[InstCombine] add more tests with poison and undef; NFC

As discussed in D48987 and D48893, there are many different
ways to go wrong depending on the binop (and as shown here
we already do go wrong in some cases).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336450 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed