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

[Magnus Ihse Bursie]

On Wed, 3 Apr 2024 14:40:42 GMT, Hamlin Li <mli at openjdk.org> wrote:

> Hi,
> Can you help to review the patch?
> This pr is based on previous work and discussion in [pr 16234](https://github.com/openjdk/jdk/pull/16234), [pr 18294](https://github.com/openjdk/jdk/pull/18294).
> 
> Compared with previous prs, the major change in this pr is to integrate the source of sleef (for the steps, please check `src/jdk.incubator.vector/linux/native/libvectormath/README`), rather than depends on external sleef things (header or lib) at build or run time.
> Besides of this change, also modify the previous changes accordingly, e.g. remove some uncessary files or changes especially in make dir of jdk.
> 
> Besides of the code changes, one important task is to handle the legal process.
> 
> Thanks!

Build libsleef using their cmake system and look at the compile command line. (You do this by `VERBOSE=1 cmake` IIRC). Then you can see what flags they are using. This is what I was referring to as "normal libsleef build". I noticed there were a lot of compiler flags. I can't say if they are needed or not. In most cases, if it compilers, it's fine, but in this case, I guess some flags can be crucial to really get the kind of performance you need, and it might not be easy to spot that something is wrong if you get them incorrect. I assume one way to make sure is to run microbenchmarks with an externally built libsleef and compare it with the one you build within the JDK. If there is no noticeable difference, then I guess it is fine.

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PR Comment: https://git.openjdk.org/jdk/pull/18605#issuecomment-2037703774