Add benchmark-clobber library (#296)

Author: tsayukov

src/library/CMakeLists.txt

@@ -1,3 +1,7 @@
+if (YDB_SDK_TESTS)
+  add_subdirectory(benchmark)
+endif()
+
 add_subdirectory(grpc/client)
 add_subdirectory(json_value)
 add_subdirectory(jwt)

src/library/benchmark/CMakeLists.txt

@@ -0,0 +1 @@
+_ydb_sdk_add_library(benchmark-clobber INTERFACE)

src/library/benchmark/clobber.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <util/system/compiler.h>
+
+namespace NBench {
+
+/**
+ * Functions that states "I can read and write everywhere in memory".
+ *
+ * Use it to prevent optimizer from reordering or discarding memory writes prior
+ * to it's call, and force memory reads after it's call.
+ */
+Y_FORCE_INLINE void Clobber() {
+#if defined(__GNUC__)
+    asm volatile(""
+                 :
+                 :
+                 : "memory");
+#elif defined(_MSC_VER)
+    _ReadWriteBarrier();
+#else
+    // Otherwise, do nothing
+#endif
+}
+
+} // namespace NBench

util/CMakeLists.txt

@@ -310,12 +310,7 @@ if (YDB_SDK_TESTS)
       system/thread_ut.cpp
 
       system/types_ut.cpp
-
-      # TODO: add library/cpp/testing/benchmark
-      #       depends only on NBench::Clobber, that's a memory optimization barrier
-      # system/unaligned_mem_ut.cpp
       system/user_ut.cpp
-
       system/yassert_ut.cpp
     LINK_LIBRARIES
       yutil
@@ -324,6 +319,19 @@ if (YDB_SDK_TESTS)
       unit
   )
 
+  add_ydb_test(NAME util-system-unaligned_mem_ut
+    WORKING_DIRECTORY
+      ${CMAKE_CURRENT_BINARY_DIR}/system
+    SOURCES
+      system/unaligned_mem_ut.cpp
+    LINK_LIBRARIES
+      yutil
+      benchmark-clobber
+      cpp-testing-unittest_main
+    LABELS
+      unit
+  )
+
   add_ydb_test(NAME util-system-fstat_ut
     WORKING_DIRECTORY
       ${CMAKE_CURRENT_BINARY_DIR}/system