Interface dispatch now unboxes a receiver it has matched by key with one
load and no reference count change, and keeps its checked fallback out of
line so the key tests inline at each call site. A loop over an array of
interface values lends each element to a dispatch whose implementing
methods cannot release it; the fallback, which can run any code, takes
its own reference to the receiver.
Chris Tate
9843f8efd2