graph: allow access to native graph object

The native graph objects should be accessible for advanced users.

cmake/kokkos_arch.cmake

@@ -674,6 +674,8 @@ IF(KOKKOS_ENABLE_SYCL)
       )
     ENDIF()
   ENDIF()
+
+  CHECK_CXX_SYMBOL_EXISTS(SYCL_EXT_ONEAPI_GRAPH "sycl/sycl.hpp" KOKKOS_IMPL_HAVE_SYCL_EXT_ONEAPI_GRAPH)
 ENDIF()
 
 SET(CUDA_ARCH_ALREADY_SPECIFIED "")

core/src/Cuda/Kokkos_Cuda_Graph_Impl.hpp

@@ -206,6 +206,9 @@ struct GraphImpl<Kokkos::Cuda> {
         m_execution_space, _graph_node_kernel_ctor_tag{},
         aggregate_kernel_impl_t{});
   }
+
+  cudaGraph_t cuda_graph() { return m_graph; }
+  cudaGraphExec_t cuda_graph_exec() { return m_graph_exec; }
 };
 
 }  // end namespace Impl

core/src/HIP/Kokkos_HIP_Graph_Impl.hpp

@@ -79,6 +79,9 @@ class GraphImpl<Kokkos::HIP> {
     KOKKOS_ENSURES(m_graph_exec);
   }
 
+  hipGraph_t hip_graph() { return m_graph; }
+  hipGraphExec_t hip_graph_exec() { return m_graph_exec; }
+
  private:
   Kokkos::HIP m_execution_space;
   hipGraph_t m_graph          = nullptr;

core/src/Kokkos_Graph.hpp

@@ -97,6 +97,10 @@ struct [[nodiscard]] Graph {
   }
 
   void submit() const { submit(get_execution_space()); }
+
+  decltype(auto) native_graph();
+
+  decltype(auto) native_graph_exec();
 };
 
 // </editor-fold> end Graph }}}1
@@ -168,6 +172,42 @@ create_graph(Closure&& arg_closure) {
 // </editor-fold> end create_graph }}}1
 //==============================================================================
 
+template <class ExecutionSpace>
+decltype(auto) Graph<ExecutionSpace>::native_graph() {
+  KOKKOS_EXPECTS(bool(m_impl_ptr));
+#if defined(KOKKOS_ENABLE_CUDA)
+  if constexpr (std::is_same_v<ExecutionSpace, Kokkos::Cuda>) {
+    return m_impl_ptr->cuda_graph();
+  }
+#elif defined(KOKKOS_ENABLE_HIP) && defined(KOKKOS_IMPL_HIP_NATIVE_GRAPH)
+  if constexpr (std::is_same_v<ExecutionSpace, Kokkos::HIP>) {
+    return m_impl_ptr->hip_graph();
+  }
+#elif defined(KOKKOS_ENABLE_SYCL) && defined(SYCL_EXT_ONEAPI_GRAPH)
+  if constexpr (std::is_same_v<ExecutionSpace, Kokkos::SYCL>) {
+    return m_impl_ptr->sycl_graph();
+  }
+#endif
+}
+
+template <class ExecutionSpace>
+decltype(auto) Graph<ExecutionSpace>::native_graph_exec() {
+  KOKKOS_EXPECTS(bool(m_impl_ptr));
+#if defined(KOKKOS_ENABLE_CUDA)
+  if constexpr (std::is_same_v<ExecutionSpace, Kokkos::Cuda>) {
+    return m_impl_ptr->cuda_graph_exec();
+  }
+#elif defined(KOKKOS_ENABLE_HIP) && defined(KOKKOS_IMPL_HIP_NATIVE_GRAPH)
+  if constexpr (std::is_same_v<ExecutionSpace, Kokkos::HIP>) {
+    return m_impl_ptr->hip_graph_exec();
+  }
+#elif defined(KOKKOS_ENABLE_SYCL) && defined(SYCL_EXT_ONEAPI_GRAPH)
+  if constexpr (std::is_same_v<ExecutionSpace, Kokkos::SYCL>) {
+    return m_impl_ptr->sycl_graph_exec();
+  }
+#endif
+}
+
 }  // end namespace Experimental
 }  // namespace Kokkos
 
