[EP ABI] Add Graph_GetGraphView API to get a OrtGraph from a subset of nodes (microsoft#25191)

Added an API that creates a sub-graph from a set of nodes in an
OrtGraph.
This API is needed in the GetCapability EP ABI porting when EP wants to
check whether a 'sub-graph' of the graph is supported by the hardware
backend.

Author: chilo-ms

include/onnxruntime/core/graph/graph.h

@@ -952,9 +952,12 @@ class Graph {  // NOLINT(clang-analyzer-optin.performance.Padding): preserve exi
     return const_cast<Graph*>(this)->GetNodeArg(name);
   }
 
-  // search this and up through any parent_graph_ instance for a NodeArg
+  // Searches for a NodeArg in the current graph and its parent graphs, and returns the corresponding mutable NodeArg
   NodeArg* GetNodeArgIncludingParentGraphs(const std::string& node_arg_name);
 
+  // Searches for a NodeArg in the current graph and its parent graphs, and returns the corresponding const NodeArg
+  const NodeArg* GetNodeArgIncludingParentGraphs(const std::string& node_arg_name) const;
+
   /** Gets a mutable NodeArg by name. Creates a new NodeArg that is owned by this Graph if not found.
   @param name The NodeArg name.
   @param[in] p_arg_type Optional TypeProto to use if the NodeArg needs to be created.

include/onnxruntime/core/session/onnxruntime_c_api.h

@@ -5748,6 +5748,24 @@ struct OrtApi {
    */
   ORT_API2_STATUS(Graph_GetParentNode, _In_ const OrtGraph* graph, _Outptr_result_maybenull_ const OrtNode** node);
 
+  /** \brief Returns an OrtGraph that contains a subset of nodes in the source OrtGraph.
+   *
+   * Note:
+   * The lifetime of "dst_graph" is tied to that of "src_graph", as they both internally reference
+   * the same underlying graph.
+   *
+   * \param[in] src_graph The source OrtGraph instance.
+   * \param[in] nodes A subset of the nodes/OrtNodes in 'graph'.
+   * \param[in] num_nodes Number of nodes.
+   * \param[out] dst_sub_graph An OrtGraph created from a given set of nodes. Must be released by calling ReleaseGraph.
+   *
+   * \snippet{doc} snippets.dox OrtStatus Return Value
+   *
+   * \since Version 1.23.
+   */
+  ORT_API2_STATUS(Graph_GetGraphView, _In_ const OrtGraph* src_graph, _In_ const OrtNode** nodes,
+                  _In_ size_t num_nodes, _Outptr_ OrtGraph** dst_graph);
+
   /// @}
 
   /// \name OrtNode

onnxruntime/core/graph/ep_api_types.cc

@@ -505,10 +505,34 @@ void EpGraph::IndexToEpNodeMap::SetEpNode(NodeIndex node_index, EpNode* ep_node)
 EpGraph::EpGraph(const GraphViewer& graph_viewer, PrivateTag)
     : OrtGraph(OrtGraphIrApi::kEpApi), graph_viewer_(graph_viewer) {}
 
+EpGraph::EpGraph(std::unique_ptr<GraphViewer> graph_viewer,
+                 std::unique_ptr<IndexedSubGraph> indexed_sub_graph,
+                 PrivateTag)
+    : OrtGraph(OrtGraphIrApi::kEpApi),
+      graph_viewer_(*graph_viewer.get()),
+      owned_graph_viewer_(std::move(graph_viewer)),
+      owned_indexed_sub_graph_(std::move(indexed_sub_graph)) {}
+
 // Static class function to create a std::unique_ptr<EpGraph>.
 Status EpGraph::Create(const GraphViewer& graph_viewer, /*out*/ std::unique_ptr<EpGraph>& result) {
   auto ep_graph = std::make_unique<EpGraph>(graph_viewer, PrivateTag{});
 
