minimum with dims keyword is type-unstable on master

[giordano]

Julia 0.6.0:

julia> @code_warntype minimum(rand(5,5), 2)
Variables:
  #self#::Base.#minimum
  A::Array{Float64,2}
  region::Int64

Body:
  begin 
      $(Expr(:inbounds, false))
      # meta: location reducedim.jl minimum 570
      # meta: location reducedim.jl mapreducedim 241
      SSAValue(0) = $(Expr(:invoke, MethodInstance for reducedim_initarray0(::Array{Float64,2}, ::Int64, ::Float64, ::Type{Float64}), :(Base.reducedim_initarray0), :(A), :(region), Inf, Float64))
      # meta: location reducedim.jl mapreducedim! 210
      $(Expr(:invoke, MethodInstance for _mapreducedim!(::Base.#identity, ::Base.#scalarmin, ::Array{Float64,2}, ::Array{Float64,2}), :(Base._mapreducedim!), :(Base.identity), :(Base.scalarmin), SSAValue(0), :(A)))
      # meta: pop location
      # meta: pop location
      # meta: pop location
      $(Expr(:inbounds, :pop))
      return SSAValue(0)
  end::Array{Float64,2}

Julia master:

julia> @code_warntype minimum(rand(5,5), dims=2)
Body::AbstractArray
 1 ─ %1  = Base.getfield(%%#temp#, :dims)::Int64                                                            │╻     getindex
 └──       goto 2 if not false                                                                              │╻     isempty
 2 ┄ %3  = Base.slt_int(0, 1)::Bool                                                                         ││╻╷╷╷  iterate
 └──       goto 4 if not %3                                                                                 │││┃│    iterate
 3 ─       goto 5                                                                                           ││││┃     iterate
 4 ─       invoke Base.getindex(()::Tuple{}, 1::Int64)                                                      │││││ 
 └──       unreachable                                                                                      │││││ 
 5 ─       goto 6                                                                                           ││││  
 6 ─       goto 7                                                                                           ││╻     iterate
 7 ─       goto 8                                                                                           ││    
 8 ─       nothing                                                                                          │     
 │   %12 = :(Base.identity)::typeof(identity)                                                               ││╻     _minimum
 │   %13 = :(Base.min)::typeof(min)                                                                         │││╻     _minimum
 │   %14 = invoke Base._mapreduce_dim(%12::Function, %13::Function, :($(QuoteNode(NamedTuple())))::NamedTuple{(),Tuple{}}, %%a::Array{Float64,2}, %1::Int64)::AbstractArray
 └──       return %14

I don't know if it's somewhat related to #27836 and fixed by #27845.

[andreasnoack]

I don't see this issue when on #27845 but I'm not sure why it would have fixed it. Would have to take a closer look.

[andreasnoack]

Somehow #27845 also fixed this.

[martinholters]

We might want to test for this. Probably adding an @inferred to an existing test should do the trick.