Burst compile "auto" mode vector ISA? (AVX, AVX2 or AVX512)?

Hi Unity devs,

Trying to vectorize some game code on X64.
Burst compile is set to "auto".
I am wondering what's the actual target of auto: AVX, AVX 2 or AVX 512?

I've combed through the documentation, the closest I can find is the example
https://docs.unity3d.com/Packages/com.unity.burst@0.2/manual/index.html
In here, it is using AVX2, not sure if that's the default or am I reading tea leaves?

And to fellow game devs, do you recommend going up to AVX-512?
The ISA extension has only been around since 2015,
so I'd guess there still are gaming rigs out there not supporting it?

 

With the Burst decompiler and some googling of instruction sets you should be able to see what instruction sets are being used?

 

Auto currently targets SSE code. Don't bother optimizing for AVX until Unity releases AVX intrinsics. Also, in the future, don't bother with AVX-512. It only works with Intel processors and needs to be crafted very carefully to keep the cores from reducing their clock speeds. AVX2 will be a good next step over SSE once Unity figures out how to build with it and not take SSE-AVX switch penalties.

 

Actually, almost no-one will have AVX512. It's too recent and my understanding is that large parts of it are not aimed at commodity customers. You can get a good overview of what users have by checking Steam's hardware survey (go all the way to the bottom to Other Settings). Note that AVX512 is effectively at 0% adoption. As @DreamingImLatios said, SSE is the standard target and virtually all modern processors support SSE3 (or even SSE4), as is visible in the survey linked above