Remove UNKNOWN_NULL_COUNT where it can be easily computed

cpp/include/cudf/detail/gather.cuh

@@ -461,8 +461,8 @@ struct column_gatherer_impl<struct_view> {
     std::transform(thrust::make_counting_iterator(0),
                    thrust::make_counting_iterator(column.num_children()),
                    std::back_inserter(sliced_children),
-                   [structs_view = structs_column_view{column}](auto const idx) {
-                     return structs_view.get_sliced_child(idx);
+                   [&stream, structs_view = structs_column_view{column}](auto const idx) {
+                     return structs_view.get_sliced_child(idx, stream);
                    });
 
     std::vector<std::unique_ptr<cudf::column>> output_struct_members;

cpp/include/cudf/detail/structs/utilities.hpp

@@ -79,7 +79,7 @@ struct temporary_nullable_data {
  * @return New column with concatenated results.
  */
 std::vector<std::vector<column_view>> extract_ordered_struct_children(
-  host_span<column_view const> struct_cols);
+  host_span<column_view const> struct_cols, rmm::cuda_stream_view stream);
 
 /**
  * @brief Check whether the specified column is of type LIST, or any LISTs in its descendent

cpp/include/cudf/structs/structs_column_view.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, NVIDIA CORPORATION.
+ * Copyright (c) 2022-2023, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,9 @@
 
 #include <cudf/column/column.hpp>
 #include <cudf/column/column_view.hpp>
+#include <cudf/utilities/default_stream.hpp>
+
+#include <rmm/cuda_stream_view.hpp>
 
 /**
  * @file
@@ -87,9 +90,12 @@ class structs_column_view : public column_view {
    * @throw cudf::logic error if this is an empty column
    *
    * @param index The index of the child column to return
+   * @param stream The stream on which to perform the operation. Uses the default CUDF
+   *        stream if none is specified.
    * @return The child column sliced relative to the parent's offset and size
    */
-  [[nodiscard]] column_view get_sliced_child(int index) const;
+  [[nodiscard]] column_view get_sliced_child(
+    int index, rmm::cuda_stream_view stream = cudf::get_default_stream()) const;
 };         // class structs_column_view;
 /** @} */  // end of group
 }  // namespace cudf

cpp/src/copying/concatenate.cu

@@ -420,7 +420,7 @@ void traverse_children::operator()<cudf::struct_view>(host_span<column_view cons
                    std::back_inserter(nth_children),
                    [child_index, stream](column_view const& col) {
                      structs_column_view scv(col);
-                     return scv.get_sliced_child(child_index);
+                     return scv.get_sliced_child(child_index, stream);
                    });
 
     bounds_and_type_check(nth_children, stream);

cpp/src/copying/contiguous_split.cu

@@ -431,6 +431,7 @@ std::pair<src_buf_info*, size_type> setup_source_buf_info(InputIter begin,
                                                           InputIter end,
                                                           src_buf_info* head,
                                                           src_buf_info* current,
+                                                          rmm::cuda_stream_view stream,
                                                           int offset_stack_pos    = 0,
                                                           int parent_offset_index = -1,
                                                           int offset_depth        = 0);
@@ -449,7 +450,8 @@ struct buf_info_functor {
                                                  src_buf_info* current,
                                                  int offset_stack_pos,
                                                  int parent_offset_index,
-                                                 int offset_depth)
+                                                 int offset_depth,
+                                                 rmm::cuda_stream_view stream)
   {
     if (col.nullable()) {
       std::tie(current, offset_stack_pos) =
@@ -491,7 +493,8 @@ std::pair<src_buf_info*, size_type> buf_info_functor::operator()<cudf::string_vi
   src_buf_info* current,
   int offset_stack_pos,
   int parent_offset_index,
-  int offset_depth)
+  int offset_depth,
+  rmm::cuda_stream_view stream)
 {
   if (col.nullable()) {
     std::tie(current, offset_stack_pos) =
@@ -548,7 +551,8 @@ std::pair<src_buf_info*, size_type> buf_info_functor::operator()<cudf::list_view
   src_buf_info* current,
   int offset_stack_pos,
   int parent_offset_index,
-  int offset_depth)
+  int offset_depth,
+  rmm::cuda_stream_view stream)
 {
   lists_column_view lcv(col);
 
