[Bug tree-optimization/21289] New: A numeric range is spoiled by a symblic one in VRP

["kazu at cs dot umass dot edu" <gcc-bugzilla@gcc.gnu.org>]

Consider

int
foo (int a, int b)
{
  if (a == 1)
    if (a < b)
      if (a == 1)
	return 1;

  return 0;
}

VRP does not remove the third "if" even though 'a' is known to be 1.

This is because the symbolic range obtained from the second "if"
spoils the numeric range [1, 1] obtained from the first "if".

extract_range_from_assert tries to refine a range from an ASSERT_EXPR
if there is another range previously available, but in this case,
VRP cannot prove that [1,1] and [-INF, b-1] intersects,
it does not refine a range.

-- 
           Summary: A numeric range is spoiled by a symblic one in VRP
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at cs dot umass dot edu
                CC: dnovillo at redhat dot com,gcc-bugs at gcc dot gnu dot
                    org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21289