Optimize away unnecessary address casts.

Removes unnecessary casts from non-generic address spaces to the generic address
space for certain code patterns.

Patch by Jingyue Wu.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205571 91177308-0d34-0410-b5e6-96231b3b80d8
Reuse existing variable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205572 91177308-0d34-0410-b5e6-96231b3b80d8