fix input field -> input layer net upgrade: only convert full defs

convert inputs in legacy definitions (prototxt), but simply strip inputs
from legacy weights (caffemodel).

fix BVLC#3750

src/caffe/util/upgrade_proto.cpp

@@ -953,29 +953,35 @@ bool NetNeedsInputUpgrade(const NetParameter& net_param) {
 }
 
 void UpgradeNetInput(NetParameter* net_param) {
-  LayerParameter* layer_param = net_param->add_layer();
-  layer_param->set_name("input");
-  layer_param->set_type("Input");
-  InputParameter* input_param = layer_param->mutable_input_param();
+  // Collect inputs and convert to Input layer definitions.
+  // If the NetParameter holds an input alone, without shape/dim, then
+  // it's a legacy caffemodel and simply stripping the input field is enough.
   bool has_shape = net_param->input_shape_size() > 0;
-  // Convert input fields into a layer.
-  for (int i = 0; i < net_param->input_size(); ++i) {
-    layer_param->add_top(net_param->input(i));
-    if (has_shape) {
-      input_param->add_shape()->CopyFrom(net_param->input_shape(i));
-    } else {
-      // Turn legacy input dimensions into shape.
-      BlobShape* shape = input_param->add_shape();
-      int first_dim = i*4;
-      int last_dim = first_dim + 4;
-      for (int j = first_dim; j < last_dim; j++) {
-        shape->add_dim(net_param->input_dim(j));
+  bool has_dim = net_param->input_dim_size() > 0;
+  if (has_shape || has_dim) {
+    LayerParameter* layer_param = net_param->add_layer();
+    layer_param->set_name("input");
+    layer_param->set_type("Input");
+    InputParameter* input_param = layer_param->mutable_input_param();
+    // Convert input fields into a layer.
+    for (int i = 0; i < net_param->input_size(); ++i) {
+      layer_param->add_top(net_param->input(i));
+      if (has_shape) {
+        input_param->add_shape()->CopyFrom(net_param->input_shape(i));
+      } else {
+        // Turn legacy input dimensions into shape.
+        BlobShape* shape = input_param->add_shape();
+        int first_dim = i*4;
+        int last_dim = first_dim + 4;
+        for (int j = first_dim; j < last_dim; j++) {
+          shape->add_dim(net_param->input_dim(j));
+        }
       }
     }
-  }
-  // Swap input layer to beginning of net to satisfy layer dependencies.
-  for (int i = net_param->layer_size() - 1; i > 0; --i) {
-    net_param->mutable_layer(i-1)->Swap(net_param->mutable_layer(i));
+    // Swap input layer to beginning of net to satisfy layer dependencies.
+    for (int i = net_param->layer_size() - 1; i > 0; --i) {
+      net_param->mutable_layer(i-1)->Swap(net_param->mutable_layer(i));
+    }
   }
   // Clear inputs.
   net_param->clear_input();