swift234

Substantially rework how weak pointers are represented in the AST and
at the SIL level.  Now, the referent type of a WeakStorageType is always
an optional type, instead of always being the underlying reference.  This
allows us to represent both optional types.  Before, both of these had the
same AST representation of WeakStorageType(T):

  weak var x : T?
  weak var x : T!

which doesn't work.  Now we represent the optional type explicitly in the
AST and at SIL level.  This also significantly simplifies a bunch of code
that was ripping off the optional type and resynthesizing it in other places,
and makes SILGen of weak pointers much more straight-forward by eliminating
the need for emitRefToOptional and emitOptionalToRef entirely (see the diffs
in test/SILGen/weak).

Weak pointers still have problems, but this is a big step forward.


Swift SVN r18312