+  return CreateImpl(std::move(ep_graph), graph_viewer, result);
+}
+
+// Static class function to create a std::unique_ptr<EpGraph>.
+Status EpGraph::Create(std::unique_ptr<GraphViewer> src_graph_viewer,
+                       std::unique_ptr<IndexedSubGraph> src_indexed_sub_graph,
+                       /*out*/ std::unique_ptr<EpGraph>& result) {
+  auto& graph_viewer = *src_graph_viewer.get();
+  auto ep_graph = std::make_unique<EpGraph>(std::move(src_graph_viewer),
+                                            std::move(src_indexed_sub_graph),
+                                            PrivateTag{});
+
+  return CreateImpl(std::move(ep_graph), graph_viewer, result);
+}
+
+Status EpGraph::CreateImpl(std::unique_ptr<EpGraph> ep_graph, const GraphViewer& graph_viewer, /*out*/ std::unique_ptr<EpGraph>& result) {
   AllocatorPtr initializer_allocator = CPUAllocator::DefaultInstance();
   std::unordered_map<std::string, std::unique_ptr<EpValueInfo>> value_infos_map;
 

onnxruntime/core/graph/ep_api_types.h

@@ -251,15 +251,32 @@ struct EpGraph : public OrtGraph {
 
  public:
   EpGraph(const GraphViewer& graph_viewer, PrivateTag);
+  EpGraph(std::unique_ptr<GraphViewer> graph_viewer,
+          std::unique_ptr<IndexedSubGraph> indexed_sub_graph,
+          PrivateTag);
 
   /// <summary>
   /// Creates an instance of EpGraph, which wraps a GraphViewer.
+  /// This call is used when creating an EpGraph from a GraphViewer instance. The GraphViewer instance is not onwed by this EpGraph.
   /// </summary>
   /// <param name="graph_viewer"></param>
   /// <param name="result"></param>
   /// <returns></returns>
   static Status Create(const GraphViewer& graph_viewer, /*out*/ std::unique_ptr<EpGraph>& result);
 
+  /// <summary>
+  /// Creates an instance of EpGraph, which wraps a GraphViewer.
+  /// This call is used when creating an EpGraph from a subset of nodes in another EpGraph.
+  /// In this case, due to the implementation of OrtApis::Graph_GetGraphView, the new EpGraph instance
+  /// must take ownership of both the GraphViewer and IndexedSubGraph.
+  /// </summary>
+  /// <param name="graph_viewer"></param>
+  /// <param name="result"></param>
+  /// <returns></returns>
+  static Status Create(std::unique_ptr<GraphViewer> graph_viewer,
+                       std::unique_ptr<IndexedSubGraph> indexed_sub_graph,
+                       /*out*/ std::unique_ptr<EpGraph>& result);
+
   // Defines ToExternal() and ToInternal() functions to convert between OrtGraph and EpGraph.
   DEFINE_ORT_GRAPH_IR_TO_EXTERNAL_INTERNAL_FUNCS(OrtGraph, EpGraph, OrtGraphIrApi::kEpApi)
 
@@ -331,9 +348,22 @@ struct EpGraph : public OrtGraph {
   const OrtValue* GetInitializerValue(std::string_view name) const;
 
  private:
+  /// <summary>
+  /// The real implementation of creating an EpGraph instance.
+  /// Please use one of the above 'Create' functions that internally call this function, and avoid calling this function directly.
+  /// </summary>
+  /// <param name="ep_graph"></param>
+  /// <param name="graph_viewer"></param>
+  /// <param name="result"></param>
+  /// <returns></returns>
+  static Status CreateImpl(std::unique_ptr<EpGraph> ep_graph, const GraphViewer& graph_viewer, /*out*/ std::unique_ptr<EpGraph>& result);
+
   const GraphViewer& graph_viewer_;
   const EpNode* parent_node_ = nullptr;
 
+  std::unique_ptr<GraphViewer> owned_graph_viewer_ = nullptr;
+  std::unique_ptr<IndexedSubGraph> owned_indexed_sub_graph_ = nullptr;
+
   std::vector<std::unique_ptr<EpNode>> nodes_;
   IndexToEpNodeMap index_to_ep_node_;
 

onnxruntime/core/graph/graph.cc

@@ -1818,6 +1818,10 @@ NodeArg* Graph::GetNodeArgIncludingParentGraphs(const std::string& node_arg_name
   return node_arg;
 }
 
