PDBFPO: Use references instead of pointers, where possible
The code was passing pointers around, expecting they would be not null.
In c++ it is possible to convey this notion explicitly by using a
Not all uses of pointers could be converted to references (e.g. one
can't store references in a container), but this will at least make it
locally obvious that code is dealing with nonnull pointers.
Reviewers: aleksandr.urakov, amccarth
Differential Revision: https://reviews.llvm.org/D60271