[Test] We can benefit from pipelining of ymm load/stores

This patch demonstrates a scenario when we need to load/store a single
64-byte value, which is done by 2 ymm loads and stores in AVX. The current
codegen choses the following sequence:

  load ymm0
  load ymm1
  store ymm1
  store ymm0

If we instead stored ymm0 before ymm1, we could execute 2nd load and 1st store
in parallel.