Teach SILGen how to emit the implicit elementwise constructor for structs and the implicit default constructor for classes, and eliminate the now dead IRGen code for them. Add a StructInst SIL instruction to represent constructing a loadable struct value from elements, analogous to TupleInst for tuples.
Swift SVN r4778
When lowering SIL builtin ConstantRefs, just stash away the FuncDecl, and pass that decl on to a tweaked version of emitBuiltinCall when the constant is applied.
Swift SVN r4736
Otherwise we try to release junk pointers when we reassign class fields in the struct. Add an attribute to InitializeVarInst so that when dataflow analysis comes online, it knows that these InitializeVars need to be eliminated and can't be lowered to default constructor calls (since we're already in a constructor).
Swift SVN r4730
take a const ValueBase* instead of a SILValue, implement SILArgument
cases for a few visitors and opt others out explicitly, and assert
that classes in the SIL value hierarchy override their superclass's
classof.
Swift SVN r4705
