[libcxx-commits] [libcxx] [libc++] Vectorize mismatch (PR #73255)

[Denis Yaroshevskiy via libcxx-commits]

================
@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <algorithm>
+#include <benchmark/benchmark.h>
+#include <random>
+
+template <class T>
+static void bm_mismatch(benchmark::State& state) {
+  std::vector<T> vec1(state.range(), '1');
+  std::vector<T> vec2(state.range(), '1');
+  std::mt19937_64 rng(std::random_device{}());
+
+  for (auto _ : state) {
+    auto idx  = rng() % vec1.size();
+    vec1[idx] = '2';
+    benchmark::DoNotOptimize(vec1);
+    benchmark::DoNotOptimize(std::mismatch(vec1.begin(), vec1.end(), vec2.begin()));
+    vec1[idx] = '1';
+  }
+}
+BENCHMARK(bm_mismatch<char>)->DenseRange(1, 8)->Range(16, 1 << 20);
+BENCHMARK(bm_mismatch<short>)->DenseRange(1, 8)->Range(16, 1 << 20);
+BENCHMARK(bm_mismatch<int>)->DenseRange(1, 8)->Range(16, 1 << 20);
+
+BENCHMARK_MAIN();
----------------
DenisYaroshevskiy wrote:

You want to compare against `memcmp`. For libstdc++ that is the best one. So that you'll see how far away are you.

https://github.com/llvm/llvm-project/pull/73255