[Bug tree-optimization/21576] New: FRE does not eliminate a redundant builtin call.

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

Consider:

int
foo (unsigned long a)
{
  int b = __builtin_clzl (a);
  int c = __builtin_clzl (a);
  if (b == c)
    return 1;
  return 0;
}

Here is what I get after FRE.

foo (a)
{
  int c;
  int b;
  int D.1235;

<bb 0>:
  b_3 = __builtin_clzl (a_2);
  c_4 = __builtin_clzl (a_2);
  if (b_3 == c_4) goto <L0>; else goto <L1>;

<L0>:;
  D.1235_7 = 1;
  goto <bb 3> (<L2>);

<L1>:;
  D.1235_6 = 0;

  # D.1235_1 = PHI <1(1), 0(2)>;
<L2>:;
  return D.1235_1;

}

DOM catches this later.

-- 
           Summary: FRE does not eliminate a redundant builtin call.
           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: dberlin at gcc dot gnu dot org,gcc-bugs at gcc dot gnu
                    dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21576