[libc++] Add a benchmark for std::reverse (llvm#125262)

Author: ldionne

libcxx/test/benchmarks/algorithms/reverse.bench.cpp

@@ -0,0 +1,48 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+#include <algorithm>
+#include <iterator>
+#include <string>
+#include <vector>
+
+#include <benchmark/benchmark.h>
+#include "../GenerateInput.h"
+
+template <class T>
+static void bm_reverse(benchmark::State& state) {
+  std::size_t const n = state.range();
+  std::vector<T> vec;
+  std::generate_n(std::back_inserter(vec), n, [] { return Generate<T>::cheap(); });
+  for (auto _ : state) {
+    std::reverse(vec.begin(), vec.end());
+    benchmark::DoNotOptimize(vec);
+  }
+}
+BENCHMARK(bm_reverse<int>)->Name("std::reverse(vector<int>)")->DenseRange(1, 8)->Range(16, 1 << 20);
+BENCHMARK(bm_reverse<std::string>)->Name("std::reverse(vector<string>)")->DenseRange(1, 8)->Range(16, 1 << 20);
+
+template <class T>
+static void bm_ranges_reverse(benchmark::State& state) {
+  std::size_t const n = state.range();
+  std::vector<T> vec;
+  std::generate_n(std::back_inserter(vec), n, [] { return Generate<T>::cheap(); });
+  for (auto _ : state) {
+    std::ranges::reverse(vec.begin(), vec.end());
+    benchmark::DoNotOptimize(vec);
+  }
+}
+BENCHMARK(bm_ranges_reverse<int>)->Name("ranges::reverse(vector<int>)")->DenseRange(1, 8)->Range(16, 1 << 20);
+BENCHMARK(bm_ranges_reverse<std::string>)
+    ->Name("ranges::reverse(vector<string>)")
+    ->DenseRange(1, 8)
+    ->Range(16, 1 << 20);
+
+BENCHMARK_MAIN();