[libcxx-commits] [libcxx] [libc++] Optimize ranges::for_each for iterating over __trees (PR #164405)

[Louis Dionne via libcxx-commits]

================
@@ -44,12 +44,52 @@ int main(int argc, char** argv) {
           ->Arg(50) // non power-of-two
           ->Arg(8192);
     };
-    bm.operator()<std::vector<int>>("std::for_each(vector<int>)", std_for_each);
-    bm.operator()<std::deque<int>>("std::for_each(deque<int>)", std_for_each);
-    bm.operator()<std::list<int>>("std::for_each(list<int>)", std_for_each);
-    bm.operator()<std::vector<int>>("rng::for_each(vector<int>)", std::ranges::for_each);
-    bm.operator()<std::deque<int>>("rng::for_each(deque<int>)", std::ranges::for_each);
-    bm.operator()<std::list<int>>("rng::for_each(list<int>)", std::ranges::for_each);
+    sequence_bm.operator()<std::vector<int>>("std::for_each(vector<int>)", std_for_each);
+    sequence_bm.operator()<std::deque<int>>("std::for_each(deque<int>)", std_for_each);
+    sequence_bm.operator()<std::list<int>>("std::for_each(list<int>)", std_for_each);
+    sequence_bm.operator()<std::vector<int>>("rng::for_each(vector<int>)", std::ranges::for_each);
+    sequence_bm.operator()<std::deque<int>>("rng::for_each(deque<int>)", std::ranges::for_each);
+    sequence_bm.operator()<std::list<int>>("rng::for_each(list<int>)", std::ranges::for_each);
+
+    auto associative_bm = []<class Container>(std::type_identity<Container>, std::string name, auto for_each) {
+      benchmark::RegisterBenchmark(
+          name,
+          [for_each](auto& st) {
+            Container c;
+            for (int64_t i = 0; i != st.range(0); ++i)
+              c.insert(i);
+
+            for (auto _ : st) {
+              benchmark::DoNotOptimize(c);
+              for_each(c.begin(), c.end(), [](auto v) { benchmark::DoNotOptimize(v); });
+            }
+          })
+          ->Arg(8)
+          ->Arg(32)
+          ->Arg(50) // non power-of-two
+          ->Arg(8192);
+    };
+    associative_bm(std::type_identity<std::set<int>>{}, "rng::for_each(set<int>::iterator)", std::ranges::for_each);
----------------
ldionne wrote:

I would also do it on `std::map` and probably `std::multimap`.

https://github.com/llvm/llvm-project/pull/164405