IVGCVSW-3088 Update the backends README file

 * Updated the src/backends/README.md file with details on the new
   OptimizeSubgraphView method
 * Added section describing the new OptimizationViews class
 * Deprecated GetOptimizations in the code

Change-Id: Icb1a9aa015394e56fb4b5120b0645a752f44134e
Signed-off-by: Matteo Martincigh <matteo.martincigh@arm.com>

3 files changed, 31 insertions, 13 deletions

diff --git a/src/armnn/Network.cpp b/src/armnn/Network.cpp
index 956d2a4bde..b80e0e7eec 100644
--- a/src/armnn/Network.cpp
+++ b/src/armnn/Network.cpp
@@ -523,7 +523,10 @@ IOptimizedNetworkPtr Optimize(const INetwork& inNetwork,
         auto backendPtr = factoryFun();
         BOOST_ASSERT(backendPtr.get() != nullptr);
 
+        ARMNN_NO_DEPRECATE_WARN_BEGIN
         auto backendSpecificOptimizations = backendPtr->GetOptimizations();
+        ARMNN_NO_DEPRECATE_WARN_END
+
         if (!backendSpecificOptimizations.empty())
         {
             Optimizer::Pass(optNetObjPtr->GetGraph(), backendSpecificOptimizations);
diff --git a/src/backends/README.md b/src/backends/README.md
index 90eeed2968..7cd7431117 100644
--- a/src/backends/README.md
+++ b/src/backends/README.md
@@ -114,13 +114,16 @@ The interface functions to be implemented are:
     virtual IWorkloadFactoryPtr CreateWorkloadFactory(
             const IMemoryManagerSharedPtr& memoryManager = nullptr) const = 0;
     virtual IBackendContextPtr CreateBackendContext(const IRuntime::CreationOptions&) const = 0;
-    virtual Optimizations GetOptimizations() const = 0;
     virtual ILayerSupportSharedPtr GetLayerSupport() const = 0;
-    virtual SubgraphUniquePtr OptimizeSubgraph(const SubgraphView& subgraph, bool& optimizationAttempted) const = 0;
+    virtual Optimizations GetOptimizations() const = 0;
+    virtual SubgraphUniquePtr OptimizeSubgraph(const SubgraphView& subgraph, bool& optimizationAttempted) const;
+    virtual OptimizationViews OptimizeSubgraphView(const SubgraphView& subgraph) const;
 ```
 
-Note that ```GetOptimizations()``` has been deprecated.
-The method ```OptimizeSubgraph(...)``` should be used instead to specific optimizations to a given sub-graph.
+Note that ```GetOptimizations()``` and ```SubgraphViewUniquePtr OptimizeSubgraphView(const SubgraphView& subgraph, bool& optimizationAttempted)```
+have been deprecated.
+The method ```OptimizationViews OptimizeSubgraph(const SubgraphView& subgraph)``` should be used instead to
+apply specific optimizations to a given sub-graph.
 
 The ArmNN framework then creates instances of the IBackendInternal interface with the help of the
 [BackendRegistry](backendsCommon/BackendRegistry.hpp) singleton.
@@ -136,10 +139,11 @@ The ArmNN framework creates the backend interfaces dynamically when
 it sees fit and it keeps these objects for a short period of time. Examples:
 
 * During optimization ArmNN needs to decide which layers are supported by the backend.
-   To do this, it creates a backends and calls the ```GetLayerSupport()``` function and creates
-   an ```ILayerSupport``` object to help deciding this.
-* During optimization ArmNN can run backend-specific optimizations. It creates backend objects
-  and calls the ```GetOptimizations()``` function and it runs them on the network.
+  To do this, it creates a backends and calls the ```GetLayerSupport()``` function and creates
+  an ```ILayerSupport``` object to help deciding this.
+* During optimization ArmNN can run backend-specific optimizations. After splitting the graph into
+  sub-graphs based on backends, it calls the ```OptimizeSubgraphView()``` function on each of them and, if possible,
+  substitutes the corresponding sub-graph in the original graph with its optimized version.
 * When the Runtime is initialized it creates an optional ```IBackendContext``` object and keeps this context alive
   for the Runtime's lifetime. It notifies this context object before and after a network is loaded or unloaded.
 * When the LoadedNetwork creates the backend-specific workloads for the layers, it creates a backend
@@ -191,10 +195,19 @@ mechanism:
 ## The Optimizations
 
 The backends may choose to implement backend-specific optimizations.
-This is supported through the method ```OptimizeSubgraph(...)``` to the backend interface
-that allows the backends to apply their specific optimizations to a given sub-grah.
-
-The way backends had to provide a list optimizations to the Optimizer (through the ```GetOptimizations()``` method)
+This is supported through the method ```OptimizationViews OptimizeSubgraph(const SubgraphView& subgraph)``` of
+the backend interface that allows the backends to apply their specific optimizations to a given sub-graph.
+
+The ```OptimizeSubgraph(...)``` method returns an OptimizationViews object containing three lists:
+* A list of the sub-graph substitutions: a "substitution" is a pair of sub-graphs, the first is the "substitutable" sub-graph,
+  representing the part of the original graph that has been optimized by the backend, while the second is the "replacement" sub-graph,
+  containing the actual optimized layers that will be replaced in the original graph correspondingly to the "substitutable" sub-graph
+* A list of the failed sub-graphs: these are the parts of the original sub-graph that are not supported by the backend,
+  thus have been rejected. ArmNN will try to re-allocate these parts on other backends if available.
+* A list of the untouched sub-graphs: these are the parts of the original sub-graph that have not been optimized,
+  but that can run (unoptimized) on the backend.
+
+The previous way backends had to provide a list optimizations to the Optimizer (through the ```GetOptimizations()``` method)
 is still in place for backward compatibility, but it's now considered deprecated and will be remove in a future release.
 
 ## The IBackendContext interface
diff --git a/src/backends/backendsCommon/IBackendInternal.hpp b/src/backends/backendsCommon/IBackendInternal.hpp
index 634e2aba94..72214b891e 100644
--- a/src/backends/backendsCommon/IBackendInternal.hpp
+++ b/src/backends/backendsCommon/IBackendInternal.hpp
@@ -54,10 +54,12 @@ public:
 
     virtual IBackendContextPtr CreateBackendContext(const IRuntime::CreationOptions&) const = 0;
 
-    virtual Optimizations GetOptimizations() const = 0;
     virtual ILayerSupportSharedPtr GetLayerSupport() const = 0;
 
     ARMNN_DEPRECATED_MSG("Use \"OptimizationViews OptimizeSubgraphView(const SubgraphView&)\" instead")
+    virtual Optimizations GetOptimizations() const = 0;
+
+    ARMNN_DEPRECATED_MSG("Use \"OptimizationViews OptimizeSubgraphView(const SubgraphView&)\" instead")
     virtual SubgraphViewUniquePtr OptimizeSubgraphView(const SubgraphView& subgraph, bool& optimizationAttempted) const
     {
         optimizationAttempted = false;