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openedon Mar 26, 2019
@peterahrens encountered an interesting type-inference corner case, where adding a level of indirection would trigger type-inferences recursion heuristic and in his case prevent inlining to happen. The code Peter was written looked a lot like this:
f(arr::AbstractArray{T, 0}) where T = arr
indirect(arr) = f(arr)
f(arr::AbstractArray{T, N}) where {T, N} = indirect(view(arr, 1, ntuple(i->:, Val(N-1))...))Inspecting this code with @code_typed f(zeros(3,3,3,3,3)) yields:
7 ─ %82 = invoke Main.f(%80::SubArray{Float64,4,Array{Float64,5},Tuple{Int64,Base.Slice{Base.OneTo{Int64}},Base.Slice{Base.OneTo{Int64}},Base.Slice{Base.OneTo{Int64}},Base.Slice{Base.OneTo{Int64}}},true})::SubArray{T,0,P,I,L} where L where I where P where T
whereas removing that level of indirection
f(arr::AbstractArray{T, 0}) where T = arr
f(arr::AbstractArray{T, N}) where {T, N} = f(view(arr, 1, ntuple(i->:, Val(N-1))...))yields:
7 ─ %82 = invoke Main.f(%80::SubArray{Float64,4,Array{Float64,5},Tuple{Int64,Base.Slice{Base.OneTo{Int64}},Base.Slice{Base.OneTo{Int64}},Base.Slice{Base.OneTo{Int64}},Base.Slice{Base.OneTo{Int64}}},true})::SubArray{Float64,0,Array{Float64,5},NTuple{5,Int64},true}
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