libstdc++: Add performance test for atomic_flag [PR 46447]

This adds a test to compare the performance of std::atomic_flag with
similar operations on std::atomic_uchar and std::atomic_int.

libstdc++-v3/ChangeLog:

	PR libstdc++/46447
	* testsuite/performance/29_atomics/atomic_flag.cc: New test.

1 files changed, 71 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/performance/29_atomics/atomic_flag.cc b/libstdc++-v3/testsuite/performance/29_atomics/atomic_flag.cc
new file mode 100644
index 0000000..af1a269
--- /dev/null
+++ b/libstdc++-v3/testsuite/performance/29_atomics/atomic_flag.cc
@@ -0,0 +1,71 @@
+// Copyright (C) 2009-2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+
+#include <atomic>
+#include <testsuite_performance.h>
+
+volatile std::atomic_flag af;
+volatile std::atomic_uchar ac;
+volatile std::atomic_int ai;
+
+int main()
+{
+  using namespace __gnu_test;
+  time_counter time;
+  resource_counter resource;
+
+  const int n = 100000000;
+
+  start_counters(time, resource);
+  for (int i = 0; i < n; ++i)
+    af.test_and_set();
+  stop_counters(time, resource);
+  report_performance(__FILE__, "atomic_flag::test_and_set()", time, resource);
+
+  start_counters(time, resource);
+  for (int i = 0; i < n; ++i)
+    af.clear();
+  stop_counters(time, resource);
+  report_performance(__FILE__, "atomic_flag::clear()", time, resource);
+
+  start_counters(time, resource);
+  for (int i = 0; i < n; ++i)
+    ac |= 1;
+  stop_counters(time, resource);
+  report_performance(__FILE__, "atomic_uchar::operator|=(1)", time, resource);
+
+  start_counters(time, resource);
+  for (int i = 0; i < n; ++i)
+    ac = 0;
+  stop_counters(time, resource);
+  report_performance(__FILE__, "atomic_flag::operator=(0)", time, resource);
+
+  start_counters(time, resource);
+  for (int i = 0; i < n; ++i)
+    ai |= 1;
+  stop_counters(time, resource);
+  report_performance(__FILE__, "atomic_int::operator|=(1)", time, resource);
+
+  start_counters(time, resource);
+  for (int i = 0; i < n; ++i)
+    ai = 0;
+  stop_counters(time, resource);
+  report_performance(__FILE__, "atomic_int::operator=(0)", time, resource);
+
+  return 0;
+}