Bug 32378

Created attachment 13723 [details]
source code test case

Performance change for full vectorization is not significant on Core 2 Duo; suggest reduced ;priority, apologies for submitting at normal severity

I think some of this is related to PR 32075.  (Looking into IR tells you that).

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?

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?

> 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)
)
)

Fixed - vectorized with versioning for aliasing (consider n == 4).  The
testcase from comment#6 is PR32375.