@@ -179,7 +219,6 @@ create_graph(Closure&& arg_closure) {
 #include <impl/Kokkos_Default_Graph_Impl.hpp>
 #include <Cuda/Kokkos_Cuda_Graph_Impl.hpp>
 #if defined(KOKKOS_ENABLE_HIP)
-// The implementation of hipGraph in ROCm 5.2 is bugged, so we cannot use it.
 #if defined(KOKKOS_IMPL_HIP_NATIVE_GRAPH)
 #include <HIP/Kokkos_HIP_Graph_Impl.hpp>
 #endif

core/src/SYCL/Kokkos_SYCL_Graph_Impl.hpp

@@ -76,6 +76,9 @@ class GraphImpl<Kokkos::SYCL> {
     m_graph_exec = m_graph.finalize();
   }
 
+  auto& sycl_graph() { return m_graph; }
+  auto& sycl_graph_exec() { return m_graph_exec; }
+
  private:
   Kokkos::SYCL m_execution_space;
   sycl::ext::oneapi::experimental::command_graph<

core/unit_test/CMakeLists.txt

@@ -837,6 +837,13 @@ if(Kokkos_ENABLE_CUDA)
       UnitTestMainInit.cpp
       cuda/TestCuda_InterOp_StreamsMultiGPU.cpp
   )
+
+  KOKKOS_ADD_EXECUTABLE_AND_TEST(
+    CoreUnitTest_CudaInterOpGraph
+    SOURCES
+      UnitTestMainInit.cpp
+      cuda/TestCuda_InterOp_Graph.cpp
+  )
 endif()
 
 if(Kokkos_ENABLE_HIP)
@@ -864,6 +871,13 @@ if(Kokkos_ENABLE_HIP)
       UnitTestMain.cpp
       hip/TestHIP_InterOp_Streams.cpp
   )
+
+  KOKKOS_ADD_EXECUTABLE_AND_TEST(
+    CoreUnitTest_HIPInterOpGraph
+    SOURCES
+      UnitTestMainInit.cpp
+      hip/TestHIP_InterOp_Graph.cpp
+  )
 endif()
 
 if(Kokkos_ENABLE_SYCL)
@@ -948,6 +962,15 @@ if(Kokkos_ENABLE_SYCL)
       UnitTestMainInit.cpp
       sycl/TestSYCL_InterOp_StreamsMultiGPU.cpp
   )
+
+  if(KOKKOS_IMPL_HAVE_SYCL_EXT_ONEAPI_GRAPH)
+    KOKKOS_ADD_EXECUTABLE_AND_TEST(
+      CoreUnitTest_SYCLInterOpGraph
+      SOURCES
+        UnitTestMainInit.cpp
+        sycl/TestSYCL_InterOp_Graph.cpp
+    )
+  endif()
 endif()
 
 SET(DEFAULT_DEVICE_SOURCES

core/unit_test/TestGraph.hpp

@@ -510,6 +510,16 @@ TEST_F(TEST_CATEGORY_FIXTURE(graph), force_global_launch) {
 #endif
 }
 
+// Ensure that an empty graph on the default host execution space
+// can be submitted.
+TEST_F(TEST_CATEGORY_FIXTURE(graph), empty_graph_default_host_exec) {
+  auto graph =
+      Kokkos::Experimental::create_graph(Kokkos::DefaultHostExecutionSpace{});
+  graph.instantiate();
+  graph.submit();
+  graph.get_execution_space().fence();
+}
+
 template <typename ViewType, size_t TargetIndex, size_t NumIndices = 0>
 struct FetchValuesAndContribute {
   static_assert(std::is_same_v<typename ViewType::value_type,

