I was reading a question about c# code optimization and one solution was to use c++ with SSE. Is it possible to do SSE directly from a c# program?
Can C# explicitly make an SSE call?
No. C# cannot produce inline IL much less inline x86/amd64 assembly.
The CLR, and more specifically the JIT, will use SSE if it's available removing the need to force it in most circumstances. I say most because I'm not an SSE expert and I'm sure that there are cases where it could be beneficial and the JIT does not make the optimization.