[TF FE] Break the cycle in the different way (#14480)

* [TF FE] Break the cycle in the different way

Earlier solution was incorrect due to inproper handling of forward edges cases
(edges going from parent to grand-child) for which topological sorting
of nodes can be interrupted.

Signed-off-by: Kazantsev, Roman <roman.kazantsev@intel.com>

* Break the cycle by NextIteration inputs

Signed-off-by: Kazantsev, Roman <roman.kazantsev@intel.com>

src/frontends/tensorflow/src/input_model.cpp

@@ -207,9 +207,12 @@ std::vector<std::shared_ptr<OpPlace>> InputModel::InputModelTFImpl::get_op_place
 std::vector<std::shared_ptr<OpPlace>> InputModel::InputModelTFImpl::determine_cut_nodes() const {
     std::vector<std::shared_ptr<OpPlace>> topologically_sorted_ops;
     std::stack<std::shared_ptr<OpPlace>> ops_to_do;
-    std::unordered_set<std::shared_ptr<OpPlace>> ops_set_to_do;
     std::unordered_set<std::shared_ptr<OpPlace>> ops_done;
 
+    // TODO: implement logic to check direct cycles in the graph
+    // and break them
+    // probably not only NextIteration can generate cycles
+
     for (const auto& output_place : m_outputs) {
         FRONT_END_GENERAL_CHECK(output_place->get_names().size() > 0, "TensorPlace must have at least one name.");
         auto output_place_name = output_place->get_names()[0];
@@ -221,7 +224,6 @@ std::vector<std::shared_ptr<OpPlace>> InputModel::InputModelTFImpl::determine_cu
                                 "Custom specified output is incorrect: " + output_place_name);
         auto output_operation_place = m_op_places_map.at(operation_name);
         ops_to_do.push(output_operation_place);
-        ops_set_to_do.insert(output_operation_place);
     }
 
     // the traversing algorithm to compute topologically sorted nodes is taken from topological_sort in
@@ -233,6 +235,12 @@ std::vector<std::shared_ptr<OpPlace>> InputModel::InputModelTFImpl::determine_cu
         if (ops_done.count(current_operation_place) == 0) {
             bool can_add = true;
             auto input_count = current_operation_decoder->get_input_size();
+            auto current_operation_type = current_operation_decoder->get_op_type();
+
+            if (current_operation_type == "NextIteration") {
+                // break the cycle created by NextIteration
+                input_count = 0;
+            }
 
             for (size_t input_port_idx = 0; input_port_idx < input_count; ++input_port_idx) {
                 std::string producer_name;
@@ -282,11 +290,9 @@ std::vector<std::shared_ptr<OpPlace>> InputModel::InputModelTFImpl::determine_cu
                 // in case presence of NextIteration in the graph (or cycle created by other operation),
                 // we break the cycle by outputs from the NextIteration operation
                 // otherwise, the operations nodes in the cycle will be added to ops_to_do infinitely
-                if (!is_input && ops_done.count(producer_operation_place) == 0 &&
-                    ops_set_to_do.count(producer_operation_place) == 0) {
+                if (!is_input && ops_done.count(producer_operation_place) == 0) {
                     can_add = false;
                     ops_to_do.push(producer_operation_place);
-                    ops_set_to_do.insert(producer_operation_place);
                 }
             }
 

src/frontends/tensorflow/tests/convert_model.cpp

@@ -13,6 +13,8 @@ using TFConvertModelTest = FrontEndConvertModelTest;
 
 static const std::vector<std::string> models{
     std::string("2in_2out/2in_2out.pb"),
+    std::string("forward_edge_model/forward_edge_model.pb"),
+    std::string("forward_edge_model2/forward_edge_model2.pb"),
 };
 
