DEX AllReduce op (#1461)

* DEX AllReduce op

* fix conversion error

* fix clang build error

src/ngraph/runtime/cpu/CMakeLists.txt

@@ -25,6 +25,7 @@ set(SRC
     cpu_tensor_view.cpp
     cpu_tracing.cpp
     builder/add.cpp
+    builder/allreduce.cpp
     builder/avg_pool.cpp
     builder/argmin.cpp
     builder/argmax.cpp

src/ngraph/runtime/cpu/builder/allreduce.cpp

+/*******************************************************************************
+* Copyright 2018 Intel Corporation
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*******************************************************************************/
+#ifdef NGRAPH_DISTRIBUTED
+
+#include "ngraph/op/allreduce.hpp"
+#include <mpi.h>
+#include "ngraph/runtime/cpu/cpu_builder.hpp"
+
+using namespace std;
+using namespace ngraph;
+
+namespace ngraph
+{
+    namespace runtime
+    {
+        namespace cpu
+        {
+            template <>
+            void Builder::BUILDER_DECL(ngraph::op::AllReduce)
+            {
+                auto& functors = external_function->get_functors();
+
+                auto& arg_tensor = external_function->get_tensor_data(args[0].get_name());
+                auto& out_tensor = external_function->get_tensor_data(out[0].get_name());
+                auto count = static_cast<int>(out[0].get_size());
+                auto data_type = MPI_FLOAT;
+
+                if (args[0].get_element_type() == element::f32)
+                {
+                    data_type = MPI_FLOAT;
+                }
+                else if (args[0].get_element_type() == element::f64)
+                {
+                    data_type = MPI_DOUBLE;
+                }
+
+                auto functor = [&, count, data_type](CPURuntimeContext* ctx) {
+                    MPI_Allreduce(
+                        arg_tensor, out_tensor, count, data_type, MPI_SUM, MPI_COMM_WORLD);
+                };
+
+                functors.emplace_back(functor);
+            }
+
+            REGISTER_OP_BUILDER(AllReduce);
+        }
+    }
+}
+#endif