You can have a compiler or assembler in a Harvard Architecture computer, but having separate instruction and data memories means that you can't generate the ins

You can have a compiler or assembler in a Harvard Architecture computer, but having separate instruction and data memories means that you can't generate the instructions and then execute them. You need some scheme to move stuff from one memory to another. Think of a PIC or AVR8, for example, rewriting its own Flash memory which isn't even the same width as the data memory.