RFR: 8256318: AArch64: Add support for floating-point absolute difference [v3]

[dongbo (E)]

On 2020/11/16 19:57, Andrew Haley wrote:
> On 11/16/20 3:15 AM, Ningsheng Jian wrote:
>> On Mon, 16 Nov 2020 02:51:05 GMT, Dong Bo <dongbo at openjdk.org> wrote:
>>
>>> But I feel a little bit inconsistent that only the new fabd is added into aarch64_neon.ad,
>>> while other NEON intructions (i.e. fabs, fsub, fdiv, fsqrt, etc) are still in aarch64.ad.
>>> And moving them all from aarch64.ad to aarch64_neon.ad deviates far away from this patch.
>> Yes, I think when we introduced aarch64_neon.ad (m4), we just tried to keep that patch simple and would move other vector rules in future patches. Maybe Andrew can comment on this?
> I wonder: I'm not sure if we should do the lot in one bang.
>
> I can't quite figure out the best thing to do. It'll be tricky to move
> all of the SIMD instructions, but I guess it's the best thing to do. It'll
> make backports hard, but we don't see many in this area.
Yes. Moving all NEON instructions to aarch64_neon.ad would make the code 
clearer and more consistent.
I put ABS/FABS/FABD into aarch64_neon.ad, hope it would be a good start 
for this work. Thanks.