8370195: [lworld] Constant-fold _layout_kind loads from constant FlatArrayKlass

[merykitty]

Hi,

The load to FlatArrayKlass::_layout_kind can be constant-folded if the receiver is a constant. This eliminates all checks when the array type is known statically or speculated correctly.

Please leave your reviews, thanks a lot.

---

Progress

• Change must not contain extraneous whitespace

Issue

• JDK-8370195: [lworld] Constant-fold _layout_kind loads from constant FlatArrayKlass (Enhancement - P4)

Reviewers

• Tobias Hartmann (@TobiHartmann - Committer)

Reviewing

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[merykitty]

Benchmark result:

Benchmark                          Mode  Cnt       Score      Error  Units
HoistArrayChecks.atomicHoisted     avgt   15  358138.658 ± 4705.964  ns/op
HoistArrayChecks.atomicNaive       avgt   15  576348.282 ± 3179.475  ns/op
HoistArrayChecks.nonAtomicHoisted  avgt   15  292872.250 ± 9536.215  ns/op
HoistArrayChecks.nonAtomicNaive    avgt   15  296264.018 ± 2185.786  ns/op
HoistArrayChecks.nullableHoisted   avgt   15  479879.297 ± 1753.756  ns/op
HoistArrayChecks.nullableNaive     avgt   15  675267.274 ± 4161.829  ns/op

[bridgekeeper]

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[openjdk]

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

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

8370195: [lworld] Constant-fold _layout_kind loads from constant FlatArrayKlass

Reviewed-by: thartmann

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At the time when this comment was updated there had been 4 new commits pushed to the lworld branch:

• 0b87efa: 8367405: [lworld] C2 compilation fails with empty program detected during loop optimization
• cccb501: 8367073: [lworld] Conform to JEP 450 encoding of mark word
• c42a95f: 8369437: [lworld] Split multiple @run statements in compiler tests into separate @test blocks
• ... and 1 more: https://git.openjdk.org/valhalla/compare/75c007b13865a023fb830805436b07f263e4abef...lworld

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[mlbridge]

Webrevs

• 01: Full - Incremental (d3fb5867)
• 00: Full (1c670353)

[liach]

I wonder if the work to constant fold Unsafe.arrayLayout is similar to this - this is currently a bottleneck in core libraries.

[TobiHartmann]

@liach That one (JDK-8369835) requires an intrinsic for the Unsafe method which is currently implemented in C++ code (there's no Java code that could be optimized/folded).

[TobiHartmann]

Looks good to me. Thanks for fixing!

[merykitty]

Thanks a lot for the reviews, I will integrate this PR.

[merykitty]

/integrate

[openjdk]

Going to push as commit be252e2.
Since your change was applied there have been 4 commits pushed to the lworld branch:

• 0b87efa: 8367405: [lworld] C2 compilation fails with empty program detected during loop optimization
• cccb501: 8367073: [lworld] Conform to JEP 450 encoding of mark word
• c42a95f: 8369437: [lworld] Split multiple @run statements in compiler tests into separate @test blocks
• ... and 1 more: https://git.openjdk.org/valhalla/compare/75c007b13865a023fb830805436b07f263e4abef...lworld

Your commit was automatically rebased without conflicts.

[openjdk]

@merykitty Pushed as commit be252e2.

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