(Patch description completely redone.)
Support deriving dereferenceability facts from allocation sites with known object sizes while correctly accounting for any possibly frees between allocation and use site. (At the moment, that's super conservative and only allowing it in functions where we know we can't free.)
This is part of the work on deref-at-point semantics. I'm making the change unconditional as the miscompile in this case is way too easy to trip by accident, and the optimization was only recently added (by me).
After this lands, the TLI wiring will be done separately in another review. That way a single review isn't both fixing a bug, and enabling further optimization.