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

[Xiaohong Gong]

On Thu, 23 Nov 2023 01:28:40 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>> Ah, now I se what you are trying to do here. First of all, in the detection part, only set `SVE_FEATURE_SUPPORT`. Then you can handle the `SVE_CFLAGS` addition elsewhere/later. 
>> 
>> Secondly, you should not mix these `SVE_CFLAGS` with the spleef C flags. Keeping them separate will allow for LIBSLEEF_CFLAGS to be named just that.
>> 
>> Thirdly, I do not like at all how you just come crashing in setting `-march` like that. The `-march` flag is handled by `FLAGS_SETUP_ABI_PROFILE`. 
>> 
>> Actually, now that I think of it, this is just completely wrong! You are checking on features on the build machine, to determine what target machine code to generate, with no way to override. 
>> 
>> You need to break out the -march handling separately. It should be moved to FLAGS_SETUP_ABI_PROFILE. I'm guessing you will need to make something like a `aarch64-sve` profile, and possibly try to auto-select it based on the result of the sve test program above. But changing `OPENJDK_TARGET_ABI_PROFILE` can have further consequences; I do not know the full extent on the top of my head.
>
> Thanks for the advice! I will take a consideration for it.

> Thirdly, I do not like at all how you just come crashing in setting -march like that. The -march flag is handled by FLAGS_SETUP_ABI_PROFILE.

`-march=armv8-a+sve` is just used in this new added module, which may not expect to be used for other libraries. Per my understanding, flags handled by `FLAGS_SETUP_ABI_PROFILE` is not used for a specified module? 

> Actually, now that I think of it, this is just completely wrong! You are checking on features on the build machine, to determine what target machine code to generate, with no way to override.

Yes, that's be a risk, although the usage to the SVE functions are controlled by SVE feature as well in runtime. I need time to find a better solution.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16234#discussion_r1403052964