[Bug tree-optimization/22196] Missed back prop

[Bug tree-optimization/22196] Missed back prop

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2007-02-09 16:10 -------
*** Bug 30747 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ak at muc dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22196

[Bug tree-optimization/22196] Missed back prop

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=22196

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This actually undos some of what phi-opt might do and only should be done for a
few operations.  I think divide, multiple, shifts and rotates should be done
and only with a constant operand.  This has to be done late very close to
expand even.

I will be implementing this but might miss GCC 12 as I have a lot on my plate
already for GCC 12.

[Bug tree-optimization/22196] Missed back prop

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=22196

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #3)
> This actually undos some of what phi-opt might do and only should be done
> for a few operations.  I think divide, multiple, shifts and rotates should
> be done and only with a constant operand.  This has to be done late very
> close to expand even.
> 
> I will be implementing this but might miss GCC 12 as I have a lot on my
> plate already for GCC 12.

It turns out this is still true. I had implemented the binary factoring out of
operations for phiopt and end up with a failure with
`gcc.dg/tree-prof/val-prof-1.c` which depends on phiopt not doing this. Note
only one of the phi nodes needs to be constant for when we want to handle it.

Oh I wonder if val-prof-1.c is still going to fail since we had originally:
if (a == CST) b = CST/c; else b = a/c;

And now we might have removed the if .. Woops. Anyways I will have to go and
dig into that failure some more but this issue is now needed again too.

[Bug tree-optimization/22196] Missed back prop

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=22196

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |goon.pri.low at gmail dot com

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 112608 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/22196] New: Missed back prop

[pinskia at gcc dot gnu dot org]

The following two functions should be equal:
unsigned f(int i, unsigned x)
{
  unsigned y;
  if (i)
    y = 1024;
  else
    y = 1024*1024;
  return x/y ;
}

unsigned f1(int i, unsigned x)
{
  unsigned y;
  if (i)
    y = x/ 1024;
  else
    y = x/(1024*1024);
  return y ;
}

-- 
           Summary: Missed back prop
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22196

[Bug tree-optimization/22196] Missed back prop

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-07-02 17:32 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-07-02 17:32:29
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22196