[Bug fortran/32378] New: can't determine dependence (distinct sections of an array)

[Bug fortran/32378] New: can't determine dependence (distinct sections of an array)

[tprince at computer dot org]

gfortran -O2  -ftree-vectorize -ftree-vectorizer-verbose=2 -c -v s174.f
The two sections of the array are clearly distinct, so it should be vectorized.


-- 
           Summary: can't determine dependence (distinct sections of an
                    array)
           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=32378

[Bug fortran/32378] can't determine dependence (distinct sections of an array)

[tprince at computer dot org]

------- Comment #1 from tprince at computer dot org  2007-06-17 15:36 -------
Created an attachment (id=13723)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=13723&action=view)
source code test case


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32378

[Bug fortran/32378] can't determine dependence (distinct sections of an array)

[tprince at computer dot org]

------- Comment #2 from tprince at computer dot org  2007-06-18 01:39 -------
Performance change for full vectorization is not significant on Core 2 Duo;
suggest reduced ;priority, apologies for submitting at normal severity


-- 

tprince at computer dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |minor


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32378

[Bug tree-optimization/32378] can't determine dependence (distinct sections of an array)

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2007-06-18 03:15 -------
I think some of this is related to PR 32075.  (Looking into IR tells you that).


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|fortran                     |tree-optimization
  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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32378

[Bug tree-optimization/32378] can't determine dependence (distinct sections of an array)

[dorit at il dot ibm dot com]

------- Comment #4 from dorit at il dot ibm dot com  2007-06-18 11:08 -------
I see this in the vectorizer dump file (with mainline from a few days ago):

(compute_affine_dependence
  (stmt_a =
D.1423_50 = (*a_49(D))[D.1422_48])
  (stmt_b =
(*a_49(D))[D.1420_51] = D.1425_54)
Data ref a:
(Data Ref:
  stmt: D.1423_50 = (*a_49(D))[D.1422_48];
  ref: (*a_49(D))[D.1422_48];
  base_object: (*a_49(D))[0];
  Access function 0: {pretmp.48_45 + 1, +, 1}_1
  Access function 1: 0B
)
Data ref b:
(Data Ref:
  stmt: (*a_49(D))[D.1420_51] = D.1425_54;
  ref: (*a_49(D))[D.1420_51];
  base_object: (*a_49(D))[0];
  Access function 0: {0, +, 1}_1
  Access function 1: 0B
)
affine dependence test not usable: access function not affine or constant.
(dependence classified: scev_not_known)
)
(compute_affine_dependence
  (stmt_a =
D.1424_53 = (*b_52(D))[D.1420_51])
  (stmt_b =
(*a_49(D))[D.1420_51] = D.1425_54)
)

(the IR looks a bit different than PR32075, but the data-rependence analysis
fails with the same problem). pinskia - are you still planning to address this
issue?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32378

[Bug tree-optimization/32378] can't determine dependence (distinct sections of an array)

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-06-21 23:32:19
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32378

[Bug tree-optimization/32378] can't determine dependence (distinct sections of an array)

[dorit at gcc dot gnu dot org]

------- Comment #5 from dorit at gcc dot gnu dot org  2007-07-01 12:43 -------
Dependence analysis now fails with a different message:

(compute_affine_dependence
  (stmt_a =
D.1373_43 = (*a_42(D))[D.1372_41])
  (stmt_b =
(*a_42(D))[D.1370_44] = D.1375_47)
(subscript_dependence_tester
(analyze_overlapping_iterations
  (chrec_a = {pretmp.50_1 + 1, +, 1}_1)
  (chrec_b = {0, +, 1}_1)
(analyze_siv_subscript
siv test failed: unimplemented.
)
  (overlap_iterations_a = not known
)
  (overlap_iterations_b = not known
)
)
(dependence classified: scev_not_known)
)
)

Sebastian - any thughts/plans?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32378

[Bug tree-optimization/32378] can't determine dependence (distinct sections of an array)

[dorit at gcc dot gnu dot org]

------- Comment #6 from dorit at gcc dot gnu dot org  2007-08-19 13:47 -------
> Sebastian - any thughts/plans?

Here's another testcase:

subroutine sub(aa,bb,n,m)
  implicit none
  integer, intent(in) :: n,m
  real, intent(inout) :: aa(n,m)
  real, intent(in)    :: bb(n,m)
  integer :: i,j
 do j= 2,n
    do i = 1,m
      aa(i,j)= aa(i,j-1)+bb(i,j-1)
    enddo
  enddo
end subroutine
end

Here too we get:

(compute_affine_dependence
  (stmt_a =
D.1385_55 = (*aa_54(D))[D.1384_53])
  (stmt_b =
(*aa_54(D))[D.1380_49] = D.1390_62)
(subscript_dependence_tester
(analyze_overlapping_iterations
  (chrec_a = {pretmp.34_76 + 1, +, 1}_2)
  (chrec_b = {pretmp.34_32 + 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)
)
)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32378