[libcxx-commits] [libcxx] [libc++] Fix performance regression in std::num_put (PR #223334)
via libcxx-commits
libcxx-commits at lists.llvm.org
Tue Sep 15 02:07:10 PDT 2026
llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
Author: Nikolas Klauser (philnik777)
<details>
<summary>Changes</summary>
`__pad_and_output` calls `std::copy` and `std::fill_n` unconditionally, even though the calls are quite likely to do nothing. Adding conditions also allows the compiler to do jump-threading.
Fixes #<!-- -->178685
---
Full diff: https://github.com/llvm/llvm-project/pull/223334.diff
4 Files Affected:
- (modified) libcxx/include/__locale_dir/pad_and_output.h (+6-3)
- (modified) libcxx/include/locale (+1)
- (modified) libcxx/test/benchmarks/text/localization/num_put.bench.cpp (+38-10)
- (modified) libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long.pass.cpp (+89)
``````````diff
diff --git a/libcxx/include/__locale_dir/pad_and_output.h b/libcxx/include/__locale_dir/pad_and_output.h
index 4b845792a3087..481961be6ed6e 100644
--- a/libcxx/include/__locale_dir/pad_and_output.h
+++ b/libcxx/include/__locale_dir/pad_and_output.h
@@ -32,9 +32,12 @@ _LIBCPP_HIDE_FROM_ABI _OutputIterator __pad_and_output(
__ns -= __sz;
else
__ns = 0;
- __s = std::copy(__ob, __op, __s);
- __s = std::fill_n(__s, __ns, __fl);
- __s = std::copy(__op, __oe, __s);
+ if (__ob != __op)
+ __s = std::copy(__ob, __op, __s);
+ if (__ns != 0)
+ __s = std::fill_n(__s, __ns, __fl);
+ if (__op != __oe)
+ __s = std::copy(__op, __oe, __s);
__iob.width(0);
return __s;
}
diff --git a/libcxx/include/locale b/libcxx/include/locale
index f0d6756338c41..c3295ef92677b 100644
--- a/libcxx/include/locale
+++ b/libcxx/include/locale
@@ -200,6 +200,7 @@ template <class charT> class messages_byname;
# include <__locale_dir/wbuffer_convert.h>
# include <__locale_dir/wstring_convert.h>
# include <ios>
+# include <streambuf>
# include <version>
# if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
diff --git a/libcxx/test/benchmarks/text/localization/num_put.bench.cpp b/libcxx/test/benchmarks/text/localization/num_put.bench.cpp
index 329b139d74df6..9b56ae41597be 100644
--- a/libcxx/test/benchmarks/text/localization/num_put.bench.cpp
+++ b/libcxx/test/benchmarks/text/localization/num_put.bench.cpp
@@ -16,25 +16,53 @@
struct num_put : std::num_put<char, std::string::iterator> {};
-template <class T>
+class grouping_numpunct : public std::numpunct<char> {
+public:
+ grouping_numpunct() : std::numpunct<char>() {}
+
+protected:
+ virtual char_type do_thousands_sep() const { return '_'; }
+ virtual std::string do_grouping() const { return std::string("\1\2\3"); }
+};
+
+template <class NumPunct, class T>
TEST_ALIGN_BENCHMARK void BM_num_put(benchmark::State& state) {
auto val = T(123);
std::ios ios(nullptr);
+ ios.imbue(std::locale(std::locale::classic(), new NumPunct));
+ ios.setf(static_cast<std::ios::fmtflags>(state.range()));
num_put np;
+ std::string str('x', 10);
for (auto _ : state) {
benchmark::DoNotOptimize(val);
- std::string str;
+ benchmark::DoNotOptimize(str);
+ if (state.range() != 0)
+ ios.width(10);
benchmark::DoNotOptimize(np.put(str.begin(), ios, ' ', val));
}
}
-BENCHMARK(BM_num_put<bool>);
-BENCHMARK(BM_num_put<long>);
-BENCHMARK(BM_num_put<long long>);
-BENCHMARK(BM_num_put<unsigned long>);
-BENCHMARK(BM_num_put<unsigned long long>);
-BENCHMARK(BM_num_put<double>);
-BENCHMARK(BM_num_put<long double>);
-BENCHMARK(BM_num_put<const void*>);
+
+void bench_padding(benchmark::Benchmark* bm) {
+ bm->Arg(0)->Arg(std::ios::internal)->Arg(std::ios::left)->Arg(std::ios::right);
+}
+
+BENCHMARK(BM_num_put<std::numpunct<char>, bool>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<std::numpunct<char>, long>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<std::numpunct<char>, long long>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<std::numpunct<char>, unsigned long>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<std::numpunct<char>, unsigned long long>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<std::numpunct<char>, double>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<std::numpunct<char>, long double>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<std::numpunct<char>, const void*>)->Apply(bench_padding);
