Type instability in fftshift/ifftshift

[ngedwin98]

Originally brought up in JuliaMath/FFTW.jl#99, but fftshift and ifftshift are reexports from this package.

It appears the problem is that circshift produces type instability when called with vector arguments for shifts (although it handles correctly):

julia> z = randn(100)
julia> @code_warntype circshift(z, div.([size(z)...],2))
Body::Any
1 ─ %1  = (Base.arraysize)(a, 1)::Int64
│   %2  = $(Expr(:foreigncall, :(:jl_alloc_array_1d), Array{Float64,1}, svec(Any, Int64), :(:ccall), 2, Array{Float64,1}, :(%1), :(%1)))::Array{Float64,1}
│   %3  = (Core._apply)(Core.tuple, shiftamt)::Tuple{Vararg{Int64,N} where N}
│   %4  = (Base.map)(Base.Integer, %3)::Any
│   %5  = (isa)(%4, Tuple{})::Bool
└──       goto #3 if not %5
2 ─ %7  = (Base.arraylen)(a)::Int64
│   %8  = invoke Base.copyto!(%2::Array{Float64,1}, 1::Int64, _2::Array{Float64,1}, 1::Int64, %7::Int64)::Array{Float64,1}
└──       goto #4
3 ─ %10 = (Base.circshift!)(%2, a, %4)::Any
└──       goto #4
4 ┄ %12 = φ (#2 => %8, #3 => %10)::Any
└──       return %12

whereas this problem doesn't appear when called with a tuple for shifts:

julia> @code_warntype circshift(z, div.(size(z),2))
Body::Array{Float64,1}
1 ─ %1 = (Base.arraysize)(a, 1)::Int64
│   %2 = $(Expr(:foreigncall, :(:jl_alloc_array_1d), Array{Float64,1}, svec(Any, Int64), :(:ccall), 2, Array{Float64,1}, :(%1), :(%1)))::Array{Float64,1}
│   %3 = invoke Base.circshift!(%2::Array{Float64,1}, _2::Array{Float64,1}, _3::Tuple{Int64})::Array{Float64,1}
└──      return %3

It seems like the solution is to change all the shifts in fftshift and ifftshift to tuples?