Yeah, I wouldn't use this type of thing for these problems, this was a huge mess. But I think code designed for autovec is resonable as a scalar base implementation for a larger set of problems than people think.

I've seen the problem before, where people explicitly vectorized (sse) something, but the code could be autovectorized (avx) and outperformed the explicitly vectorized one, because the compiler could take advantage of newer extensions.

You really should be able to use a ISPC like subset in your C code, OpenMP goes into the right direction, but it's not designed with SIMD as the highest priority.