Fix target counting in strings char-parallel replace

cpp/src/strings/replace/replace.cu

@@ -238,6 +238,31 @@ struct replace_parallel_chars_fn {
   cudf::size_type maxrepl;
 };
 
+template <int64_t block_size, size_type bytes_per_thread>
+CUDF_KERNEL void count_targets_kernel(replace_parallel_chars_fn fn,
+                                      int64_t chars_bytes,
+                                      int64_t* d_output)
+{
+  auto const idx      = cudf::detail::grid_1d::global_thread_id();
+  auto const byte_idx = static_cast<int64_t>(idx) * bytes_per_thread;
+  auto const lane_idx = static_cast<cudf::size_type>(threadIdx.x);
+
+  using block_reduce = cub::BlockReduce<int64_t, block_size>;
+  __shared__ typename block_reduce::TempStorage temp_storage;
+
+  int64_t count = 0;
+  // each thread processes multiple bytes
+  for (auto i = byte_idx; (i < (byte_idx + bytes_per_thread)) && (i < chars_bytes); ++i) {
+    count += fn.has_target(i);
+  }
+  auto const total = block_reduce(temp_storage).Reduce(count, cub::Sum());
+
+  if ((lane_idx == 0) && (total > 0)) {
+    cuda::atomic_ref<int64_t, cuda::thread_scope_device> ref{*d_output};
+    ref.fetch_add(total, cuda::std::memory_order_relaxed);
+  }
+}
+
 std::unique_ptr<column> replace_character_parallel(strings_column_view const& input,
                                                    string_view const& d_target,
                                                    string_view const& d_replacement,
@@ -260,10 +285,14 @@ std::unique_ptr<column> replace_character_parallel(strings_column_view const& in
 
   // Count the number of targets in the entire column.
   // Note this may over-count in the case where a target spans adjacent strings.
-  auto target_count = thrust::count_if(rmm::exec_policy_nosync(stream),
-                                       thrust::make_counting_iterator<int64_t>(0),
-                                       thrust::make_counting_iterator<int64_t>(chars_bytes),
-                                       [fn] __device__(int64_t idx) { return fn.has_target(idx); });
+  rmm::device_scalar<int64_t> d_target_count(0, stream);
+  constexpr int64_t block_size         = 512;
+  constexpr size_type bytes_per_thread = 4;
+  auto const num_blocks                = util::div_rounding_up_safe(
+    util::div_rounding_up_safe(chars_bytes, static_cast<int64_t>(bytes_per_thread)), block_size);
+  count_targets_kernel<block_size, bytes_per_thread>
+    <<<num_blocks, block_size, 0, stream.value()>>>(fn, chars_bytes, d_target_count.data());
+  auto target_count = d_target_count.value(stream);
 
   // Create a vector of every target position in the chars column.
   // These may also include overlapping targets which will be resolved later.

cpp/tests/CMakeLists.txt

@@ -571,9 +571,9 @@ ConfigureTest(
   large_strings/concatenate_tests.cpp
   large_strings/case_tests.cpp
   large_strings/large_strings_fixture.cpp
-  large_strings/many_strings_tests.cpp
   large_strings/merge_tests.cpp
   large_strings/parquet_tests.cpp
+  large_strings/replace_tests.cpp
   large_strings/reshape_tests.cpp
   large_strings/split_strings_tests.cpp
   GPUS 1

cpp/tests/large_strings/many_strings_tests.cpp → cpp/tests/large_strings/replace_tests.cpp

@@ -21,16 +21,17 @@
 #include <cudf/concatenate.hpp>
 #include <cudf/copying.hpp>
 #include <cudf/scalar/scalar.hpp>
+#include <cudf/strings/combine.hpp>
 #include <cudf/strings/replace.hpp>
 #include <cudf/strings/strings_column_view.hpp>
 #include <cudf/table/table_view.hpp>
 
 #include <limits>
 #include <vector>
 
-struct StringsManyTest : public cudf::test::StringsLargeTest {};
+struct ReplaceTest : public cudf::test::StringsLargeTest {};
 
-TEST_F(StringsManyTest, Replace)
+TEST_F(ReplaceTest, ReplaceLong)
 {
   auto const expected = this->very_long_column();
   auto const view     = cudf::column_view(expected);
@@ -65,3 +66,22 @@ TEST_F(StringsManyTest, Replace)
     CUDF_TEST_EXPECT_COLUMNS_EQUIVALENT(c, expected);
   }
 }
+
+TEST_F(ReplaceTest, ReplaceWide)
+{
+  auto const expected   = this->long_column();
+  auto const view       = cudf::column_view(expected);
+  auto const multiplier = 10;
+  auto const separator  = cudf::string_scalar("|");
+  auto const input      = cudf::strings::concatenate(
+    cudf::table_view(std::vector<cudf::column_view>(multiplier, view)), separator);
+
+  auto const input_view = cudf::strings_column_view(input->view());
+  auto const target     = cudf::string_scalar("3");  // fake the actual replace;
+  auto const repl       = cudf::string_scalar("3");  // logic still builds the output
+  auto result           = cudf::strings::replace(input_view, target, repl);
+
+  auto sv = cudf::strings_column_view(result->view());
+  EXPECT_EQ(sv.offsets().type(), cudf::data_type{cudf::type_id::INT64});
+  CUDF_TEST_EXPECT_COLUMNS_EQUIVALENT(input->view(), result->view());
+}