RFR: 8331558: AArch64: optimize integer remainder [v2]

[Eric Liu]

On Mon, 6 May 2024 05:50:13 GMT, Jin Guojie <duke at openjdk.org> wrote:

>> 8331558: AArch64: optimize integer remainder
>>     On some Arm processors, a separate multiply/subtract is actually faster than the combined instruction.
>> 
>> 8331556: AArch64: CPU_Model support for Neoverse N1/N2/V1/V2
>>     Add full platform coverage for Neoverse variants in vm_version.?pp
>> 
>> The following test has passed, which shows definite performance improvement.
>> 
>> make test TEST="micro:java.lang.IntegerDivMod"
>> make test TEST="micro:java.lang.LongDivMod"
>> 
>> * IntegerDivMod.testDivideRemainderUnsigned
>> baseline(ns/ops)                2223
>> with this pacth(ns/ops)         1885    
>> improvement(%)                  17.93%
>> 
>> * IntegerDivMod.testRemainderUnsigned
>> baseline(ns/ops)                2225
>> with this pacth(ns/ops)         1885    
>> improvement(%)                  18.03%
>> 
>> * LongDivMod.testDivideRemainderUnsigned
>> baseline(ns/ops)                2231
>> with this pacth(ns/ops)         1894    
>> improvement(%)                  17.79%
>> 
>> * LongDivMod.testRemainderUnsigned
>> baseline(ns/ops)                2232
>> with this pacth(ns/ops)         1891
>> improvement(%)                  18.03%
>
> Jin Guojie has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Merge branch 'openjdk:master' into dev
>  - Update vm_version_aarch64.hpp
>  - 8331558: AArch64: optimize integer remainder
>    
>    On some Arm processors, a separate multiply/subtract is actually faster than the combined instruction.
>  - 8331556: AArch64: CPU_Model support for Neoverse N1/N2/V1/V2
>    
>    Add full platform coverage for Neoverse variants in vm_version.?pp

src/hotspot/cpu/aarch64/macroAssembler_aarch64.hpp line 447:

> 445:   inline void msub(Register Rd, Register Rn, Register Rm, Register Ra) {
> 446:     if (VM_Version::supports_a53mac() && Ra != zr)
> 447:       nop();

It was in JDK-8079203 [1] for the first time. May I ask what's the specials on a53mac?

[1] https://github.com/openjdk/jdk/commit/a65f9f95894e22ce2fd160024ce46f6aaa6c8bd3

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PR Review Comment: https://git.openjdk.org/jdk/pull/19093#discussion_r1590760051