[libcxx-commits] [libcxx] [libc++] fix minor performance issue in `basic_string<C>::append()` (PR #210078)

[Nikolas Klauser via libcxx-commits]

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@@ -482,6 +483,41 @@ int main(int argc, char** argv) {
           std::bind_front(bench_impl, std::integral_constant<size_t, large_size>{}, std::false_type{}));
   }
 
+  {
+    static auto bench_impl =
+        []<size_t size, bool opaque, class CharT>(
+            std::integral_constant<size_t, size>,
+            std::bool_constant<opaque>,
+            std::type_identity<CharT>,
+            benchmark::State& state) {
+          std::basic_string<CharT> src(size, 'a');
+          auto getIterator = [&src](size_t i) {
+            // INT_MAX because we want overhead of ThrowingIterator without actually throwing
+            return ThrowingIterator<CharT>(src.data() + i, src.data() + src.size(), INT_MAX);
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philnik777 wrote:

The compiler can simply remove the loop if it can prove that it has no side-effects, which is definitely the case for our `forward_iterator`, and even for more complicated ones like `map::iterator`: https://godbolt.org/z/4hdTnbsPd

https://github.com/llvm/llvm-project/pull/210078