+const NodeArg* Graph::GetNodeArgIncludingParentGraphs(const std::string& node_arg_name) const {
+  return const_cast<Graph*>(this)->GetNodeArgIncludingParentGraphs(node_arg_name);
+}
+
 void Graph::ReverseDFSFrom(gsl::span<NodeIndex const> from,
                            const std::function<void(const Node*)>& enter,
                            const std::function<void(const Node*)>& leave,

onnxruntime/core/graph/graph_viewer.cc

@@ -168,7 +168,15 @@ GraphViewer::GraphViewer(const Graph& graph, const IndexedSubGraph* filter_info)
     filtered_node_inputs_including_initializers_.reserve(metadef->inputs.size());
 
     for (const auto& input : metadef->inputs) {
-      const auto* nodearg = graph.GetNodeArg(input);
+      // NodeArgs from the current scope or any outer scopes should be handled correctly.
+      //
+      // There is an edge case where the model consists of a graph with subgraphs nested across three levels.
+      // In this scenario, a third-layer subgraph consumes an input from the first-layer graph (not an initializer).
+      // When constructing a new GraphViewer for the second- and third-layer subgraphs,
+      // the second-layer graph may not have the corresponding value_info for that first-layer input,
+      // because the second-layer graph itself doesn't consume it.
+      // Therefore, when working within the second-layer graph, we need to search outer scopes for the missing value_info.
+      const auto* nodearg = graph.GetNodeArgIncludingParentGraphs(input);
       ORT_ENFORCE(nodearg, "Mismatch between Graph and IndexedSubGraph. Input not found:", input);
       filtered_node_inputs_including_initializers_.push_back(nodearg);
       if (!graph.IsInitializedTensor(input)) {
@@ -177,7 +185,7 @@ GraphViewer::GraphViewer(const Graph& graph, const IndexedSubGraph* filter_info)
     }
 
     for (const auto& output : metadef->outputs) {
-      const auto* nodearg = graph.GetNodeArg(output);
+      const auto* nodearg = graph.GetNodeArgIncludingParentGraphs(output);
       ORT_ENFORCE(nodearg, "Mismatch between Graph and IndexedSubGraph. Output not found:", output);
       filtered_node_outputs_.push_back(nodearg);
     }

onnxruntime/core/session/onnxruntime_c_api.cc

@@ -2714,6 +2714,91 @@ ORT_API_STATUS_IMPL(OrtApis::Graph_GetParentNode, _In_ const OrtGraph* graph, _O
   API_IMPL_END
 }
 
+ORT_API_STATUS_IMPL(OrtApis::Graph_GetGraphView, _In_ const OrtGraph* src_graph,
+                    _In_ const OrtNode** nodes,
+                    _In_ size_t num_nodes,
+                    _Outptr_ OrtGraph** dst_graph) {
+  API_IMPL_BEGIN
+
+  if (num_nodes == 0) {
+    return OrtApis::CreateStatus(ORT_INVALID_ARGUMENT, "'num_nodes' argument should be > 0");
+  }
+
+  const EpGraph* ep_graph = EpGraph::ToInternal(src_graph);
+  if (ep_graph == nullptr) {
+    return OrtApis::CreateStatus(OrtErrorCode::ORT_INVALID_ARGUMENT, "src_graph is a ModelEditorGraph which doesn't support Graph_GetSubGraph.");
+  }
+  const Graph& graph = ep_graph->GetGraphViewer().GetGraph();
+
+  // Create a GraphViewer with filtered info
+  std::unique_ptr<IndexedSubGraph> indexed_sub_graph = std::make_unique<IndexedSubGraph>();
+  std::unique_ptr<IndexedSubGraph::MetaDef> metadef = std::make_unique<IndexedSubGraph::MetaDef>();
+  metadef->name = "sub_graph";
+  metadef->since_version = 1;
+  std::unordered_set<std::string> outputs;
+  std::unordered_set<const NodeArg*> initializers;
+
+  auto add_inputs = [&](ConstPointerContainer<std::vector<NodeArg*>> defs) {
+    for (const auto* def : defs) {
+      if (def->Exists()) {
+        // not the output of a previous node
+        if (outputs.count(def->Name()) == 0) {
+          metadef->inputs.push_back(def->Name());
+        } else {
+          // consumed by node so no longer subgraph output
+          // NOTE: Ignoring edge case where a node output is an overall graph output AND a node input
+          outputs.erase(def->Name());
+        }
+
+        if (graph.IsInitializedTensor(def->Name())) {
+          initializers.insert(def);
+        }
+      }
+    }
+  };
+
+  auto add_node = [&](const Node& node) {
+    indexed_sub_graph->nodes.push_back(node.Index());
+    add_inputs(node.InputDefs());
+    add_inputs(node.ImplicitInputDefs());
+
+    for (const auto* def : node.OutputDefs()) {
+      outputs.insert(def->Name());
+    }
+  };
+
+  // Add nodes
+  for (size_t node_idx = 0; node_idx < num_nodes; node_idx++) {
+    const OrtNode* ort_node = nodes[node_idx];
+    const EpNode* ep_node = EpNode::ToInternal(ort_node);
+    if (ep_node == nullptr) {
+      return OrtApis::CreateStatus(OrtErrorCode::ORT_INVALID_ARGUMENT, "node is a ModelEditorNode which doesn't support Graph_GetSubGraph.");
+    }
+    add_node(ep_node->GetInternalNode());
+  }
+
+  // Add initializers
+  for (auto& initializer : initializers) {
+    metadef->constant_initializers.push_back(initializer->Name());
+  }
+
+  // Add outputs
+  for (auto& output : outputs) {
+    metadef->outputs.push_back(output);
+  }
+
+  indexed_sub_graph->SetMetaDef(std::move(metadef));
+  auto graph_viewer = std::make_unique<GraphViewer>(graph, *indexed_sub_graph.get());
+
+  std::unique_ptr<EpGraph> result;
+  ORT_API_RETURN_IF_STATUS_NOT_OK(EpGraph::Create(std::move(graph_viewer), std::move(indexed_sub_graph), result));
+
+  *dst_graph = result.release();
+
+  return nullptr;
+  API_IMPL_END
+}
+
 //
 // OrtNode
 //
@@ -3629,6 +3714,7 @@ static constexpr OrtApi ort_api_1_to_23 = {
     &OrtApis::Graph_GetNumNodes,
     &OrtApis::Graph_GetNodes,
     &OrtApis::Graph_GetParentNode,
+    &OrtApis::Graph_GetGraphView,
     &OrtApis::Node_GetId,
     &OrtApis::Node_GetName,
     &OrtApis::Node_GetOperatorType,

