Why vectorization is not beneficial in this for loop?

  auto-vectorization, c++, clang, llvm, vectorization

I am trying to vectorize the for loop. After using the Rpass flag in flag, I am getting following remark for it.

int someOuterVariable = 0;

for (unsigned int i = 7; i != -1; i--)
  array[someOuterVariable + i] -= 0.3 * anotherArray[i];

The cost-model indicates that vectorization is not beneficial
the cost-model indicates that interleaving is not beneficial

I want to understand what does this mean ? Interleaving not benficial mean the array indexing not proper ???

Source: Windows Questions C++