COMPMID-2076: Add StackLayer to the graph API

Change-Id: Ifae23659c2471d9c052bc8adf066c5228d6e8b23
Signed-off-by: Michele Di Giorgio <michele.digiorgio@arm.com>
Reviewed-on: https://review.mlplatform.org/c/893
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>

13 files changed, 369 insertions, 16 deletions

diff --git a/arm_compute/graph/GraphBuilder.h b/arm_compute/graph/GraphBuilder.h
index 590e4d9b44..bcf80f9c02 100644
--- a/arm_compute/graph/GraphBuilder.h
+++ b/arm_compute/graph/GraphBuilder.h
@@ -168,12 +168,12 @@ public:
      *
      * @param[in] g                 Graph to add the node to
      * @param[in] params            Common node parameters
-     * @param[in] inputs            Inputs to the depth concatenate layer node as a NodeID-Index pair
+     * @param[in] inputs            Inputs to the concatenate layer node as a NodeID-Index pair
      * @param[in] concat_descriptor Concatenation layer descriptor
      *
      * @return Node ID of the created node, EmptyNodeID in case of error
      */
-    static NodeID add_concatenate_node(Graph &g, NodeParams params, std::vector<NodeIdxPair> inputs, descriptors::ConcatLayerDescriptor concat_descriptor);
+    static NodeID add_concatenate_node(Graph &g, NodeParams params, const std::vector<NodeIdxPair> &inputs, descriptors::ConcatLayerDescriptor concat_descriptor);
     /** Adds a depth-wise convolution layer node to the graph
      *
      * @param[in] g                     Graph to add the node to
@@ -443,6 +443,16 @@ public:
      * @return Node ID of the created node, EmptyNodeID in case of error
      */
     static NodeID add_split_node(Graph &g, NodeParams params, NodeIdxPair input, unsigned int num_splits, unsigned int axis = 0);
+    /** Adds a stack layer node to the graph
+     *
+     * @param[in] g      Graph to add the node to
+     * @param[in] params Common node parameters
+     * @param[in] inputs Inputs to the reorg layer node as a NodeID-Index pair
+     * @param[in] axis   Axis along which the input tensors have to be packed
+     *
+     * @return Node ID of the created node, EmptyNodeID in case of error
+     */
+    static NodeID add_stack_node(Graph &g, NodeParams params, const std::vector<NodeIdxPair> &inputs, int axis);
     /** Adds an upsample layer to the graph
      *
      * @param[in] g                 Graph to add the node to
diff --git a/arm_compute/graph/INodeVisitor.h b/arm_compute/graph/INodeVisitor.h
index 842ca4bfb3..291fe7c3cc 100644
--- a/arm_compute/graph/INodeVisitor.h
+++ b/arm_compute/graph/INodeVisitor.h
@@ -141,6 +141,11 @@ public:
      * @param[in] n Node to visit.
      */
     virtual void visit(SplitLayerNode &n) = 0;
+    /** Visit StackLayerNode.
+     *
+     * @param[in] n Node to visit.
+     */
+    virtual void visit(StackLayerNode &n) = 0;
 };
 
 /** Default visitor implementation
@@ -240,6 +245,10 @@ public:
     {
         default_visit();
     }
+    virtual void visit(StackLayerNode &n) override
+    {
+        default_visit();
+    }
 #endif /* DOXYGEN_SKIP_THIS */
 
