Use local vars to improve readability. No functional change.

Completes what was started in r216611 and r216623. 
Used const refs instead of pointers; not sure if one is preferable to the other.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216672 91177308-0d34-0410-b5e6-96231b3b80d8