IVGCVSW-3423 Add TfLite parser support for Stack (Pack) layer

* Added ParsePack method
* New unit test Pack.cpp
* Updated TensorFlowLiteSupport.md with new supported operator

Signed-off-by: Matthew Jackson <matthew.jackson@arm.com>
Change-Id: I2310b33ee26959b036bb4452a25c90cc1d4cbf20

6 files changed, 199 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index dbb212ff73..9bc4201a5e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -570,6 +570,7 @@ if(BUILD_UNIT_TESTS)
              src/armnnTfLiteParser/test/Mean.cpp
              src/armnnTfLiteParser/test/Minimum.cpp
              src/armnnTfLiteParser/test/Multiplication.cpp
+             src/armnnTfLiteParser/test/Pack.cpp
              src/armnnTfLiteParser/test/Pad.cpp
              src/armnnTfLiteParser/test/Reshape.cpp
              src/armnnTfLiteParser/test/ResizeBilinear.cpp
diff --git a/src/armnn/InternalTypes.cpp b/src/armnn/InternalTypes.cpp
index 417581f010..896e4161ba 100644
--- a/src/armnn/InternalTypes.cpp
+++ b/src/armnn/InternalTypes.cpp
@@ -55,6 +55,7 @@ char const* GetLayerTypeAsCString(LayerType type)
         case LayerType::Softmax: return "Softmax";
         case LayerType::SpaceToBatchNd: return "SpaceToBatchNd";
         case LayerType::Splitter: return "Splitter";
+        case LayerType::Stack: return "Stack";
         case LayerType::StridedSlice: return "StridedSlice";
         case LayerType::Subtraction: return "Subtraction";
         case LayerType::Switch: return "Switch";
diff --git a/src/armnnTfLiteParser/TensorFlowLiteSupport.md b/src/armnnTfLiteParser/TensorFlowLiteSupport.md
index 9dd68a3372..8a8b7bed6d 100644
--- a/src/armnnTfLiteParser/TensorFlowLiteSupport.md
+++ b/src/armnnTfLiteParser/TensorFlowLiteSupport.md
@@ -32,6 +32,8 @@ The Arm NN SDK TensorFlow Lite parser currently supports the following operators
 
 * MUL
 
+* PACK
+
 * PAD
 
 * RELU
diff --git a/src/armnnTfLiteParser/TfLiteParser.cpp b/src/armnnTfLiteParser/TfLiteParser.cpp
index 9ee327933a..21c17155b5 100644
--- a/src/armnnTfLiteParser/TfLiteParser.cpp
+++ b/src/armnnTfLiteParser/TfLiteParser.cpp
@@ -455,6 +455,7 @@ TfLiteParser::TfLiteParser()
     m_ParserFunctions[tflite::BuiltinOperator_ADD]               =  &TfLiteParser::ParseAdd;
     m_ParserFunctions[tflite::BuiltinOperator_MUL]               =  &TfLiteParser::ParseMul;
     m_ParserFunctions[tflite::BuiltinOperator_MEAN]              =  &TfLiteParser::ParseMean;
+    m_ParserFunctions[tflite::BuiltinOperator_PACK]              =  &TfLiteParser::ParsePack;
     m_ParserFunctions[tflite::BuiltinOperator_PAD]               =  &TfLiteParser::ParsePad;
     m_ParserFunctions[tflite::BuiltinOperator_SPLIT]             =  &TfLiteParser::ParseSplit;
     m_ParserFunctions[tflite::BuiltinOperator_TANH]              =  &TfLiteParser::ParseTanH;
@@ -1906,6 +1907,46 @@ void TfLiteParser::ParseDetectionPostProcess(size_t subgraphIndex, size_t operat
                                                               outputTensorIndexes[3]});
 }
 
