[Bug tree-optimization/101009] [12 Regression] wrong code with "-O3 -fno-tree-sra"
rguenth at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Fri Jun 11 07:19:39 GMT 2021
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101009
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
So interestingly we do compute a distance vector of zero but we fail to add it,
instead we end up returning true from build_classic_dist_vector_1 without
setting *init_b to true (the access fns are not POLYNOMIAL_CHREC but are
equal). Then in build_classic_dist_vector we skip
/* Save the distance vector if we initialized one. */
if (init_b)
..
and run into
/* There is a distance of 1 on all the outer loops: Example:
there is a dependence of distance 1 on loop_1 for the array A.
| loop_1
| A[5] = ...
| endloop
*/
add_outer_distances (ddr, dist_v,
lambda_vector_first_nz (dist_v,
DDR_NB_LOOPS (ddr), 0));
which ends up pushing a distance vector (1) as "outer distance". But in
the skipped if () case we'd only ever do that if DDR_NB_LOOPS > 1.
Both
@@ -5435,7 +5437,7 @@ build_classic_dist_vector (struct
data_dependence_relation
*ddr,
save_dist_v (ddr, save_v);
}
}
- else
+ else if (DDR_NB_LOOPS (ddr) > 1)
{
/* There is a distance of 1 on all the outer loops: Example:
there is a dependence of distance 1 on loop_1 for the array A.
and
@@ -5121,6 +5121,8 @@ build_classic_dist_vector_1 (struct
data_dependence_relati
on *ddr,
non_affine_dependence_relation (ddr);
return false;
}
+ else
+ *init_b = true;
}
return true;
fix the miscompilation. For the first patch we end up with no distance
vector in ddr->dist_vects and for the second with a single { 0 } distance
vector. IMHO the second looks more correct to me but maybe it is intended
that non-affine but constant indexes do not get a distance vector.
Anybody with some insights here?
More information about the Gcc-bugs
mailing list