A FieldName is a kind of Value that may be
used as an Operand to an Instruction. It references a Field definition. It may be used
in an Operand to an Instruction. It lets the
Instruction reference a member of a Class.
Note that fields may also be placed directly in an AssemblyDef, the FieldName would be
used to reference those as well.
A FieldName may be constructed either directly or through the Allocator object.
FieldName(Field *F);
It is possible to get the field reference.
Field *GetField()
const { return field_; }