Frontend See files in compiler/ with nx in their name. Backend VINSNs VINSN means Virtual Instruction. Those likely belong to the same category of SBCL's Virtual Operations (VOPs). <- copy register @ label @= label (aligned) -> jump to label ^ branch ? register (unwired) $ register (wired) (from compiler/X86/x862.lisp) LAP LAP means Lisp Assembly Parser (probably). It's a DSL that compiles into op