Arm Neon Intrinsics vs hand assembly

Question

https://web.archive.org/web/20170227190422/http://hilbert-space.de/?p=22

On this site which is quite dated it shows that hand written asm would give a much greater improvement then the intrinsics. I am wondering if this is the current truth even now in 2012.

So has the compilation optimization improved for intrinsics using gnu cross compiler?

Answer 1

So this question is four years old, now, and still shows up in search results...

In 2016 things are much better.

A lot of simple code that I've transcribed from assembly to intrinsics is now optimised better by the compilers than by me because I'm too lazy to do the pipeline work (for how many different pipelines now?), while the compilers just needs me to pass the right --mtune=.

For complex code where register allocation can get tight, GCC and Clang both can still produce slower than handwritten code by a factor of two... or three(ish). It's mostly on register spills, so you should know from the structure of your code whether that's a risk.

But they both sometimes have disappointing accidents. I'd say that right now that's worth the risk (although I'm paid to take risk), and if you do get hit by something then file a bug. That way things will keep on getting better.