Mostly straightforward as we ignore addressing modes and just
use the base + unsigned immediate offset (always 0) variants.
This currently fails to select extloads because we have yet to
agree on a representation.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277171 91177308-0d34-0410-b5e6-96231b3b80d8