[Bug tree-optimization/88844] New: poor range info for number of loop iterations with a known upper bound

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88844

            Bug ID: 88844
           Summary: poor range info for number of loop iterations with a
                    known upper bound
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

The number of iterations of the loop below is bounded by the size of i so the
value of n on loop exit is in the range [0, 4] but get_range_info() reports it
as [0, +INF].  As a result, the if statement is not eliminated.

void f (unsigned i)
{ 
  unsigned n = 0;

  while (i) {
    i >>= 4;
    ++n;
  }

  if (n > sizeof i)
    __builtin_abort ();
}