From Roman Zulak: Flush stdout less (cling).

lib/MetaProcessor/MetaProcessor.cpp

@@ -46,13 +46,11 @@ namespace cling {
   class MetaProcessor::RedirectOutput {
 
     static int dupOnce(int Fd, int& Bak) {
-#ifdef LLVM_ON_WIN32
-      // Possibly because Windows isn't really Posix, we need to flush
-      // now or can drop the buffer when dup2 is called with Fd later.
+      // Flush now or can drop the buffer when dup2 is called with Fd later.
       // This seems only neccessary when piping stdout or stderr, but do it
       // for ttys to avoid over complicated code for minimal benefit.
       ::fflush(Fd==STDOUT_FILENO ? stdout : stderr);
-#endif
+
       if (Bak == kInvalidFD)
         Bak = ::dup(Fd);
 

tools/driver/cling.cpp

@@ -113,5 +113,8 @@ int main( int argc, char **argv ) {
     client->BeginSourceFile(CI->getLangOpts(), &CI->getPreprocessor());
   }
 
+  // Only for test/OutputRedirect.C, but shouldn't affect performance too much.
+  ::fflush(stdout);
+  ::fflush(stderr);
   return ret;
 }