Maybe the next paragraph in the link is a crucial bit of missing context here? > Skip-list chains: The IR is threaded with segregated, per-opcode skip-list cha

Maybe the next paragraph in the link is a crucial bit of missing context here? > Skip-list chains: The IR is threaded with segregated, per-opcode skip-list chains. The links are stored in a multi-purpose 16 bit field in the instruction. This facilitates low-overhead lookup for CSE, DSE and alias analysis. Back-linking enables short-cut searches (average overhead is less than 1 lookup). Incremental build-up is trivial. No hashes, no sets, no complex updates. Seems like there is more going on than just replacing pointers with arrays 1:1.