Value witness markers note the location within a generic function
type's list of requirements where the value witness table will be
placed when calling a generic function with that type. It allows one
to get the same effect from walking the requirements of a generic
function that one would get from walking all levels of a
GenericParamList, with all archetypes of each generic parameter list,
along with all of the protocols to which each archetype conforms,
which SILGen and IRGen both do.
AST verification ensures that the property above holds; we're not
making use of it just yet.
Swift SVN r9509
Introduces a new kind of function type, GenericFunctionType, that
represents a polymorphic function type with all of its generic
parameters and requirements stored in a more readily canonicalizable
form. It is meant to eventually replace PolymorphicFunctionType, but
for now we build it up in parallel so we can switch over to it
pieacemeal.
Note: this representation is built and then thrown away. We'll start
recording it soon.
Swift SVN r8881
