1 files changed, 87 insertions, 0 deletions
diff --git a/src/armnn/optimizations/PermuteAndBatchToSpaceAsDepthToSpace.cpp b/src/armnn/optimizations/PermuteAndBatchToSpaceAsDepthToSpace.cpp
new file mode 100644
index 0000000000..c42162b6c1
--- /dev/null
+++ b/src/armnn/optimizations/PermuteAndBatchToSpaceAsDepthToSpace.cpp
@@ -0,0 +1,87 @@
+//
+// Copyright © 2019 Arm Ltd. All rights reserved.
+// SPDX-License-Identifier: MIT
+//
+
+#include "PermuteAndBatchToSpaceAsDepthToSpace.hpp"
+
+using namespace armnn;
+using namespace armnn::optimizations;
+
+void PermuteAndBatchToSpaceAsDepthToSpaceImpl::Run(Graph& graph, InputSlot& connection) const
+{
+    // Validate base layer (the Permute) is compatible
+    Layer& base = connection.GetConnectedOutputSlot()->GetOwningLayer();
+    BOOST_ASSERT(base.GetType() == LayerType::Permute);
+    const TensorInfo& inputInfo        = base.GetInputSlot(0).GetConnection()->GetTensorInfo();
+    const TensorInfo& intermediateInfo = base.GetOutputSlot(0).GetTensorInfo();
+    if (intermediateInfo.GetNumDimensions() != 4)
+    {
+        // Must be 4D, otherwise the below checks do not make sense
+        return;
+    }
+    if (!static_cast<PermuteLayer&>(base).GetParameters().m_DimMappings.IsEqual(PermutationVector{ 3, 1, 2, 0 }))
+    {
+        // Must swap batch and channels dimensions, otherwise it is not the (original) channels dimension
+        // that is being decomposed.
+        return;
+    }
+
+    // Validate child layer (the BatchToSpace) is compatible
+    Layer& child = connection.GetOwningLayer();
+    BOOST_ASSERT(child.GetType() == LayerType::BatchToSpaceNd);
+    const TensorInfo& outputInfo                     = child.GetOutputSlot(0).GetTensorInfo();
+    const BatchToSpaceNdDescriptor& batchToSpaceDesc = static_cast<BatchToSpaceNdLayer&>(child).GetParameters();
+    if (batchToSpaceDesc.m_DataLayout != DataLayout::NHWC)
+    {
+        // The rest of this function assumes NHWC, although in future this restriction could be lifted.
+        return;
+    }
+    if (batchToSpaceDesc.m_Crops != std::vector<std::pair<unsigned int, unsigned int>>{ { 0, 0 }, { 0, 0 } })
+    {
+        // Cropping is not supported in DepthToSpace
+        return;
+    }
+    if (batchToSpaceDesc.m_BlockShape.size() != 2 ||
+        batchToSpaceDesc.m_BlockShape[0] != batchToSpaceDesc.m_BlockShape[1])
+    {
+        // Asymmetric or non-2D block sizes are not supported by DepthToSpace
+        return;
+    }
+    uint32_t blockSize = batchToSpaceDesc.m_BlockShape[0];
+    if (outputInfo.GetShape()[0] != 1 || outputInfo.GetShape()[3] != 1)
+    {
+        // The final output must have 1 batch and 1 channel because these dimensions will be swapped around
+        // once we make the substitution, and it needs to be equivalent.
+        return;
+    }
+
+    // Validate the intermediate tensor quantization params.
+    // These must be identical to either the input or output quantization params, otherwise the intermediate tensor
+    // may not have sufficient range/precision to preserve the values.
+    // This would mean that once we perform the substitution this loss of precision will no longer occur,
+    // so we would have changed the meaning of the network.
+    bool isIntermediateQuantParamsSameAsInput =
+        intermediateInfo.GetQuantizationScale() == inputInfo.GetQuantizationScale() &&
+        intermediateInfo.GetQuantizationOffset() == inputInfo.GetQuantizationOffset();
+    bool isIntermediateQuantParamsSameAsOutput =
+        intermediateInfo.GetQuantizationScale() == outputInfo.GetQuantizationScale() &&
+        intermediateInfo.GetQuantizationOffset() == outputInfo.GetQuantizationOffset();
+    if (!isIntermediateQuantParamsSameAsInput && !isIntermediateQuantParamsSameAsOutput)
+    {
+        return;
+    }
+
+    // Insert equivalent DepthToSpace layer
+    const std::string name = std::string("merged-") + base.GetName() + std::string("-with-") + child.GetName();
+
+    // Inserts equivalent reshape before base layer.
+    const DepthToSpaceDescriptor depthToSpaceDesc(blockSize, DataLayout::NHWC);
+    auto& depthToSpace = *graph.InsertNewLayer<DepthToSpaceLayer>(base.GetInputSlot(0), depthToSpaceDesc, name.c_str());
+    depthToSpace.GetOutputHandler().SetTensorInfo(outputInfo);
+
+    // Moves connections from child output to new layer.
+    // Child layer will be removed as it's left unconnected.
+    // Base layer will be removed if left unconnected.
+    child.GetOutputSlot().MoveAllConnections(depthToSpace.GetOutputSlot());
+}