@@ -587,6 +591,7 @@ std::pair<src_buf_info*, size_type> buf_info_functor::operator()<cudf::list_view
                                col.child_end(),
                                head,
                                current,
+                               stream,
                                offset_stack_pos,
                                parent_offset_index,
                                offset_depth);
@@ -598,7 +603,8 @@ std::pair<src_buf_info*, size_type> buf_info_functor::operator()<cudf::struct_vi
   src_buf_info* current,
   int offset_stack_pos,
   int parent_offset_index,
-  int offset_depth)
+  int offset_depth,
+  rmm::cuda_stream_view stream)
 {
   if (col.nullable()) {
     std::tie(current, offset_stack_pos) =
@@ -616,14 +622,16 @@ std::pair<src_buf_info*, size_type> buf_info_functor::operator()<cudf::struct_vi
   cudf::structs_column_view scv(col);
   std::vector<column_view> sliced_children;
   sliced_children.reserve(scv.num_children());
-  std::transform(thrust::make_counting_iterator(0),
-                 thrust::make_counting_iterator(scv.num_children()),
-                 std::back_inserter(sliced_children),
-                 [&scv](size_type child_index) { return scv.get_sliced_child(child_index); });
+  std::transform(
+    thrust::make_counting_iterator(0),
+    thrust::make_counting_iterator(scv.num_children()),
+    std::back_inserter(sliced_children),
+    [&scv, &stream](size_type child_index) { return scv.get_sliced_child(child_index, stream); });
   return setup_source_buf_info(sliced_children.begin(),
                                sliced_children.end(),
                                head,
                                current,
+                               stream,
                                offset_stack_pos,
                                parent_offset_index,
                                offset_depth);
@@ -634,6 +642,7 @@ std::pair<src_buf_info*, size_type> setup_source_buf_info(InputIter begin,
                                                           InputIter end,
                                                           src_buf_info* head,
                                                           src_buf_info* current,
+                                                          rmm::cuda_stream_view stream,
                                                           int offset_stack_pos,
                                                           int parent_offset_index,
                                                           int offset_depth)
@@ -645,7 +654,8 @@ std::pair<src_buf_info*, size_type> setup_source_buf_info(InputIter begin,
                                                                 current,
                                                                 offset_stack_pos,
                                                                 parent_offset_index,
-                                                                offset_depth);
+                                                                offset_depth,
+                                                                stream);
   });
   return {current, offset_stack_pos};
 }
@@ -1044,7 +1054,7 @@ std::vector<packed_table> contiguous_split(cudf::table_view const& input,
   std::copy(splits.begin(), splits.end(), std::next(h_indices));
 
   // setup source buf info
-  setup_source_buf_info(input.begin(), input.end(), h_src_buf_info, h_src_buf_info);
+  setup_source_buf_info(input.begin(), input.end(), h_src_buf_info, h_src_buf_info, stream);
 
   // HtoD indices and source buf info to device
   CUDF_CUDA_TRY(cudaMemcpyAsync(

cpp/src/io/json/write_json.cu

@@ -562,8 +562,8 @@ struct column_to_strings_fn {
   operator()(column_view const& column, host_span<column_name_info const> children_names) const
   {
     auto const child_it = cudf::detail::make_counting_transform_iterator(
-      0, [structs_view = structs_column_view{column}](auto const child_idx) {
-        return structs_view.get_sliced_child(child_idx);
+      0, [&stream = stream_, structs_view = structs_column_view{column}](auto const child_idx) {
+        return structs_view.get_sliced_child(child_idx, stream);
       });
     auto col_string = operator()(
       child_it, child_it + column.num_children(), children_names, row_end_wrap.value(stream_));

cpp/src/io/parquet/writer_impl.cu

@@ -97,7 +97,7 @@ size_t column_size(column_view const& column, rmm::cuda_stream_view stream)
     auto const scol = structs_column_view(column);
     size_t ret      = 0;
     for (int i = 0; i < scol.num_children(); i++) {
-      ret += column_size(scol.get_sliced_child(i), stream);
+      ret += column_size(scol.get_sliced_child(i, stream), stream);
     }
     return ret;
   } else if (column.type().id() == type_id::LIST) {

cpp/src/lists/copying/copying.cu

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020-2022, NVIDIA CORPORATION.
+ * Copyright (c) 2020-2023, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@
 #include <cudf/detail/get_value.cuh>
 #include <cudf/detail/null_mask.hpp>
 #include <cudf/lists/lists_column_view.hpp>
+#include <cudf/types.hpp>
 
 #include <rmm/cuda_stream_view.hpp>
 #include <rmm/exec_policy.hpp>
@@ -81,10 +82,13 @@ std::unique_ptr<cudf::column> copy_slice(lists_column_view const& lists,
   // Compute the null mask of the result:
   auto null_mask = cudf::detail::copy_bitmask(lists.null_mask(), start, end, stream, mr);
 
