When we inline a callee into a callsite that has attributes on return, we need to add the attributes on calls that feed into the return value in the callee definition.
Currently, we do this for only for calls feeding into the return.
A following patch, will do this also for loads feeding into the return, by adding it as a metadata on the load (i.e. loaded value is nonnull).
The analysis is added to handle the simple cases.