8 ms·

Thanks for reading everyone. I’ve gotten some feedback over on Reddit as well that the example is not effectively showing the benefits of SIMD. I plan on revisi

Thanks for reading everyone. I’ve gotten some feedback over on Reddit as well that the example is not effectively showing the benefits of SIMD. I plan on revising this. One of my goals of writing these articles is to learn so feedback is more than welcome!

KineticLensman 2y ago
Great read! > One of my goals of writing these articles is to learn so feedback is more than welcome! When I went into the Rust playground to see the assembly output for the Cumulative Sum example, I could only get it to show the compiler warnings, not the actual assembly. I'm probably doing something wrong, but for me this was a barrier that detracted from the article. I'd suggest incorporating the assembly directly into the article, although keeping the playground link for people who are more dedicated / competent than I am.
- the8472 2y ago
  The function has to be made pub so it doesn't get optimized out as unusued private function. Godbolt is a better choice for looking at asm anyway. https://rust.godbolt.org/z/3Y9ovsoz9 https://rust.godbolt.org/z/3Y9ovsoz9
  - KineticLensman 2y ago
    Ah, that worked, thanks! Although I can now see why he didn't include the output directly.
  - hayley-patton 2y ago
    Narrator: "The code did not, in fact, auto-vectorise." (There's only addsd/movsd instructions, which are add/move scalar-double; we want addpd/movpd which are add/move packed-double in vectorised code.)
devit 2y ago
Are you really writing them? Seems written by an LLM for the most part.
dzaima 2y ago
What's fun is that, as the use of SIMD in your example is useless, LLVM correctly completely removes it, and makes your "neon" and "fallback" versions exactly the same - without any SIMD (compiler explorer: https://godbolt.org/z/YWoMGoaxT https://godbolt.org/z/YWoMGoaxT). As an additional note, aarch64 always has NEON (similar to how x86-64 always has SSE2; extensions useful to dispatch would be SVE on aarch64 and AVX/AVX2/AVX-512 on x86-64), so no point dynamically checking for it.

KineticLensman 2y ago

Great read! > One of my goals of writing these articles is to learn so feedback is more than welcome! When I went into the Rust playground to see the assembly output for the Cumulative Sum example, I could only get it to show the compiler warnings, not the actual assembly. I'm probably doing something wrong, but for me this was a barrier that detracted from the article. I'd suggest incorporating the assembly directly into the article, although keeping the playground link for people who are more dedicated / competent than I am.

the8472 2y ago
The function has to be made pub so it doesn't get optimized out as unusued private function. Godbolt is a better choice for looking at asm anyway. https://rust.godbolt.org/z/3Y9ovsoz9 https://rust.godbolt.org/z/3Y9ovsoz9
- KineticLensman 2y ago
  Ah, that worked, thanks! Although I can now see why he didn't include the output directly.
- hayley-patton 2y ago
  Narrator: "The code did not, in fact, auto-vectorise." (There's only addsd/movsd instructions, which are add/move scalar-double; we want addpd/movpd which are add/move packed-double in vectorised code.)

devit 2y ago

Are you really writing them? Seems written by an LLM for the most part.

dzaima 2y ago

What's fun is that, as the use of SIMD in your example is useless, LLVM correctly completely removes it, and makes your "neon" and "fallback" versions exactly the same - without any SIMD (compiler explorer: https://godbolt.org/z/YWoMGoaxT https://godbolt.org/z/YWoMGoaxT). As an additional note, aarch64 always has NEON (similar to how x86-64 always has SSE2; extensions useful to dispatch would be SVE on aarch64 and AVX/AVX2/AVX-512 on x86-64), so no point dynamically checking for it.