Adding smart_ptr benchmark

Initial draft here:
https://reviews.llvm.org/D22470
... though this is Eric Fiselier's rewrite to fit in with Google
Benchmark.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@277373 91177308-0d34-0410-b5e6-96231b3b80d8

benchmarks/util_smartptr.bench.cpp

@@ -0,0 +1,42 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include <memory>
+
+#include "benchmark/benchmark_api.h"
+
+static void BM_SharedPtrCreateDestroy(benchmark::State& st) {
+  while (st.KeepRunning()) {
+    auto sp = std::make_shared<int>(42);
+    benchmark::DoNotOptimize(sp.get());
+  }
+}
+BENCHMARK(BM_SharedPtrCreateDestroy);
+
+static void BM_SharedPtrIncDecRef(benchmark::State& st) {
+  auto sp = std::make_shared<int>(42);
+  benchmark::DoNotOptimize(sp.get());
+  while (st.KeepRunning()) {
+    std::shared_ptr<int> sp2(sp);
+    benchmark::ClobberMemory();
+  }
+}
+BENCHMARK(BM_SharedPtrIncDecRef);
+
+static void BM_WeakPtrIncDecRef(benchmark::State& st) {
+  auto sp = std::make_shared<int>(42);
+  benchmark::DoNotOptimize(sp.get());
+  while (st.KeepRunning()) {
+    std::weak_ptr<int> wp(sp);
+    benchmark::ClobberMemory();
+  }
+}
+BENCHMARK(BM_WeakPtrIncDecRef);
+
+BENCHMARK_MAIN()