[mips] Add comment and simplify function.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187371 91177308-0d34-0410-b5e6-96231b3b80d8
Debug Info: enable verifier for testing cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187375 91177308-0d34-0410-b5e6-96231b3b80d8