[InstCombine] new testcases for OverflowingBinaryOperators and PossiblyExactOperators transformations; NFC

instcombine should transform the relevant cases if the OverflowingBinaryOperator/PossiblyExactOperator can be proven to be safe.

Change-Id: I7aec62a31a894e465e00eb06aed80c3ea0c9dd45

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331265 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed