Previously, if a basic block ended with a FRMIDX instruction, we would
end up doing something like this.
*std::next(MBB.end())
Which would hit an error:
"Assertion `!NodePtr->isKnownSentinel()' failed."
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307057 91177308-0d34-0410-b5e6-96231b3b80d8
Dylan McKay