[GraphBolt] Hetero CPU sampling bug fix. (#7369)

graphbolt/src/fused_csc_sampling_graph.cc

@@ -557,7 +557,8 @@ FusedCSCSamplingGraph::SampleNeighborsImpl(
   // it equals to `num_seeds`.
   const int64_t num_rows = etype_id_to_num_picked_offset[num_etypes];
   torch::Tensor num_picked_neighbors_per_node =
-      torch::empty({num_rows}, indptr_options);
+      // Need to use zeros because all nodes don't have all etypes.
+      torch::zeros({num_rows}, indptr_options);
 
   AT_DISPATCH_INDEX_TYPES(
       indptr_.scalar_type(), "SampleNeighborsImplWrappedWithIndptr", ([&] {
@@ -571,14 +572,6 @@ FusedCSCSamplingGraph::SampleNeighborsImpl(
               num_picked_neighbors_data_ptr[0] = 0;
               const auto seeds_data_ptr = seeds.data_ptr<seeds_t>();
 
-              // Initialize the empty spots in `num_picked_neighbors_per_node`.
-              if (hetero_with_seed_offsets) {
-                for (auto i = 0; i < num_etypes; ++i) {
-                  num_picked_neighbors_data_ptr
-                      [etype_id_to_num_picked_offset[i]] = 0;
-                }
-              }
-
               // Step 1. Calculate pick number of each node.
               torch::parallel_for(
                   0, num_seeds, grain_size, [&](int64_t begin, int64_t end) {
@@ -612,40 +605,36 @@ FusedCSCSamplingGraph::SampleNeighborsImpl(
                     }
                   });
 
+              // Step 2. Calculate prefix sum to get total length and offsets of
+              // each node. It's also the indptr of the generated subgraph.
+              subgraph_indptr = num_picked_neighbors_per_node.cumsum(
+                  0, indptr_.scalar_type());
+              auto subgraph_indptr_data_ptr =
+                  subgraph_indptr.data_ptr<indptr_t>();
+
               if (hetero_with_seed_offsets) {
                 torch::Tensor num_picked_offset_tensor =
-                    torch::zeros({num_etypes + 1}, indptr_options);
+                    torch::empty({num_etypes + 1}, indptr_options);
+                const auto num_picked_offset_data_ptr =
+                    num_picked_offset_tensor.data_ptr<indptr_t>();
+                std::copy(
+                    etype_id_to_num_picked_offset.begin(),
+                    etype_id_to_num_picked_offset.end(),
+                    num_picked_offset_data_ptr);
                 torch::Tensor substract_offset =
-                    torch::zeros({num_etypes}, indptr_options);
+                    torch::empty({num_etypes}, indptr_options);
                 const auto substract_offset_data_ptr =
                     substract_offset.data_ptr<indptr_t>();
-                const auto num_picked_offset_data_ptr =
-                    num_picked_offset_tensor.data_ptr<indptr_t>();
                 for (auto i = 0; i < num_etypes; ++i) {
-                  num_picked_offset_data_ptr[i + 1] =
-                      etype_id_to_num_picked_offset[i + 1];
-                  // Collect the total pick number for each edge type.
-                  if (i + 1 < num_etypes)
-                    substract_offset_data_ptr[i + 1] =
-                        num_picked_neighbors_data_ptr
-                            [etype_id_to_num_picked_offset[i]];
-                  num_picked_neighbors_data_ptr
-                      [etype_id_to_num_picked_offset[i]] = 0;
+                  // Collect the total pick number subtract offsets.
+                  substract_offset_data_ptr[i] = subgraph_indptr_data_ptr
+                      [etype_id_to_num_picked_offset[i]];
                 }
-                substract_offset =
-                    substract_offset.cumsum(0, indptr_.scalar_type());
                 subgraph_indptr_substract = ops::ExpandIndptr(
                     num_picked_offset_tensor, indptr_.scalar_type(),
                     substract_offset);
               }
 
-              // Step 2. Calculate prefix sum to get total length and offsets of
-              // each node. It's also the indptr of the generated subgraph.
-              subgraph_indptr = num_picked_neighbors_per_node.cumsum(
-                  0, indptr_.scalar_type());
-              auto subgraph_indptr_data_ptr =
-                  subgraph_indptr.data_ptr<indptr_t>();
-
               // When doing non-temporal hetero sampling, we generate an
               // edge_offsets tensor.
               if (hetero_with_seed_offsets) {
@@ -1277,11 +1266,6 @@ void NumPickByEtype(
             NumPick(
                 fanouts[etype], replace, probs_or_mask, etype_begin,
                 etype_end - etype_begin, num_picked_ptr + offset);
-            // Use the skipped position of each edge type in the
-            // num_picked_tensor to sum up the total pick number for each edge
-            // type.
-            num_picked_ptr[etype_id_to_num_picked_offset[etype] - 1] +=
-                num_picked_ptr[offset];
           } else {
             PickedNumType picked_count = 0;
             NumPick(