representation of struct field offsets

[Richard Kenner]

> The only trouble you'll probably run into is with fields whose offset  
> from the start of a structure is variable.

Exactly.  That's the reason it's defined the way it is.  There is no way
to synthesize that field from any other in the FIELD_DECL in the most
general case: it is unique information.  I'm traveling now, but should be
able to give some examples of this early next week.