@nutilius I have never seen any assembly instruction, which is similar to SPLIT-SEQUENCE. However, I coded only some toy programs in PIC asssembly, and 8051.
@screwtape I agree. Some Lisp compilers are written in Lisp. Yesterday, I checked SBCL. It can compile Lisp to machine code with AVX2 instructions. So SBCL has ability to access low level ops.