On 10/4/19 6:59 AM, Aldy Hernandez wrote: > When I did the value_range canonicalization work, I noticed that an > unsigned [1,MAX] and an ~[0,0] could be two different representations > for the same thing. I didn't address the problem then because callers > to ranges_from_anti_range() would go into an infinite loop trying to > extract ~[0,0] into [1,MAX] and []. We had a lot of callers to > ranges_from_anti_range, and it smelled like a rat's nest, so I bailed. > > Now that we have one main caller (from the symbolic PLUS/MINUS > handling), it's a lot easier to contain. Well, singleton_p also calls > it, but it's already handling nonzero specially, so it wouldn't be affected. > > > With some upcoming cleanups I'm about to post, the fact that [1,MAX] and > ~[0,0] are equal_p(), but not nonzero_p(), matters. Plus, it's just > good form to have one representation, giving us the ability to pick at > nonzero_p ranges with ease. > > The code in extract_range_from_plus_minus_expr() continues to be a mess > (as it has always been), but at least it's contained, and with this > patch, it's slightly smaller. > > Note, I'm avoiding adding a comment header for functions with highly > descriptive obvious names. > > OK? > > Aldy > > canonicalize-nonzero-ranges.patch > > commit 1c333730deeb4ddadc46ad6d12d5344f92c0352c > Author: Aldy Hernandez <al...@redhat.com> > Date: Fri Oct 4 08:51:25 2019 +0200 > > Canonicalize UNSIGNED [1,MAX] into ~[0,0]. > > Adapt PLUS/MINUS symbolic handling, so it doesn't call > ranges_from_anti_range with a VR_ANTI_RANGE containing one sub-range. > > diff --git a/gcc/ChangeLog b/gcc/ChangeLog > index 6e4f145af46..3934b41fdf9 100644 > --- a/gcc/ChangeLog > +++ b/gcc/ChangeLog > @@ -1,3 +1,18 @@ > +2019-10-04 Aldy Hernandez <al...@redhat.com> > + > + * tree-vrp.c (value_range_base::singleton_p): Use num_pairs > + instead of calling vrp_val_is_*. > + (value_range_base::set): Canonicalize unsigned [1,MAX] into > + non-zero. > + (range_has_numeric_bounds_p): New. > + (range_int_cst_p): Use range_has_numeric_bounds_p. > + (ranges_from_anti_range): Assert that we won't recurse > + indefinitely. > + (extract_extremes_from_range): New. > + (extract_range_from_plus_minus_expr): Adapt so we don't call > + ranges_from_anti_range with an anti-range containing only one > + sub-range. So no problem with the implementation, but I do have a higher level question.
One of the goals of the representation side of the Ranger project is to drop anti-ranges. Canonicalizing [1, MAX] to ~[0,0] seems to be going in the opposite direction. So do we really want to canonicalize to ~[0,0]? jeff
