Now that generic subclasses of @objc classes are supported, dust off
Doug Gregor's fix for <rdar://problem/20385288>. It is now an error
to override an @objc declaration with something that cannot be
represented as @objc.
For example, the override of foo() here will not compile unless
it is explicitly marked @nonobjc:
func foo(i: Int) {}
...
override func foo(i: Int?) {}
Note that I updated IRGen to delete some logic for figuring out when
to emit @objc metadata. We can now rely on Sema to correctly set
isObjC(), instead of checking overrides ourselves. This was wrong
anyway, now that we can have @nonobjc overrides of @objc methods,
and vice versa.
Swift SVN r29263
When a derived class specializes its base class, e.g. 'class Derived: Base<Int>', the natural abstraction levels of its methods may differ from the original base class's more abstract methods. Handle this by using the reabstraction machinery to thunk values when necessary. Merge the existing optionality thunking support into the reabstraction code, where witness thunking and similar convention adjustments may also be able to use it, if we desire. Fixes rdar://problem/19760292.
Swift SVN r28505
We no longer need or use it since we can always refer to the same bit on
the applied function when deciding whether to inline during mandatory
inlining.
Resolves rdar://problem/19478366.
Swift SVN r26534
If a grandchild class inherits a thunked override from the child class, use that thunk in the grandchild vtable too. Should round out the fix for rdar://problem/19321484.
Swift SVN r24735
If a subclass overrides methods with variance in the optionality of non-class-type members, emit a thunk to handle wrapping more optional parameters or results and force-unwrapping any IUO parameters made non-optional in the derived. For this to be useful, we need IRGen to finally pay attention to SILVTables, but this is a step on the way to fixing rdar://problem/19321484.
Swift SVN r24705
