C# portable SIMD is very nice indeed, but it's also not usable without unsafety. On the other hand, Rust compiler (LLVM) has a fairly competent autovectorizer, so you may be able to simply write loops the right way instead of the fancy API.

Unsafety means different things. In C#, SIMD is possible via `ref`s, which maintains GC safety (no GC holes), but removes bounds safety (array length check). The API is called appropriately Vector.LoadUnsafe

You are not "forced" into unsafe APIs with Vector<T>/Vector128/256/512<T>. While it is a nice improvement and helps with achieving completely optimal compiler output, you can use it without unsafe. For example, ZLinq even offers .AsVectorizable LINQ-style API, where you pass lambdas which handle vectors and scalars separately. It the user code cannot go out of bounds and the resulting logic even goes through (inlined later by JIT) delegates, yet still offers a massive speed-up (https://github.com/Cysharp/ZLinq?tab=readme-ov-file#vectoriz...).

Another example, note how these implementations, one in unsafe C# and another in safe F# have almost identical performance: https://benchmarksgame-team.pages.debian.net/benchmarksgame/..., https://benchmarksgame-team.pages.debian.net/benchmarksgame/...