------- Comment #6 from victork at gcc dot gnu dot org 2008-04-10 10:36 -------
The problem in reduced testcase is that loop gets vectorized by gcc 4.2 despite
a dependency between iterations with distance 1.
compute_data_dependences_for_loop () returns "chrec_known" for DDR {
ivec(iclass), ivec(iclass-1) }.
Here is part of dump produced by scev in 4.2:
(compute_affine_dependence
(stmt_a =
D.1282_9 = (*ivec_8)[D.1281_7])
(stmt_b =
(*ivec_8)[D.1280_6] = D.1284_13)
(subscript_dependence_tester
(analyze_overlapping_iterations
(chrec_a = {0, +, 1}_1)
(chrec_b = {1, +, 1}_1)
(analyze_siv_subscript
(analyze_subscript_affine_affine
(overlaps_a = scev_known)
(overlaps_b = scev_known)
)
)
(overlap_iterations_a = scev_known)
(overlap_iterations_b = scev_known)
)
(dependence classified: scev_known)
)
)
While in gcc 4.3 the scev produces the following dump for same DDR:
(compute_affine_dependence
(stmt_a =
D.970_9 = (*ivec_8(D))[D.969_7])
(stmt_b =
(*ivec_8(D))[D.968_6] = D.972_13)
(subscript_dependence_tester
(analyze_overlapping_iterations
(chrec_a = {0, +, 1}_1)
(chrec_b = {1, +, 1}_1)
(analyze_siv_subscript
(analyze_subscript_affine_affine
(overlaps_a = [1 + 1 * x_1]
)
(overlaps_b = [0 + 1 * x_1]
)
)
)
(overlap_iterations_a = [1 + 1 * x_1]
)
(overlap_iterations_b = [0 + 1 * x_1]
)
)
(analyze_overlapping_iterations
(chrec_a = 0B)
(chrec_b = 0B)
(analyze_ziv_subscript
)
(overlap_iterations_a = [0]
)
(overlap_iterations_b = [0]
)
)
(build_classic_dist_vector
dist_vector = ( 1
)
)
)
)
Sebastian, can you take a look?
Thanks.
--
victork at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |spop at gcc dot gnu dot org
AssignedTo|victork at gcc dot gnu dot |spop at gcc dot gnu dot org
|org |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34006