     /** Function to be overloaded by the client and implement default behavior for the
diff --git a/arm_compute/graph/TypePrinter.h b/arm_compute/graph/TypePrinter.h
index b1cfbcf658..29a2981463 100644
--- a/arm_compute/graph/TypePrinter.h
+++ b/arm_compute/graph/TypePrinter.h
@@ -143,6 +143,9 @@ inline ::std::ostream &operator<<(::std::ostream &os, const NodeType &node_type)
         case NodeType::SplitLayer:
             os << "SplitLayer";
             break;
+        case NodeType::StackLayer:
+            os << "StackLayer";
+            break;
         case NodeType::UpsampleLayer:
             os << "UpsampleLayer";
             break;
diff --git a/arm_compute/graph/Types.h b/arm_compute/graph/Types.h
index 2905dfcbf6..582e6f6434 100644
--- a/arm_compute/graph/Types.h
+++ b/arm_compute/graph/Types.h
@@ -153,6 +153,7 @@ enum class NodeType
     SoftmaxLayer,
     SliceLayer,
     SplitLayer,
+    StackLayer,
     UpsampleLayer,
     YOLOLayer,
 
diff --git a/arm_compute/graph/backends/FunctionHelpers.h b/arm_compute/graph/backends/FunctionHelpers.h
index 4a423d2490..e05f4bc8cf 100644
--- a/arm_compute/graph/backends/FunctionHelpers.h
+++ b/arm_compute/graph/backends/FunctionHelpers.h
@@ -1276,6 +1276,49 @@ std::unique_ptr<IFunction> create_softmax_layer(SoftmaxLayerNode &node, GraphCon
 
     return std::move(func);
 }
+
+/** Create a backend layer stack function
+ *
+ * @tparam StackLayerFunction Backend stack function
+ * @tparam TargetInfo         Target-specific information
+ *
+ * @param[in] node Node to create the backend function for
+ *
+ * @return Backend stack layer function
+ */
+template <typename StackLayerFunction, typename TargetInfo>
+std::unique_ptr<arm_compute::IFunction> create_stack_layer(StackLayerNode &node)
+{
+    ARM_COMPUTE_LOG_GRAPH_VERBOSE("Creating Stack node with ID : " << node.id() << " and Name: " << node.name() << std::endl);
+    ARM_COMPUTE_ERROR_ON(node.num_outputs() != 1);
+
+    // Extract IO and info
+    std::vector<typename TargetInfo::TensorType *> inputs;
+    for(unsigned int i = 0; i < node.num_inputs(); ++i)
+    {
+        inputs.push_back(get_backing_tensor<TargetInfo>(node.input(i)));
+    }
+    typename TargetInfo::TensorType *output = get_backing_tensor<TargetInfo>(node.output(0));
+    const int                        axis   = node.axis();
+
+    // Create and configure function
+    auto func = support::cpp14::make_unique<StackLayerFunction>();
+    func->configure(inputs, axis, output);
+
+    // Log info
+    ARM_COMPUTE_LOG_GRAPH_INFO("Instantiated "
+                               << node.name()
+                               << " Type: " << node.type()
+                               << " Target: " << TargetInfo::TargetType
+                               << " Data Type: " << output->info()->data_type()
+                               << " Inputs shape: " << inputs[0]->info()->tensor_shape()
+                               << " Output shape: " << output->info()->tensor_shape()
+                               << " Num Inputs: " << inputs.size()
+                               << " Axis: " << axis
+                               << std::endl);
+
+    return std::move(func);
+}
 /** Create a backend Upsample layer function
  *
  * @tparam UpsampleLayerFunction Backend Upsample function
diff --git a/arm_compute/graph/frontend/Layers.h b/arm_compute/graph/frontend/Layers.h
index 67dc06c878..4e6f0eee2d 100644
--- a/arm_compute/graph/frontend/Layers.h
+++ b/arm_compute/graph/frontend/Layers.h
@@ -1038,6 +1038,92 @@ private:
     float _beta;
 };
 
