expression too large

I think I'm hitting a limit to the number of variables I can have near 100,000, e.g.,

$ julia 
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.5.0 (2016-09-19 18:14 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-pc-linux-gnu

julia> using ReverseDiff: compile_gradient

julia> compile_gradient(x->norm(x), rand(10000))
(::#301) (generic function with 1 method)

julia> compile_gradient(x->norm(x), rand(100000))
ERROR: syntax: expression too large
 in compile(::ReverseDiff.GradientTape{##7#8,ReverseDiff.TrackedArray{Float64,Float64,1,Array{Float64,1},Array{Float64,1}},ReverseDiff.TrackedReal{Float64,Float64,Void}}) at /home/marius/.julia/v0.5/ReverseDiff/src/api/tape.jl:83
 in compile_gradient(::Function, ::Array{Float64,1}, ::Vararg{Array{Float64,1},N}) at /home/marius/.julia/v0.5/ReverseDiff/src/api/tape.jl:104

Is there any way to go beyond this or is it just impractical?

Actually, where I'd be interested if I can get to is about O(10,000,000)... is that just too crazy to even consider?

Start with compile_gradient and the compile path in src/api/tape.jl, especially the reported lines 83 and 104, and reproduce the failure with the 100,000-element example. Determine whether the expression-size limit can be addressed and define supported behavior for substantially larger inputs, including the requested million-scale case.