Merge pull request opencv#17663 from alalek:backport_17658

Author: alalek

modules/dnn/src/dnn.cpp

@@ -3263,6 +3263,9 @@ Net Net::Impl::createNetworkFromModelOptimizer(InferenceEngine::CNNNetwork& ieNe
                 }
                 else
                 {
+#if INF_ENGINE_VER_MAJOR_GT(INF_ENGINE_RELEASE_2020_4)
+                    CV_Error(Error::StsNotImplemented, "This OpenCV version is built with Inference Engine which has dropped IR v7 support");
+#else
                     CV_TRACE_REGION("legacy_cnn_layer");
                     try
                     {
@@ -3278,6 +3281,8 @@ Net Net::Impl::createNetworkFromModelOptimizer(InferenceEngine::CNNNetwork& ieNe
                         CV_LOG_DEBUG(NULL, "IE layer extraction failure: '" << name << "' - " << e.what());
                         return false;
                     }
+#endif
+
                 }
             };
 

modules/dnn/src/op_inf_engine.hpp

@@ -26,6 +26,7 @@
 #define INF_ENGINE_RELEASE_2020_1 2020010000
 #define INF_ENGINE_RELEASE_2020_2 2020020000
 #define INF_ENGINE_RELEASE_2020_3 2020030000
+#define INF_ENGINE_RELEASE_2020_4 2020040000
 
 #ifndef INF_ENGINE_RELEASE
 #warning("IE version have not been provided via command-line. Using 2020.3 by default")