Test case for r191314. 

Some supplemental information for r191314: We would like to make sure SLP Vectorizer will not try to vectorize tiny trees even with a negative threshold so we set the cost to INT_MAX. 



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191327 91177308-0d34-0410-b5e6-96231b3b80d8