Merge pull request #11080 from yomichi/fix-cumprod

fixed `cumprod` and `cumprod!`

Author: tkelman

base/array.jl

@@ -1509,7 +1509,7 @@ for (f, f!, fp, op) = ((:cumsum, :cumsum!, :cumsum_pairwise!, :+),
         else
             n2 = n >> 1
             s_ = ($fp)(v, c, s, i1, n2)
-            s_ = $(op)(s_, ($fp)(v, c, s + s_, i1+n2, n-n2))
+            s_ = $(op)(s_, ($fp)(v, c, ($op)(s, s_), i1+n2, n-n2))
         end
         return s_
     end

test/arrayops.jl

@@ -1092,3 +1092,8 @@ end
 # PR #10164
 @test eltype(Array{Int}) == Int
 @test eltype(Array{Int,1}) == Int
+
+# PR #11080
+let x = fill(0.9, 1000)
+    @test_approx_eq prod(x) cumprod(x)[end]
+end