+/** Stack Layer */
+class StackLayer final : public ILayer
+{
+public:
+    /** Construct a concatenation layer
+     *
+     * @param[in] sub_stream1      First graph branch
+     * @param[in] sub_stream2      Second graph branch
+     * @param[in] rest_sub_streams Rest sub-graph branches
+     */
+    template <typename... Ts>
+    StackLayer(SubStream &&sub_stream1, SubStream &&sub_stream2, Ts &&... rest_sub_streams)
+        : _sub_streams(), _axis(0)
+    {
+        _sub_streams.push_back(arm_compute::support::cpp14::make_unique<SubStream>(std::move(sub_stream1)));
+        _sub_streams.push_back(arm_compute::support::cpp14::make_unique<SubStream>(std::move(sub_stream2)));
+
+        utility::for_each([&](SubStream && sub_stream)
+        {
+            _sub_streams.push_back(arm_compute::support::cpp14::make_unique<SubStream>(std::move(sub_stream)));
+        },
+        std::move(rest_sub_streams)...);
+    }
+    /** Construct a concatenation layer
+     *
+     * @param[in] axis             Stack layer axis along which to stack the inputs
+     * @param[in] sub_stream1      First graph branch
+     * @param[in] sub_stream2      Second graph branch
+     * @param[in] rest_sub_streams Rest sub-graph branches
+     */
+    template <typename... Ts>
+    StackLayer(int axis, SubStream &&sub_stream1, SubStream &&sub_stream2, Ts &&... rest_sub_streams)
+        : _sub_streams(), _axis(axis)
+    {
+        _sub_streams.push_back(arm_compute::support::cpp14::make_unique<SubStream>(std::move(sub_stream1)));
+        _sub_streams.push_back(arm_compute::support::cpp14::make_unique<SubStream>(std::move(sub_stream2)));
+
+        utility::for_each([&](SubStream && sub_stream)
+        {
+            _sub_streams.push_back(arm_compute::support::cpp14::make_unique<SubStream>(std::move(sub_stream)));
+        },
+        std::move(rest_sub_streams)...);
+    }
+    /** Construct a concat layer
+     *
+     * @param[in] sub_stream Sub-stream
+     */
+    template <typename... Ts>
+    StackLayer(SubStream &&sub_stream)
+        : _sub_streams(), _axis(0)
+    {
+        _sub_streams.push_back(arm_compute::support::cpp14::make_unique<SubStream>(std::move(sub_stream)));
+    }
+    NodeID create_layer(IStream &s) override
+    {
+        NodeID     nid           = EmptyNodeID;
+        NodeParams common_params = { name(), s.hints().target_hint };
+        if(_sub_streams.size() == 1 && _sub_streams.at(0) != nullptr)
+        {
+            nid = _sub_streams[0]->tail_node();
+        }
+        else
+        {
+            // Collect tail nodes and stack
+            std::vector<NodeIdxPair> nodes;
+            for(auto &ss : _sub_streams)
+            {
+                if(ss && (ss->tail_node() != EmptyNodeID))
+                {
+                    const auto tail_node = s.graph().node(ss->tail_node());
+                    if(tail_node != nullptr && tail_node->type() != NodeType::Output)
+                    {
+                        nodes.push_back({ ss->tail_node(), 0 });
+                    }
+                }
+            }
+            nid = GraphBuilder::add_stack_node(s.graph(), common_params, nodes, _axis);
+        }
+        return nid;
+    }
+
+private:
+    std::vector<std::unique_ptr<SubStream>> _sub_streams;
+    int                                     _axis;
+};
+
 /** Upsample Layer */
 class UpsampleLayer final : public ILayer
 {
diff --git a/arm_compute/graph/nodes/Nodes.h b/arm_compute/graph/nodes/Nodes.h
index e23b2b9897..4eb6a0f886 100644
--- a/arm_compute/graph/nodes/Nodes.h
+++ b/arm_compute/graph/nodes/Nodes.h
@@ -55,6 +55,7 @@
 #include "arm_compute/graph/nodes/SliceLayerNode.h"
 #include "arm_compute/graph/nodes/SoftmaxLayerNode.h"
 #include "arm_compute/graph/nodes/SplitLayerNode.h"
+#include "arm_compute/graph/nodes/StackLayerNode.h"
 #include "arm_compute/graph/nodes/UpsampleLayerNode.h"
 #include "arm_compute/graph/nodes/YOLOLayerNode.h"
 
