[libcxx-commits] [libcxx] [libc++] Optimize map::insert_or_assign (PR #155816)

[Louis Dionne via libcxx-commits]

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@@ -259,6 +259,57 @@ void associative_container_benchmarks(std::string container) {
     }
   });
 
+  if constexpr (is_map_like && !is_multi_key_container) {
+    bench("insert_or_assign(key, value) (already present)", [=](auto& st) {
+      const std::size_t size = st.range(0) ? st.range(0) : 1;
+      std::vector<Value> in  = make_value_types(generate_unique_keys(size));
+      Value to_insert        = in[in.size() / 2]; // pick any existing value
+      std::vector<Container> c(BatchSize, Container(in.begin(), in.end()));
+      typename Container::iterator inserted[BatchSize];
+
+      while (st.KeepRunningBatch(BatchSize)) {
+        for (std::size_t i = 0; i != BatchSize; ++i) {
+          inserted[i] =
+              adapt_operations<Container>::get_iterator(c[i].insert_or_assign(to_insert.first, to_insert.second));
+          benchmark::DoNotOptimize(inserted[i]);
+          benchmark::DoNotOptimize(c[i]);
+          benchmark::ClobberMemory();
+        }
+
+        if constexpr (is_multi_key_container) {
+          st.PauseTiming();
+          for (std::size_t i = 0; i != BatchSize; ++i) {
+            c[i].erase(inserted[i]);
+          }
+          st.ResumeTiming();
+        }
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ldionne wrote:

This is always false.
```suggestion

```

https://github.com/llvm/llvm-project/pull/155816