[Bug tree-optimization/23821] New: Dom creating harder to optimize code

[Bug tree-optimization/23821] New: Dom creating harder to optimize code

[rakdver at gcc dot gnu dot org]

Dom transforms the following testcase:

static int a[199];

int
main ()
{
  int i, x;
  for (i = 0; i < 199; i++)
    {
      x = a[i];
      if (x != i)
        abort ();
    }
  return 0;
}

to

int
main ()
{
  int i;
  for (i = 0; i < 199; i = x + 1)
    {
      x = a[i];
      if (x != i)
        abort ();
    }
  return 0;
}

Now we are not able to determine that i is an induction variable.

-- 
           Summary: Dom creating harder to optimize code
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rakdver at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23821

[Bug tree-optimization/23821] [4.0/4.1 Regression] Dom creating harder to optimize code

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-09-11 15:16 -------
Confirmed a regression.
The mainline and 4.0.0 on PPC gives:
L3:
        addi r9,r9,1
        bdz L10
L2:
        slwi r0,r9,2
        lwzx r2,r11,r0
        cmpw cr7,r2,r9
        beq+ cr7,L3

While 3.3 gives:
L7:
        lwz r3,0(r9)
        addi r9,r9,4
        cmpw cr0,r3,r2
        beq+ cr0,L4
        bl L_abort$stub
L4:
        addi r2,r2,1
        cmpwi cr1,r2,198
        ble+ cr1,L7

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2005-09-11 15:16:17
               date|                            |
            Summary|Dom creating harder to      |[4.0/4.1 Regression] Dom
                   |optimize code               |creating harder to optimize
                   |                            |code
   Target Milestone|---                         |4.0.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23821

[Bug tree-optimization/23821] [4.0/4.1 Regression] DOM and VRP creating harder to optimize code

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-09-11 15:19 -------
It is not just DOM on the mainline, it is also VRP

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.0/4.1 Regression] Dom    |[4.0/4.1 Regression] DOM and
                   |creating harder to optimize |VRP creating harder to
                   |code                        |optimize code


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23821

[Bug tree-optimization/23821] [4.0/4.1 Regression] DOM and VRP creating harder to optimize code

[mmitchel at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.0.2                       |4.0.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23821