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char ref (managed pointer) is cast to byte ref https://github.com/dotnet/coreclr/blob/04d9b557ef8b7c60a1194...

Then it uses SpanHelpers.SequenceEqual for byte which is vectorized

https://github.com/dotnet/coreclr/blob/04d9b557ef8b7c60a1194...

>char is cast to byte

To be clear, char is not cast to byte (which would truncate). A char ref (ie a char pointer) is cast to a byte ref (ie a byte pointer).

Good point :) Updated

Oh thanks! Was looking at the wrong SequenceEqual

Maybe there is an autovectorizer in the compiler that recognizes the shape of that loop and uses SSE to do it 16 bytes at a time instead of 8 at a time?

The CLR/runtime to optimizes that code into SIMD instructions, if the hardware allows for it.