I came here via the Reddit thread. I read the topic two weeks ago but it was already long back then, so I only skimmed through what happened since. I’m sorry for going a bit off topic, but this seems like the best way to share my opinion.
Almost a year ago I wrote Convector, a project in Rust that heavily exercises AVX. This is my experience/wishlist:
- The tooling around target features could indeed be better. I proposed a way to deal with this in Cargo, but we could not reach consensus in the topic. Then we got support for
RUSTFLAGSin.cargo/config, so I just put that under source control. It is an ugly hack, but it actually works fine. - I want access to the raw platform intrinsics with the same names as in the Intel Intrinsics Guide. I’m glad this topic is going in that direction. They are weird and ugly, but at least they are documented and searchable, and they would be consistent with C/C++. One of the things that surprised me about the current intrinsics, is that e.g.
_mm256_add_psis calledsimd_addinstead. The latter looks friendlier, but it is undiscoverable (also because it is not documented, I suppose), but the main issue is, if you go this way you have to draw the line somewhere about what to rename. I propose to not rename anything, especially since the consensus seems to be to not focus on portable SIMD at the moment. - The types of these intrinsics are sometimes weird (e.g.
_mm256_and_psoperates on floats?), but at this level types have little meaning anyway. To some operations, the operands are just “a sequence of bits”, and they might later be interpreted as floats or integers or bitmasks or whatever. Code full of these intrinsics is hard enough to read without all the transmutes. I’m not sure what the best way to go about this is. Maybe an opaque 128/256/512 bit type with methods to cast from and to tuples of float and integer types?