RFR: 8269725: AArch64: Add VectorMask query implementation for NEON [v5]

[Xiaohong Gong]

On Wed, 14 Jul 2021 10:13:34 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Xiaohong Gong has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:
>> 
>>  - Merge jdk:master into JDK-8269725
>>  - Add more comments
>>  - Remove the begining "negr" for "firsttrue,lasttrue"
>>  - Merge branch 'jdk:master' into JDK-8269725
>>  - 8269725: AArch64: Add VectorMask query implementation for NEON
>
> src/hotspot/cpu/aarch64/aarch64_neon_ad.m4 line 2318:
> 
>> 2316:   %}
>> 2317:   ins_pipe(pipe_slow);
>> 2318: %}
> 
> Why write `vmask_firsttrue8B` and `vmask_firsttrue_LT8B` separately? All you need is `if (vector_length < 8)` in the encoding rule.

The main reason is the argument difference that `vmask_firsttrue_LT8B` needs to clear the `rFlagsReg` while `vmask_firsttrue8B`. It doesn't matter too much if the rule always clear the flag, right？

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PR: https://git.openjdk.java.net/jdk/pull/4699