an undef value. This is only going to come up for bugpoint-reduced tests --
correct programs will not access memory at undefined addresses -- so it's not
worth the effort of doing anything more aggressive.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97745 91177308-0d34-0410-b5e6-96231b3b80d8