We marked values which are 'undef' as constant instead of undefined
which violates SCCP's invariants. If we can figure out that a
computation results in 'undef', leave it in the undefined state.
This fixes PR16052.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@257102 91177308-0d34-0410-b5e6-96231b3b80d8
David Majnemer