Here's more on the problem of SIMD and C compilers:

https://pharr.org/matt/blog/2018/04/18/ispc-origins.html#aut...

> as long as vectorization can fail (and it will), […] you must come to deeply understand the auto-vectorizer. […] This is a horrible way to program; it’s all alchemy and guesswork and you need to become deeply specialized about the nuances of a single compiler’s implementation