+/// The TfLite Pack operator is equivalent to the ArmNN Stack operator
+void TfLiteParser::ParsePack(size_t subgraphIndex, size_t operatorIndex)
+{
+    CHECK_MODEL(m_Model, subgraphIndex, operatorIndex);
+
+    auto inputs = GetInputs(m_Model, subgraphIndex, operatorIndex);
+    auto outputs = GetOutputs(m_Model, subgraphIndex, operatorIndex);
+    CHECK_VALID_SIZE(outputs.size(), 1);
+
+    if (inputs.size() < 1)
+    {
+        throw ParseException("Pack must have at least one input.");
+    }
+
+    const auto& operatorPtr = m_Model->subgraphs[subgraphIndex]->operators[operatorIndex];
+    const auto* options = operatorPtr->builtin_options.AsPackOptions();
+
+    StackDescriptor desc;
+    desc.m_Axis = static_cast<uint32_t>(options->axis);
+    desc.m_NumInputs = static_cast<uint32_t>(inputs.size());
+
+    // Use the tensor shape of the first input as the "correct" input shape in the descriptor
+    armnn::TensorInfo inputTensorInfo = ToTensorInfo(inputs[0]);
+    desc.m_InputShape = inputTensorInfo.GetShape();
+
+    auto layerName = boost::str(boost::format("Pack:%1%:%2%") % subgraphIndex % operatorIndex);
+    IConnectableLayer* layer = m_Network->AddStackLayer(desc, layerName.c_str());
+
+    BOOST_ASSERT(layer != nullptr);
+
+    armnn::TensorInfo outputTensorInfo = ToTensorInfo(outputs[0]);
+    layer->GetOutputSlot(0).SetTensorInfo(outputTensorInfo);
+
+    auto inputTensorIndexes = AsUnsignedVector(GetInputTensorIds(m_Model, subgraphIndex, operatorIndex));
+    RegisterInputSlots(subgraphIndex, operatorIndex, layer, {inputTensorIndexes});
+
+    auto outputTensorIndexes = AsUnsignedVector(GetOutputTensorIds(m_Model, subgraphIndex, operatorIndex));
+    RegisterOutputSlots(subgraphIndex, operatorIndex, layer, {outputTensorIndexes[0]});
+}
+
 void TfLiteParser::ParseUnpack(size_t subgraphIndex, size_t operatorIndex)
 {
     CHECK_MODEL(m_Model, subgraphIndex, operatorIndex);
diff --git a/src/armnnTfLiteParser/TfLiteParser.hpp b/src/armnnTfLiteParser/TfLiteParser.hpp
index 07a0f26590..437e459732 100644
--- a/src/armnnTfLiteParser/TfLiteParser.hpp
+++ b/src/armnnTfLiteParser/TfLiteParser.hpp
@@ -105,6 +105,7 @@ private:
     void ParseMean(size_t subgraphIndex, size_t operatorIndex);
     void ParseMinimum(size_t subgraphIndex, size_t operatorIndex);
     void ParseMul(size_t subgraphIndex, size_t operatorIndex);
+    void ParsePack(size_t subgraphIndex, size_t operatorIndex);
     void ParsePad(size_t subgraphIndex, size_t operatorIndex);
     void ParsePool(size_t subgraphIndex, size_t operatorIndex, armnn::PoolingAlgorithm algorithm);
     void ParseRelu(size_t subgraphIndex, size_t operatorIndex);
diff --git a/src/armnnTfLiteParser/test/Pack.cpp b/src/armnnTfLiteParser/test/Pack.cpp
new file mode 100644
index 0000000000..011312f7c9
--- /dev/null
+++ b/src/armnnTfLiteParser/test/Pack.cpp
@@ -0,0 +1,153 @@
+//
+// Copyright © 2017 Arm Ltd. All rights reserved.
+// SPDX-License-Identifier: MIT
+//
+
+#include <boost/test/unit_test.hpp>
+#include "ParserFlatbuffersFixture.hpp"
+#include "../TfLiteParser.hpp"
+
+#include <string>
+#include <iostream>
+
+BOOST_AUTO_TEST_SUITE(TensorflowLiteParser)
+
+struct PackFixture : public ParserFlatbuffersFixture
+{
+    explicit PackFixture(const std::string & inputShape,
+                         const unsigned int numInputs,
+                         const std::string & outputShape,
+                         const std::string & axis)
+    {
+        m_JsonString = R"(
+            {
+                "version": 3,
+                "operator_codes": [ { "builtin_code": "PACK" } ],
+                "subgraphs": [ {
+                    "tensors": [)";
+
+        for (unsigned int i = 0; i < numInputs; ++i)
+        {
+            m_JsonString += R"(
+                        {
+                            "shape": )" + inputShape + R"(,
+                            "type": "FLOAT32",