 INSTANTIATE_TEST_SUITE_P(TFConvertModelTest,

src/frontends/tensorflow/tests/test_models/models_pbtxt/forward_edge_model.pbtxt

@@ -0,0 +1,79 @@
+node {
+  name: "Const"
+  op: "Const"
+  attr {
+    key: "dtype"
+    value {
+      type: DT_FLOAT
+    }
+  }
+  attr {
+    key: "value"
+    value {
+      tensor {
+        dtype: DT_FLOAT
+        tensor_shape {
+        }
+        float_val: 2.0
+      }
+    }
+  }
+}
+node {
+  name: "x"
+  op: "Placeholder"
+  attr {
+    key: "dtype"
+    value {
+      type: DT_FLOAT
+    }
+  }
+  attr {
+    key: "shape"
+    value {
+      shape {
+        dim {
+          size: 2
+        }
+        dim {
+          size: 3
+        }
+      }
+    }
+  }
+}
+node {
+  name: "Relu"
+  op: "Relu"
+  input: "x"
+  attr {
+    key: "T"
+    value {
+      type: DT_FLOAT
+    }
+  }
+}
+node {
+  name: "add"
+  op: "AddV2"
+  input: "Relu"
+  input: "Const"
+  attr {
+    key: "T"
+    value {
+      type: DT_FLOAT
+    }
+  }
+}
+node {
+  name: "Mul"
+  op: "Mul"
+  input: "add"
+  input: "Relu"
+  attr {
+    key: "T"
+    value {
+      type: DT_FLOAT
+    }
+  }
+}

src/frontends/tensorflow/tests/test_models/models_pbtxt/forward_edge_model.py

@@ -0,0 +1,19 @@
+# Copyright (C) 2018-2022 Intel Corporation
+# SPDX-License-Identifier: Apache-2.0
+
+
+import tensorflow.compat.v1 as tf
+
+tf.reset_default_graph()
+
+with tf.Session() as sess:
+    const2 = tf.constant(2.0, dtype=tf.float32)
+    x = tf.placeholder(dtype=tf.float32, shape=[2, 3], name='x')
+    relu = tf.nn.relu(x)    
+    add = tf.add(relu, const2, name="add")
+    # it has forward-edge from relu to multiply
+    # i.e. edge skipping direct child
+    tf.multiply(add, relu)
+
+    tf.global_variables_initializer()
+    tf.io.write_graph(sess.graph, '.', 'forward_edge_model.pb', as_text=False)

src/frontends/tensorflow/tests/test_models/models_pbtxt/forward_edge_model2.pbtxt

@@ -0,0 +1,79 @@
+node {
+  name: "Const"
+  op: "Const"
+  attr {
+    key: "dtype"
+    value {
+      type: DT_FLOAT
+    }
+  }
+  attr {
+    key: "value"
+    value {
+      tensor {
+        dtype: DT_FLOAT
+        tensor_shape {
+        }
+        float_val: 2.0
+      }
+    }
+  }
+}
+node {
+  name: "x"
+  op: "Placeholder"
+  attr {
+    key: "dtype"
+    value {
+      type: DT_FLOAT
+    }
+  }
+  attr {
+    key: "shape"
+    value {
+      shape {
+        dim {
+          size: 2
+        }
+        dim {
+          size: 3
+        }
+      }
+    }
+  }
+}
+node {
+  name: "Relu"
+  op: "Relu"
+  input: "x"
+  attr {
+    key: "T"
+    value {
+      type: DT_FLOAT
+    }
+  }
+}
+node {
+  name: "mul"
+  op: "Mul"
+  input: "Relu"
+  input: "Const"
+  attr {
+    key: "T"
+    value {
+      type: DT_FLOAT
+    }
+  }
+}
+node {
+  name: "Add"
+  op: "AddV2"
+  input: "Relu"
+  input: "mul"
+  attr {
+    key: "T"
+    value {
+      type: DT_FLOAT
+    }
+  }
+}

src/frontends/tensorflow/tests/test_models/models_pbtxt/forward_edge_model2.py

@@ -0,0 +1,19 @@
+# Copyright (C) 2018-2022 Intel Corporation
+# SPDX-License-Identifier: Apache-2.0
+
+
+import tensorflow.compat.v1 as tf
+
+tf.reset_default_graph()
+
+with tf.Session() as sess:
+    const2 = tf.constant(2.0, dtype=tf.float32)
+    x = tf.placeholder(dtype=tf.float32, shape=[2, 3], name='x')
+    relu = tf.nn.relu(x)    
+    mul = tf.multiply(relu, const2, name="mul")
+    # it has forward-edge from relu to multiply
+    # i.e. edge skipping direct child
+    tf.add(relu, mul)
+
+    tf.global_variables_initializer()
+    tf.io.write_graph(sess.graph, '.', 'forward_edge_model2.pb', as_text=False)