I have written a lot of SIMD for both x86 and ARM over many years and many microarchitectures. Every abstraction, including autovectorization, is universally pretty poor outside of narrow cases because they don’t (and mostly can’t) capture what is possible with intrinsics and their rather extreme variation across microarchitectures. If I want good results, I have to write intrinsics. No library can optimally generate non-trivial SIMD code. Neither can the compiler. Portability just amplifies this gap.
I think a legitimate criticism is that it is unclear who std::simd is for. People that don’t use SIMD today are unlikely to use std::simd tomorrow. At the same time, this does nothing for people that use SIMD for serious work. Who is expected to use this?
The intrinsics are not difficult but you do have to learn how the hardware works. This is true even if you are using a library. A good software engineer should have a rough understanding of this regardless.
That certainly convinced me. When I was doing my taxes recently and had to watch those forced loading animations, I kept asking myself "why can't my compiler do this?" Thanks to std::simd, now it can!
4 comments:
I have written a lot of SIMD for both x86 and ARM over many years and many microarchitectures. Every abstraction, including autovectorization, is universally pretty poor outside of narrow cases because they don’t (and mostly can’t) capture what is possible with intrinsics and their rather extreme variation across microarchitectures. If I want good results, I have to write intrinsics. No library can optimally generate non-trivial SIMD code. Neither can the compiler. Portability just amplifies this gap.
I think a legitimate criticism is that it is unclear who std::simd is for. People that don’t use SIMD today are unlikely to use std::simd tomorrow. At the same time, this does nothing for people that use SIMD for serious work. Who is expected to use this?
The intrinsics are not difficult but you do have to learn how the hardware works. This is true even if you are using a library. A good software engineer should have a rough understanding of this regardless.
The linked[1] "six reasons to use std::simd" was just what I needed after a long week. Hilarious!
[1]: https://github.com/NoNaeAbC/std_simd
isn't that just QoI issues? There's a reason why the libstdc++ folks labelled their implementation as experimental.
That certainly convinced me. When I was doing my taxes recently and had to watch those forced loading animations, I kept asking myself "why can't my compiler do this?" Thanks to std::simd, now it can!