8296170: Refactor stack-locking path in C2_MacroAssembler::fast_unlock()

[rkennke]

The code in C2_MacroAssembler::fast_unlock() has several (minor) issues:

• The stack-locking path for x86_32 is not under UseHeavyMonitors - it would be executed even when stack-locking is disabled.
• The stack-locking paths are the same for x86_32 and x86_64 - they can be merged into a common path.
• In x86_32 path, we call get_thread(boxReg) which is totally bogus because we clear boxReg right afterwards with xorptr(boxReg, boxReg).
• In x86_32 path, the CheckSucc label is identical to the DONE label, and in-fact CheckSucc is only ever really used in the x86_64 path and can be moved there.

Testing:

• tier1 (x86_32, x86_64)
• tier2 (x86_32, x86_64)

---

Progress

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Issue

• JDK-8296170: Refactor stack-locking path in C2_MacroAssembler::fast_unlock()

Reviewers

• Tobias Hartmann (@TobiHartmann - Reviewer) ⚠️ Review applies to 153353ac
• Paul Hohensee (@phohensee - Reviewer) ⚠️ Review applies to 153353ac

Reviewing

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[openjdk]

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[mlbridge]

Webrevs

• 03: Full - Incremental (a75c36b2)
• 02: Full - Incremental (153353ac)
• 01: Full - Incremental (bc4fd918)
• 00: Full (40817c8f)

[TobiHartmann]

We have the same comment here:

jdk/src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp

Line 707 in 12e76cb

// DONE_LABEL is a hot target - we'd really like to place it at the

And it seems to be there from the beginning:
https://hg.openjdk.java.net/jdk/jdk/annotate/74aaad871363/hotspot/src/cpu/x86/vm/x86_32.ad#l3441

I think instead of adding a TODO, we should either completely remove the comments or file a follow-up enhancement to investigate.

[rkennke]

I decided to remove the TODO. If we were to optimize this, then there are probably lower-hanging fruits like looking at the subsequent branch after the DONE_LABEL where we jump around the counting code.

[TobiHartmann]

Looks reasonable to me but I'm not an expert in that code.

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

8296170: Refactor stack-locking path in C2_MacroAssembler::fast_unlock()

Reviewed-by: thartmann, phh

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[phohensee]

The changes net to no change to the executed code, so also lgtm.

There is, however, a pre-submit linux-x86 tier1 test failure that should be resolved.

[rkennke]

The changes net to no change to the executed code, so also lgtm.

There is, however, a pre-submit linux-x86 tier1 test failure that should be resolved.

Yes, that is a known issue. #11065 should fix it, I will pull in latest master and let GHA run again.

[rkennke]

Thanks for reviewing! GHA is green now, let's
/integrate

[openjdk]

Going to push as commit e81359f.
Since your change was applied there have been 18 commits pushed to the master branch:

• 502fa3e: 8296912: C2: CreateExNode::Identity fails with assert(i < _max) failed: oob: i=1, _max=1
• 5795c76: 8296222: SwingEventMonitor - installListeners(Component , int ) - CELLEDITOR - bug
• b9d6e83: 8296906: VMError::controlled_crash crashes with wrong code and address
• cd9c688: 8276064: CheckCastPP with raw oop input floats below a safepoint
• d61720a: 8218885: Restore pop_frame and force_early_return functionality for Graal
• dd9aa72: 8296083: javax/swing/JTree/6263446/bug6263446.java fails intermittently on a VM
• cc44419: 8295407: C2 crash: Error: ShouldNotReachHere() in multiple vector tests with -XX:-MonomorphicArrayCheck -XX:-UncommonNullCast
• e2269fd: 8296968: Update langtools tests to use @enablePreview
• 2159170: 8296453: Simplify resource_area uses in ClassPathDirEntry::open_stream
• 95c390e: 8296956: [JVMCI] HotSpotResolvedJavaFieldImpl.getIndex returns wrong value
• ... and 8 more: https://git.openjdk.org/jdk/compare/8752bb4be8ff71b57ddc262fde73fb3102a1a179...master

Your commit was automatically rebased without conflicts.

[openjdk]

@rkennke Pushed as commit e81359f.

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