8286190: Add test to verify constant folding for Enum fields

[shipilev]

There is the JDK-8161245 to make compilers trust Enum final fields. It was implicitly implemented by JDK-8234049, which added the wildcard trust for everything in java/lang:

jdk/src/hotspot/share/ci/ciField.cpp

Line 230 in c5a0687

holder->is_in_package("java/lang"))

It would be better to have the explicit test that verifies the constant folding of Enum fields indeed happens.

Additional testing:

• Linux x86_64 fastdebug, new test passes
• Linux x86_64 release, new test passes
• Linux x86_32 fastdebug, new test passes

---

Progress

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Issue

• JDK-8286190: Add test to verify constant folding for Enum fields

Reviewers

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

Reviewing

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[openjdk]

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[mlbridge]

Webrevs

• 00: Full (2052cd5c)

[vnkozlov]

Nice find. So we are doing ENUM constant folding since JDK 14 and did not notice it ;)

Test is good. Thanks!

[openjdk]

@shipilev This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8286190: Add test to verify constant folding for Enum fields

Reviewed-by: kvn, thartmann

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At the time when this comment was updated there had been 33 new commits pushed to the master branch:

• 015cfda: 8262004: Classpath separator: Man page says semicolon; should be colon on Linux
• 9425ab2: 8286153: Remove redundant casts and other cleanup
• 7ebc4bc: 8286066: assert(k != __null) failed: klass not loaded caused by FillerObject_klass
• 6a1b145: 8286029: Add classpath exemption to globals_vectorApiSupport_***.S.inc
• 59ef76a: 8285497: Add system property for Java SE specification maintenance version
• 6d7e446: 8283306: re-resolving indirect call to non-entrant nmethod can crash
• 4957bc7: 8286056: AArch64: clarify uses of MacroAssembler::far_call/MacroAssembler::far_jump
• e7adc28: 8284675: "jpackage.exe" creates application launcher without Windows Application Manfiest
• 9644a31: 8285616: [macos] Incorrect path for launcher-as-service.txt in .cfg file
• 2f995c8: 8286199: ProblemList jdk/jshell/ExternalEditorTest.java
• ... and 23 more: https://git.openjdk.java.net/jdk/compare/497a94fead145788af6f196d2c7166efc46a9e9e...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.

[mlbridge]

Mailing list message from John Rose on hotspot-compiler-dev:

This reminds me that our enum switches do not allow constant folding,
because of our translation strategy.

The root cause is that the T.S. open-codes the discrimination logic for
switches, and it happens to use Java arrays, which cannot be
constant-folded. There is a way to ?trust? an array element, called
`@Stable`, but it can only be used inside a JDK runtime support method,
not in a random classfile generated by javac.

So the T.S. should encapsulate switch discrimination logic so that a
runtime support routine can use appropriate technology, such as stable
arrays and/or perfect hashes and/or binary searches. It?s not really
javac?s job to build such things, and when it tries it just gets in
the way of doing a better job in the runtime.

https://bugs.openjdk.java.net/browse/JDK-8161250 tracks this general
issue.

These points relate to this bug only in that, if we had our ducks in a
row with translation of switch, we could test also for constant-folding
of switch logic.

On 5 May 2022, at 8:45, Vladimir Kozlov wrote:

[TobiHartmann]

Looks good.

[shipilev]

Thanks!

/integrate

[openjdk]

Going to push as commit 080f3c5.
Since your change was applied there have been 40 commits pushed to the master branch:

• 1277f5d: 8286154: Fix 3rd party notices in test files
• 2dd4dfd: 8286291: G1: Remove unused segment allocator printouts
• b9f4370: 8286189: G1: Change "wasted" memory to "unused" memory in reporting
• c6eab98: 8285378: Remove unnecessary nop for C1 exception and deopt handler
• 3cdedf1: 8248863: Add search landing page to API documentation
• fa1ca98: 8281429: PhiNode::Value() is too conservative for tripcount of CountedLoop
• dd06cc6: 8283807: Handle CompileThreshold the same as other thresholds when scaled with -XX:CompileThresholdScaling
• 015cfda: 8262004: Classpath separator: Man page says semicolon; should be colon on Linux
• 9425ab2: 8286153: Remove redundant casts and other cleanup
• 7ebc4bc: 8286066: assert(k != __null) failed: klass not loaded caused by FillerObject_klass
• ... and 30 more: https://git.openjdk.java.net/jdk/compare/497a94fead145788af6f196d2c7166efc46a9e9e...master

Your commit was automatically rebased without conflicts.

[openjdk]

@shipilev Pushed as commit 080f3c5.

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