revert timer changes

tools/timer/SysTimer_windows.cpp

Index: tools/timer/SysTimer_windows.cpp
diff --git a/tools/timer/SysTimer_windows.cpp b/tools/timer/SysTimer_windows.cpp
index d24a6aae71bbf9a9353ae0fb3fed6cbc74338188..2f9d0a5d58ec7f53cf71ee2104f45383ff6a2406 100644
--- a/tools/timer/SysTimer_windows.cpp
+++ b/tools/timer/SysTimer_windows.cpp
@@ -6,8 +6,6 @@
  */
 #include "SysTimer_windows.h"
 
-#include <intrin.h>
-
 static ULONGLONG win_cpu_time() {
     FILETIME createTime;
     FILETIME exitTime;
@@ -25,6 +23,11 @@ static ULONGLONG win_cpu_time() {
     return start_cpu_sys.QuadPart + start_cpu_usr.QuadPart;
 }
 
+void SysTimer::startWall() {
+    if (0 == ::QueryPerformanceCounter(&fStartWall)) {
+        fStartWall.QuadPart = 0;
+    }
+}
 void SysTimer::startCpu() {
     fStartCpu = win_cpu_time();
 }
@@ -33,22 +36,11 @@ double SysTimer::endCpu() {
     ULONGLONG end_cpu = win_cpu_time();
     return static_cast<double>(end_cpu - fStartCpu) / 10000.0L;
 }
-
-static void wall_timestamp(LARGE_INTEGER* now) {
-    _ReadWriteBarrier();
-    if (0 == ::QueryPerformanceCounter(now)) {
-        now->QuadPart = 0;
-    }
-    _ReadWriteBarrier();
-}
-
-void SysTimer::startWall() {
-    wall_timestamp(&fStartWall);
-}
-
 double SysTimer::endWall() {
     LARGE_INTEGER end_wall;
-    wall_timestamp(&end_wall);
+    if (0 == ::QueryPerformanceCounter(&end_wall)) {
+        end_wall.QuadPart = 0;
+    }
 
     LARGE_INTEGER ticks_elapsed;
     ticks_elapsed.QuadPart = end_wall.QuadPart - fStartWall.QuadPart;