According to FIXME of the DataLayout APIs, the default argument is not preferred anymore. Update those APIs, and clean up clients of them as well.
This isn't really the meaning of the FIXME.
The issues is that at each call site we actually need to do careful analysis to understand what the address space should be and only move away from the default argument when we understand the *correct* address space for a particular call site.
This way, the default argument serves as a marker for when a caller hasn't yet been updated to carefully consider the address space implications.
That means this can't just be a cleanup. =/