This is what you need to correctly analyze OSSA.
- computeLinearLiveness
- computeInteriorLiveness
- InteriorUseVisitor
- OwnershipUseVisitor
- LivenessBoundary
Along with BorrowUtils.swift, all of our OSSA transformations are
built on top of these fundamentals. With these APIs, we can build
anything OSSA-related in SwiftCompilerSources. These utilities are
immediately needed for borrowed arguments and lifetime dependence. In
the near future, we can also use them to complete OSSA lifetimes and
*correctly* fixup OSSA after transformation without introducing lots
of copies and creating lots of incorrect corner cases.
