[libcxx/variant] Add a few benchmarks for `std::visit`.
This patch adds a few `std::visit` benchmarks as a starting point.
Reviewed By: ldionne, #libc
Differential Revision: https://reviews.llvm.org/D85419
Cr-Mirrored-From: https://chromium.googlesource.com/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: c6f51377e12b343ca2f712b6af6908555f07ad04
diff --git a/benchmarks/VariantBenchmarks.h b/benchmarks/VariantBenchmarks.h
new file mode 100644
index 0000000..2feaeab
--- /dev/null
+++ b/benchmarks/VariantBenchmarks.h
@@ -0,0 +1,58 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef BENCHMARK_VARIANT_BENCHMARKS_H
+#define BENCHMARK_VARIANT_BENCHMARKS_H
+
+#include <array>
+#include <cstddef>
+#include <tuple>
+#include <type_traits>
+#include <variant>
+
+#include "benchmark/benchmark.h"
+
+#include "GenerateInput.h"
+
+namespace VariantBenchmarks {
+
+template <std::size_t I>
+struct S {
+ static constexpr size_t v = I;
+};
+
+template <std::size_t N, std::size_t... Is>
+static auto genVariants(std::index_sequence<Is...>) {
+ using V = std::variant<S<Is>...>;
+ using F = V (*)();
+ static constexpr F fs[] = {[] { return V(std::in_place_index<Is>); }...};
+
+ std::array<V, N> result = {};
+ for (auto& v : result) {
+ v = fs[getRandomInteger(0ul, sizeof...(Is) - 1)]();
+ }
+
+ return result;
+}
+
+template <std::size_t N, std::size_t Alts>
+static void BM_Visit(benchmark::State& state) {
+ auto args = genVariants<N>(std::make_index_sequence<Alts>{});
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(std::apply(
+ [](auto... vs) {
+ return std::visit([](auto... is) { return (is.v + ... + 0); }, vs...);
+ },
+ args));
+ }
+}
+
+} // end namespace VariantBenchmarks
+
+#endif // BENCHMARK_VARIANT_BENCHMARKS_H