Allow early exit for left semi-/anti- joins with empty build/probe tables

cpp/src/join/filtered_join.cu

@@ -28,6 +28,7 @@
 #include <cuco/static_set_ref.cuh>
 #include <cuda/std/iterator>
 #include <thrust/iterator/counting_iterator.h>
+#include <thrust/sequence.h>
 
 namespace cudf {
 namespace detail {
@@ -218,6 +219,7 @@ filtered_join::filtered_join(cudf::table_view const& build,
                     rmm::mr::polymorphic_allocator<char>{},
                     stream.value()}
 {
+  if (_build.num_rows() == 0) return;
   _bucket_storage.initialize(empty_sentinel_key, stream);
 }
 
@@ -228,6 +230,7 @@ distinct_filtered_join::distinct_filtered_join(cudf::table_view const& build,
   : filtered_join(build, compare_nulls, load_factor, stream)
 {
   cudf::scoped_range range{"distinct_filtered_join::distinct_filtered_join"};
+  if (_build.num_rows() == 0) return;
   // Any mismatch in nullate between probe and build row operators results in UB. Ideally, nullate
   // should be determined by the logical OR of probe nulls and build nulls. However, since we do not
   // know if the probe has nulls apriori, we set nullate::DYNAMIC{true} (in the case of primitive
@@ -334,12 +337,28 @@ std::unique_ptr<rmm::device_uvector<cudf::size_type>> distinct_filtered_join::se
 std::unique_ptr<rmm::device_uvector<cudf::size_type>> distinct_filtered_join::semi_join(
   cudf::table_view const& probe, rmm::cuda_stream_view stream, rmm::device_async_resource_ref mr)
 {
+  // Early return for empty build or probe table
+  if (_build.num_rows() == 0 || probe.num_rows() == 0) {
+    return std::make_unique<rmm::device_uvector<cudf::size_type>>(0, stream, mr);
+  }
+
   return semi_anti_join(probe, join_kind::LEFT_SEMI_JOIN, stream, mr);
 }
 
 std::unique_ptr<rmm::device_uvector<cudf::size_type>> distinct_filtered_join::anti_join(
   cudf::table_view const& probe, rmm::cuda_stream_view stream, rmm::device_async_resource_ref mr)
 {
+  // Early return for empty probe table
+  if (probe.num_rows() == 0) {
+    return std::make_unique<rmm::device_uvector<cudf::size_type>>(0, stream, mr);
+  }
+  if (_build.num_rows() == 0) {
+    auto result =
+      std::make_unique<rmm::device_uvector<cudf::size_type>>(probe.num_rows(), stream, mr);
+    thrust::sequence(rmm::exec_policy_nosync(stream), result->begin(), result->end());
+    return result;
+  }
+
   return semi_anti_join(probe, join_kind::LEFT_ANTI_JOIN, stream, mr);
 }
 

cpp/tests/join/semi_anti_join_tests.cpp

@@ -322,3 +322,61 @@ TEST_F(JoinTest, AntiJoinWithStructsAndNullsOnOneSide)
   auto expected             = cudf::gather(left, expected_indices_col);
   CUDF_TEST_EXPECT_TABLES_EQUIVALENT(*expected, *result);
 }
+
+TEST_F(JoinTest, AntiJoinEmptyTables)
+{
+  cudf::table empty_build_table{};
+  cudf::table empty_probe_table{};
+  column_wrapper<int32_t> col{0, 1, 2};
+  auto nonempty_table = cudf::table_view{{col}};
+  // Empty build and probe tables
+  {
+    auto result               = left_anti_join(empty_probe_table, empty_build_table, {}, {});
+    auto expected_indices_col = column_wrapper<cudf::size_type>{};
+    auto expected             = cudf::gather(empty_probe_table, expected_indices_col);
+    CUDF_TEST_EXPECT_TABLES_EQUIVALENT(*expected, *result);
+  }
+  // Empty build table
+  {
+    auto result               = left_anti_join(nonempty_table, empty_build_table, {0}, {});
+    auto expected_indices_col = column_wrapper<cudf::size_type>{0, 1, 2};
+    auto expected             = cudf::gather(nonempty_table, expected_indices_col);
+    CUDF_TEST_EXPECT_TABLES_EQUIVALENT(*expected, *result);
+  }
+  // Empty probe table
+  {
+    auto result               = left_anti_join(empty_probe_table, nonempty_table, {}, {0});
+    auto expected_indices_col = column_wrapper<cudf::size_type>{};
+    auto expected             = cudf::gather(empty_probe_table, expected_indices_col);
+    CUDF_TEST_EXPECT_TABLES_EQUIVALENT(*expected, *result);
+  }
+}
+
+TEST_F(JoinTest, SemiJoinEmptyTables)
+{
+  cudf::table empty_build_table{};
+  cudf::table empty_probe_table{};
+  column_wrapper<int32_t> col{0, 1, 2};
+  auto nonempty_table = cudf::table_view{{col}};
+  // Empty build and probe tables
+  {
+    auto result               = left_semi_join(empty_probe_table, empty_build_table, {}, {});
+    auto expected_indices_col = column_wrapper<cudf::size_type>{};
+    auto expected             = cudf::gather(empty_probe_table, expected_indices_col);
+    CUDF_TEST_EXPECT_TABLES_EQUIVALENT(*expected, *result);
+  }
+  // Empty build table
+  {
+    auto result               = left_semi_join(nonempty_table, empty_build_table, {0}, {});
+    auto expected_indices_col = column_wrapper<cudf::size_type>{};
+    auto expected             = cudf::gather(empty_probe_table, expected_indices_col);
+    CUDF_TEST_EXPECT_TABLES_EQUIVALENT(*expected, *result);
+  }
+  // Empty probe table
+  {
+    auto result               = left_semi_join(empty_probe_table, nonempty_table, {}, {0});
+    auto expected_indices_col = column_wrapper<cudf::size_type>{};
+    auto expected             = cudf::gather(empty_probe_table, expected_indices_col);
+    CUDF_TEST_EXPECT_TABLES_EQUIVALENT(*expected, *result);
+  }
+}