Teach CodeGenPrepare about address spaces

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190112 91177308-0d34-0410-b5e6-96231b3b80d8
Use type helper functions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190113 91177308-0d34-0410-b5e6-96231b3b80d8