[Bug tree-optimization/32075] New: can't determine dependence between p->a[x+i] and p->a[x+i+1] where x is invariant but defined in the function

[Bug tree-optimization/32075] New: can't determine dependence between p->a[x+i] and p->a[x+i+1] where x is invariant but defined in the function

[pinskia at gcc dot gnu dot org]

While looking into some failures on the pointer plus branch after fixing up
forwprop, I noticed that we would get a failure in the vectorizer testsuite and
the reason is because we no longer could determine dependence for the two data
accesses.

Here is the testcase which is a modified version of vect-102.c which gets us
the same IR as what the pointer plus branch gives:
/* { dg-require-effective-target vect_int } */

#include <stdlib.h>
#include <stdarg.h>
#include "tree-vect.h"

#define N 9

struct extraction
{
  int a[N];
  int b[N];
};

static int a[N] = {1,2,3,4,5,6,7,8,9};
static int b[N] = {2,3,4,5,6,7,8,9,9};

int main1 (int x, int y) {
  int i;
  unsigned x1 = x;  
  struct extraction *p;
  p = (struct extraction *) malloc (sizeof (struct extraction));

  for (i = 0; i < N; i++)
    {
       p->a[i] = a[i];
       if (x == 135)
         abort (); /* to avoid vectorization  */
    }

  /* Not vectorizable: distance 1.  */
  for (i = 0; i < N - 1; i++)
    {
       p->a[x1 + i] = p->a[x1 + i + 1];
    }

  /* check results: */
  for (i = 0; i < N; i++)
    {
       if (p->a[i] != b[i])
         abort();
    }
  return 0;
}

int main (void)
{ 
  check_vect ();

  return main1 (0, N);
}

/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 0 "vect" } } */
/* { dg-final { scan-tree-dump-times "possible dependence between data-refs" 1
"vect" } } */
/* { dg-final { cleanup-tree-dump "vect" } } */

-------------------------- cut ---------------
if you change the 1 to 8, we should be able to vectorize that loop too.

Note I was wrong in PR 31995, that we got the same IR for that testcase as we
got for this bug, I had missed the cast in the IR.  Anyways this is
represenative of what the IR looks like for the testcase on the pointer plus
branch.


-- 
           Summary: can't determine dependence between p->a[x+i] and p-
                    >a[x+i+1] where x is invariant but defined in the
                    function
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32075

[Bug tree-optimization/32075] can't determine dependence between p->a[x+i] and p->a[x+i+1] where x is invariant but defined in the function

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-05-25 02:05 -------
Ok, I have a patch for this issue, I am going to test it with -ftree-vectorize
-msse2 while bootstrapping too to make sure that we don't have really any
regression due to data reference going wrong (the previous patch I should have
done the same too).


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |pinskia at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-05-25 02:05:50
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32075

[Bug tree-optimization/32075] can't determine dependence between p->a[x+i] and p->a[x+i+1] where x is invariant but defined in the function

[dorit at il dot ibm dot com]

------- Comment #2 from dorit at il dot ibm dot com  2007-06-18 11:03 -------
I see this in the vectorizer dump file (with mainline from a few days ago):

(compute_affine_dependence
  (stmt_a =
D.3027_19 = p_7->a[D.3026_18])
  (stmt_b =
p_7->a[D.3025_17] = D.3027_19)
Data ref a:
(Data Ref:
  stmt: D.3027_19 = p_7->a[D.3026_18];
  ref: p_7->a[D.3026_18];
  base_object: p_7->a[0];
  Access function 0: {x1_5 + 1, +, 1}_2
  Access function 1: 0B
)
Data ref b:
(Data Ref:
  stmt: p_7->a[D.3025_17] = D.3027_19;
  ref: p_7->a[D.3025_17];
  base_object: p_7->a[0];
  Access function 0: {x1_5, +, 1}_2
  Access function 1: 0B
)
affine dependence test not usable: access function not affine or constant.
(dependence classified: scev_not_known)
)

