I think they mean writing code using compiler intrinsics, which are one layer above assembly (and how you should write most “assembly” these days). Many of the

I think they mean writing code using compiler intrinsics, which are one layer above assembly (and how you should write most “assembly” these days). Many of the modern intrinsics in silicon are sufficiently complex in how they manipulate the data that it is effectively impossible for a compiler to detect applications of those instructions to normal idiomatic code. If you want to use those instructions, you will have to use them directly because the compiler can’t do it for you. The nice thing about intrinsics is that they look like C functions so they are easy to use. There is definitely a growing cottage industry for writing high-performance kernels using this increasingly rich set of intrinsics. I find myself writing a lot more intrinsics code than I used to.