diff --git a/src/compiler/graph.jl b/src/compiler/graph.jl
index 5ee0add9..3a9b02f9 100644
--- a/src/compiler/graph.jl
+++ b/src/compiler/graph.jl
@@ -4,9 +4,11 @@ splitnode(v, n) = vertex(Split(n), v)
 
 inputnode(n) = splitnode(constant(ModelInput()), n)
 
+isinput(v::IVertex) = isa(value(v), Split) && value(v[1]) == Constant(ModelInput())
+
 function bumpinputs(v::IVertex)
   prewalk(v) do v
-    isa(value(v), Split) && value(v[1]) == Constant(ModelInput()) ?
+    isinput(v) ?
       inputnode(value(v).n + 1) :
       v
   end
@@ -21,6 +23,15 @@ end
 spliceinputs(v::IVertex, inputs::Vertex...) =
   spliceinput(v, vertex(Group(), inputs...))
 
+function ninputs(v::IVertex)
+  n = 0
+  prewalk(v) do v
+    isinput(v) && (n = max(n, value(v).n))
+    v
+  end
+  return n
+end
+
 function detuple(v::IVertex)
   postwalk(v) do v
     if isa(value(v), Split) && isa(value(v[1]), Group)