(In reply to comment #1)
> Ok, I have a patch for this issue, I am going to test it with -ftree-vectorize

so how is that coming along? do you think it will also address PRs
32375/6/7/8/9 ?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32075

[Bug tree-optimization/32075] can't determine dependence between p->a[x+i] and p->a[x+i+1] where x is invariant but defined in the function

[spop at gcc dot gnu dot org]

------- Comment #3 from spop at gcc dot gnu dot org  2007-06-20 16:57 -------
Subject: Re:  can't determine dependence between p->a[x+i] and p->a[x+i+1]
where x is invariant but defined in the function

The problem has been introduced in version 124927.

@@ -3182,7 +3182,7 @@ access_functions_are_affine_or_constant_

   for (i = 0; VEC_iterate (tree, fns, i, t); i++)
     if (!evolution_function_is_constant_p (t)
-       && !evolution_function_is_affine_multivariate_p (t))
+       && !evolution_function_is_affine_multivariate_p (t, 0))
       return false;

   return true;

The problem is that this line is saying that t has to be an affine
function with respect to the outermost loop_0.  That means {x, +, 1}_2
with x defined in loop_0, will be considered as non affine, just
because x is varying in loop_0.  So in the above patch, we have to
replace all these zeros with some other loop number...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32075

[Bug tree-optimization/32075] can't determine dependence between p->a[x+i] and p->a[x+i+1] where x is invariant but defined in the function

[spop at gcc dot gnu dot org]

------- Comment #4 from spop at gcc dot gnu dot org  2007-06-20 23:42 -------
Subject: Bug 32075

Author: spop
Date: Wed Jun 20 23:42:28 2007
New Revision: 125900

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=125900
Log:
        PR tree-optimization/32075
        * tree-data-ref.c (subscript_dependence_tester_1, 
        analyze_miv_subscript, analyze_overlapping_iterations,
        add_distance_for_zero_overlaps, build_classic_dist_vector,
        subscript_dependence_tester_1, analyze_overlapping_iterations,
        subscript_dependence_tester, access_functions_are_affine_or_constant_p,
        compute_affine_dependence, compute_all_dependences): Pass loop_nest 
        to evolution_function_is_affine_multivariate_p.


Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/tree-data-ref.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32075

[Bug tree-optimization/32075] can't determine dependence between p->a[x+i] and p->a[x+i+1] where x is invariant but defined in the function

[spop at gcc dot gnu dot org]

------- Comment #5 from spop at gcc dot gnu dot org  2007-06-20 23:45 -------
Subject: Bug 32075

Author: spop
Date: Wed Jun 20 23:44:56 2007
New Revision: 125901

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=125901
Log:
        PR tree-optimization/32075
        * tree-data-ref.c (subscript_dependence_tester_1, 
        analyze_miv_subscript, analyze_overlapping_iterations,
        add_distance_for_zero_overlaps, build_classic_dist_vector,
        subscript_dependence_tester_1, analyze_overlapping_iterations,
        subscript_dependence_tester, access_functions_are_affine_or_constant_p,
        compute_affine_dependence, compute_all_dependences): Pass loop_nest 
        to evolution_function_is_affine_multivariate_p.


Modified:
    trunk/gcc/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32075

[Bug tree-optimization/32075] can't determine dependence between p->a[x+i] and p->a[x+i+1] where x is invariant but defined in the function

[ubizjak at gmail dot com]

------- Comment #6 from ubizjak at gmail dot com  2007-06-21 21:05 -------
(In reply to comment #4)

> Author: spop
> Date: Wed Jun 20 23:42:28 2007
> New Revision: 125900

This commit causes PR32457.


-- 

ubizjak at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |32457
              nThis|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32075

[Bug tree-optimization/32075] can't determine dependence between p->a[x+i] and p->a[x+i+1] where x is invariant but defined in the function

[pinskia at gcc dot gnu dot org]

------- Comment #7 from pinskia at gcc dot gnu dot org  2007-06-24 04:07 -------
Fixed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32075