+  auto null_count = cudf::detail::null_count(
+    static_cast<bitmask_type const*>(null_mask.data()), 0, end - start, stream);
+
   return make_lists_column(lists_count,
                            std::move(offsets),
                            std::move(child),
-                           cudf::UNKNOWN_NULL_COUNT,
+                           null_count,
                            std::move(null_mask),
                            stream,
                            mr);

cpp/src/merge/merge.cu

@@ -364,8 +364,12 @@ std::unique_ptr<column> column_merger::operator()<cudf::struct_view>(
 
   auto it = cudf::detail::make_counting_transform_iterator(
     0, [&, merger = column_merger{row_order_}](size_type i) {
-      return cudf::type_dispatcher<dispatch_storage_type>(
-        lhs.child(i).type(), merger, lhs.get_sliced_child(i), rhs.get_sliced_child(i), stream, mr);
+      return cudf::type_dispatcher<dispatch_storage_type>(lhs.child(i).type(),
+                                                          merger,
+                                                          lhs.get_sliced_child(i, stream),
+                                                          rhs.get_sliced_child(i, stream),
+                                                          stream,
+                                                          mr);
     });
 
   auto merged_children   = std::vector<std::unique_ptr<column>>(it, it + lhs.num_children());

cpp/src/reductions/scan/scan_inclusive.cu

@@ -173,8 +173,8 @@ struct scan_functor<Op, cudf::struct_view> {
     // handle input in case it is a sliced view.
     auto const input_children = [&] {
       auto const it = cudf::detail::make_counting_transform_iterator(
-        0, [structs_view = structs_column_view{input}, stream](auto const child_idx) {
-          return structs_view.get_sliced_child(child_idx);
+        0, [structs_view = structs_column_view{input}, &stream](auto const child_idx) {
+          return structs_view.get_sliced_child(child_idx, stream);
         });
       return std::vector<column_view>(it, it + input.num_children());
     }();

cpp/src/reshape/interleave_columns.cu

@@ -93,9 +93,9 @@ struct interleave_columns_impl<T, std::enable_if_t<std::is_same_v<T, cudf::struc
     std::vector<std::unique_ptr<cudf::column>> output_struct_members;
     for (size_type child_idx = 0; child_idx < num_children; ++child_idx) {
       // Collect children columns from the input structs columns at index `child_idx`.
-      auto const child_iter =
-        thrust::make_transform_iterator(structs_columns.begin(), [child_idx](auto const& col) {
-          return structs_column_view(col).get_sliced_child(child_idx);
+      auto const child_iter = thrust::make_transform_iterator(
+        structs_columns.begin(), [&stream = stream, child_idx](auto const& col) {
+          return structs_column_view(col).get_sliced_child(child_idx, stream);
         });
       auto children = std::vector<column_view>(child_iter, child_iter + num_columns);
 

cpp/src/strings/copying/copying.cu

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2022, NVIDIA CORPORATION.
+ * Copyright (c) 2019-2023, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -73,10 +73,13 @@ std::unique_ptr<cudf::column> copy_slice(strings_column_view const& strings,
   auto null_mask = cudf::detail::copy_bitmask(
     strings.null_mask(), offsets_offset, offsets_offset + strings_count, stream, mr);
 
+  auto null_count = cudf::detail::null_count(
+    static_cast<bitmask_type const*>(null_mask.data()), 0, strings_count, stream);
+
   return make_strings_column(strings_count,
                              std::move(offsets_column),
                              std::move(chars_column),
-                             UNKNOWN_NULL_COUNT,
+                             null_count,
                              std::move(null_mask));
 }
 

cpp/src/structs/copying/concatenate.cu

@@ -42,7 +42,7 @@ std::unique_ptr<column> concatenate(host_span<column_view const> columns,
                                     rmm::mr::device_memory_resource* mr)
 {
   // get ordered children
-  auto ordered_children = extract_ordered_struct_children(columns);
+  auto ordered_children = extract_ordered_struct_children(columns, stream);
 
   // concatenate them
   std::vector<std::unique_ptr<column>> children;

cpp/src/structs/structs_column_view.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020-2022, NVIDIA CORPORATION.
+ * Copyright (c) 2020-2023, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,7 +15,9 @@
  */
 
