[Bug tree-optimization/19788] New: Inconsistent handling of -1.

[kazu at cs dot umass dot edu]

Consider:

int
foo (void)
{
  return -1;
}

int
bar (void)
{
  unsigned int a = 0xffffffff;
  return a;
}

int
baz (void)
{
  int a = -1;
  unsigned int b = 0xffffffff;
  return a == (int) b;
}

Here is what I get:

;; Function foo (foo)

foo ()
{
<bb 0>:
  return -1;

}

;; Function bar (bar)

bar ()
{
  int D.1124;

<bb 0>:
  D.1124 = -000000001;
  return D.1124;

}

;; Function baz (baz)

baz ()
{
  int b.0;

<bb 0>:
  b.0 = -000000001;
  return b.0 == -1;

}

Note that -1 is represented in two different ways in foo and bar.
Worse yet, the tree optimizers do not know that they are equal in baz.
baz is optimized as expected at RTL level.

-- 
           Summary: Inconsistent handling of -1.
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: missed-optimization, TREE
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        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=19788