onnxruntime/core/session/ort_apis.h

@@ -649,6 +649,8 @@ ORT_API_STATUS_IMPL(Graph_GetNumNodes, _In_ const OrtGraph* graph, _Out_ size_t*
 ORT_API_STATUS_IMPL(Graph_GetNodes, const OrtGraph* graph,
                     _Out_writes_(num_nodes) const OrtNode** nodes, _In_ size_t num_nodes);
 ORT_API_STATUS_IMPL(Graph_GetParentNode, _In_ const OrtGraph* graph, _Outptr_result_maybenull_ const OrtNode** node);
+ORT_API_STATUS_IMPL(Graph_GetGraphView, _In_ const OrtGraph* graph, _In_ const OrtNode** nodes, _In_ size_t num_nodes,
+                    _Outptr_ OrtGraph** subgraph);
 
 // OrtNode
 ORT_API_STATUS_IMPL(Node_GetId, _In_ const OrtNode* node, _Out_ size_t* node_id);

onnxruntime/test/ep_graph/test_ep_graph.cc

@@ -7,12 +7,15 @@
 #include <gsl/gsl>
 #include <memory>
 #include <vector>
+#include <fstream>
 
 #include "core/common/common.h"
 #include "core/framework/tensorprotoutils.h"
 #include "core/framework/tensor_type_and_shape.h"
 #include "core/framework/onnxruntime_typeinfo.h"
 #include "core/session/onnxruntime_cxx_api.h"
+#include "core/graph/ep_api_types.h"
+#include "core/graph/graph_proto_serializer.h"
 
 #define ORT_EP_UTILS_ORT_GRAPH_TO_PROTO_IMPL
 #include "core/providers/utils/ort_graph_to_proto.h"
@@ -31,6 +34,7 @@ namespace test {
 // forward-declaration for utility that uses public C APIs to check that an OrtGraph is equivalent
 // to a graph represented by the internal ORT GraphViewer class.
 static void CheckGraphCApi(const GraphViewer& graph_viewer, const OrtGraph& api_graph);
+static void Check_Graph_GetSubgraph(const OrtGraph& api_graph);
 
 //
 //  Tests
@@ -73,6 +77,16 @@ TEST(EpGraphTest, Check3LayerNestedSubgraph) {
   CheckGraphCApi(test_graph->GetGraphViewer(), test_graph->GetOrtGraph());
 }
 
