[Bug tree-optimization/18940] New: Loop is not vectorized when it should be

[Bug tree-optimization/18940] New: Loop is not vectorized when it should be

[pinskia at gcc dot gnu dot org]

Here is another case which my tree combiner confuses the other tree optimizations but it should not.
I get in .vect: "not vectorized: number of iterations cannot be computed.".
If I change D1360 to be just n, it works.
If I change "n <= 1" to be "D1360 <= 0" It works (on the mainline without my tree combiner which is 
the opposite of what my tree combiner does).


typedef float afloat __attribute__ ((__aligned__(16)));
int
main1 (int n , afloat * __restrict__ pa, afloat * __restrict__ pb)
{
  int i;
  int ivtmp51;
  int ivtmp35;
  int D1360 = n/2;
  
  if (n <= 1) return 0;
  
  ivtmp35 = 1;

  do {
    ivtmp51 = ivtmp35;
    pa[ivtmp51] = pb[ivtmp51];
    ivtmp35 = ivtmp51 + 1;
  }  while (D1360 > ivtmp51);
  
  return 0;
}

-- 
           Summary: Loop is not vectorized when it should be
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: minor
          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=18940

[Bug tree-optimization/18940] Loop is not vectorized when it should be

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-12-11 18:52 -------
This problem causes the following "regressions" with my tree combiner:
FAIL: gcc.dg/vect/vect-58.c scan-tree-dump-times vectorized 1 loops 1
FAIL: gcc.dg/vect/vect-60.c scan-tree-dump-times vectorized 1 loops 1

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18940

[Bug tree-optimization/18940] Loop is not vectorized when it should be

[dberlin at gcc dot gnu dot org]

------- Additional Comments From dberlin at gcc dot gnu dot org  2004-12-12 04:59 -------
These are real regressions because we are losing information.
In particular, when you replace D1360 <= 0 with n <= 1, we no longer can
determine that D1360 is <= 1.

This would require a pretty powerful assertion framework (when we learn
something about n, we'd have to know all expressions whose value depends on n,
which seems a bit much) to make up for.
I think for now we shouldn't combine before trying these transformations, or
limit combine until at least after loop, for things like conditionals whose
values have immediate uses in loop exit tests or something.



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18940

[Bug tree-optimization/18940] Loop is not vectorized when it should be

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-12-22 07:38 -------
I was able to work around the problem which my tree combiner causes by doing what the old forward-
pro did which is only combine into a COND_EXPR if we used the SSA_NAME only once in the COND_EXPR 
or when the resulting result is a constant (so we don't miss some optimizations).

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|minor                       |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-12-22 07:38:34
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18940

[Bug tree-optimization/18940] Loop is not vectorized when it should be

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-03-23 03:08 -------
suspend this one as this is hard and most likely not going to happen.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |SUSPENDED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18940