8350095: RISC-V: Refactor string_compare

[Hamlin-Li]

Hi,
Can you help to review this patch?

Currently, string_compare code is a bit complicated, main reasons include:

1. it has 2 piece of code respectively for LU and UL case, this is not necessary, basically LU and UL behaviour quite similar.
2. it mixed LL/UU and LU/UL case together, better to separate them, as they are quite different from each other.

This is not good for code reading and maintaining.

So, this patch does following refactoring:

1. merge LU and UL code into one, i.e. remove UL code.
2. seperate the code into 2 methods: LL/UU and LU/UL.
3. some other misc improvement.

I could do the following refactoring in another following pr, as in this pr I'm just moving code and removing code, it's easier to do it and review it. In particular the first one, as it needs to rewrite the existing code for UL/LU case.

1. move alignment code of generate_compare_long_string_different_encoding upwards to string_compare_long_LU.
2. make SHORT_STRING case simpler.

Thanks

---

Progress

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Issue

• JDK-8350095: RISC-V: Refactor string_compare (Enhancement - P4)

Reviewers

• Fei Yang (@RealFYang - Reviewer)

Reviewing

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[bridgekeeper]

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[openjdk]

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

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

8350095: RISC-V: Refactor string_compare

Reviewed-by: fyang

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At the time when this comment was updated there had been 64 new commits pushed to the master branch:

• 885338b: 8323582: C2 SuperWord AlignVector: misaligned vector memory access with unaligned native memory
• bb48b73: 8350723: RISC-V: debug.cpp help() is missing riscv line for pns
• b29f8b0: 8350665: SIZE_FORMAT_HEX macro undefined in gtest
• 78c18cf: 8349399: GHA: Add static-jdk build on linux-x64
• e43960a: 8350616: Skip ValidateHazardPtrsClosure in non-debug builds
• 9ec4696: 8350313: Include timings for leaving safepoint in safepoint logging
• ec6624b: 8350649: Class unloading accesses/resurrects dead Java mirror after JDK-8346567
• 9477c70: 8024695: new File("").exists() returns false whereas it is the current working directory
• 3e46480: 8350770: [BACKOUT] Protection zone for easier detection of accidental zero-nKlass use
• bd112c4: 8350443: GHA: Split static-libs-bundles into a separate job
• ... and 54 more: https://git.openjdk.org/jdk/compare/dfcd0df60c60cf89dc01682264a573ad39e61a17...master

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[openjdk]

@Hamlin-Li The following label will be automatically applied to this pull request:

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[mlbridge]

Webrevs

• 06: Full - Incremental (b3891a47)
• 05: Full - Incremental (e9c1807e)
• 04: Full - Incremental (d67a23e3)
• 03: Full - Incremental (fe0efa0e)
• 02: Full - Incremental (4f5ae272)
• 01: Full - Incremental (543c8635)
• 00: Full (eaa34661)

[RealFYang]

Hi, there is a difference between LU and UL when calculating the difference [1]. The tmp1 and tmp2 here represent characters from the first and second string respectively. So the order of the two strings matters here. But that doesn't seem to be reflected by this change?

BTW: Seems more readable if we move the difference calcuation code to string_compare_long_LU and string_compare_long_LL_UU at the same time.

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp#L1571

[Hamlin-Li]

Thanks for catching and suggestion, I'll modify it accordingly.

[RealFYang]

Thanks for the update. A couple of comments remain.

[RealFYang]

Do you mind several more tweaks? Looks good otherwise. Thanks.

[RealFYang]

Latest version looks good to me. Thanks!

[Hamlin-Li]

Latest version looks good to me. Thanks!

Thank you!

[Hamlin-Li]

/integrate

[openjdk]

Going to push as commit e470f47.
Since your change was applied there have been 115 commits pushed to the master branch:

• f53de92: 8350931: RISC-V: remove unnecessary src register for fp_sqrt_d/f
• e1fc14f: 8350940: RISC-V: remove unnecessary assert_different_registers in minmax_fp
• 79880e5: 8351033: RISC-V: TestFloat16ScalarOperations asserts with offset (4210) is too large to be patched in one beq/bge/bgeu/blt/bltu/bne instruction!
• bb70896: 8350903: Remove explicit libjvm.so dependency for libVThreadEventTest
• 7c187b5: 8338737: Shenandoah: Reset marking bitmaps after the cycle
• 3602c8c: 8350955: Fix repetitions of the word "the" in runtime component comments
• c988d7d: 8350767: Fix -Wzero-as-null-pointer-constant warnings in nsk jni stress tests
• 67dfdfa: 8350623: Fix -Wzero-as-null-pointer-constant warnings in nsk native test utilities
• 4a51c61: 8350567: NMT: update VMATree::register_mapping to copy the existing tag of the region
• db69ec9: 8344009: Improve compiler memory statistics
• ... and 105 more: https://git.openjdk.org/jdk/compare/dfcd0df60c60cf89dc01682264a573ad39e61a17...master

Your commit was automatically rebased without conflicts.

[openjdk]

@Hamlin-Li Pushed as commit e470f47.

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