8371534: C2: Missed Ideal optimization opportunity with AndL and URShiftL

[benoitmaillard]

This PR addresses a missed optimization in PhaseIterGVN due to a missing notification to indirect users within PhaseIterGVN::add_users_of_use_to_worklist.

The affected optimization is the transformation of (x & mask) >> shift into (x >> shift) & (mask >> shift), where mask is a constant, for URShiftL and URShiftI nodes. This transformation is handled in URShiftLNode::Ideal and URShiftINode::Ideal. JDK-8361700 addressed the analog case for RShiftL and RShiftI, but lacked the notification for unsigned shifting.

This PR builds on top of JDK-8361700 and adds the following changes:

• Fix the notification mechanism in add_users_of_use_to_worklist
• Add the URShiftL in TestMaskAndRShiftReorder.java
• Drive-by changes: simplify the RShiftL test case slightly, and add the missing analog case for RShiftI

I tried to reproduce the missing optimization for the URShiftI without success. There must be some subtle difference with the long case that causes the optimization to be triggered in this specific setup. I still added the case to the fix in add_users_of_use_to_worklist, as there are likely cases where the notification is missing (but I was just not able to find one).

Testing

• GitHub Actions
• tier1-4, plus some internal testing

Thank you for reviewing!

---

Progress

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Issue

• JDK-8371534: C2: Missed Ideal optimization opportunity with AndL and URShiftL (Bug - P4)

Reviewers

• Tobias Hartmann (@TobiHartmann - Reviewer)
• Manuel Hässig (@mhaessig - Committer)

Reviewing

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[bridgekeeper]

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[openjdk]

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

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

8371534: C2: Missed Ideal optimization opportunity with AndL and URShiftL

Reviewed-by: thartmann, mhaessig

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At the time when this comment was updated there had been 8 new commits pushed to the master branch:

• 72989e0: 8340093: C2 SuperWord: implement cost model
• 6e838d6: 8371474: Wrong object class or methodID passed to JNI call in TestSharedCloseJvmti with -Xshare:off
• 2d4f2fd: 8349732: Add support for JARs signed with ML-DSA
• ... and 5 more: https://git.openjdk.org/jdk/compare/49f51f9450ac3b923f83ba7d9089e5560e25ec7a...master

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[openjdk]

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• hotspot-compiler

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[mlbridge]

Webrevs

• 00: Full (a5184343)

[TobiHartmann]

That looks good to me. Thanks for quickly jumping on this!

[mhaessig]

Thank you for fixing this, @benoitmaillard! This looks good to me.

[benoitmaillard]

Thank you for the reviews @TobiHartmann @mhaessig!
/integrate

[openjdk]

Going to push as commit f5eacbe.
Since your change was applied there have been 20 commits pushed to the master branch:

• bbeb6bf: 8371493: Simplify search for AdapterHandlerEntry
• 405d5f7: 8371297: C2: assert triggered in BoolTest::BoolTest
• cbd77fc: 8370244: [PPC64] Several vector tests fail on Power8
• ... and 17 more: https://git.openjdk.org/jdk/compare/49f51f9450ac3b923f83ba7d9089e5560e25ec7a...master

Your commit was automatically rebased without conflicts.

[openjdk]

@benoitmaillard Pushed as commit f5eacbe.

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