Simple type inference failure setting Tuple field in-place on 0.6/0.7

[marius311]

I just ran into the following surprising (to me) inference failure on both 0.6.2 / 0.7.0-DEV.4959 (output below is for 0.6.2):

julia> zero_field1(t) = (t[1] .= 0)
zero_field1 (generic function with 1 method)

julia> @code_warntype zero_field1(([1.],[2]))
Variables:
  #self# <optimized out>
  t::Tuple{Array{Float64,1},Array{Int64,1}}
  #temp#@_3::Core.MethodInstance
  #temp#@_4::Any

Body:
  begin 
      SSAValue(1) = t::Tuple{Array{Float64,1},Array{Int64,1}}
      unless ((Base.getfield)(SSAValue(1), 1)::Union{Array{Float64,1}, Array{Int64,1}} isa Array{Float64,1})::Bool goto 5
      #temp#@_3::Core.MethodInstance = MethodInstance for broadcast!(::Base.#identity, ::Array{Float64,1}, ::Int64)
      goto 14
      5: 
      unless ((Base.getfield)(SSAValue(1), 1)::Union{Array{Float64,1}, Array{Int64,1}} isa Array{Int64,1})::Bool goto 9
      #temp#@_3::Core.MethodInstance = MethodInstance for broadcast!(::Base.#identity, ::Array{Int64,1}, ::Int64)
      goto 14
      9: 
      goto 11
      11: 
      #temp#@_4::Any = (Base.broadcast!)(Base.identity, (Base.getfield)(SSAValue(1), 1)::Union{Array{Float64,1}, Array{Int64,1}}, 0)::Union{Array{Float64,1}, Array{Int64,1}}
      goto 16
      14: 
      #temp#@_4::Any = $(Expr(:invoke, :(#temp#@_3), :(Base.broadcast!), :(Base.identity), :((Base.getfield)(SSAValue(1), 1)::Union{Array{Float64,1}, Array{Int64,1}}), 0))
      16: 
      return #temp#@_4::Any
  end::Union{Array{Float64,1}, Array{Int64,1}}

It can be fixed in the following odd way (which makes me believe this is more a bug than just a sub-optimality of inference),

julia> zero_field1(t) = (t[1] :: typeof(t[1]) .= 0)
zero_field1 (generic function with 1 method)

julia> @code_warntype zero_field1(([1.],[2]))
Variables:
  #self# <optimized out>
  t::Tuple{Array{Float64,1},Array{Int64,1}}

Body:
  begin 
      return $(Expr(:invoke, MethodInstance for fill!(::Array{Float64,1}, ::Int64), :(Base.Broadcast.fill!), :((Base.getfield)(t, 1)::Array{Float64,1}), 0))
  end::Array{Float64,1}

Hope this is helpful!

[KristofferC]

This also fixes it

julia> function zero_field1(t)
              x = t[1]
              return x .= 0
          end

Difference in lowered code is

      Core.SSAValue(1) = (Base.dotview)(t, 1)

vs

    x = (Base.getindex)(t, 1)
    Core.SSAValue(1) = x

Diff in inferred is

    # meta: location tuple.jl getindex 22
    Core.SSAValue(15) = (Base.getfield)(t::Tuple{Array{Float64,1},Array{Int64,1}}, 1, true)::Union{Array{Float64,1}, Array{Int64,1}}

vs

    # meta: location tuple.jl getindex 22
    Core.SSAValue(5) = (Base.getfield)(t::Tuple{Array{Float64,1},Array{Int64,1}}, 1, true)::Array{Float64,1

Perhaps the constant propagation doesn't get through the whole dotview-> maybeview machinery.

[KristofferC]

Fixed now. Probably #26826.