This lets us serialize that decision, which means we can conceivably
/change/ the decision in later versions of the compiler without
breaking existing code. More immediately, it's groundwork that will
eventually allow us to drop decls from the AST without affecting
vtable layout.
This isn't actually a great answer; what we really want is for SIL
vtables to be serialized consistently and treated as the point of
truth. But that would be more change than we're comfortable taking in
the Swift 4 timeframe.
First part of rdar://problem/31878396.
This replaces SILDeclRef::getBaseOverriddenVTableEntry(). It lives
in the TypeConverter because it needs to use type lowering information
to determine if the method requires a new vtable entry or not.
In the old vtable emission code, IRGen would skip addressors,
but they had entries in the SILVTable. This is still correct
behavior, so skip addressors explicitly in SILVTableVisitor.
We never call addressors dynamically, only inside a getter,
setter or materializeForSet. When a property with addressors
is overridden we provide new getters and setters (which may
or may not statically dispatch to a peer addressor).
This is a CRTP utility to walk the members of a class and
produce vtable entries. It will be used to clean up some
code duplication between SILGen and IRGen, and to provide
missing functionality for multiple vtable entries per
method.