diff --git a/arm_compute/graph/nodes/NodesFwd.h b/arm_compute/graph/nodes/NodesFwd.h
index 80576d4608..06c2e1f1ae 100644
--- a/arm_compute/graph/nodes/NodesFwd.h
+++ b/arm_compute/graph/nodes/NodesFwd.h
@@ -61,6 +61,7 @@ class ROIAlignLayerNode;
 class SoftmaxLayerNode;
 class SliceLayerNode;
 class SplitLayerNode;
+class StackLayerNode;
 class UpsampleLayerNode;
 class YOLOLayerNode;
 } // namespace graph
diff --git a/arm_compute/graph/nodes/StackLayerNode.h b/arm_compute/graph/nodes/StackLayerNode.h
new file mode 100644
index 0000000000..6c83fe22c2
--- /dev/null
+++ b/arm_compute/graph/nodes/StackLayerNode.h
@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2019 ARM Limited.
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+#ifndef __ARM_COMPUTE_GRAPH_STACK_LAYER_NODE_H__
+#define __ARM_COMPUTE_GRAPH_STACK_LAYER_NODE_H__
+
+#include "arm_compute/graph/INode.h"
+
+namespace arm_compute
+{
+namespace graph
+{
+/** Stack Layer node */
+class StackLayerNode final : public INode
+{
+public:
+    /** Constructor
+     *
+     * @param[in] total_nodes Number of nodes that will get stacked
+     * @param[in] axis        Axis alogn which to stack the input tensors
+     */
+    StackLayerNode(unsigned int total_nodes, int axis);
+    /** Computes stack output descriptor
+     *
+     * @param[in] input_descriptors Input descriptors
+     * @param[in] axis              Axis along which to stack the input tensors
+     *
+     * @return Expected output descriptor
+     */
+    static TensorDescriptor compute_output_descriptor(const std::vector<TensorDescriptor> &input_descriptors, int axis);
+    /** Stack axis parameter accessor
+     *
+     * @return Stack axis
+     */
+    int axis() const;
+
+    // Inherited overridden methods:
+    NodeType         type() const override;
+    bool             forward_descriptors() override;
+    TensorDescriptor configure_output(size_t idx) const override;
+    void accept(INodeVisitor &v) override;
+
+private:
+    unsigned int _total_nodes;
+    int          _axis;
+};
+} // namespace graph
+} // namespace arm_compute
+#endif /* __ARM_COMPUTE_GRAPH_STACK_LAYER_NODE_H__ */
diff --git a/src/graph/GraphBuilder.cpp b/src/graph/GraphBuilder.cpp
index 74f60d5354..3f40aeadcb 100644
--- a/src/graph/GraphBuilder.cpp
+++ b/src/graph/GraphBuilder.cpp
@@ -81,6 +81,24 @@ NodeID create_simple_single_input_output_node(Graph &g, NodeParams &params, Node
 
     return nid;
 }
+
+template <typename NT, typename... Args>
+NodeID create_simple_multiple_input_single_output_node(Graph &g, NodeParams &params, std::vector<NodeIdxPair> inputs, Args &&... args)
+{
+    ARM_COMPUTE_ERROR_ON(inputs.size() == 0);
+
+    NodeID nid = g.add_node<NT>(std::forward<Args>(args)...);
+
+    unsigned int i = 0;
+    for(const auto &input : inputs)
+    {
+        CHECK_NODEIDX_PAIR(input, g);
+        g.add_connection(input.node_id, input.index, nid, i++);
+    }
+    set_node_params(g, nid, params);
+
+    return nid;
+}
 } // namespace
 
 NodeID GraphBuilder::add_const_node(Graph &g, NodeParams params, TensorDescriptor desc, ITensorAccessorUPtr accessor)
@@ -294,21 +312,9 @@ NodeID GraphBuilder::add_deconvolution_node(Graph &g, NodeParams params, NodeIdx
     return deconv_nid;
 }
 
