[Bug libstdc++/109022] New: Low performance of std::map constructor for already sorted data of std::pair
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109022
Bug ID: 109022
Summary: Low performance of std::map constructor for already
sorted data of std::pair
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: marekr22 at wp dot pl
Target Milestone: ---
Performance of constructor accepting iterators to sorted data of
std::pair is much lower then inserting same data for
std::pair (matches value_type of std::map).
Here is benchmark showing the issue:
```
#include
#include
#include
#include
#include
constexpr size_t DataSizeStart = 8 << 0;
constexpr size_t DataSizeStop = 8 << 3;
using TestData = std::vector>;
using TestDataConst = std::vector>;
std::string makeStringFor(size_t x)
{
std::ostringstream out;
out << std::setfill('0') << std::setw(6) << x;
return out.str();
}
TestData sortedData(size_t n)
{
TestData r;
r.reserve(n);
size_t i = 0;
std::generate_n(std::back_inserter(r), n, []() {
return std::pair{makeStringFor(++i), i};
});
return r;
}
TestData shuffledData(size_t n)
{
auto data = sortedData(n);
std::random_device rd;
std::mt19937 g(rd());
std::shuffle(data.begin(), data.end(), g);
return data;
}
TestDataConst sortedConstData(size_t n)
{
auto r = sortedData(n);
return {r.begin(), r.end()};
}
TestDataConst shuffledConstData(size_t n)
{
auto r = shuffledData(n);
return {r.begin(), r.end()};
}
template
static void CreateMapInsert(benchmark::State& state) {
auto n = state.range(0);
auto data = Data(n);
for (auto _ : state) {
benchmark::DoNotOptimize(data);
std::map m;
for (auto& p : data) {
m.insert(m.end(), p);
}
benchmark::DoNotOptimize(m);
}
}
BENCHMARK(CreateMapInsert)->RangeMultiplier(2)->Range(DataSizeStart,
DataSizeStop);
//
BENCHMARK(CreateMapInsert)->RangeMultiplier(2)->Range(DataSizeStart,
DataSizeStop);
BENCHMARK(CreateMapInsert)->RangeMultiplier(2)->Range(DataSizeStart,
DataSizeStop);
//
BENCHMARK(CreateMapInsert)->RangeMultiplier(2)->Range(DataSizeStart,
DataSizeStop);
template
static void CreateMapDirectly(benchmark::State& state) {
auto n = state.range(0);
auto data = Data(n);
for (auto _ : state) {
benchmark::DoNotOptimize(data);
std::map m{data.begin(), data.end()};
benchmark::DoNotOptimize(m);
}
}
BENCHMARK(CreateMapDirectly)->RangeMultiplier(2)->Range(DataSizeStart,
DataSizeStop);
//
BENCHMARK(CreateMapDirectly)->RangeMultiplier(2)->Range(DataSizeStart,
DataSizeStop);
BENCHMARK(CreateMapDirectly)->RangeMultiplier(2)->Range(DataSizeStart,
DataSizeStop);
//
BENCHMARK(CreateMapDirectly)->RangeMultiplier(2)->Range(DataSizeStart,
DataSizeStop);
```
Live demo gcc 12.2: https://quick-bench.com/q/H8lqugNgMG-sWQ6cKBsdB7EBRpU
Note that CreateMapInsert performs best since it feeds to
constructos to iterators to std::pair while
CreateMapInsert performs badly (looks like time complexity is
worse) adn only diffrence is that it provides iterators to std::.
Same issue is observed for clang 14.0 and libstdc++:
https://quick-bench.com/q/6VA3vRdKmqPEYrvTnFFla4gxwXk
but it is not a problem on clang 14.0 and libc++:
https://quick-bench.com/q/-S-lX3N8Y-8vL9CCl-5bW5jolWA
here is result for sing size input data (easier to read):
https://quick-bench.com/q/kbDOPA8PNZFfrzUH_-70cJgApeE
Issue was observed when filing answer on
https://stackoverflow.com/a/75535056/1387438
[Bug c++/102493] New: non-type template specialization for member pointer to field and function reports leads to unexpected conflict
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102493
Bug ID: 102493
Summary: non-type template specialization for member pointer to
field and function reports leads to unexpected
conflict
Product: gcc
Version: 11.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: marekr22 at wp dot pl
Target Milestone: ---
Here is minimum complete verifiable example (C++17):
```cpp
#include
#include
#include
template
struct field_type;
template
struct field_type
{
using type = R;
};
template
struct field_type
{
using type = R;
};
template
using field_type_t = typename field_type::type;
class Foo {
public:
int x = 0;
double y = 0;
std::string s;
const int cx = 0;
Foo() = default;
void bar() {
std::cout << "bar\n";
}
int par(int z) {
std::cout << "bar\n";
return z;
}
};
template
constexpr bool test = std::is_same_v, T>;
static_assert(test<::x,int>, "");
static_assert(test<::cx, const int>, "");
static_assert(test<::s,std::string>, "");
static_assert(test<::y,double>, "");
#ifndef HIDE_PROBLEM_ON_GCC_11
static_assert(test<::bar, void>,"");
static_assert(test<::par, int>, "");
#endif
```
This compile on all compilers https://godbolt.org/z/31svobz3z
except for gcc 11.1 and 11.2 (gcc 10.3 works).
