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

[Jin Guojie]

On Tue, 7 May 2024 14:01:31 GMT, Bhavana Kilambi <bkilambi at openjdk.org> wrote:

>> 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 462:
> 
>> 460:     if (VM_Version::supports_a53mac() && Ra != zr)
>> 461:       nop();
>> 462:     if (VM_Version::is_neoverse_n_series()) {
> 
> Why only Neoverse N series? Even on the V series (V1 and V2), both `sdiv/udiv` and `msub` instructions are executed in M0 unit (Integer multi cycle). It should benefit the V series as well. Source: https://developer.arm.com/documentation/pjdoc466751330-9685/latest/ and https://developer.arm.com/documentation/PJDOC-466751330-593177/latest/
> 
> A quick run on a V1 machine shows ~15% performance gain for the `IntegerDivMod` tests if we generate separate `mul` and `sub` instructions instead of a single `msub`.

Thanks for your review.
This new commit includes the support for V1/V2 you mentioned.

https://github.com/openjdk/jdk/pull/19093/commits/d8b8dbfe102d2716ef9e332aec7c52e566bf1727

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/19093#discussion_r1593296677