-NodeID GraphBuilder::add_concatenate_node(Graph &g, NodeParams params, std::vector<NodeIdxPair> inputs, descriptors::ConcatLayerDescriptor concat_descriptor)
+NodeID GraphBuilder::add_concatenate_node(Graph &g, NodeParams params, const std::vector<NodeIdxPair> &inputs, descriptors::ConcatLayerDescriptor concat_descriptor)
 {
-    ARM_COMPUTE_ERROR_ON(inputs.size() == 0);
-
-    NodeID nid = g.add_node<ConcatenateLayerNode>(inputs.size(), concat_descriptor);
-
-    unsigned int i = 0;
-    for(const auto &input : inputs)
-    {
-        CHECK_NODEIDX_PAIR(input, g);
-        g.add_connection(input.node_id, input.index, nid, i++);
-    }
-    set_node_params(g, nid, params);
-
-    return nid;
+    return create_simple_multiple_input_single_output_node<ConcatenateLayerNode>(g, params, inputs, inputs.size(), concat_descriptor);
 }
 
 NodeID GraphBuilder::add_depthwise_convolution_node(Graph &g, NodeParams params, NodeIdxPair input, Size2D kernel_spatial_extend,
@@ -627,6 +633,11 @@ NodeID GraphBuilder::add_split_node(Graph &g, NodeParams params, NodeIdxPair inp
     return create_simple_single_input_output_node<SplitLayerNode>(g, params, input, num_splits, axis);
 }
 
