Added benchmark for expression tree creation

bench/overhead.cpp

@@ -0,0 +1,27 @@
+#include "atidlas/array.h"
+#include "atidlas/tools/timer.hpp"
+
+#include <vector>
+
+namespace ad = atidlas;
+
+int main()
+{
+  ad::array x(10, ad::FLOAT_TYPE), y(10, ad::FLOAT_TYPE), z(10, ad::FLOAT_TYPE);
+  ad::tools::timer t;
+  std::cout << "-------------------------" << std::endl;
+  std::cout << "Expression tree creation:" << std::endl;
+#define BENCH(CREATE, STR) \
+  {\
+  std::vector<int> flusher(10000000, 1);\
+  t.start();\
+  ad::array_expression tmp(CREATE);\
+  std::cout << STR << ": " << t.get() << std::endl;\
+  }
+
+  BENCH(x + y, "2 terms");
+  BENCH(x + y + x, "3 terms");
+  BENCH(x + y + x + y, "4 terms");
+  BENCH(x + y + x + y + x, "5 terms");
+  std::cout << "-------------------------" << std::endl;
+}