AFAIU, as compared to pure monomorphization, yes, sometimes the model imposes runtime indirection. This is particularly the case for methods. However, for simple yet common cases, such as functions taking []T, the model permits inlining into the caller.
They aren’t performance related because idiomatic Go pushes people toward performance. Generics currently push people away from performance (of course there are exceptions). I don’t expect it will be a huge deal either way, but it would be nice not to have to choose between performance and expressiveness.
I believe Lemire's point is that the compiler is still able to inline the function despite the generic definition, so at least in this somewhat narrow case generics are a zero-cost abstraction.
