In the wild, many cases of null pointer dereference, or uninitialized value read occur because the value was meant to be initialized by the inlined function, but did not, most often due to error condition in the inlined function.
This change highlights the return branch taken by the inlined function, in order to help user understand the error report and see why the value was uninitialized.
rdar://36287652
It would be good to extend the comment to say that it emits the diagnostic note when the region of interested is a *passed to a function* but the function doesn't store into it.