RFC: define_predicate

[Joern Rennecke]

> Independent of what I said in my other message - the current version
> of the patch handles predicates calling other predicates in an elegant
> manner.  This won't be a problem.

That sounds quite intriguig.  How do you handle

  if (GET_CODE (op) == TRUNCATE && ...)
    ...
  if (tm_foo_operand (op, mode))
    ...
  else
    return register_operand (op, mode);