[k_g_b_]

I've worked on a research project using LLVM as a backend but with it's own SSA implementation at the chair of Sebastian Hack. One of his well known scientific contributions was on optimal register allocation with SSA. The chair also published http://dx.doi.org/10.1007/978-3-642-37051-9_6 a very good and easy way to do SSA construction directly from the AST without computing dominance frontiers.

You should probably start on the Wikipedia page for SSA, which - since the dragon book doesn't teach what SSA actually is, is a reasonable starting point https://en.m.wikipedia.org/wiki/Static_single-assignment_for... Note that even though it provides many examples and other comparisons it not once mentions 3AC (and vice versa actually). Under Benefits you can find links to various optimizations some of whose pages reference what SSA helps with. None of them have much if anything to do with 3AC.

That the CMU simply copies an example straight from the book and provides no further explanation and maybe even doesn't mention PHIs (?) doesn't speak for that course at all. Especially if you take a look at the list of compilers that do use SSA on Wikipedia and note that pretty much all major programming language implementations use SSA.

Of course you can lower an AST to SSA that looks like the example (except the example is so rudimentary it's still missing the very necessary PHI functions) and you can even make it have 3AC form and still exploit the SSA properties in optimizations. It's just that the properties and the SSA form still have no real relation except that both modify your list of instructions and claiming that there's one that's somehow meaningful or that 3AC gives you anything that SSA does is at best grossly misleading by a textbook.