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

[Wang Huang]

On Mon, 5 Jul 2021 06:37:01 GMT, Wang Huang <whuang at openjdk.org> wrote:

>> 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.

* Why we unroll 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 unroll the loop to remove these comparsion.

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

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