+                            "buffer": )" + std::to_string(i) + R"(,
+                            "name": "inputTensor)" + std::to_string(i + 1) + R"(",
+                            "quantization": {
+                                "min": [ 0.0 ],
+                                "max": [ 255.0 ],
+                                "scale": [ 1.0 ],
+                                "zero_point": [ 0 ],
+                            }
+                        },)";
+        }
+
+        std::string inputIndexes;
+        for (unsigned int i = 0; i < numInputs-1; ++i)
+        {
+            inputIndexes += std::to_string(i) + R"(, )";
+        }
+        inputIndexes += std::to_string(numInputs-1);
+
+        m_JsonString += R"(
+                        {
+                            "shape": )" + outputShape + R"( ,
+                            "type": "FLOAT32",
+                            "buffer": )" + std::to_string(numInputs) + R"(,
+                            "name": "outputTensor",
+                            "quantization": {
+                                "min": [ 0.0 ],
+                                "max": [ 255.0 ],
+                                "scale": [ 1.0 ],
+                                "zero_point": [ 0 ],
+                            }
+                        }
+                    ],
+                    "inputs": [ )" + inputIndexes + R"( ],
+                    "outputs": [ 2 ],
+                    "operators": [
+                        {
+                            "opcode_index": 0,
+                            "inputs": [ )" + inputIndexes + R"( ],
+                            "outputs": [ 2 ],
+                            "builtin_options_type": "PackOptions",
+                            "builtin_options": {
+                                "axis": )" + axis + R"(,
+                                "values_count": )" + std::to_string(numInputs) + R"(
+                            },
+                            "custom_options_format": "FLEXBUFFERS"
+                        }
+                    ],
+                } ],
+                "buffers" : [)";
+            
+            for (unsigned int i = 0; i < numInputs-1; ++i)
+            {
+                m_JsonString += R"(
+                    { },)";
+            }
+            m_JsonString += R"(
+                    { }
+                ]
+            })";
+        Setup();
+    }
+};
+
+struct SimplePackFixture : PackFixture
+{
+    SimplePackFixture() : PackFixture("[ 3, 2, 3 ]",
+                                      2,
+                                      "[ 3, 2, 3, 2 ]",
+                                      "3") {}
+};
+
+BOOST_FIXTURE_TEST_CASE(ParsePack, SimplePackFixture)
+{
+    RunTest<4, armnn::DataType::Float32>(
+    0,
+    { {"inputTensor1", { 1, 2, 3,
+                         4, 5, 6,
+
+                         7, 8, 9,
+                         10, 11, 12,
+
+                         13, 14, 15,
+                         16, 17, 18 } },
+    {"inputTensor2", { 19, 20, 21,
+                       22, 23, 24,
+
+                       25, 26, 27,
+                       28, 29, 30,
+
+                       31, 32, 33,
+                       34, 35, 36 } } },
+    { {"outputTensor", { 1, 19,
+                         2, 20,
+                         3, 21,
+
+                         4, 22,
+                         5, 23,
+                         6, 24,
+
+
+                         7, 25,
+                         8, 26,
+                         9, 27,
+
+                         10, 28,
+                         11, 29,
+                         12, 30,
+ 
+
+                         13, 31,
+                         14, 32,
+                         15, 33,
+
+                         16, 34,
+                         17, 35,
+                         18, 36 } } });
+}
+
+BOOST_AUTO_TEST_SUITE_END()