is_predicate_p?

[Robert Dewar]

> Predicates in GCC come in a wide variety of spellings.  Some end in _p,
> some start with is_, some have _is_ in the middle, some just expect you to
> know they're predicates based on the meaning of the name.  Should we set
> some sort of standard spelling for future additions?

I would have guidelines rather than a standard here. I would avoid the use
of _p unless you do decide to standardize on this (which seems very dubious
to me). The use of _p is simply not intuitive. All the other three cases
sound plausible to me, and I would hesitate to mandate any one over the others.