Reported error is:
```
: In substitution of 'template using field_type_t = typename
field_type::type [with auto FP = ::bar]':
:44:28: required from 'constexpr const bool test<::bar, void>'
:51:15: required from here
:21:7: error: ambiguous template instantiation for 'struct
field_type<::bar>'
21 | using field_type_t = typename field_type::type;
| ^~~~
:9:8: note: candidates are: 'template
struct field_type [with R = void(); T = Foo; R T::* FP = ::bar]'
9 | struct field_type
|^~
:15:8: note: 'template struct field_type [with R = void; T = Foo;
Args = {}; R (T::* FP)(Args ...) = ::bar]'
15 | struct field_type
|^~
:21:7: error: invalid use of incomplete type 'struct
field_type<::bar>'
21 | using field_type_t = typename field_type::type;
| ^~~~
:6:8: note: declaration of 'struct field_type<::bar>'
6 | struct field_type;
|^~
```
[Bug c++/98798] New: Custom operator new[] and delete[] is buggy for aligned class
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98798
Bug ID: 98798
Summary: Custom operator new[] and delete[] is buggy for
aligned class
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: marekr22 at wp dot pl
Target Milestone: ---
Basically when class has alignment requirement and custom operators `new[]` and
`delete[]` (C++17), then address sanitizer reports buffer overflow:
## MCVE:
```cpp
#include
#include
class EndlineOnDone {
std::ostream& out;
public:
EndlineOnDone(std::ostream& out) : out{out} {}
~EndlineOnDone()
{
out << std::endl;
}
std::ostream& stream() { return out; }
};
#define VAR(x) " " #x "=[" << x << "]"
#define LOG EndlineOnDone(std::cout).stream() << __PRETTY_FUNCTION__
std::ostream& operator<<(std::ostream& out, std::align_val_t a)
{
return out << static_cast(a);
}
class alignas(32) Foo
{
public :
double x, y, z;
void * operator new (size_t s, std::align_val_t a)
{
auto p = aligned_alloc(static_cast(a), s);
LOG << VAR(p) << VAR(s) << VAR(a);
return p;
}
void operator delete (void * p, size_t s, std::align_val_t a)
{
LOG << VAR(p) << VAR(s) << VAR(a);
if (p) free(p);
}
#if 1
void * operator new[ ] (size_t s, std::align_val_t a)
{
auto p = aligned_alloc(static_cast(a), s);
LOG << VAR(p) << VAR(s) << VAR(a);
return p;
}
void operator delete[ ] (void *p, size_t s, std::align_val_t a)
{
LOG << VAR(p) << VAR(s) << VAR(a);
if (p) free(p);
}
#endif
};
int main()
{
{
LOG << " std::make_unique";
auto p = std::make_unique();
}
{
LOG << " std::make_unique";
auto p = std::make_unique(3);
}
}
```
https://godbolt.org/z/7xd8YM
## gcc logs (no address sanitizer):
```txt
int main() std::make_unique
static void* Foo::operator new(size_t, std::align_val_t) p=[0x21d6ec0] s=[32]
a=[32]
static void Foo::operator delete(void*, size_t, std::align_val_t) p=[0x21d6ec0]
s=[32] a=[32]
int main() std::make_unique
static void* Foo::operator new [](size_t, std::align_val_t) p=[0x21d6f40]
s=[96] a=[32]
static void Foo::operator delete [](void*, size_t, std::align_val_t)
p=[0x21d6f40] s=[3616] a=[32]
```
Note that `s` value for `Foo[]` doesn't match for `new[]` and `delete[]`
operations.
Address sanitizer reports buffer overflow.
clang is fine (didn't check msvc).
## Workaround
Adding explicit destructor `~Foo() {}` fixes this issue:
https://godbolt.org/z/WoM91Y (use of `~Foo() = default;` doesn't fix it).
https://stackoverflow.com/q/65826663/1387438
