Collapsing Owned Places

At the outset of each program point, the collapse_owned_places operation eagerly collapses the Owned PCG.

This operation is implemented as PcgVisitor::collapse_owned_places (see https://github.com/viperproject/pcg/blob/main/src/pcg/visitor/pack.rs

It is implemented as follows:

• For each place $p$ for which there exists a place node (from longest to shortest):
  • If no expansion of $p$ is blocked by a borrow and every expansion of $p$ has the same capability:
    • perform the collapse(p) operation
    • if $p$ has no projection and has $R$ capability, upgrade $p$'s capability to $E$