Wondered about the same thing. Perhaps the author deals with graphs with no side effects or branches? It would then trivially become CSE on a single basic block.
SSA transformations are essentially equivalent to what the author appears to be doing in terms of let-bindings [0].
SSA transformations are essentially equivalent to what the author appears to be doing in terms of let-bindings [0].
[0] https://dl.acm.org/doi/10.1145/278283.278285