logbeta is type-unstable

[stevengj]

julia> @code_warntype logbeta(0.2, 0.3)
Variables
  #self#::Core.Const(SpecialFunctions.logbeta)
  a::Float64
  b::Float64
  @_4::Int64
  sign::Union{Int32, Int64}
  lab::Union{Float64, Int32, Int64}

Body::Union{Float64, Int32, Int64}
1 ─ %1  = SpecialFunctions.logabsbeta(a, b)::Tuple{Union{Float64, Int32, Int64}, Union{Int32, Int64}}
│   %2  = Base.indexed_iterate(%1, 1)::Core.PartialStruct(Tuple{Union{Float64, Int32, Int64}, Int64}, Any[Union{Float64, Int32, Int64}, Core.Const(2)])
│         (lab = Core.getfield(%2, 1))
│         (@_4 = Core.getfield(%2, 2))
│   %5  = Base.indexed_iterate(%1, 2, @_4::Core.Const(2))::Core.PartialStruct(Tuple{Union{Int32, Int64}, Int64}, Any[Union{Int32, Int64}, Core.Const(3)])
│         (sign = Core.getfield(%5, 1))
│   %7  = (sign < 0)::Bool
└──       goto #3 if not %7
2 ─ %9  = Core.tuple(a, b)::Tuple{Float64, Float64}
│   %10 = SpecialFunctions.DomainError(%9, "`beta(a, b)` must be non-negative")::Any
└──       SpecialFunctions.throw(%10)
3 ┄       return lab