https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87665
--- Comment #14 from Richard Biener <rguenth at gcc dot gnu.org> ---
diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
index 4b3711442e6..a24e1853e03 100644
--- a/gcc/tree-vect-data-refs.c
+++ b/gcc/tree-vect-data-refs.c
@@ -210,16 +210,26 @@ vect_preserves_scalar_order_p (dr_vec_info *dr_info_a,
dr_vec_info *dr_info_b)
return true;
/* STMT_A and STMT_B belong to overlapping groups. All loads in a
- group are emitted at the position of the first scalar load and all
+ group are emitted at the position of the last scalar load and all
stores in a group are emitted at the position of the last scalar store.
- Thus writes will happen no earlier than their current position
- (but could happen later) while reads will happen no later than their
- current position (but could happen earlier). Reordering is therefore
- only possible if the first access is a write. */
- stmtinfo_a = vect_orig_stmt (stmtinfo_a);
- stmtinfo_b = vect_orig_stmt (stmtinfo_b);
- stmt_vec_info earlier_stmt_info = get_earlier_stmt (stmtinfo_a, stmtinfo_b);
- return !DR_IS_WRITE (STMT_VINFO_DATA_REF (earlier_stmt_info));
+ Compute that position and check whether the resulting order matches
+ the current one. */
+ stmt_vec_info last_a = DR_GROUP_FIRST_ELEMENT (stmtinfo_a);
+ if (last_a)
+ for (stmt_vec_info s = DR_GROUP_NEXT_ELEMENT (last_a); s;
+ s = DR_GROUP_NEXT_ELEMENT (s))
+ last_a = get_later_stmt (last_a, s);
+ else
+ last_a = stmtinfo_a;
+ stmt_vec_info last_b = DR_GROUP_FIRST_ELEMENT (stmtinfo_b);
+ if (last_b)
+ for (stmt_vec_info s = DR_GROUP_NEXT_ELEMENT (last_b); s;
+ s = DR_GROUP_NEXT_ELEMENT (s))
+ last_b = get_later_stmt (last_b, s);
+ else
+ last_b = stmtinfo_b;
+ return ((get_later_stmt (last_a, last_b) == last_a)
+ == (get_later_stmt (stmtinfo_a, stmtinfo_b) == stmtinfo_a));
}
/* A subroutine of vect_analyze_data_ref_dependence. Handle