+NodeID GraphBuilder::add_stack_node(Graph &g, NodeParams params, const std::vector<NodeIdxPair> &inputs, int axis)
+{
+    return create_simple_multiple_input_single_output_node<StackLayerNode>(g, params, inputs, inputs.size(), axis);
+}
+
 NodeID GraphBuilder::add_upsample_node(Graph &g, NodeParams params, NodeIdxPair input, Size2D info, InterpolationPolicy upsampling_policy)
 {
     return create_simple_single_input_output_node<UpsampleLayerNode>(g, params, input, info, upsampling_policy);
diff --git a/src/graph/backends/CL/CLFunctionsFactory.cpp b/src/graph/backends/CL/CLFunctionsFactory.cpp
index 7473ff480f..90c1613604 100644
--- a/src/graph/backends/CL/CLFunctionsFactory.cpp
+++ b/src/graph/backends/CL/CLFunctionsFactory.cpp
@@ -229,6 +229,8 @@ std::unique_ptr<IFunction> CLFunctionFactory::create(INode *node, GraphContext &
             return detail::create_slice_layer<CLSlice, CLTargetInfo>(*polymorphic_downcast<SliceLayerNode *>(node));
         case NodeType::SoftmaxLayer:
             return detail::create_softmax_layer<CLSoftmaxLayer, CLTargetInfo>(*polymorphic_downcast<SoftmaxLayerNode *>(node), ctx);
+        case NodeType::StackLayer:
+            return detail::create_stack_layer<CLStackLayer, CLTargetInfo>(*polymorphic_downcast<StackLayerNode *>(node));
         case NodeType::UpsampleLayer:
             return detail::create_upsample_layer<CLUpsampleLayer, CLTargetInfo>(*polymorphic_downcast<UpsampleLayerNode *>(node), ctx);
         case NodeType::YOLOLayer:
diff --git a/src/graph/backends/NEON/NEFunctionFactory.cpp b/src/graph/backends/NEON/NEFunctionFactory.cpp
index 81c6e09f92..690a311408 100644
--- a/src/graph/backends/NEON/NEFunctionFactory.cpp
+++ b/src/graph/backends/NEON/NEFunctionFactory.cpp
@@ -238,6 +238,8 @@ std::unique_ptr<IFunction> NEFunctionFactory::create(INode *node, GraphContext &
             return detail::create_resize_layer<NEScale, NETargetInfo>(*polymorphic_downcast<ResizeLayerNode *>(node));
         case NodeType::SoftmaxLayer:
             return detail::create_softmax_layer<NESoftmaxLayer, NETargetInfo>(*polymorphic_downcast<SoftmaxLayerNode *>(node), ctx);
+        case NodeType::StackLayer:
+            return detail::create_stack_layer<NEStackLayer, NETargetInfo>(*polymorphic_downcast<StackLayerNode *>(node));
         case NodeType::UpsampleLayer:
             return detail::create_upsample_layer<NEUpsampleLayer, NETargetInfo>(*polymorphic_downcast<UpsampleLayerNode *>(node), ctx);
         case NodeType::YOLOLayer:
diff --git a/src/graph/nodes/StackLayerNode.cpp b/src/graph/nodes/StackLayerNode.cpp
new file mode 100644
index 0000000000..d26498ad77
--- /dev/null
+++ b/src/graph/nodes/StackLayerNode.cpp
@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2019 ARM Limited.
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+#include "arm_compute/graph/nodes/StackLayerNode.h"
+
+#include "arm_compute/core/TensorInfo.h"
+#include "arm_compute/core/Utils.h"
+#include "arm_compute/graph/Graph.h"
+#include "arm_compute/graph/INodeVisitor.h"
+#include "arm_compute/graph/Utils.h"
+
+#include "arm_compute/core/utils/misc/ShapeCalculator.h"
+
+namespace arm_compute
+{
+namespace graph
+{
+StackLayerNode::StackLayerNode(unsigned int total_nodes, int axis)
+    : _total_nodes(total_nodes), _axis(axis)
+{
+    _input_edges.resize(_total_nodes, EmptyEdgeID);
+    _outputs.resize(1, NullTensorID);
+}
+
+int StackLayerNode::axis() const
+{
+    return _axis;
+}
+
+TensorDescriptor StackLayerNode::compute_output_descriptor(const std::vector<TensorDescriptor> &input_descriptors,
+                                                           int                                  axis)
+{
+    ARM_COMPUTE_ERROR_ON(input_descriptors.size() == 0);
+
+    TensorDescriptor output_descriptor = input_descriptors[0];
+
+    const TensorInfo   input_info(input_descriptors[0].shape, 1, input_descriptors[0].data_type);
+    const unsigned int num_tensors = input_descriptors.size();
+
+    output_descriptor.shape = arm_compute::misc::shape_calculator::compute_stack_shape(input_info, axis, num_tensors);
+
+    return output_descriptor;
+}
+
+bool StackLayerNode::forward_descriptors()
+{
+    if(_outputs[0] != NullTensorID)
+    {
+        Tensor *dst = output(0);
+        ARM_COMPUTE_ERROR_ON(dst == nullptr);
+        dst->desc() = configure_output(0);
+        return true;
+    }
+    return false;
+}
+
+TensorDescriptor StackLayerNode::configure_output(size_t idx) const
+{
+    ARM_COMPUTE_UNUSED(idx);
+    ARM_COMPUTE_ERROR_ON(idx >= _outputs.size());
+
+    // Check if all input tensors are set
+    bool are_all_inputs_set = std::all_of(std::begin(_input_edges), std::end(_input_edges), [](const EdgeID & eid)
+    {
+        return eid != EmptyEdgeID;
+    });
+
+    TensorDescriptor output_info = {};
+
+    if(are_all_inputs_set)
+    {
+        std::vector<TensorDescriptor> inputs_descriptors;
+        for(unsigned int i = 0; i < _input_edges.size(); ++i)
+        {
+            const Tensor *t = _graph->tensor(input_id(i));
+            ARM_COMPUTE_ERROR_ON(t == nullptr);
+            inputs_descriptors.push_back(t->desc());
+        }
+        output_info = compute_output_descriptor(inputs_descriptors, _axis);
+    }
+
+    return output_info;
+}
+
+NodeType StackLayerNode::type() const
+{
+    return NodeType::StackLayer;
+}
+
+void StackLayerNode::accept(INodeVisitor &v)
+{
+    v.visit(*this);
+}
+} // namespace graph
+} // namespace arm_compute