Most middle-end compiler IRs are built on conditional/unconditional branches rather than high-level control flow structures. The key concepts at that level can

Most middle-end compiler IRs are built on conditional/unconditional branches rather than high-level control flow structures. The key concepts at that level can usually be expressed in terms of dominators, postdominators, and/or control-dependence [1]. For example, a (natural) loop exists when a block dominates one of its predecessors. Induction variables in such loop can be very easily discovered, especially if you're already in SSA form (already usually the case at this level of IR). So, in short, structured control flow--or at least a sufficient subset of such structured control flow--can be easily recovered from low-level information, and you're generally not going to lose much information going down to that level. LLVM even has a way to attach metadata to loops despite not having any dedicated loop construct. [1] You only need two of these concepts: the third falls out from the definition of the other two.