RFR: 8269725: AArch64: Add VectorMask query implementation for NEON [v3]

[Xiaohong Gong]

On Fri, 9 Jul 2021 08:24:29 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Xiaohong Gong has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove the begining "negr" for "firsttrue,lasttrue"
>
> src/hotspot/cpu/aarch64/aarch64_neon.ad line 5340:
> 
>> 5338:   format %{ "vmask_firsttrue $dst, $src\t# vector (4I/4S/2I)" %}
>> 5339:   ins_encode %{
>> 5340:     // Input "src" is a vector of boolean with "0/1" as the element values.
> 
> Say "vector of bytes." I read this as a vector of bits.

I use the "vector of boolean" here because the type of the input `(src)` is a `TypeVect` with `T_BOOLEAN` as the basic element type, although the size is the same with `byte`.

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