diff --git a/library/init/compiler/ir.lean b/library/init/compiler/ir.lean
index 784e1680a3..9abbd943c4 100644
--- a/library/init/compiler/ir.lean
+++ b/library/init/compiler/ir.lean
@@ -232,62 +232,6 @@ def valid_ssa (d : decl) : bool :=
 let (e, _) := d.valid_ssa.run.run (mk_var2blockid, mk_var_set)
 in  e.to_bool
 
-/- Collect used variables -/
-@[reducible] def collector : Type :=
-state var_set unit
-
-def var.collect (x : var) : collector :=
-do s ← get, put (s.insert x)
-
-def instr.collect_vars : instr → collector
-| (instr.lit x _ _)       := x.collect
-| (instr.cast x _ y)      := x.collect >> y.collect
-| (instr.unop x _ _ y)    := x.collect >> y.collect
-| (instr.binop x _ _ y z) := x.collect >> y.collect >> z.collect
-| (instr.call xs _ ys)    := xs.mmap' var.collect >> ys.mmap' var.collect
-| (instr.cnstr o _ _ _)   := o.collect
-| (instr.set o _ x)       := o.collect >> x.collect
-| (instr.get x y _)       := x.collect >> y.collect
-| (instr.sets o _ x)      := o.collect >> x.collect
-| (instr.gets x _ y _)    := x.collect >> y.collect
-| (instr.closure x _ ys)  := x.collect >> ys.mmap' var.collect
-| (instr.apply x ys)      := x.collect >> ys.mmap' var.collect
-| (instr.array a sz c)    := a.collect >> sz.collect >> c.collect
-| (instr.write a i v)     := a.collect >> i.collect >> v.collect
-| (instr.read x a i)      := x.collect >> a.collect >> i.collect
-| (instr.sarray x _ sz c) := x.collect >> sz.collect >> c.collect
-| (instr.swrite a i v)    := a.collect >> i.collect >> v.collect
-| (instr.sread x _ a i)   := x.collect >> a.collect >> i.collect
-| (instr.inc x)           := x.collect
-| (instr.decs x)          := x.collect
-| (instr.dealloc x)       := x.collect
-| (instr.dec x)           := x.collect
-
-def phi.collect_vars : phi → collector
-| {x := x, ys := ys, ..} := x.collect >> ys.mmap' var.collect
-
-def terminator.collect_vars : terminator → collector
-| (terminator.ret ys)     := ys.mmap' var.collect
-| (terminator.case x _)   := x.collect
-| (terminator.jmp _)      := return ()
-
-def block.collect_vars : block → collector
-| {phis := ps, instrs := is, term := r, ..} :=
-  ps.mmap' phi.collect_vars >>
-  is.mmap' instr.collect_vars >>
-  r.collect_vars
-
-def arg.collect : arg → collector
-| {n := x, ..} := x.collect
-
-def decl.collect_vars : decl → collector
-| {as := as, bs := bs, ..} :=
-  as.mmap' arg.collect >> bs.mmap' block.collect_vars
-
-def collect_vars (d : decl) : var_set :=
-let (_, r) := d.collect_vars.run mk_var_set
-in r
-
 /- Check blockids -/
 @[reducible] def blockid_check : Type :=
 except_t string (state blockid_set) unit