CPU: Eliminate trivial sum reductions (#703)

src/ngraph/runtime/cpu/pass/cpu_nop_elimination.cpp

@@ -22,6 +22,7 @@
 
 #include "cpu_nop_elimination.hpp"
 #include "ngraph/ops/pad.hpp"
+#include "ngraph/ops/sum.hpp"
 
 #define TI(x) std::type_index(typeid(x))
 
@@ -40,10 +41,21 @@ HANDLER_DECL(eliminate_pad)
     return false;
 }
 
+HANDLER_DECL(eliminate_sum)
+{
+    auto sum = std::dynamic_pointer_cast<ngraph::op::Sum>(node);
+    if (sum->get_reduction_axes().empty())
+    {
+        function->replace_node(node, node->get_input_op(0));
+        return true;
+    }
+    return false;
+}
+
 static const std::unordered_map<std::type_index,
                                 std::function<bool(const std::shared_ptr<ngraph::Function>&,
                                                    const std::shared_ptr<ngraph::Node>&)>>
-    dispatcher{{TI(ngraph::op::Pad), &eliminate_pad}};
+    dispatcher{{TI(ngraph::op::Pad), &eliminate_pad}, {TI(ngraph::op::Sum), &eliminate_sum}};
 
 bool ngraph::runtime::cpu::pass::CPUNopElimination::run_on_function(
     std::shared_ptr<ngraph::Function> function)