8377808: compiler/c2/irTests/TestFloat16ScalarOperations.java is fragile in the presence of special constants by mhaessig · Pull Request #31370 · openjdk/jdk

mhaessig · 2026-06-03T14:19:02Z

TestFlaot16ScalarOperations.java is fragile when it comes to unexpected constant folding. Previously, #28678 addressed constant folding for addition with zero. This PR addresses the optimization of division by constants that are reciprocals of powers of two. This is done by reducing the range further to 0.6 to 0.9 as this excludes those reciprocals, which are <= 0.5. In this test we mainly care about the IR matching, so the further reduction of the input space is fine.

Testing:

Gitub Actions
tier1,tier2 and additional stress testing
250 repetitions of TestFlaot16ScalarOperations.java on aarch64

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Issue

JDK-8377808: compiler/c2/irTests/TestFloat16ScalarOperations.java is fragile in the presence of special constants (Bug - P4)

Reviewers

Quan Anh Mai (@merykitty - Reviewer)
Emanuel Peter (@eme64 - Reviewer)
SendaoYan (@sendaoYan - Committer)
Jatin Bhateja (@jatin-bhateja - Reviewer)

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mhaessig · 2026-06-03T14:21:32Z

@eme64 and @jatin-bhateja, may I kindly ask for your review?

bridgekeeper · 2026-06-03T14:21:47Z

👋 Welcome back mhaessig! 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 · 2026-06-03T14:25:19Z

@mhaessig 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:

8377808: compiler/c2/irTests/TestFloat16ScalarOperations.java is fragile in the presence of special constants

Reviewed-by: qamai, epeter, syan, jbhateja

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 19 new commits pushed to the master branch:

bbb4dd8: 8385622: [s390x] Debugger very slow during stepping
b7e2635: 8384442: Shenandoah: Remove vestigial CAS barrier code
19146ad: 8385915: RISC-V: Remove unused cmpxchg* methods
... and 16 more: https://git.openjdk.org/jdk/compare/ec1bffd9a51ae06479a261a6a106f44866212ae7...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.

openjdk · 2026-06-03T14:27:08Z

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

hotspot-compiler

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

openjdk · 2026-06-03T14:27:14Z

The total number of required reviews for this PR has been set to 2 based on the presence of this label: hotspot-compiler. This can be overridden with the /reviewers command.

mlbridge · 2026-06-03T14:31:10Z

Webrevs

mhaessig · 2026-06-03T14:50:31Z

Thank you for taking a look, @sendaoYan! I addressed your comments in the latest commit.

sendaoYan · 2026-06-03T14:52:41Z

Does this missed addScenarios(s0)

It does, but I also do not see the point of running an IR test with value validation with -Xint. Perhaps @jatin-bhateja remembers from back when he wrote that test?

I just went ahead and refactored it.

merykitty

Looks good to me, thanks for making the change.

eme64

Looks good, thanks for fixing this!

eme64 · 2026-06-04T06:37:31Z

-        Scenario s0 = new Scenario(0, "--add-modules=jdk.incubator.vector", "-Xint");
-        Scenario s1 = new Scenario(1, "--add-modules=jdk.incubator.vector");
-        new TestFramework().addScenarios(s1).start();
+        new TestFramework().addFlags("--add-modules=jdk.incubator.vector").start();


Looks like we actually never ran the Xint path! Thanks for cleaning that up.

eme64 · 2026-06-04T06:38:13Z

@jatin-bhateja just tagging you here, this is a test we had designed together, and it has now been flaky multiple times. Just so you are aware ;)

mhaessig · 2026-06-04T07:49:33Z

Thank you all for reviewing!

/integrate

openjdk · 2026-06-04T07:51:24Z

Going to push as commit 8fad96d.
Since your change was applied there have been 19 commits pushed to the master branch:

bbb4dd8: 8385622: [s390x] Debugger very slow during stepping
b7e2635: 8384442: Shenandoah: Remove vestigial CAS barrier code
19146ad: 8385915: RISC-V: Remove unused cmpxchg* methods
... and 16 more: https://git.openjdk.org/jdk/compare/ec1bffd9a51ae06479a261a6a106f44866212ae7...master

Your commit was automatically rebased without conflicts.

openjdk · 2026-06-04T07:51:35Z

@mhaessig Pushed as commit 8fad96d.

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

Restrict input range

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openjdk Bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Jun 3, 2026

openjdk Bot added the rfr Pull request is ready for review label Jun 3, 2026

sendaoYan reviewed Jun 3, 2026

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Comment thread test/hotspot/jtreg/compiler/c2/irTests/TestFloat16ScalarOperations.java

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merykitty approved these changes Jun 3, 2026

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Replace Scenarios with addFlags

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Comment thread test/hotspot/jtreg/compiler/c2/irTests/TestFloat16ScalarOperations.java Outdated

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eme64 approved these changes Jun 4, 2026

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