[Bug tree-optimization/32375] not vectorized: can't determine dependence (array sections)

[Bug tree-optimization/32375] not vectorized: can't determine dependence (array sections)

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32375

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |53947

--- Comment #7 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-07-13 08:58:32 UTC ---
Link to vectorizer missed-optimization meta-bug.

[Bug tree-optimization/32375] not vectorized: can't determine dependence (array sections)

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32375

--- Comment #8 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-07-16 13:03:10 UTC ---
The issue is that we have

<bb 5>:
  # j_2 = PHI <2(4), j_30(10)>
  pretmp.38_71 = (integer(kind=8)) j_2;
  pretmp.38_72 = stride.2_6 * pretmp.38_71;
  pretmp.38_73 = offset.3_8 + pretmp.38_72;
  pretmp.39_75 = j_2 + -1;
  pretmp.40_76 = (integer(kind=8)) pretmp.39_75;
  pretmp.40_77 = stride.2_6 * pretmp.40_76;
  pretmp.40_78 = offset.3_8 + pretmp.40_77;

<bb 6>:
  # i_37 = PHI <i_29(7), 1(5)>
...
  D.1940_22 = *aa_21(D)[D.1939_20];
  *aa_21(D)[D.1934_14] = D.1950_28;

and data-dependence analysis sees

(analyze_overlapping_iterations
  (chrec_a = {pretmp.40_78 + 1, +, 1}_2)
  (chrec_b = {pretmp.38_73 + 1, +, 1}_2)

and

(analyze_overlapping_iterations
  (chrec_a = {{(stride.2_6 + offset.3_8) + 1, +, stride.2_6}_1, +, 1}_2)
  (chrec_b = {{(stride.2_6 * 2 + offset.3_8) + 1, +, stride.2_6}_1, +, 1}_2)

[Bug fortran/32375] New: not vectorized: can't determine dependence (array sections)

[tprince at computer dot org]

gfortran -O2  -ftree-vectorize -ftree-vectorizer-verbose=2 -c -v s414a.f

The source and destination sections of aa(:,:) do not overlap, unless there is
a subscript over-run.  Even that case could be taken care of by loop reversal.

This is a simplification of a case from:
http://www.netlib.org/benchmark/vectors


-- 
           Summary: not vectorized: can't determine dependence (array
                    sections)
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tprince at computer dot org
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32375

[Bug tree-optimization/32375] not vectorized: can't determine dependence (array sections)

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2007-06-18 03:13 -------
I think some of this is related to PR 32075.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |32075
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
          Component|fortran                     |tree-optimization
     Ever Confirmed|0                           |1
  GCC build triplet|x86_64-unknown-linux-gnu    |
   GCC host triplet|x86_64-unknown-linux-gnu    |
 GCC target triplet|x86_64-unknown-linux-gnu    |
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2007-06-18 03:13:55
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32375

[Bug tree-optimization/32375] not vectorized: can't determine dependence (array sections)

[dorit at gcc dot gnu dot org]

------- Comment #3 from dorit at gcc dot gnu dot org  2007-07-01 12:46 -------
Looks like a similar problem to PR32378:

(compute_affine_dependence
  (stmt_a =
D.1398_74 = (*aa_73(D))[D.1397_72])
  (stmt_b =
(*aa_73(D))[D.1393_68] = D.1408_88)
(subscript_dependence_tester
(analyze_overlapping_iterations
  (chrec_a = {D.1396_71 + 1, +, 1}_2)
  (chrec_b = {D.1392_67 + 1, +, 1}_2)
(analyze_siv_subscript
siv test failed: unimplemented.
)
  (overlap_iterations_a = not known
)
  (overlap_iterations_b = not known
)
)
(dependence classified: scev_not_known)


-- 

dorit at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |spop at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32375

[Bug tree-optimization/32375] not vectorized: can't determine dependence (array sections)

[spop at gcc dot gnu dot org]

------- Comment #4 from spop at gcc dot gnu dot org  2007-10-30 17:01 -------
Subject: Re:  not vectorized: can't determine dependence (array sections)

On 1 Jul 2007 12:46:31 -0000, dorit at gcc dot gnu dot org
<gcc-bugzilla@gcc.gnu.org> wrote:
> (dependence classified: scev_not_known)
>

I still see the data dependence problem, but now the loop gets
vectorized on i686-linux with "-O3 -msse2" and also with "-O2
-ftree-vectorize -msse2"

> Looks like a similar problem to PR32378:

The same with this other PR.  The testcase gets vectorized even with
the failed dependence test.

Sebastian


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32375

[Bug tree-optimization/32375] not vectorized: can't determine dependence (array sections)

[spop at gcc dot gnu dot org]

------- Comment #5 from spop at gcc dot gnu dot org  2007-10-30 17:36 -------
Subject: Re:  not vectorized: can't determine dependence (array sections)

> The testcase gets vectorized even with the failed dependence test.
>

This is okay.  The test for non-dependence is added to the run-time
condition with which we version the code.  We call the function
vect_mark_for_runtime_alias_test instead of failing because of the
undetermined dependence test.

Sebastian


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32375

[Bug tree-optimization/32375] not vectorized: can't determine dependence (array sections)

[sebpop at gmail dot com]

------- Comment #6 from sebpop at gmail dot com  2007-10-30 17:59 -------
Subject: Re:  not vectorized: can't determine dependence (array sections)

I would like to keep the two bugs, PR32375 and PR32378, open as we can
vectorize them without having to version the code.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32375