and retrieving it from instructions. I don't have a use for this but is seems
logical for it to exist. While there, remove some 'const' markings from methods
which are in fact 'const' in practice, but aren't logically 'const'.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154811 91177308-0d34-0410-b5e6-96231b3b80d8