[Bug c++/97288] New: Assignment sequence before order - evaluating reference to value of right side not in order
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97288
Bug ID: 97288
Summary: Assignment sequence before order - evaluating
reference to value of right side not in order
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: kirshamir at gmail dot com
Target Milestone: ---
Following code results with different result in gcc and clang, seems that gcc
get wrong the sequence before:
class Number {
int num = 0;
public:
Number(int n): num(n) {
std::cout << "in ctor of Number for: " << num << std::endl;
}
// Number(const Number& n): num(n.num) {
// std::cout << "in copy of Number for: " << num << std::endl;
// }
Number& operator+=(int i) {
std::cout << "in +=(int) for *this = " << num << " and int = " << i <<
std::endl;
num += i;
return *this;
}
Number& operator+=(Number n) {
std::cout << "in +=(Number) for *this = " << num << " and Number = " <<
n << std::endl;
num += n.num;
return *this;
}
operator int() const {
return num;
}
};
int main() {
Number a {5};
(a += 1) += a;
std::cout << a << std::endl;
}
Code: https://godbolt.org/z/1P63z7
Based on stackoverflow:
https://stackoverflow.com/questions/64195482/chained-compound-assignments-with-c17-sequencing-are-still-undefined-behaviour
[Bug c++/97288] Assignment sequence before order - evaluating reference to value of right side not in order
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97288
--- Comment #1 from Amir Kirsh ---
For user defined type this behavior might be ok, as the order of evaluation of
parameters is not defined, however this behavior is reflected also for
primitive types:
int main() {
int a {5};
(a += 1) += a;
std::cout << a << std::endl;
}
gcc gives a warning:
warning: operation on 'a' may be undefined [-Wsequence-point]
5 | (a += 1) += a;
| ~~~^
:5:8: warning: operation on 'a' may be undefined [-Wsequence-point]
and result is 12.
Though based on C++17 sequencing rules for assignment, seems that the operation
shall be valid (no warning) and result with 11.
http://eel.is/c++draft/expr.ass#1
Code: https://godbolt.org/z/G1Kahh
[Bug c++/97402] Value of dependent partial-concept-id is not usable in a constant expression
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97402 Amir Kirsh changed: What|Removed |Added CC||kirshamir at gmail dot com --- Comment #2 from Amir Kirsh --- See also: https://stackoverflow.com/questions/65653983/gcc-stdis-same-vint-t-is-not-usable-in-a-constant-expression
[Bug c++/97402] Value of dependent partial-concept-id is not usable in a constant expression
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97402 --- Comment #3 from Amir Kirsh --- Playing with the code even leads to compiler seg-fault, see: https://stackoverflow.com/a/65654043/2085626
[Bug c++/99158] New: [Enhancement] Better error message when missing #include and using placement new
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99158 Bug ID: 99158 Summary: [Enhancement] Better error message when missing #include and using placement new Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: kirshamir at gmail dot com Target Milestone: --- Use of placement new requires #include Without this include the error message is something like: error: no matching function for call to 'operator new(sizetype, A*)' 8 | new (this) A(other); | ^ note: candidate function not viable: no known conversion from 'A *' to 'std::align_val_t' for 2nd argument note: candidate function not viable: requires 1 argument, but 2 were provided Many std headers have #include thus users just usually write placement new without a special include and everything works fine, but when code moves around above error message may just pop up. A better error might be: error: no matching function for call to 'operator new' Note: use of placement new requires #include ...
