dont force unroll loop in reductions

src/mapreduce.jl

@@ -66,18 +66,18 @@ end
 
 @generated function _mapreduce(f, op, dims::Colon, nt::NamedTuple{()},
                                ::Size{S}, a::StaticArray...) where {S}
-    tmp = [:(a[$j][1]) for j ∈ 1:length(a)]
-    expr = :(f($(tmp...)))
-    for i ∈ 2:prod(S)
-        tmp = [:(a[$j][$i]) for j ∈ 1:length(a)]
-        expr = :(op($expr, f($(tmp...))))
-    end
+    tmp = [:(a[$j][i]) for j ∈ 1:length(a)]
     return quote
         @_inline_meta
-        @inbounds return $expr
+        i = 1
+        @inbounds s = f($(tmp...))
+        @inbounds @simd for i = 2:$(prod(S))
+            s = op(s, f($(tmp...)))
+        end
+        return s
     end
 end
-    
+
 @generated function _mapreduce(f, op, dims::Colon, nt::NamedTuple{(:init,)},
                                ::Size{S}, a::StaticArray...) where {S}    
     expr = :(nt.init)