Of course our a modern CPUs have generic enough instructions that let you do that. Harvard pretty much forces it though, so much so that many Harvard CPUs don't

Of course our a modern CPUs have generic enough instructions that let you do that. Harvard pretty much forces it though, so much so that many Harvard CPUs don't have a way to get code into data registers and vice versa. Since they are separate busses they may be different data widths and therefor incompatible.