core/unit_test/cuda/TestCuda_InterOp_Graph.cpp

@@ -0,0 +1,143 @@
+//@HEADER
+// ************************************************************************
+//
+//                        Kokkos v. 4.0
+//       Copyright (2022) National Technology & Engineering
+//               Solutions of Sandia, LLC (NTESS).
+//
+// Under the terms of Contract DE-NA0003525 with NTESS,
+// the U.S. Government retains certain rights in this software.
+//
+// Part of Kokkos, under the Apache License v2.0 with LLVM Exceptions.
+// See https://kokkos.org/LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//@HEADER
+
+#include <filesystem>
+#include <fstream>
+#include <regex>
+
+#include <TestCuda_Category.hpp>
+#include <Kokkos_Core.hpp>
+#include <Kokkos_Graph.hpp>
+
+#include <gtest/gtest.h>
+
+namespace {
+
+template <typename ViewType>
+struct Increment {
+  ViewType data;
+
+  KOKKOS_FUNCTION
+  void operator()(const int) const { ++data(); }
+};
+
+class TEST_CATEGORY_FIXTURE(GraphInterOp) : public ::testing::Test {
+ public:
+  using execution_space = Kokkos::Cuda;
+  using view_t =
+      Kokkos::View<int, execution_space, Kokkos::MemoryTraits<Kokkos::Atomic>>;
+  using graph_t = Kokkos::Experimental::Graph<execution_space>;
+
+  void SetUp() override {
+    data = view_t(Kokkos::view_alloc(exec, "witness"));
+
+    graph = Kokkos::Experimental::create_graph(exec);
+
+    auto root = Kokkos::Impl::GraphAccess::create_root_ref(*graph);
+
+    root.then_parallel_for(1, Increment<view_t>{data});
+  }
+ protected:
+  const execution_space exec{};
+  view_t data;
+  std::optional<graph_t> graph;
+};
+
+// This test checks the promises of Kokkos::Graph against its
+// underlying Cuda native objects.
+TEST_F(TEST_CATEGORY_FIXTURE(GraphInterOp), promises_on_native_objects) {
+  // Before instantiation, the Cuda graph is valid, but the Cuda executable
+  // graph is still null.
+  cudaGraph_t cuda_graph = graph->native_graph();
+
+  ASSERT_NE(cuda_graph, nullptr);
+  ASSERT_EQ(graph->native_graph_exec(), nullptr);
+
+  // After instantiation, both native objects are valid.
+  graph->instantiate();
+
+  cudaGraphExec_t cuda_graph_exec = graph->native_graph_exec();
+
+  ASSERT_EQ(graph->native_graph(), cuda_graph);
+  ASSERT_NE(cuda_graph_exec, nullptr);
+
+  // Submission should not affect the underlying objects.
+  graph->submit();
+
+  ASSERT_EQ(graph->native_graph(), cuda_graph);
+  ASSERT_EQ(graph->native_graph_exec(), cuda_graph_exec);
+}
+
+// Count the number of nodes. This is useful to ensure no spurious
+// (possibly empty) node is added.
+TEST_F(TEST_CATEGORY_FIXTURE(GraphInterOp), count_nodes) {
+  graph->instantiate();
+
+  size_t num_nodes = 0;
+
+  KOKKOS_IMPL_CUDA_SAFE_CALL(
+      cudaGraphGetNodes(graph->native_graph(), nullptr, &num_nodes));
+
+  ASSERT_EQ(num_nodes, 2u);
+}
+
+// Use native Cuda graph to generate a DOT representation.
+TEST_F(TEST_CATEGORY_FIXTURE(GraphInterOp), debug_dot_print) {
+#if CUDA_VERSION < 11600
+  GTEST_SKIP() << "Export a graph to DOT requires Cuda 11.6.";
+#else
+  graph->instantiate();
+
+  const auto dot = std::filesystem::temp_directory_path() / "cuda_graph.dot";
+
+  // Convert path to string then to const char * to make it work on Windows.
+  KOKKOS_IMPL_CUDA_SAFE_CALL(
+      cudaGraphDebugDotPrint(graph->native_graph(), dot.string().c_str(),
+                             cudaGraphDebugDotFlagsVerbose));
+
+  ASSERT_TRUE(std::filesystem::exists(dot));
+  ASSERT_GT(std::filesystem::file_size(dot), 0u);
+
+  // We could write a check against the full kernel's function signature, but
+  // it would make the test rely too much on internal implementation details.
+  // Therefore, we just look for the functor and policy. Note that the
+  // signature is mangled in the 'dot' output.
+  const std::string expected("[A-Za-z0-9_]+Increment[A-Za-z0-9_]+RangePolicy");
+
+  std::stringstream buffer;
+  buffer << std::ifstream(dot).rdbuf();
+
+  ASSERT_TRUE(std::regex_search(buffer.str(), std::regex(expected)))
+      << "Could not find expected signature regex " << std::quoted(expected)
+      << " in " << dot;
+#endif
+}
+
+// Ensure that the graph has been instantiated with the default flag.
+TEST_F(TEST_CATEGORY_FIXTURE(GraphInterOp), instantiation_flags) {
+#if CUDA_VERSION < 12000
+  GTEST_SKIP() << "Graph instantiation flag inspection requires Cuda 12.";
+#else
+  unsigned long long flags =
+      Kokkos::Experimental::finite_max_v<unsigned long long>;
+  KOKKOS_IMPL_CUDA_SAFE_CALL(
+      cudaGraphExecGetFlags(graph->native_graph_exec(), &flags));
+
+  ASSERT_EQ(flags, 0u);
+#endif
+}
+
+}  // namespace