Now, IMVHO, having two different predicates with so similar names is a
potential source of confusion and mistakes, for both code readers and
code writers.
If we're going the extra predicate way as suggested, could we please
take the opportunity to introduce slightly more descriptive names, for
example SUBREG_OF_REG_P and REG_OR_SUBREG_OF_REG_P ?
I think the disambiguation-hence-mistake-avoidance is well worth
having slightly longer names to type and read. In this particular
case, I'd actually rather not have a second predicate instead of
one with so similar a name.