[Bug tree-optimization/97185] inconsistent builtin elimination for impossible range

["msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97185

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
There's a heuristic for ranges of allocation sizes to exclude zero
(size_range_flags) that comes into play here.  The actual range isn't
"impossible" in the sense it's necessarily invalid.  It just means the string
function call is either a no-op or out of bounds, and so can be eliminated as
an optimization.  With the optimization consistently implemented the warning
will also go away (eliminating the calls will prevent sanitizers from detecting
the out of bounds ones, so that might be a consideration).

In general, a low > high range denoted an anti-range before Ranger was
introduced (i.e., ~[high, low]).  With Ranger it's the corresponding union of
two ranges.  Some of the cruft for dealing with anti-ranges is still around,
such as in get_size_range() in pointer-query.cc.  The code should be migrated
to the irange class and the representation probably also updated to print
something more sensible (e.g., the union [MIN, high) U (low, MAX]; we talked
about introducing a pretty-printer % directive for ranges to make the format
consistent across all diagnostics).