 #include <cudf/column/column.hpp>
+#include <cudf/detail/null_mask.hpp>
 #include <cudf/structs/structs_column_view.hpp>
+#include <cudf/types.hpp>
 #include <cudf/utilities/error.hpp>
 
 namespace cudf {
@@ -27,22 +29,24 @@ structs_column_view::structs_column_view(column_view const& rhs) : column_view{r
 
 column_view structs_column_view::parent() const { return *this; }
 
-column_view structs_column_view::get_sliced_child(int index) const
+column_view structs_column_view::get_sliced_child(int index, rmm::cuda_stream_view stream) const
 {
   std::vector<column_view> children;
   children.reserve(child(index).num_children());
   for (size_type i = 0; i < child(index).num_children(); i++) {
     children.push_back(child(index).child(i));
   }
-  return column_view{child(index).type(),
-                     size(),
-                     child(index).head<uint8_t>(),
-                     child(index).null_mask(),
-                     // TODO: could potentially compute the actual count here, but at
-                     // the moment this interface doesn't take a stream.
-                     UNKNOWN_NULL_COUNT,
-                     offset(),
-                     children};
+
+  return column_view{
+    child(index).type(),
+    size(),
+    child(index).head<uint8_t>(),
+    child(index).null_mask(),
+    child(index).null_count()
+      ? cudf::detail::null_count(child(index).null_mask(), offset(), offset() + size(), stream)
+      : 0,
+    offset(),
+    children};
 }
 
 }  // namespace cudf

cpp/src/structs/utilities.cpp

@@ -36,7 +36,7 @@ namespace cudf::structs::detail {
  * @copydoc cudf::structs::detail::extract_ordered_struct_children
  */
 std::vector<std::vector<column_view>> extract_ordered_struct_children(
-  host_span<column_view const> struct_cols)
+  host_span<column_view const> struct_cols, rmm::cuda_stream_view stream)
 {
   auto const num_children = struct_cols[0].num_children();
   auto const num_cols     = static_cast<size_type>(struct_cols.size());
@@ -56,7 +56,7 @@ std::vector<std::vector<column_view>> extract_ordered_struct_children(
                    "Mismatch in number of children during struct concatenate");
       CUDF_EXPECTS(struct_cols[0].child(child_index).type() == scv.child(child_index).type(),
                    "Mismatch in child types during struct concatenate");
-      children.push_back(scv.get_sliced_child(child_index));
+      children.push_back(scv.get_sliced_child(child_index, stream));
     }
 
     result.push_back(std::move(children));
@@ -161,7 +161,7 @@ struct table_flattener {
       if (not null_precedence.empty()) { flat_null_precedence.push_back(col_null_order); }
     }
     for (decltype(col.num_children()) i = 0; i < col.num_children(); ++i) {
-      auto const& child = col.get_sliced_child(i);
+      auto const& child = col.get_sliced_child(i, stream);
       if (child.type().id() == type_id::STRUCT) {
         flatten_struct_column(structs_column_view{child}, col_order, col_null_order);
       } else {
@@ -270,11 +270,12 @@ std::unique_ptr<column> superimpose_nulls_no_sanitize(bitmask_type const* null_m
   auto content              = input->release();
 
   // Build new children columns.
-  std::for_each(
-    content.children.begin(), content.children.end(), [current_mask, stream, mr](auto& child) {
-      child = superimpose_nulls_no_sanitize(
-        current_mask, cudf::UNKNOWN_NULL_COUNT, std::move(child), stream, mr);
-    });
+  std::for_each(content.children.begin(),
+                content.children.end(),
+                [current_mask, new_null_count, stream, mr](auto& child) {
+                  child = superimpose_nulls_no_sanitize(
+                    current_mask, new_null_count, std::move(child), stream, mr);
+                });
 
   // Replace the children columns.
   return cudf::make_structs_column(num_rows,
@@ -304,7 +305,7 @@ std::pair<column_view, temporary_nullable_data> push_down_nulls_no_sanitize(
 
   // Function to rewrite child null mask.
   auto const child_with_new_mask = [&](auto const& child_idx) {
-    auto child = structs_view.get_sliced_child(child_idx);
+    auto child = structs_view.get_sliced_child(child_idx, stream);
 
     // If struct is not nullable, child null mask is retained. NOOP.
     if (not structs_view.nullable()) { return child; }

cpp/src/transform/row_bit_count.cu

@@ -246,7 +246,7 @@ struct flatten_functor {
 
     structs_column_view scv(col);
     auto iter = cudf::detail::make_counting_transform_iterator(
-      0, [&scv](auto i) { return scv.get_sliced_child(i); });
+      0, [&scv, &stream](auto i) { return scv.get_sliced_child(i, stream); });
     flatten_hierarchy(iter,
                       iter + scv.num_children(),
                       out,