Collision of generated names in generated functions

[yuyichao]

To reproduce:

@generated function f(::Any)
    :(for i in 1
      end)
end

println(@code_typed f(1.2))

Output is attached below. Somehow the automatically generated names in the body of the generated function uses a independent counter from the original function and this causes the generated variable names to collide.

Since the generated names in the argument lists are never used, this may not cause any behavioral difference but it does cause the variable to be lifted to Any and introduce all kinds of boxing etc. (See the Any[symbol("#s1"),Any,2] in the code_typed output below)

(@code_warntype can show that the variable is not type stable but it is almost impossible to tell from it's output why this is happening...)

Output

Any[:($(Expr(:lambda, Any[:(#s1::Any)], Any[Any[Any[symbol("#s1"),Any,2],Any[:i,Int64,18]],Any[],Any[Int64,Tuple{Int64,Bool},Int64],Any[]], :(begin  # /home/yuyichao/projects/explore/julia/generated_anon_val/generated_anon_val.jl, line 4:
        GenSym(0) = 1
        #s1 = false
        unless (Base.box)(Base.Bool,(Base.not_int)(#s1::Bool))::Bool goto 1
        2: 
        GenSym(2) = GenSym(0)
        i = GenSym(2)
        #s1 = true
        3: 
        unless (Base.box)(Base.Bool,(Base.not_int)((Base.box)(Base.Bool,(Base.not_int)(#s1::Bool))::Bool))::Bool goto 2
        1: 
        0: 
        return
    end::Void))))]