The interesting question for me is whether Rust makes it easier for the compiler to extract SIMD parallelism automatically given the restrictions imposed by its type system.
The main thing I can think of that would help here is the fact that Rust has stricter alignment requirements than C++ does. Any live reference can more or less be assumed to point to validly-aligned memory at all times, which isn't true in C++.
As to whether LLVM actually takes advantage of this effectively, I don't know. I know that we do supply the necessary attributes to LLVM in most cases, but I haven't looked at the individual transform and optimization passes to see whether they take advantage of this (e.g. emitting movdqa vs. falling back to movdqu).
Aside from aliasing restrictions, you can use chunked iterators which IIRC make it easier for the compiler to auto-vectorize your loop. The actual code changes very little.
