define _maxndims methods for small tuples to help inference

Author: BSnelling

base/broadcast.jl

@@ -263,11 +263,15 @@ end
 
 Base.IteratorSize(::Type{T}) where {T<:Broadcasted} = Base.HasShape{ndims(T)}()
 Base.ndims(BC::Type{<:Broadcasted{<:Any,Nothing}}) = _maxndims(fieldtype(BC, 2))
-function Base.ndims(BC::Type{<:Broadcasted{<:AbstractArrayStyle{N},Nothing}}) where {N}
-    N isa Integer && return N
-    _maxndims(fieldtype(BC, 2))
+Base.ndims(::Type{<:Broadcasted{<:AbstractArrayStyle{N},Nothing}}) where {N<:Integer} = N
+
+_maxndims(T::Type{<:Tuple}) = reduce(max, (ntuple(n -> _ndims(fieldtype(T, n)), Base._counttuple(T))))
+_maxndims(::Type{<:Tuple{T}}) where {T} = ndims(T)
+_maxndims(::Type{<:Tuple{T}}) where {T<:Tuple} = _ndims(T)
+function _maxndims(::Type{<:Tuple{T, S}}) where {T, S}
+    return T<:Tuple || S<:Tuple ? max(_ndims(T), _ndims(S)) : max(ndims(T), ndims(S))
 end
-Base.@pure _maxndims(T) = mapfoldl(_ndims, max, fieldtypes(T))
+
 _ndims(x) = ndims(x)
 _ndims(::Type{<:Tuple}) = 1