Re: SSA range class and removal of VR_ANTI_RANGEs

[Martin Sebor <msebor at gmail dot com>]

> > --- /dev/null
> > +++ b/gcc/range.h
> > +
> > +You should have received a copy of the GNU General Public License
> > +along with GCC; see the file COPYING3.  If not see
> > +<http://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef GCC_RANGE_H
> > +#define GCC_RANGE_H
> > +#define MAX_RANGES	6
> > +
> > +typedef class irange *irange_p;
> > +enum irange_type { RANGE_PLAIN, RANGE_INVERT };
> > +
> > +class GTY(()) irange
> > +{
> > + private:
> > +  bool overflow;
> > +  size_t n;

Since space usage is of concern, defining the biggest member first
and using a smaller type should help as the first step.  Say:

  tree type;
  wide_int bounds[MAX_RANGES];
  unsigned char n: 7;   // 127 > MAX_RANGES
  bool overflow: 1 ;

There may be other tricks to play with the array although turning
it into a flexible array member will defeat the bit-field gain.

> > +  void prepend (wide_int x, wide_int y);
> > +  void append (wide_int x, wide_int y);
> > +  void remove (unsigned i, unsigned j);
> > +  void canonicalize ();
> > +  /* This is stupid.  These two should be private, but the GTY
> > +     machinery can't look inside an irange.  */
> > + public:
> > +  tree type;
> > +  wide_int bounds[MAX_RANGES];
> > +
> > +public:
> ...
> > +  void Union (wide_int x, wide_int y);
> > +  bool Union (const irange &r);
> > +  bool Union (const irange &r1, const irange &r2);
>
> Do we really want methods starting with capital letters?
> I understand why you can't use union, but I don't think we use CamelCase
> anywhere.

One way to get around the problem is to make the functions non-
members and rename them in the process:

  irange& irange_union (irange &, wide_int, wide_int);
  irange& irange_union (irange &, const irange &);
  irange& irange_union (irange &, const irange &, const irange &);

Making them friends of class irange will let them access private
members.  Returning irange& makes chaining multiple calls possible.

I think making interfaces thin and providing operations as non
member functions is also considered the preferable design these
days.

Martin