Don't classify idiv/udiv as a reduction operation. Integer division is lossy. For example : (1 / 2) * 4 != 4/2. Example: int a[] = { 2, 5, 2, 2} int x = 80; for() x /= a[i]; Scalar: x /= 2 // = 40 x /= 5 // = 8 x /= 2 // = 4 x /= 2 // = 2 Vectorized: <80, 1> / <2,5> //= <40,0> <40, 0> / <2,2> //= <20,0> 20*0 = 0 radar://13640654 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179381 91177308-0d34-0410-b5e6-96231b3b80d8