Redesign PrunedLiveness APIs, introducing live ranges
First restore the basic PrunedLiveness abstraction to its original
intention. Move code outside of the basic abstraction that polutes the
abstraction and is fundamentally wrong from the perspective of the
liveness abstraction.
Most clients need to reason about live ranges, including the def
points, not just liveness based on use points. Add a PrunedLiveRange
layer of types that understand where the live range is
defined. Knowing where the live range is defined (the kill set) helps
reliably check that arbitrary points are within the boundary. This
way, the client doesn't need to be manage this on its own. We can also
support holes in the live range for non-SSA liveness. This makes it
safe and correct for the way liveness is now being used. This layer
safety handles:
- multiple defs
- instructions that are both uses and defs
- dead values
- unreachable code
- self-loops
So it's no longer the client's responsibility to check these things!
Add SSAPrunedLiveness and MultiDefPrunedLiveness to safely handle each
situation.
Split code that I can't figure out into
DiagnosticPrunedLiveness. Hopefully it will be deleted soon.
