Merge pull request tensorflow#3423 from Mistobaan/remove-warnings

Fix few warnings on macosx-clang compilation

Author: yifeif

tensorflow/core/common_runtime/optimization_registry.h

@@ -27,7 +27,7 @@ limitations under the License.
 #include "tensorflow/core/graph/graph.h"
 
 namespace tensorflow {
-class SessionOptions;
+struct SessionOptions;
 
 // All the parameters used by an optimization pass are packaged in
 // this struct. They should be enough for the optimization pass to use

tensorflow/core/common_runtime/simple_graph_execution_state.h

@@ -35,7 +35,7 @@ limitations under the License.
 #include "tensorflow/core/platform/types.h"
 
 namespace tensorflow {
-class SessionOptions;
+struct SessionOptions;
 class StepStats;
 class Timeline;
 

tensorflow/core/graph/gradients.cc

@@ -35,8 +35,6 @@ namespace tensorflow {
 // TODO(andydavis) Remove some of the code duplicated between this module
 // and that in 'common_runtime/function.cc'.
 // A few string constant used throughout this module.
-static const char* const kArgOp = "_Arg";
-static const char* const kRetOp = "_Retval";
 static const char* const kGradientOp = "SymbolicGradient";
 static const char* const kNodeLabel = "Func";
 

tensorflow/core/graph/graph.cc

@@ -29,9 +29,6 @@ namespace tensorflow {
 // Node
 
 string Node::DebugString() const {
-  if (this == nullptr) {
-    return "{nullptr}";
-  }
   string ret = strings::StrCat("{name:'", name(), "' id:", id_);
   if (IsSource()) {
     strings::StrAppend(&ret, " source}");

tensorflow/core/kernels/lookup_table_init_op.cc

@@ -80,7 +80,7 @@ class KeyValueTensorIterator
 
   Status status() const override { return status_; }
 
-  int64 total_size() const {
+  int64 total_size() const override {
     return keys_ == nullptr ? -1 : keys_->NumElements();
   }