fix slice_boxing s2s multi-machine when empty intersection (#4169)

* fix slice_boxing s2s multi-machine when empty intersection

* refine
Co-authored-by: NJuncheng <liujuncheng1022@gmail.com>
Co-authored-by: Noneflow-ci-bot <69100618+oneflow-ci-bot@users.noreply.github.com>

oneflow/core/graph/boxing/slice_boxing_sub_task_graph_builder.cpp

@@ -238,12 +238,16 @@ Maybe<SubTskGphBuilderStatus> SliceBoxingSubTskGphBuilder::Build(
             }
           }
         } else {
-          std::vector<TensorSliceView> intersections;
+          HashMap<int64_t, TensorSliceView> in_id2intersection;
+          std::vector<TensorSliceView> non_empty_intersections;
           for (const int64_t in_id : in_parallel_ids) {
-            intersections.push_back(out_slice.Intersect(in_slices.at(in_id)));
+            const TensorSliceView& intersection = out_slice.Intersect(in_slices.at(in_id));
+            in_id2intersection[in_id] = intersection;
+            if (!intersection.IsEmpty()) { non_empty_intersections.push_back(intersection); }
           }
+          if (non_empty_intersections.empty()) { continue; }
           const TensorSliceView concat_slice =
-              TensorSliceView::Concatenate(intersections, in_sbp.split_parallel().axis());
+              TensorSliceView::Concatenate(non_empty_intersections, in_sbp.split_parallel().axis());
           SliceBoxingTaskNode* local_concat_node =
               ctx->task_graph()->NewNode<SliceBoxingTaskNode>();
           int64_t local_concat_thrd_id = -1;
@@ -261,8 +265,10 @@ Maybe<SubTskGphBuilderStatus> SliceBoxingSubTskGphBuilder::Build(
           local_concat_node->Init(lbi, concat_slice, kSliceBoxingTaskModeCopy, in_machine_id,
                                   local_concat_thrd_id, Global<IDMgr>::Get()->CpuMemZoneId());
           for (const int64_t in_id : in_parallel_ids) {
-            local_concat_node->ConnectToSrcNodeWithSlice(in_nodes.at(in_id), NewEdge(),
-                                                         in_slices.at(in_id));
+            if (!in_id2intersection.at(in_id).IsEmpty()) {
+              local_concat_node->ConnectToSrcNodeWithSlice(in_nodes.at(in_id), NewEdge(),
+                                                           in_slices.at(in_id));
+            }
           }
           TaskNode* local_add_proxy_node =
               ctx->GetProxyNode(local_concat_node, Global<IDMgr>::Get()->CpuMemZoneId(),