[libcxx-commits] [libcxx] [libc++] Optimize map::insert_or_assign (PR #155816)
via libcxx-commits
libcxx-commits at lists.llvm.org
Thu Aug 28 09:10:04 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
Author: Nikolas Klauser (philnik777)
<details>
<summary>Changes</summary>
```
Zen 2:
--------------------------------------------------------------------------------------------------------
Benchmark old new
--------------------------------------------------------------------------------------------------------
std::map<int, int>::insert_or_assign(key, value) (already present)/0 1.62 ns 1.53 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/32 5.78 ns 5.99 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/1024 21.5 ns 15.4 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/8192 26.2 ns 20.5 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/0 22.5 ns 21.1 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/32 42.9 ns 28.4 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/1024 118 ns 92.0 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/8192 227 ns 173 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/0 13.2 ns 18.9 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/32 65.6 ns 39.0 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/1024 127 ns 64.4 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/8192 134 ns 71.4 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/0 45.6 ns 37.3 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/32 142 ns 93.3 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/1024 288 ns 147 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/8192 368 ns 182 ns
Apple M4:
--------------------------------------------------------------------------------------------------------
Benchmark old new
--------------------------------------------------------------------------------------------------------
std::map<int, int>::insert_or_assign(key, value) (already present)/0 0.784 ns 0.740 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/32 2.52 ns 1.77 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/1024 8.72 ns 4.06 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/8192 10.6 ns 3.98 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/0 17.3 ns 17.2 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/32 22.5 ns 19.3 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/1024 56.8 ns 33.5 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/8192 88.2 ns 41.0 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/0 16.6 ns 11.8 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/32 13.7 ns 30.7 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/1024 46.7 ns 49.1 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/8192 41.9 ns 76.9 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/0 40.0 ns 40.5 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/32 38.9 ns 40.0 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/1024 84.9 ns 96.9 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/8192 166 ns 149 ns
```
---
Full diff: https://github.com/llvm/llvm-project/pull/155816.diff
3 Files Affected:
- (modified) libcxx/docs/ReleaseNotes/22.rst (+1)
- (modified) libcxx/include/map (+10-12)
- (modified) libcxx/test/benchmarks/containers/associative/associative_container_benchmarks.h (+51)
``````````diff
diff --git a/libcxx/docs/ReleaseNotes/22.rst b/libcxx/docs/ReleaseNotes/22.rst
index 4ad5452cc29cc..cd8171dc5d1e8 100644
--- a/libcxx/docs/ReleaseNotes/22.rst
+++ b/libcxx/docs/ReleaseNotes/22.rst
@@ -57,6 +57,7 @@ Improvements and New Features
has been improved by up to 3x
- The performance of ``insert(iterator, iterator)`` of ``multimap`` and ``multiset`` has been improved by up to 2.5x
- The performance of ``erase(iterator, iterator)`` in the unordered containers has been improved by up to 1.9x
+- The performance of ``map::insert_or_assign`` has been improved by up to 2x
- ``ofstream::write`` has been optimized to pass through large strings to system calls directly instead of copying them
in chunks into a buffer.
diff --git a/libcxx/include/map b/libcxx/include/map
index b53e1c4213487..395b434fe4a5b 100644
--- a/libcxx/include/map
+++ b/libcxx/include/map
@@ -1144,22 +1144,20 @@ public:
template <class _Vp>
_LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert_or_assign(const key_type& __k, _Vp&& __v) {
- iterator __p = lower_bound(__k);
- if (__p != end() && !key_comp()(__k, __p->first)) {
- __p->second = std::forward<_Vp>(__v);
- return std::make_pair(__p, false);
- }
- return std::make_pair(emplace_hint(__p, __k, std::forward<_Vp>(__v)), true);
+ auto __result = __tree_.__emplace_unique(__k, std::forward<_Vp>(__v));
+ auto& [__iter, __inserted] = __result;
+ if (!__inserted)
+ __iter->second = std::forward<_Vp>(__v);
+ return __result;
}
template <class _Vp>
_LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert_or_assign(key_type&& __k, _Vp&& __v) {
- iterator __p = lower_bound(__k);
- if (__p != end() && !key_comp()(__k, __p->first)) {
- __p->second = std::forward<_Vp>(__v);
- return std::make_pair(__p, false);
- }
- return std::make_pair(emplace_hint(__p, std::move(__k), std::forward<_Vp>(__v)), true);
+ auto __result = __tree_.__emplace_unique(std::move(__k), std::forward<_Vp>(__v));
+ auto& [__iter, __inserted] = __result;
+ if (!__inserted)
+ __iter->second = std::forward<_Vp>(__v);
+ return __result;
}
template <class _Vp>
diff --git a/libcxx/test/benchmarks/containers/associative/associative_container_benchmarks.h b/libcxx/test/benchmarks/containers/associative/associative_container_benchmarks.h
index 535a52f0a08ab..3daa7e1843f5c 100644
--- a/libcxx/test/benchmarks/containers/associative/associative_container_benchmarks.h
+++ b/libcxx/test/benchmarks/containers/associative/associative_container_benchmarks.h
@@ -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();
+ }
+ }
+ });
+
+ bench("insert_or_assign(key, value) (new value)", [=](auto& st) {
+ const std::size_t size = st.range(0);
+ std::vector<Value> in = make_value_types(generate_unique_keys(size + 1));
+ Value to_insert = in.back();
+ in.pop_back();
+ std::vector<Container> c(BatchSize, Container(in.begin(), in.end()));
+
+ while (st.KeepRunningBatch(BatchSize)) {
+ for (std::size_t i = 0; i != BatchSize; ++i) {
+ auto result = c[i].insert_or_assign(to_insert.first, to_insert.second);
+ benchmark::DoNotOptimize(result);
+ benchmark::DoNotOptimize(c[i]);
+ benchmark::ClobberMemory();
+ }
+
+ st.PauseTiming();
+ for (std::size_t i = 0; i != BatchSize; ++i) {
+ c[i].erase(get_key(to_insert));
+ }
+ st.ResumeTiming();
+ }
+ });
+ }
+
// The insert(hint, ...) methods are only relevant for ordered containers, and we lack
// a good way to compute a hint for unordered ones.
if constexpr (is_ordered_container) {
``````````
</details>
https://github.com/llvm/llvm-project/pull/155816
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