[libcxx-commits] [libcxx] [libc++] Try to make vector benchmarks less dependent on surrounding benchmarks (PR #213938)
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libcxx-commits at lists.llvm.org
Tue Aug 4 07:26:47 PDT 2026
llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
Author: Nikolas Klauser (philnik777)
<details>
<summary>Changes</summary>
We're currently having the problem that clearly unrelated benchmarks sometimes change performance in significant ways. This is an attempt to mitigate that issue by aligning the functions and thus making it less likely that unrelated changes cause changes in cache behaviour.
---
Full diff: https://github.com/llvm/llvm-project/pull/213938.diff
1 Files Affected:
- (modified) libcxx/test/benchmarks/containers/sequence/sequence_container_benchmarks.h (+23-19)
``````````diff
diff --git a/libcxx/test/benchmarks/containers/sequence/sequence_container_benchmarks.h b/libcxx/test/benchmarks/containers/sequence/sequence_container_benchmarks.h
index 5210008989ff7..c3c4c7533f693 100644
--- a/libcxx/test/benchmarks/containers/sequence/sequence_container_benchmarks.h
+++ b/libcxx/test/benchmarks/containers/sequence/sequence_container_benchmarks.h
@@ -35,6 +35,9 @@ void DoNotOptimizeData(Container& c) {
}
}
+// Align benchmark functions and never inline them to reduce changes in performance in unrelated benchmarks
+#define BENCHMARK_ATTRS [[gnu::aligned(128), gnu::noinline]]
+
template <class Container>
void sequence_container_benchmarks(std::string container) {
using ValueType = typename Container::value_type;
@@ -65,7 +68,7 @@ void sequence_container_benchmarks(std::string container) {
/////////////////////////
if constexpr (std::is_constructible_v<Container, std::size_t>) {
// not all containers provide this constructor
- bench("ctor(size_type)", [](auto& st) {
+ bench("ctor(size_type)", [] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
for ([[maybe_unused]] auto _ : st) {
@@ -76,7 +79,7 @@ void sequence_container_benchmarks(std::string container) {
}
for (auto gen : generators)
- bench("ctor(size_type, const value_type&)" + tostr(gen), [gen](auto& st) {
+ bench("ctor(size_type, const value_type&)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
ValueType value = gen();
benchmark::DoNotOptimize(value);
@@ -88,7 +91,7 @@ void sequence_container_benchmarks(std::string container) {
});
for (auto gen : generators)
- bench("ctor(Iterator, Iterator)" + tostr(gen), [gen](auto& st) {
+ bench("ctor(Iterator, Iterator)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -104,7 +107,7 @@ void sequence_container_benchmarks(std::string container) {
#if defined(__cpp_lib_containers_ranges) && __cpp_lib_containers_ranges >= 202202L
for (auto gen : generators)
- bench("ctor(Range)" + tostr(gen), [gen](auto& st) {
+ bench("ctor(Range)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -118,7 +121,7 @@ void sequence_container_benchmarks(std::string container) {
#endif
for (auto gen : generators)
- bench("ctor(const Self&)" + tostr(gen), [gen](auto& st) {
+ bench("ctor(const Self&)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
Container in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -135,7 +138,7 @@ void sequence_container_benchmarks(std::string container) {
// Assignment
/////////////////////////
for (auto gen : generators)
- bench("operator=(const Self&)" + tostr(gen), [gen](auto& st) {
+ bench("operator=(const Self&)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
Container in1, in2;
std::generate_n(std::back_inserter(in1), size, gen);
@@ -161,7 +164,7 @@ void sequence_container_benchmarks(std::string container) {
// implementation basically creates a new container from scratch or manages to reuse the
// pre-existing storage.
