Use generic fallback for arrays with !(eltype >: Missing)

Author: nalimilan

base/missing.jl

@@ -190,7 +190,10 @@ function iterate(itr::SkipMissing, state...)
 end
 
 # Optimized mapreduce implementation
-mapreduce(f, op, itr::SkipMissing{<:AbstractArray}) = _mapreduce(f, op, IndexStyle(itr.x), itr)
+# The generic method is faster when !(eltype(A) >: Missing) since it does not need
+# additional loops to identify the two first non-missing values of each block
+mapreduce(f, op, itr::SkipMissing{<:AbstractArray}) =
+    _mapreduce(f, op, IndexStyle(itr.x), eltype(itr.x) >: Missing ? itr : itr.x)
 
 function _mapreduce(f, op, ::IndexLinear, itr::SkipMissing{<:AbstractArray})
     A = itr.x