TCG is actually the 2nd generation backend. The 1st generation was much worse, but it was incredibly elegant: the operations were just written as functions in C, as you may do for an interpreter - and then memcpy’d one after the other.

So a compiler from one architecture to another which is as easy to write as an interpreter (but without interpreter overhead), is independent of the target architecture - and it just works. I remember being blown away by the elegance.