IVGCVSW-2458 Refactor the Optimize function (Network.cpp) so that

subgraphs are optimized by the backends

 * Added a new method OptimizeSubGraph to the backend interface
 * Refactored the Optimize function so that the backend-specific
   optimization is performed by the backend itself (through the new
   OptimizeSubGraph interface method)
 * Added a new ApplyBackendOptimizations function to apply the new
   changes
 * Added some new convenient constructors to the SubGraph class
 * Added AddLayer method and a pointer to the parent graph to the
   SubGraph class
 * Updated the sub-graph unit tests to match the changes
 * Added SelectSubGraphs and ReplaceSubGraphConnections overloads
   that work with sub-graphs
 * Removed unused code and minor refactoring where necessary

Change-Id: I46181794c6a9e3b10558944f804e06a8f693a6d0

1 files changed, 21 insertions, 16 deletions

diff --git a/src/armnn/SubGraphSelector.cpp b/src/armnn/SubGraphSelector.cpp
index d0542fd41f..4abf01c88f 100644
--- a/src/armnn/SubGraphSelector.cpp
+++ b/src/armnn/SubGraphSelector.cpp
@@ -69,25 +69,25 @@ struct LayerSelectionInfo
         return m_Layer->GetType() == armnn::LayerType::Input;
     }
 
-    void CollectNonSelectedInputs(SubGraph::InputSlots& slots,
+    void CollectNonSelectedInputs(SubGraph::InputSlots& inputSlots,
                                   const SubGraphSelector::LayerSelectorFunction& selector)
     {
         for (auto&& slot = m_Layer->BeginInputSlots(); slot != m_Layer->EndInputSlots(); ++slot)
         {
             OutputSlot* parentLayerOutputSlot = slot->GetConnectedOutputSlot();
-            BOOST_ASSERT_MSG(parentLayerOutputSlot != nullptr, "The slots must be connected here.");
+            BOOST_ASSERT_MSG(parentLayerOutputSlot != nullptr, "The input slots must be connected here.");
             if (parentLayerOutputSlot)
             {
                 Layer& parentLayer = parentLayerOutputSlot->GetOwningLayer();
                 if (selector(parentLayer) == false)
                 {
-                    slots.push_back(&(*slot));
+                    inputSlots.push_back(&(*slot));
                 }
             }
         }
     }
 
-    void CollectNonSelectedOutputSlots(SubGraph::OutputSlots& slots,
+    void CollectNonSelectedOutputSlots(SubGraph::OutputSlots& outputSlots,
                                        const SubGraphSelector::LayerSelectorFunction& selector)
     {
         for (auto&& slot = m_Layer->BeginOutputSlots(); slot != m_Layer->EndOutputSlots(); ++slot)
@@ -97,7 +97,7 @@ struct LayerSelectionInfo
                 Layer& childLayer = childLayerInputSlot->GetOwningLayer();
                 if (selector(childLayer) == false)
                 {
-                    slots.push_back(&(*slot));
+                    outputSlots.push_back(&(*slot));
                 }
             }
         }
@@ -112,12 +112,18 @@ struct LayerSelectionInfo
 } // namespace <anonymous>
 
 SubGraphSelector::SubGraphs
-SubGraphSelector::SelectSubGraphs(Graph& graph,
-                                  const LayerSelectorFunction& selector)
+SubGraphSelector::SelectSubGraphs(Graph& graph, const LayerSelectorFunction& selector)
+{
+    SubGraph subGraph(graph);
+    return SubGraphSelector::SelectSubGraphs(subGraph, selector);
+}
+
+SubGraphSelector::SubGraphs
+SubGraphSelector::SelectSubGraphs(SubGraph& subGraph, const LayerSelectorFunction& selector)
 {
     LayerSelectionInfo::LayerInfoContainer layerInfo;
 
-    for (auto& layer : graph)
+    for (auto& layer : subGraph)
     {
         layerInfo.emplace(layer, LayerSelectionInfo{layer, selector});
     }
@@ -127,7 +133,7 @@ SubGraphSelector::SelectSubGraphs(Graph& graph,
     {
         if (info.second.IsInputLayer())
         {
-            // for each input layer we mark the graph where subgraph
+            // For each input layer we mark the graph where subgraph
             // splits need to happen because of the dependency between
             // the selected and non-selected nodes
             info.second.MarkChildrenSplits(layerInfo, splitNo, false);
@@ -159,20 +165,19 @@ SubGraphSelector::SelectSubGraphs(Graph& graph,
     {
         if (splitGraph.second.empty() == false)
         {
-            SubGraph::OutputSlots outputs;
             SubGraph::InputSlots inputs;
+            SubGraph::OutputSlots outputs;
             SubGraph::Layers layers;
             for (auto&& infoPtr : splitGraph.second)
             {
-                infoPtr->CollectNonSelectedOutputSlots(outputs, selector);
                 infoPtr->CollectNonSelectedInputs(inputs, selector);
+                infoPtr->CollectNonSelectedOutputSlots(outputs, selector);
                 layers.push_back(infoPtr->m_Layer);
             }
-            result.emplace_back(
-                std::make_unique<SubGraph>(
-                    std::move(inputs),
-                    std::move(outputs),
-                    std::move(layers)));
+            result.emplace_back(std::make_unique<SubGraph>(subGraph,
+                                                           std::move(inputs),
+                                                           std::move(outputs),
+                                                           std::move(layers)));
         }
     }