8359603: Missed optimization in PhaseIterGVN for redundant ConvX2Y->ConvY2X->ConvX2Y sequences due to missing notification in PhaseIterGVN::add_users_of_use_to_worklist #26368

benoitmaillard · 2025-07-17T12:25:33Z

This PR addresses a missed optimization in PhaseIterGVN due to the lack of change notification to indirect users within PhaseIterGVN::add_users_of_use_to_worklist (again). This is similar to JDK-8361700.

The optimization in question is the removal of redundant ConvX2Y->ConvY2X->ConvX2Y sequences (where X and Y are primitive number types), which get replaced by a single ConvX2Y as an identity optimization. This missing optimization was originally reported only for ConvD2LNode, but it turns out that other conversion nodes have analog optimization patterns. After manual inspection of identity optimizations in convertnode.cpp, I was able to reproduce missing optimizations for the following conversion sequences:

ConvD2L->ConvL2D->ConvD2L
ConvF2I->ConvI2F->ConvF2I
ConvF2L->ConvL2F->ConvF2L
ConvI2F->ConvF2I->ConvI2F

Similar optimization patterns exist for additional conversion nodes. However, it is not clear if these nodes are subject to the same missed optimization issue. Further investigation may be needed, as I was unable to reproduce such cases with simple tests.

This is again a case where an optimization depends on the input of its input. Currently, PhaseIterGVN::add_users_of_use_to_worklist contains specific logic to handle similar dependencies for other cases, but this specific scenario is not addressed. The proposed fix adds the necessary logic in add_users_of_use_to_worklist to ensure proper notification for this optimization pattern.

Testing

GitHub Actions
tier1-3, plus some internal testing
Added test from the fuzzer, and tests for other sequences (manually derived from the original one)

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Issue

JDK-8359603: Missed optimization in PhaseIterGVN for redundant ConvX2Y->ConvY2X->ConvX2Y sequences due to missing notification in PhaseIterGVN::add_users_of_use_to_worklist (Bug - P4)

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Christian Hagedorn (@chhagedorn - Reviewer)

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bridgekeeper · 2025-07-17T12:26:39Z

👋 Welcome back bmaillard! 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 · 2025-07-17T12:28:03Z

@benoitmaillard 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:

8359603: Missed optimization in PhaseIterGVN for redundant ConvX2Y->ConvY2X->ConvX2Y sequences due to missing notification in PhaseIterGVN::add_users_of_use_to_worklist

Reviewed-by: chagedorn

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 35 new commits pushed to the master branch:

9f796da: 8362972: C2 fails with unexpected node in SuperWord truncation: IsFiniteF, IsFiniteD
ceb0c0f: 8360941: [ubsan] MemRegion::end() shows runtime error: applying non-zero offset 8388608 to null pointer
5160cfb: 8362889: [GCC static analyzer] leak in libstringPlatformChars.c
... and 32 more: https://git.openjdk.org/jdk/compare/62a58062e5f3d0a723608d98d2412ea779f73897...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 · 2025-07-17T12:28:43Z

@benoitmaillard 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.

…t could be trigerred

… optimization patterns

openjdk · 2025-07-21T07:58:34Z

@benoitmaillard this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout JDK-8359603
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

mlbridge · 2025-07-21T08:17:58Z

Webrevs

00: Full (9c49b040)

chhagedorn

Two minor comments, otherwise, it looks good to me!

chhagedorn · 2025-07-23T08:43:48Z

test/hotspot/jtreg/compiler/c2/TestEliminateRedundantConversionSequences.java

+ * @summary Redundant ConvX2Y->ConvY2X->ConvX2Y sequences should be
+ *          simplified to a single ConvX2Y operation when applicable
+ *          VerifyIterativeGVN checks that this optimization was applied
+ * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -XX:CompileCommand=quiet


I think you can remove quiet:

Suggested change

* @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -XX:CompileCommand=quiet

* @run main/othervm -XX:+IgnoreUnrecognizedVMOptions

chhagedorn · 2025-07-23T08:44:36Z

test/hotspot/jtreg/compiler/c2/TestEliminateRedundantConversionSequences.java

+    }
+
+    public static void main(String[] strArr) {
+        for (int i = 0; i < 50_000; ++i) {


Do you really need 50000 iterations each? Would less also trigger the bug?

chhagedorn · 2025-07-23T08:49:38Z

src/hotspot/share/opto/phaseX.cpp

+  // ConvD2L->ConvL2D->ConvD2L
+  // ConvF2I->ConvI2F->ConvF2I
+  // ConvF2L->ConvL2F->ConvF2L
+  // ConvI2F->ConvF2I->ConvI2F


Another thought: Since this is an incomplete list of variations (especially missing, for example, the I2D version while the I2F version is here), should we leave a comment about not being able to trigger issues with the other versions? Otherwise, it could suggest that it was just forgotten.

benoitmaillard added 4 commits July 17, 2025 14:20

8359603: Add missing notification

da34188

8359603: Add test from fuzzer

0202f02

8359603: Add comment explaining the notification

760f10f

8359603: Add opcode check on current node

08d8360

openjdk bot changed the title ~~8359603~~ 8359603: Missed optimization in PhaseIterGVN for redundant ConvD2L->ConvL2D->ConvD2L sequences due to missing notification in PhaseIterGVN::add_users_of_use_to_worklist Jul 17, 2025

openjdk bot added the hotspot-compiler [email protected] label Jul 17, 2025

benoitmaillard added 2 commits July 17, 2025 16:48

8359603: Add other similar conversion patterns for which a missing op…

c829e6c

…t could be trigerred

8359603: Rename test and add cases for other number types with analog…

425bcac

… optimization patterns

8359603: Remove switch in tests

7576633

openjdk bot added the merge-conflict Pull request has merge conflict with target branch label Jul 21, 2025

Merge branch 'master' of https://git.openjdk.org/jdk into JDK-8359603

9c49b04

benoitmaillard marked this pull request as ready for review July 21, 2025 08:13

openjdk bot added rfr Pull request is ready for review and removed merge-conflict Pull request has merge conflict with target branch labels Jul 21, 2025

chhagedorn approved these changes Jul 23, 2025

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openjdk bot added the ready Pull request is ready to be integrated label Jul 23, 2025

chhagedorn reviewed Jul 23, 2025

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8359603: Missed optimization in PhaseIterGVN for redundant ConvX2Y->ConvY2X->ConvX2Y sequences due to missing notification in PhaseIterGVN::add_users_of_use_to_worklist #26368

8359603: Missed optimization in PhaseIterGVN for redundant ConvX2Y->ConvY2X->ConvX2Y sequences due to missing notification in PhaseIterGVN::add_users_of_use_to_worklist #26368

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	* @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -XX:CompileCommand=quiet
	* @run main/othervm -XX:+IgnoreUnrecognizedVMOptions

8359603: Missed optimization in PhaseIterGVN for redundant ConvX2Y->ConvY2X->ConvX2Y sequences due to missing notification in PhaseIterGVN::add_users_of_use_to_worklist #26368

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8359603: Missed optimization in PhaseIterGVN for redundant ConvX2Y->ConvY2X->ConvX2Y sequences due to missing notification in PhaseIterGVN::add_users_of_use_to_worklist #26368

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benoitmaillard commented Jul 17, 2025 •

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