[Bug tree-optimization/21031] New: Another missed forward propagation opportunity

[kazu at cs dot umass dot edu]

Consider:

int
foo (int a)
{
  int b = a != 0;
  unsigned char c = b;
  if (c)
    return 1;
  else
    return 0;
}

We end up with code like this:

  b_3 = a_2 != 0;
  c_4 = (unsigned char) b_3;
  if (c_4 != 0) goto <L0>; else goto <L2>;

We want to forward-propagate the preceding two statements into the COND_EXPR
and get

  if (a_2 != 0) goto <L0>; else goto <L2>;

Unlike forward propagation opportunities noted in PR 14754 or PR15558,
this kind of opportunity occurs often in practice.

-- 
           Summary: Another missed forward propagation opportunity
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: kazu at cs dot umass dot edu
        ReportedBy: kazu at cs dot umass dot edu
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21031