Yeah, that's exactly right. It's operating on an SSA-based intermediate representation. So if an operation gets removed, the arguments are still being computed.

Yeah, that's exactly right. It's operating on an SSA-based intermediate representation. So if an operation gets removed, the arguments are still being computed. The earlier operations that produce those arguments can also be removed by dead code elimination (which runs later), but indeed only if they have no side effects. I suppose the notation of the rule heads makes it look like there actually are expression trees, which is maybe sort of confusing.