+
+BENCHMARK(BM_num_put<grouping_numpunct, bool>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<grouping_numpunct, long>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<grouping_numpunct, long long>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<grouping_numpunct, unsigned long>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<grouping_numpunct, unsigned long long>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<grouping_numpunct, double>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<grouping_numpunct, long double>)->Apply(bench_padding);
+BENCHMARK(BM_num_put<grouping_numpunct, const void*>)->Apply(bench_padding);
BENCHMARK_MAIN();
diff --git a/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long.pass.cpp b/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long.pass.cpp
index 7f034d487e57e..1042a1656cb43 100644
--- a/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long.pass.cpp
+++ b/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long.pass.cpp
@@ -96,6 +96,47 @@ int main(int, char**) {
std::string ex(str, base(iter));
assert(ex == "+0");
}
+ { // Ensure that padding is done properly without any grouping
+ {
+ std::ios ios(0);
+ ios.width(10);
+ long v = 1;
+ char str[50];
+ cpp17_output_iterator<char*> iter = f.put(cpp17_output_iterator<char*>(str), ios, '*', v);
+ std::string ex(str, base(iter));
+ assert(ex == "*********1");
+ }
+ {
+ std::ios ios(0);
+ ios.width(10);
+ ios.setf(std::ios::internal);
+ long v = -1;
+ char str[50];
+ cpp17_output_iterator<char*> iter = f.put(cpp17_output_iterator<char*>(str), ios, '*', v);
+ std::string ex(str, base(iter));
+ assert(ex == "-********1");
+ }
+ {
+ std::ios ios(0);
+ ios.width(10);
+ ios.setf(std::ios::left);
+ long v = -1;
+ char str[50];
+ cpp17_output_iterator<char*> iter = f.put(cpp17_output_iterator<char*>(str), ios, '*', v);
+ std::string ex(str, base(iter));
+ assert(ex == "-1********");
+ }
+ {
+ std::ios ios(0);
+ ios.width(10);
+ ios.setf(std::ios::right);
+ long v = -1;
+ char str[50];
+ cpp17_output_iterator<char*> iter = f.put(cpp17_output_iterator<char*>(str), ios, '*', v);
+ std::string ex(str, base(iter));
+ assert(ex == "********-1");
+ }
+ }
}
{ // test octal
{
@@ -137,6 +178,54 @@ int main(int, char**) {
std::string ex(str, base(iter));
assert(ex == "0");
}
+ { // Ensure that padding is done properly without any grouping
+ {
+ std::ios ios(0);
+ std::oct(ios);
+ ios.width(10);
+ long v = 1;
+ char str[50];
+ cpp17_output_iterator<char*> iter = f.put(cpp17_output_iterator<char*>(str), ios, '*', v);
+ std::string ex(str, base(iter));
+ assert(ex == "*********1");
+ }
+ {
+ std::ios ios(0);
+ std::oct(ios);
+ std::showbase(ios);
+ ios.width(10);
+ ios.setf(std::ios::internal);
+ long v = 1;
+ char str[50];
+ cpp17_output_iterator<char*> iter = f.put(cpp17_output_iterator<char*>(str), ios, '*', v);
+ std::string ex(str, base(iter));
+ assert(ex == "********01");
+ }
+ {
+ std::ios ios(0);
+ std::oct(ios);
+ std::showbase(ios);
+ ios.width(10);
+ ios.setf(std::ios::left);
+ long v = 1;
+ char str[50];
+ cpp17_output_iterator<char*> iter = f.put(cpp17_output_iterator<char*>(str), ios, '*', v);
+ std::string ex(str, base(iter));
+ assert(ex == "01********");
+ }
+ {
+ std::ios ios(0);
+ std::oct(ios);
+ std::showbase(ios);
+ ios.width(10);
+ ios.setf(std::ios::right);
+ long v = 1;
+ char str[50];
+ cpp17_output_iterator<char*> iter = f.put(cpp17_output_iterator<char*>(str), ios, '*', v);
+ std::string ex(str, base(iter));
+ assert(ex == "********01");
+ }
+ }
}
{ // test hexadecimal
{
``````````
</details>
https://github.com/llvm/llvm-project/pull/223334
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