt issues
• cf8d706: 8308463: Refactor regenerated class handling in lambdaFormInvokers.cpp
• 6f58ab2: 8301569: jmod list option and jimage list --help not interpreted correctly on turkish locale
• 8f5a384: 8311032: Empty value for java.protocol.handler.pkgs system property can lead to unnecessary classloading attempts of protocol handlers
• ded1370: 8309811: BytecodePrinter cannot handle unlinked classes
• 02b17d7: 8310264: In PhaseChaitin::Split defs and phis are leaked
• a63afa4: 8294427: Check boxes and radio buttons have rendering issues on Windows in High DPI env
• ... and 155 more: https://git.openjdk.org/jdk/compare/a45f92961bd0dd603daad8149da4a976d60425f9...master

Your commit was automatically rebased without conflicts.

[openjdk]

@rwestrel Pushed as commit be64d3a.

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

[sviswa7]

/backport jdk21

[openjdk]

@sviswa7 Could not apply backport be64d3ac to openjdk/jdk21 because the change is already present in the target.