> That still just gets you autovectorization

Erm, not sure how direct you want. But at least in dotnet you can use the Vector64, Vector128, Vector256, and Vector512 types [1] where each method gets effectively directly converted to a raw SIMD instruction. So, Vector512.LoadAligned call will be replaced with a raw SIMD register load instruction - supported by the CPU it is running on; and generally a JIT compiler will spot common patterns-of-use to optimise those too. There's no runtime check to see what is supported and no per-function-branching. It's as close to the CPU as you can get really (in a compiled language). Maybe I'm missing something?

If you just mean the difference between hand-coded assembly and the output of an optimising compiler, then sure, you can always be better with hand-coded assembly.

[1] https://learn.microsoft.com/en-us/dotnet/api/system.runtime....