Performance regression 1.5 -> 1.6 calling fieldname(T, i)

[quinnj]

Julia 1.5.2:

julia> function ff(::Type{T}, i) where {T}
       return fieldname(T, i)
       end
ff (generic function with 1 method)

julia> @btime ff(A, 2)
  7.048 ns (0 allocations: 0 bytes)
:b

Julia 1.6.0-DEV.1640

julia> struct A
              a::Int
              b::Float64
              c::String
              end

julia> function ff(::Type{T}, i) where {T}
              return fieldname(T, i)
              end
ff (generic function with 1 method)

julia> @btime ff(A, 2)
  305.302 ns (0 allocations: 0 bytes)
:b