for (auto gen : generators)
- bench("assign(input-iter, input-iter) (full container)" + tostr(gen), [gen](auto& st) {
+ bench("assign(input-iter, input-iter) (full container)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in1, in2;
std::generate_n(std::back_inserter(in1), size, gen);
@@ -185,7 +188,7 @@ void sequence_container_benchmarks(std::string container) {
// Insertion
/////////////////////////
for (auto gen : generators)
- bench("insert(begin)" + tostr(gen), [gen](auto& st) {
+ bench("insert(begin)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -207,7 +210,7 @@ void sequence_container_benchmarks(std::string container) {
if constexpr (std::random_access_iterator<typename Container::iterator>) {
for (auto gen : generators)
- bench("insert(middle)" + tostr(gen), [gen](auto& st) {
+ bench("insert(middle)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -233,7 +236,7 @@ void sequence_container_benchmarks(std::string container) {
// Insert at the start of a vector in a scenario where the vector already
// has enough capacity to hold all the elements we are inserting.
for (auto gen : generators)
- bench("insert(begin, input-iter, input-iter) (no realloc)" + tostr(gen), [gen](auto& st) {
+ bench("insert(begin, input-iter, input-iter) (no realloc)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -260,7 +263,7 @@ void sequence_container_benchmarks(std::string container) {
// has almost enough capacity to hold all the elements we are inserting,
// but does need to reallocate.
for (auto gen : generators)
- bench("insert(begin, input-iter, input-iter) (half filled)" + tostr(gen), [gen](auto& st) {
+ bench("insert(begin, input-iter, input-iter) (half filled)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -286,7 +289,7 @@ void sequence_container_benchmarks(std::string container) {
// more elements, but needs to reallocate almost immediately to fit the remaining
// elements.
for (auto gen : generators)
- bench("insert(begin, input-iter, input-iter) (near full)" + tostr(gen), [gen](auto& st) {
+ bench("insert(begin, input-iter, input-iter) (near full)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -320,7 +323,7 @@ void sequence_container_benchmarks(std::string container) {
// For containers where we can observe capacity(), push_back a single element
// without reserving to ensure the container needs to grow
for (auto gen : generators)
- bench("push_back() (growing)" + tostr(gen), [gen](auto& st) {
+ bench("push_back() (growing)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -355,7 +358,7 @@ void sequence_container_benchmarks(std::string container) {
// ensure the container doesn't grow
if constexpr (has_reserve) {
for (auto gen : generators)
- bench("push_back() (with reserve)" + tostr(gen), [gen](auto& st) {
+ bench("push_back() (with reserve)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -379,7 +382,7 @@ void sequence_container_benchmarks(std::string container) {
// push_back many elements: this is amortized constant for std::vector but not all containers
for (auto gen : generators)
- bench("push_back() (many elements)" + tostr(gen), [gen](auto& st) {
+ bench("push_back() (many elements)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -401,7 +404,7 @@ void sequence_container_benchmarks(std::string container) {
#if TEST_STD_VER >= 23
for (auto gen : generators)
- bench("append_range() (into empty container)" + tostr(gen), [gen](auto& state) {
+ bench("append_range() (into empty container)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& state) {
auto const size = state.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -428,8 +431,9 @@ void sequence_container_benchmarks(std::string container) {
if constexpr (has_prepend_range) {
for (auto gen : generators)
- bench("prepend_range() (into empty container)" + tostr(gen), [gen](auto& state) {
+ bench("prepend_range() (into empty container)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& state) {
auto const size = state.range(0);
+ BENCHMARK_ATTRS
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
DoNotOptimizeData(in);
@@ -451,7 +455,7 @@ void sequence_container_benchmarks(std::string container) {
// Erasure
/////////////////////////
for (auto gen : generators)
- bench("erase(begin)" + tostr(gen), [gen](auto& st) {
+ bench("erase(begin)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
@@ -473,7 +477,7 @@ void sequence_container_benchmarks(std::string container) {
if constexpr (std::random_access_iterator<typename Container::iterator>) {
for (auto gen : generators)
- bench("erase(middle)" + tostr(gen), [gen](auto& st) {
+ bench("erase(middle)" + tostr(gen), [gen] BENCHMARK_ATTRS(auto& st) {
auto const size = st.range(0);
std::vector<ValueType> in;
std::generate_n(std::back_inserter(in), size, gen);
``````````
</details>
https://github.com/llvm/llvm-project/pull/213938
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