+TEST(EpGraphTest, Check3LayerNestedSubgraphV2) {
+  // The overall structure of this model is similar to the one used in "Check3LayerNestedSubgraph" test.
+  // The model consists of a graph with subgraphs nested across three levels.
+  // In this scenario, a third-layer subgraph consumes an input from the first-layer graph (not an initializer).
+  auto test_graph = TestGraph::Load(ORT_TSTR("testdata/three_layer_nested_subgraph_v2.onnx"));
+  ASSERT_NE(test_graph, nullptr) << "Failed to load test model";
+
+  CheckGraphCApi(test_graph->GetGraphViewer(), test_graph->GetOrtGraph());
+}
+
 static void RunMNISTModel(const ORTCHAR_T* model_path, std::vector<float>& output_data) {
   auto memory_info = Ort::MemoryInfo::CreateCpu(OrtDeviceAllocator, OrtMemTypeCPU);
   Ort::SessionOptions sess_options;
@@ -474,6 +488,48 @@ static void CheckValueInfosCApi(const GraphViewer& graph_viewer, gsl::span<const
   }
 }
 
+// Checks the Graph_GetSubgraph C API
+static void Check_Graph_GetSubgraph(const OrtGraph& api_graph) {
+  const OrtApi& ort_api = Ort::GetApi();
+
+  // Get all the nodes
+  size_t num_nodes = 0;
+  ASSERT_ORTSTATUS_OK(ort_api.Graph_GetNumNodes(&api_graph, &num_nodes));
+
+  std::vector<const OrtNode*> nodes(num_nodes);
+  ASSERT_ORTSTATUS_OK(ort_api.Graph_GetNodes(&api_graph, nodes.data(), nodes.size()));
+
+  // Select a half of nodes to create a OrtGraph
+  size_t num_selected_nodes = std::max((nodes.size() >> 1), (size_t)1);
+  std::vector<const OrtNode*> selected_nodes(num_selected_nodes);
+
+  for (size_t i = 0; i < num_selected_nodes; i++) {
+    selected_nodes[i] = nodes[i];
+  }
+
+  OrtGraph* sub_graph;
+  ASSERT_ORTSTATUS_OK(ort_api.Graph_GetGraphView(&api_graph, selected_nodes.data(), selected_nodes.size(), &sub_graph));
+
+  // Convert OrtGraph/GraphViewer to ModelProto and dump it to disk.
+  // If the GraphViewer associated with the OrtGraph somehow is incorrect, GraphViewerToProto() will throw.
+  const GraphViewer& sub_graph_viewer = EpGraph::ToInternal(sub_graph)->GetGraphViewer();
+  std::unique_ptr<Model> model = std::make_unique<Model>(sub_graph_viewer.Name(), true, sub_graph_viewer.GetGraph().GetLogger());
+  auto model_proto = std::make_unique<ONNX_NAMESPACE::ModelProto>(model->ToProto());
+  GraphViewerToProto(sub_graph_viewer, *model_proto->mutable_graph(), true, true, static_cast<ExecutionOrder>(1));
+  model_proto->set_ir_version(ONNX_NAMESPACE::Version::IR_VERSION);
+
+  const char* graph_name = nullptr;
+  ASSERT_ORTSTATUS_OK(ort_api.Graph_GetName(&api_graph, &graph_name));
+  std::string name = graph_name;
+  name += "_half.onnx";
+
+  // Dump the graph for debugging
+  // std::fstream dump(name, std::ios::out | std::ios::trunc | std::ios::binary);
+  // model_proto->SerializeToOstream(&dump);
+
+  ort_api.ReleaseGraph(sub_graph);
+}
+
 // Checks that the contents of the original GraphViewer matches the contents of the OrtGraph.
 // Uses the public C APIs to traverse the OrtGraph.
 static void CheckGraphCApi(const GraphViewer& graph_viewer, const OrtGraph& api_graph) {
@@ -682,6 +738,9 @@ static void CheckGraphCApi(const GraphViewer& graph_viewer, const OrtGraph& api_
       }
     }
   }
+
+  // Check creating an OrtGraph from a subset of nodes in an OrtGraph
+  Check_Graph_GetSubgraph(api_graph);
 }
 
 }  // namespace test