https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94043
--- Comment #4 from Kewen Lin <linkw at gcc dot gnu.org> ---
This was just exposed from my commit, it can also be reproduced without my
commit but with -fno-vect-cost-model.
Some loops we have for this case:
;; Loop 1
;; header 3, latch 10
;; depth 1, outer 0
;; nodes: 3 10 8 23 25 34 35 26 29 32 33 38 4 11 37 31
;; Loop 2
;; header 4, latch 11
;; depth 2, outer 1
;; nodes: 4 11
;; Loop 4
;; header 26, latch 29
;; depth 2, outer 1
;; nodes: 26 29
When we are doing versioning for loop4 required for aliasing check, the related
scalar_loop_iters is based on e2.2_31, which is defined in BB 4, that is:
<bb 4> [local count: 4343773762]:
# e2.2_31 = PHI <_15(11), 1(37)>
# ivtmp_14 = PHI <ivtmp_23(11), 4(37)>
For the codes:
if ((def_bb = gimple_bb (SSA_NAME_DEF_STMT (USE_FROM_PTR (use_p))))
&& flow_bb_inside_loop_p (outermost, def_bb))
outermost = superloop_at_depth (loop, bb_loop_depth (def_bb) + 1)
bb_loop_depth is 2, the +1 make the assertion in superloop_at_depth fail since
the current loop 4 only has the depth 2. I think the existing code has the
assumption that all operands in stmts of cond_expr_stmt_list are defined in
some outer loop of current, but the assumption breaks in this case.
I guess the current scalar_loop_iters is valid? Then the fix can be:
--- a/gcc/tree-vect-loop-manip.c
+++ b/gcc/tree-vect-loop-manip.c
@@ -3312,7 +3312,13 @@ vect_loop_versioning (loop_vec_info loop_vinfo,
FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE)
if ((def_bb = gimple_bb (SSA_NAME_DEF_STMT (USE_FROM_PTR (use_p))))
&& flow_bb_inside_loop_p (outermost, def_bb))
- outermost = superloop_at_depth (loop, loop_depth (outermost) + 1);
+ {
+ /* Def block can be in either one outer loop of loop_to_version or
+ one sibling of outer loop of loop_to_version. */
+ class loop *common_loop
+ = find_common_loop (def_bb->loop_father, loop);
+ outermost = superloop_at_depth (loop, loop_depth (common_loop) +
1);
+ }
}
