--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libcxx/utils/google-benchmark/src/log.h	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,74 @@
+#ifndef BENCHMARK_LOG_H_
+#define BENCHMARK_LOG_H_
+
+#include <iostream>
+#include <ostream>
+
+#include "benchmark/benchmark.h"
+
+namespace benchmark {
+namespace internal {
+
+typedef std::basic_ostream<char>&(EndLType)(std::basic_ostream<char>&);
+
+class LogType {
+  friend LogType& GetNullLogInstance();
+  friend LogType& GetErrorLogInstance();
+
+  // FIXME: Add locking to output.
+  template <class Tp>
+  friend LogType& operator<<(LogType&, Tp const&);
+  friend LogType& operator<<(LogType&, EndLType*);
+
+ private:
+  LogType(std::ostream* out) : out_(out) {}
+  std::ostream* out_;
+  BENCHMARK_DISALLOW_COPY_AND_ASSIGN(LogType);
+};
+
+template <class Tp>
+LogType& operator<<(LogType& log, Tp const& value) {
+  if (log.out_) {
+    *log.out_ << value;
+  }
+  return log;
+}
+
+inline LogType& operator<<(LogType& log, EndLType* m) {
+  if (log.out_) {
+    *log.out_ << m;
+  }
+  return log;
+}
+
+inline int& LogLevel() {
+  static int log_level = 0;
+  return log_level;
+}
+
+inline LogType& GetNullLogInstance() {
+  static LogType log(nullptr);
+  return log;
+}
+
+inline LogType& GetErrorLogInstance() {
+  static LogType log(&std::clog);
+  return log;
+}
+
+inline LogType& GetLogInstanceForLevel(int level) {
+  if (level <= LogLevel()) {
+    return GetErrorLogInstance();
+  }
+  return GetNullLogInstance();
+}
+
+}  // end namespace internal
+}  // end namespace benchmark
+
+// clang-format off
+#define VLOG(x)                                                               \
+  (::benchmark::internal::GetLogInstanceForLevel(x) << "-- LOG(" << x << "):" \
+                                                                         " ")
+// clang-format on
+#endif