4 ms·

Hello, this is the compiler calling back at you. I am very sorry that I cannot write efficient SIMD code but neither can you. If we can work together, we will o

by exDM69 14y ago

Hello, this is the compiler calling back at you. I am very sorry that I cannot write efficient SIMD code but neither can you. If we can work together, we will outperform our individual selves as a team. So you go ahead and write clever SIMD code but please use the SIMD intrinsics I can understand, not inline assembler which I cannot do anything with. You are very good in expressing algorithms in a SIMD friendly way and do a decent job in instruction selection. You, however, are not very good in doing instruction scheduling and register allocation, so let me handle that and we can achieve a result that can keep the CPU pipelines busy. When you make the tiniest change to the program, I can re-do instruction scheduling and register allocation in an instant, when that would take you hours to rewrite the whole algorithm to use different registers. my point: SIMD intrinsics + a smart C compiler produces a lot better code than a programmer writing assembly. Clang + vector extensions in particular is very good at it.

loup-vaillant 14y ago
Reminds me that the best current chess player is actually a team mixing humans and computers. Even in that domain where computers are undoubtedly better than humans, the best solution still involve humans.
- EvilLook 14y ago
  Who else is going to drive the computer to the event and set it up until Google get their why and we all have self-driving cars?
- Jabbles 14y ago
  That sounds interesting. Do you have a paper on that?
  - loup-vaillant 14y ago
    Here is an entry point: https://en.wikipedia.org/wiki/Advanced_Chess https://en.wikipedia.org/wiki/Advanced_Chess I don't recall any specific paper, but I think tournament were played.
to3m 14y ago
This has never quite been my experience. Look-mummy-my-first-SIMD-routine is usually within spitting distance of the compiler's best effort, and a lot neater-looking. Then you can just take it from there. The compiler's output is far from useless, because compilers generally know a few tricks and/or cute sequences that you can copy. And using intrinsics is certainly better than relying on it to automatically vectorize things itself - I've never heard of that do anything remotely interesting. But, even though it's 2013, it still seems like the compiler is easier to beat by hand than you'd think. I make no claim that this is worth doing in every case. (As for the suggestion that the compiler can't rearrange inline assembly language, or provide symbolic register names - whyever not? Perhaps people have been conditioned by gcc and VC++ never to expect anything except the absolute bare minimum from inline assembly language support, but that's no reason to assume that these tasks are impossible. Code Warrior for Wii would rearrange assembly language for you to avoid holdups due to instruction latencies, and while automatically assigning registers for you. I believe most modern assemblers will do similar reordering and at least let you assign names to the registers you're using.)

by exDM69 14y ago

loup-vaillant 14y ago

Reminds me that the best current chess player is actually a team mixing humans and computers. Even in that domain where computers are undoubtedly better than humans, the best solution still involve humans.

EvilLook 14y ago
Who else is going to drive the computer to the event and set it up until Google get their why and we all have self-driving cars?
Jabbles 14y ago
That sounds interesting. Do you have a paper on that?
- loup-vaillant 14y ago
  Here is an entry point: https://en.wikipedia.org/wiki/Advanced_Chess https://en.wikipedia.org/wiki/Advanced_Chess I don't recall any specific paper, but I think tournament were played.

to3m 14y ago

This has never quite been my experience. Look-mummy-my-first-SIMD-routine is usually within spitting distance of the compiler's best effort, and a lot neater-looking. Then you can just take it from there. The compiler's output is far from useless, because compilers generally know a few tricks and/or cute sequences that you can copy. And using intrinsics is certainly better than relying on it to automatically vectorize things itself - I've never heard of that do anything remotely interesting. But, even though it's 2013, it still seems like the compiler is easier to beat by hand than you'd think. I make no claim that this is worth doing in every case. (As for the suggestion that the compiler can't rearrange inline assembly language, or provide symbolic register names - whyever not? Perhaps people have been conditioned by gcc and VC++ never to expect anything except the absolute bare minimum from inline assembly language support, but that's no reason to assume that these tasks are impossible. Code Warrior for Wii would rearrange assembly language for you to avoid holdups due to instruction latencies, and while automatically assigning registers for you. I believe most modern assemblers will do similar reordering and at least let you assign names to the registers you're using.)