RFR: 8312425: [vectorapi] AArch64: Optimize vector math operations with SLEEF [v3]

[Xiaohong Gong]

On Wed, 22 Nov 2023 09:05:31 GMT, Andrew Haley <aph at openjdk.org> wrote:

>>> Have you considered the possibility of copying the sleef source to the OpenJDK repository and thereby it becomes part of the build process? I don't know how straightforward that is technically and IANAL but I think it's worth exploring.
>>> 
>> 
>> Hi @PaulSandoz ! Thanks for the suggestion! Copying the sleef source sounds good. However, I actually have no idea about how to handle the third-party licence in OpenJDK project. Do you have any idea about this area? Some suggestions/guidence   from the JDK team will be much helpful. Thanks!
>
>> > Have you considered the possibility of copying the sleef source to the OpenJDK repository and thereby it becomes part of the build process? I don't know how straightforward that is technically and IANAL but I think it's worth exploring.
>> 
>> Hi @PaulSandoz ! Thanks for the suggestion! Copying the sleef source sounds good. However, I actually have no idea about how to handle the third-party licence in OpenJDK project. Do you have any idea about this area? Some suggestions/guidence from the JDK team will be much helpful. Thanks!
> 
> From a legal pespective, we can do this. SLEEF is distributed under Boost Software License Version 1.0., which is a GPL-compatible free software licence. The only issue is whether we want to do so. It would certainly be convenient.

Hi @theRealAph , @magicus ,

The latest commit renamed `vmath` in configure to `sleef`, and the Arm SVE cflags is removed to `flags-cflags.m4` now. I was thinking about separating the NEON and SVE functions in `libvmath.so` to two source files, and add the SVE cflags just for SVE functions as needed. But it seems I have to write the make commands manually, which I think is not good? But I can have a try if it's necessary.

Since the sve flags is just used for building `libvmath.so` now, moving it to `flags-cflags.m4` seems not so right? 

@magicus , may I have your comments on this part? Thanks in advance!

> Don't touch the make system.Instead, try to open the library at runtime with os::dll_open(), after (or inside) VM_Version::initialize().
>
> If you're not running on an SVE system, none of the SVE routines will be called, so it doesn't matter, right?

Yes, the SVE routines are called only on the SVE system. So I think it doesn't matter. I tested with the image built on non-sve machine and ran the Vector API tests on SVE machine, and it works well. It also works well on the contrary situation.

Best Regards,
Xiaohong

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PR Comment: https://git.openjdk.org/jdk/pull/16234#issuecomment-1833278899