RFR: 8268229: Aarch64: Use Neon in intrinsics for String.equals [v3]

[Wang Huang]

On Fri, 2 Jul 2021 14:24:33 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Wang Huang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   unroll when small string sizes
>
> src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 4816:
> 
>> 4814:     cbnz(rscratch2, DONE);
>> 4815:     b(SAME);
>> 4816: 
> 
> No, we are not going to do all this unrolling at the call site.

* Why we unrolling the loop ?
*  It is found that these codes degrades performance 
 ```
    br(LE, B16);
    subs(cnt1, cnt1, wordSize);
    br(LE, B24);
    subs(cnt1, cnt1, wordSize);

 We unrolls the loop to remove these comparsion.

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PR: https://git.openjdk.java.net/jdk/pull/4423