Fold PAD into Pooling2d

Some models would add a PAD layer before a pooling when they can't
express their padding configuration as SAME or VALID.

Arm NN can merge the two because pooling layers are described with
explicit padding.

Signed-off-by: Diego Lopez Recas <diego.lopez.recas@gmail.com>
Change-Id: Id048186db6a005e0257bfbc1406c3b0dab2cdd58

1 files changed, 117 insertions, 0 deletions

diff --git a/src/armnn/optimizations/FoldPadIntoLayer2d.hpp b/src/armnn/optimizations/FoldPadIntoLayer2d.hpp
new file mode 100644
index 0000000000..cadc2f3017
--- /dev/null
+++ b/src/armnn/optimizations/FoldPadIntoLayer2d.hpp
@@ -0,0 +1,117 @@
+//
+// Copyright © 2017 Arm Ltd. All rights reserved.
+// SPDX-License-Identifier: MIT
+//
+
+#pragma once
+
+#include "Optimization.hpp"
+
+#include <armnn/utility/PolymorphicDowncast.hpp>
+
+namespace armnn
+{
+namespace optimizations
+{
+namespace
+{
+template <typename Layer2dT>
+Layer2dT* FoldPadIntoLayer2dImpl(Graph& graph, InputSlot& connection)
+{
+    Layer& base = connection.GetConnectedOutputSlot()->GetOwningLayer();
+    Layer& child = connection.GetOwningLayer();
+
+    ARMNN_ASSERT(base.GetType() == LayerType::Pad);
+    ARMNN_ASSERT(child.GetType() == LayerEnumOf<Layer2dT>());
+
+    PadLayer* padLayer = PolymorphicDowncast<PadLayer*>(&base);
+    Layer2dT* layer2d = PolymorphicDowncast<Layer2dT*>(&child);
+
+    OutputSlot* parentOut = base.GetInputSlot(0).GetConnectedOutputSlot();
+
+    const std::string name = std::string("folded-") + base.GetName() + std::string("-into-") + child.GetName();
+    auto descriptor = layer2d->GetParameters();
+
+    auto padList = padLayer->GetParameters().m_PadList;
+
+    armnn::DataLayout dataLayout = descriptor.m_DataLayout;
+
+    // In Convolution2dDescriptor/Pooling2dDescriptor, padLeft and padRight are defined as paddings
+    // on width dimension whereas padTop and padBottom - paddings on height dimension, so setting these
+    // according to data layout
+    if(dataLayout == armnn::DataLayout::NHWC)
+    {
+        descriptor.m_PadLeft = padList[2].first;
+        descriptor.m_PadRight = padList[2].second;
+        descriptor.m_PadTop = padList[1].first;
+        descriptor.m_PadBottom = padList[1].second;
+    }
+    else
+    {
+        descriptor.m_PadLeft = padList[3].first;
+        descriptor.m_PadRight = padList[3].second;
+        descriptor.m_PadTop = padList[2].first;
+        descriptor.m_PadBottom = padList[2].second;
+    }
+
+    const auto newLayer2d = graph.InsertNewLayer<Layer2dT>(base.GetInputSlot(0), descriptor, name.c_str());
+
+    // Reconnects with original parent.
+    newLayer2d->GetOutputSlot().MoveAllConnections(*parentOut);
+    // Parent is now the new layer.
+    parentOut = &newLayer2d->GetOutputSlot();
+
+    // Moves connections in child output to parent layer.
+    // Child layer will be removed as it's left unconnected.
+    // Base layer will be removed if left unconnected.
+    child.GetOutputSlot().MoveAllConnections(*parentOut);
+
+    return newLayer2d;
+}
+} // namespace
+
+class FoldPadIntoConvolution2dImpl
+{
+public:
+    void Run(Graph& graph, InputSlot& connection) const
+    {
+        const auto conv2dLayer = PolymorphicDowncast<Convolution2dLayer*>(&connection.GetOwningLayer());
+        const auto newConv2dLayer = FoldPadIntoLayer2dImpl<Convolution2dLayer>(graph, connection);
+
+        // Copy weights and bias to the new convolution layer
+        ARMNN_ASSERT_MSG(conv2dLayer->m_Weight != nullptr,
+                         "FoldPadIntoConvolution2d: Weights data should not be null.");
+        newConv2dLayer->m_Weight = std::move(conv2dLayer->m_Weight);
+        if (conv2dLayer->GetParameters().m_BiasEnabled)
+        {
+            ARMNN_ASSERT_MSG(conv2dLayer->m_Bias != nullptr,
+                             "FoldPadIntoConvolution2d: Bias data should not be null if bias is enabled.");
+            newConv2dLayer->m_Bias = std::move(conv2dLayer->m_Bias);
+        }
+    }
+
+protected:
+    FoldPadIntoConvolution2dImpl() =  default;
+    ~FoldPadIntoConvolution2dImpl() = default;
+};
+
+class FoldPadIntoPooling2dImpl
+{
+public:
+    void Run(Graph& graph, InputSlot& connection) const
+    {
+        FoldPadIntoLayer2dImpl<Pooling2dLayer>(graph, connection);
+    }
+
+protected:
+    FoldPadIntoPooling2dImpl() =  default;
+    ~FoldPadIntoPooling2dImpl() = default;
+};
+
+using FoldPadIntoConvolution2d = OptimizeForConnection<PadLayer, Convolution2dLayer, FoldPadIntoConvolution2dImpl>;
+using FoldPadIntoPooling2d = OptimizeForConnection<PadLayer, Pooling2dLayer, FoldPadIntoPooling2dImpl>;
+
+} // namespace optimizations
+} // namespace armnn
+
+