[ONNX] remove unnecessary nodes when handling Identity op (#8060)

ngraph/frontend/onnx/frontend/src/op/identity.hpp

@@ -15,13 +15,7 @@ namespace onnx_import {
 namespace op {
 namespace set_1 {
 inline OutputVector identity(const Node& node) {
-    auto input = node.get_ng_inputs().at(0);
-    if (input.get_element_type() == ngraph::element::boolean) {
-        const auto logic_zero = default_opset::Constant::create(ngraph::element::boolean, {}, {false});
-        return {std::make_shared<default_opset::LogicalOr>(input, logic_zero)};
-    }
-    const auto zero = default_opset::Constant::create(input.get_element_type(), {}, {0});
-    return {std::make_shared<default_opset::Add>(input, zero)};
+    return node.get_ng_inputs();
 }
 }  // namespace set_1
 

ngraph/frontend/onnx/frontend/src/op/loop.cpp

@@ -28,24 +28,13 @@ namespace {
 ///             As a result ngraph Loop shape inference is able to handle more
 ///             cases.
 ///
-/// \param[in]  body_out_cond   Termination loop condition input of the body of
-///                             the Loop (value updated during Loop iterations).
+/// \param[in]  cond_in    boolean input to the loop body depicting loop termination condition
 ///
-/// \return true if termination condition is true and it cannot be changed
-///         during Loop iterations, false otherwise.
-bool is_termination_condition_always_true(const Output<ngraph::Node>& body_out_cond) {
-    // If body termination condition input matches Indentity op pattern the has
-    // value of loop_cond - true
-    // Identity op for boolean value is represented by LogicalOr op whose second
-    // input is always false
-    if (ov::is_type<default_opset::LogicalOr>(body_out_cond.get_node_shared_ptr())) {
-        const auto second_input = body_out_cond.get_node_shared_ptr()->input_value(1).get_node_shared_ptr();
-        if (ngraph::op::is_constant(second_input) && second_input->get_element_type() == element::boolean &&
-            ov::as_type_ptr<default_opset::Constant>(second_input)->cast_vector<bool>().at(0) == false) {
-            return true;
-        }
-    }
-    return false;
+/// \param[in]  cond_out   loop termination condition computed after each iteration
+///
+/// \return true if termination condition is not modified during loop iterations, false otherwise.
+bool is_termination_condition_always_true(const ngraph::Node* cond_in, const ngraph::Node* cond_out) {
+    return cond_in == cond_out;
 }
 }  // namespace
 
@@ -112,9 +101,10 @@ OutputVector loop(const Node& node) {
         body_outputs[i] = std::make_shared<default_opset::Unsqueeze>(body_outputs[i], concat_axis_const);
     }
 
-    const auto& body_loop_out_cond = body_outputs.at(0).get_node_shared_ptr();
+    const auto& cond_in = body_inputs[1];
+    const auto& cond_out = body_outputs[0];
     // optimization allow to improve nG Loop shape inference
-    if (is_termination_condition_always_true(body_loop_out_cond)) {
+    if (is_termination_condition_always_true(cond_in.get(), cond_out.get_node())) {
         body_outputs[0] = ngraph::op::Constant::create(ngraph::element::boolean, {1}, {true});
     }
 

ngraph/test/models/onnx/tensor_names.prototxt

@@ -9,6 +9,12 @@ graph {
   }
   node {
     input: "relu_t"
+    output: "abs_t"
+    op_type: "Abs"
+    name: "abs"
+  }
+  node {
+    input: "abs_t"
     output: "final_output"
     name: "ident"
     op_type: "Identity"

ngraph/test/onnx/onnx_tensor_names.cpp

@@ -22,14 +22,20 @@ NGRAPH_TEST(onnx_tensor_names, simple_model) {
     auto function = onnx_import::import_onnx_model(file_util::path_join(SERIALIZED_ZOO, "onnx/tensor_names.onnx"));
 
     auto ops = function->get_ordered_ops();
+    // Parameter
     ASSERT_EQ(ops[0]->get_friendly_name(), "input");
     ASSERT_EQ(ops[0]->get_output_tensor(0).get_names(), std::unordered_set<std::string>{"input"});
+
     ASSERT_EQ(ops[1]->get_friendly_name(), "relu_t");
     ASSERT_EQ(ops[1]->get_output_tensor(0).get_names(), std::unordered_set<std::string>{"relu_t"});
-    // ops[2] is a constant created in the ONNX importer as part of Identity operator
+
+    // should be abs_t, but Identity operator gets cut out and that makes Abs become the 'final_output'
+    ASSERT_EQ(ops[2]->get_friendly_name(), "final_output");
+    ASSERT_EQ(ops[2]->get_output_tensor(0).get_names(), std::unordered_set<std::string>{"final_output"});
+
+    // Result node
     ASSERT_EQ(ops[3]->get_friendly_name(), "final_output");
     ASSERT_EQ(ops[3]->get_output_tensor(0).get_names(), std::unordered_set<std::string>{"final_output"});
-    ASSERT_EQ(ops[4]->get_friendly_name(), "final_output");
 
     ASSERT_EQ(function->get_result()->get_input_tensor(0).get_names(), std::unordered_set<std::string>{"final_output"});
     ASSERT_EQ(function->get_result()->input_value(0).get_tensor().get_names(),