[libcxx-commits] [libcxx] [libc++] Optimize ranges::{for_each, for_each_n} for segmented iterators (PR #132896)

[Peng Liu via libcxx-commits]

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@@ -0,0 +1,76 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+#include <algorithm>
+#include <cstddef>
+#include <deque>
+#include <list>
+#include <string>
+#include <vector>
+
+#include <benchmark/benchmark.h>
+
+int main(int argc, char** argv) {
+  auto std_for_each_n = [](auto first, auto n, auto f) { return std::for_each_n(first, n, f); };
+
+  // {std,ranges}::for_each_n
+  {
+    auto bm = []<class Container>(std::string name, auto for_each_n) {
+      using ElemType = typename Container::value_type;
+      benchmark::RegisterBenchmark(
+          name,
+          [for_each_n](auto& st) {
+            std::size_t const n = st.range(0);
+            Container c(n, 1);
+            auto first = c.begin();
+
+            for ([[maybe_unused]] auto _ : st) {
+              benchmark::DoNotOptimize(c);
+              auto result = for_each_n(first, n, [](ElemType& x) { x = std::clamp<ElemType>(x, 10, 100); });
+              benchmark::DoNotOptimize(result);
+            }
+          })
+          ->Arg(8)
+          ->Arg(32)
+          ->Arg(50) // non power-of-two
+          ->Arg(1024)
+          ->Arg(4096)
+          ->Arg(8192)
+          ->Arg(1 << 14)
+          ->Arg(1 << 16)
+          ->Arg(1 << 18);
+    };
+    bm.operator()<std::vector<char>>("std::for_each_n(vector<char>)", std_for_each_n);
+    bm.operator()<std::deque<char>>("std::for_each_n(deque<char>)", std_for_each_n);
+    bm.operator()<std::list<char>>("std::for_each_n(list<char>)", std_for_each_n);
+    bm.operator()<std::vector<char>>("rng::for_each_n(vector<char>)", std::ranges::for_each_n);
+    bm.operator()<std::deque<char>>("rng::for_each_n(deque<char>)", std::ranges::for_each_n);
+    bm.operator()<std::list<char>>("rng::for_each_n(list<char>)", std::ranges::for_each_n);
+
+    bm.operator()<std::vector<short>>("std::for_each_n(vector<short>)", std_for_each_n);
+    bm.operator()<std::deque<short>>("std::for_each_n(deque<short>)", std_for_each_n);
+    bm.operator()<std::list<short>>("std::for_each_n(list<short>)", std_for_each_n);
+    bm.operator()<std::vector<short>>("rng::for_each_n(vector<short>)", std::ranges::for_each_n);
+    bm.operator()<std::deque<short>>("rng::for_each_n(deque<short>)", std::ranges::for_each_n);
+    bm.operator()<std::list<short>>("rng::for_each_n(list<short>)", std::ranges::for_each_n);
----------------
winner245 wrote:

Done.

https://github.com/llvm/llvm-project/pull/132896