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
Handle overridden visitFunction and visitBasicBlock methods, and in the default implementation of visitBasicBlock, recur into the block's arguments in addition to its instructions.
Swift SVN r3726
return values. Now the base class of the value hierarchy is "ValueBase"
instead of "Value", and "Value" is now a PointerIntPair indicating the
ValueBase (e.g. an instruction) being referenced along with what result
value is being referenced.
By default, any place you used "Value*" before, you should now use "Value".
Swift SVN r3207
