Make length for Date ranges type stable

[omus]

On 32-bit systems the length method for a StepRange{<:TimeType} was type instable:

julia> @code_warntype length(Date(2014):Dates.Day(1):Date(2015))
Variables:
  #self#::Base.#length
  r::StepRange{Date,Base.Dates.Day}

Body:
  begin 
      unless (Base.and_int)((Base.not_int)(((Core.getfield)(r::StepRange{Date,Base.Dates.Day},:start)::Date === (Core.getfield)(r::StepRange{Date,Base.Dates.Day},:stop)::Date)::Bool)::Bool,(Base.not_int)(((Base.slt_int)((Base.sext_int)(Int64,0)::Int64,(Core.getfield)((Core.getfield)(r::StepRange{Date,Base.Dates.Day},:step)::Base.Dates.Day,:value)::Int64)::Bool === (Base.slt_int)((Core.getfield)((Core.getfield)((Core.getfield)((Core.getfield)(r::StepRange{Date,Base.Dates.Day},:start)::Date,:instant)::Base.Dates.UTInstant{Base.Dates.Day},:periods)::Base.Dates.Day,:value)::Int64,(Core.getfield)((Core.getfield)((Core.getfield)((Core.getfield)(r::StepRange{Date,Base.Dates.Day},:stop)::Date,:instant)::Base.Dates.UTInstant{Base.Dates.Day},:periods)::Base.Dates.Day,:value)::Int64)::Bool)::Bool)::Bool)::Bool goto 3
      return 0
      3: 
      SSAValue(0) = $(Expr(:invoke, MethodInstance for len(::Date, ::Date, ::Base.Dates.Day), :(Base.Dates.len), :((Core.getfield)(r,:start)::Date), :((Core.getfield)(r,:stop)::Date), :((Core.getfield)(r,:step)::Base.Dates.Day)))
      return (Base.add_int)(SSAValue(0),(Base.sext_int)(Int64,1)::Int64)::Int64
  end::Union{Int32,Int64}

[tkelman]

how many types do we have give Int64 lengths on 32 bit?

[omus]

I'm not sure. Anything that uses a type larger than Int32 will probably return an Int64 or larger:

On 32-bit:

julia> typeof(length(Int64(1):Int64(2)))
Int64

julia> typeof(length(Int64(1)//2:1//4:1))
Int64

julia> typeof(length(Int128(1):Int128(2)))
Int128

julia> typeof(length(UInt16(1):UInt16(2)))
Int32

julia> typeof(length(UInt32(1):UInt32(2)))
UInt32