https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101173
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
So we're exchanging the inner two loops
a[1][3] = 8;
for (int b = 1; b <= 5; b++)
for (int d = 0; d <= 5; d++)
for (c = 0; c <= 5; c++)
a[b][c] = a[b][c + 2] & 216;
to
a[1][3] = 8;
for (int b = 1; b <= 5; b++)
for (c = 0; c <= 5; c++)
for (int d = 0; d <= 5; d++)
a[b][c] = a[b][c + 2] & 216;
but that looks wrong from a dependence analysis perspective. We have
(compute_affine_dependence
ref_a: a[b_33][_1], stmt_a: _2 = a[b_33][_1];
ref_b: a[b_33][c.3_32], stmt_b: a[b_33][c.3_32] = _3;
(analyze_overlapping_iterations
(chrec_a = {2, +, 1}_5)
(chrec_b = {0, +, 1}_5)
(analyze_siv_subscript
(analyze_subscript_affine_affine
(overlaps_a = [0 + 1 * x_1])
(overlaps_b = [2 + 1 * x_1]))
)
(overlap_iterations_a = [0 + 1 * x_1])
(overlap_iterations_b = [2 + 1 * x_1]))
(analyze_overlapping_iterations
(chrec_a = {1, +, 1}_1)
(chrec_b = {1, +, 1}_1)
(overlap_iterations_a = [0])
(overlap_iterations_b = [0]))
(analyze_overlapping_iterations
(chrec_a = {0, +, 1}_5)
(chrec_b = {2, +, 1}_5)
(analyze_siv_subscript
(analyze_subscript_affine_affine
(overlaps_a = [2 + 1 * x_1])
(overlaps_b = [0 + 1 * x_1]))
)
(overlap_iterations_a = [2 + 1 * x_1])
(overlap_iterations_b = [0 + 1 * x_1]))
(analyze_overlapping_iterations
(chrec_a = {1, +, 1}_1)
(chrec_b = {1, +, 1}_1)
(overlap_iterations_a = [0])
(overlap_iterations_b = [0]))
(build_classic_dist_vector
dist_vector = ( 0 0 2
)
)
)
I don't see anything wrong with that at a first glance so the bug must be in
tree_loop_interchange::valid_data_dependences it checks
/* Be conservative, skip case if either direction at i_idx/o_idx
levels is not '=' or '<'. */
if (dist_vect[i_idx] < 0 || dist_vect[o_idx] < 0)
return false;
dist_vect is [0 0 2], i_idx 2 and o_idx 1 but I think that dist_vect[o_idx]
should exclude zero, thus
diff --git a/gcc/gimple-loop-interchange.cc b/gcc/gimple-loop-interchange.cc
index f45b9364644..265e36c48d4 100644
--- a/gcc/gimple-loop-interchange.cc
+++ b/gcc/gimple-loop-interchange.cc
@@ -1043,8 +1043,8 @@ tree_loop_interchange::valid_data_dependences (unsigned
i_idx, unsigned o_idx,
continue;
/* Be conservative, skip case if either direction at i_idx/o_idx
- levels is not '=' or '<'. */
- if (dist_vect[i_idx] < 0 || dist_vect[o_idx] < 0)
+ levels is not '=' (for the inner loop) or '<'. */
+ if (dist_vect[i_idx] < 0 || dist_vect[o_idx] <= 0)
return false;
}
}
Bin - does this analysis look sound?
