[Bug tree-optimization/30104] New: missed code motion optimization (invariant control structures)

[Bug tree-optimization/30104] New: missed code motion optimization (invariant control structures)

[dann at godzilla dot ics dot uci dot edu]

The following 2 functions should be compiled to the same assembly. 
This is one of Briggs' compiler benchmarks.

void motion_test10(int *data)
{
  int j;
  int p = data[1];
  int i = data[0];
  do {
    if (p)
      j = 1;
    else
      j = 2;
    i = i + j;
    data[data[2]] = 2;
  } while (i < data[3]);
}
void motion_result10(int *data)
{
  int j;
  int p = data[1];
  int i = data[0];
  if (p)
    j = 1;
  else
    j = 2;
  do {
    i = i + j;
    data[data[2]] = 2;
  } while (i < data[3]);
}


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           Summary: missed code motion optimization (invariant control
                    structures)
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dann at godzilla dot ics dot uci dot edu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30104

[Bug tree-optimization/30104] missed code motion optimization (invariant control structures)

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2006-12-07 14:17 -------
Confirmed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2006-12-07 14:17:34
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30104

[Bug tree-optimization/30104] missed code motion optimization (invariant control structures)

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2006-12-07 16:46 -------
isn't this the same as loop  unswitching?
PS This was done from a PS3! 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30104

[Bug tree-optimization/30104] missed code motion optimization (invariant control structures)

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2006-12-07 16:49 -------
unswitching would duplicate the whole loop here, so not exactly I think.  But
if-conversion to

  j = COND_EXPR <p, 1, 2>

or

  j = 2 - (int)p;

would make j loop invariant.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30104

[Bug tree-optimization/30104] missed code motion optimization (invariant control structures)

[dann at godzilla dot ics dot uci dot edu]

------- Comment #4 from dann at godzilla dot ics dot uci dot edu  2006-12-07 18:24 -------
(In reply to comment #3)
> unswitching would duplicate the whole loop here, so not exactly I think.  But
> if-conversion to
> 
>   j = COND_EXPR <p, 1, 2>
> 
> or
> 
>   j = 2 - (int)p;
> 
> would make j loop invariant.

if-conversion would solve this particular testcase, but the more general case
of moving invariant control structures out of the loop is probably more
interesting. 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30104