[Bug c++/100838] New: -fno-elide-constructors for C++14 missing required destructor call
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100838
Bug ID: 100838
Summary: -fno-elide-constructors for C++14 missing required
destructor call
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: kirshamir at gmail dot com
Target Milestone: ---
Code: https://godbolt.org/z/jKnKTds7s
#include
class MyString {
public:
MyString(const char* s = "") {
std::cout << "ctor" << std::endl;
}
~MyString() {
std::cout << "dtor" << std::endl;
}
MyString(const MyString& s) {
std::cout << "copy ctor" << std::endl;
}
MyString& operator=(const MyString& s) {
std::cout << "operator=" << std::endl;
return *this;
}
};
int main() {
MyString s1 = "Hello";
std::cout << __LINE__ << std::endl;
}
---
When compiled with:
-std=c++14 -fno-elide-constructors
Output:
ctor
copy ctor
22
dtor
Expected output:
ctor
copy ctor
dtor
22
dtor
[Bug c++/100838] -fno-elide-constructors for C++14 missing required destructor call
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100838
--- Comment #1 from Amir Kirsh ---
This main:
int main() {
MyString s1 = MyString{"Hello"}; // same also for rounded brackets
std::cout << __LINE__ << std::endl;
}
works as expected.
Output with C++14 and -fno-elide-constructors:
ctor
copy ctor
dtor
22
dtor
[Bug c++/100992] New: Wrong result for is_constructible for const ref of tuple of tuples
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100992
Bug ID: 100992
Summary: Wrong result for is_constructible for const ref of
tuple of tuples
Product: gcc
Version: 11.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: kirshamir at gmail dot com
CC: kirshamir at gmail dot com
Target Milestone: ---
The second static_assert below fails, should pass:
#include
struct F {
F() { }
F(const std::tuple& foo) {}
};
static_assert(std::is_constructible_v&>);
static_assert(std::is_constructible_v>&>); //
fails, unjustifiably
int main() {
F f1{std::tuple{F{}}};
auto tup = std::tuple{std::tuple{f1}};
F f2{tup}; // constructible
}
https://godbolt.org/z/3KfbxfhWE
[Bug libstdc++/100992] Wrong result for is_constructible for const ref of tuple of tuples
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100992 --- Comment #2 from Amir Kirsh --- Maybe a dup of: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96592
[Bug c++/104850] New: Instantiating a destructor for a template class too early, before the calling destructor is seen - rejects valid code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104850
Bug ID: 104850
Summary: Instantiating a destructor for a template class too
early, before the calling destructor is seen - rejects
valid code
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: kirshamir at gmail dot com
Target Milestone: ---
The following code is rejected as trying to use incomplete type, while when the
actual use would actually appear the type would be complete:
template
struct uptr {
uptr(nullptr_t) {}
~uptr() {
delete (new T);
}
};
class A
{
public:
A();
~A();
private:
class B;
uptr m_b = nullptr; // the dtor of uptr tries to be instantiated here
};
If we change the initialization of:
uptr m_b = nullptr;
To:
uptr m_b {nullptr};
The destructor instantiation is delayed, till ~A() is seen, and the code can be
compiled.
See:
https://stackoverflow.com/questions/71397495/why-does-default-member-initializer-request-instantiation-of-unique-ptr-destru
[Bug c++/104850] Instantiating a destructor for a template class too early, before the calling destructor is seen - rejects valid code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104850
--- Comment #2 from Amir Kirsh ---
// adding the required include to the example
#include // for nullptr_t
template
struct uptr {
uptr(nullptr_t) {}
~uptr() {
delete (new T);
}
};
class A
{
public:
A();
~A();
private:
class B;
uptr m_b = nullptr; // the dtor of uptr tries to be instantiated here
};
https://wandbox.org/permlink/rJeeB3Sliey6tGzR
If we change the initialization of:
uptr m_b = nullptr;
To:
uptr m_b {nullptr};
Relevant SO post:
https://stackoverflow.com/questions/71397495/why-does-default-member-initializer-request-instantiation-of-unique-ptr-destru/71402270#71402270
[Bug c++/67969] [concepts] bug with overloaded function when using constraints
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67969
Amir Kirsh changed:
What|Removed |Added
CC||kirshamir at gmail dot com
--- Comment #4 from Amir Kirsh ---
// Bug still exists in gcc 11.2
template
concept SmallVar = (sizeof(T) <= sizeof(int));
void print(SmallVar auto t) {
std::cout << t << std::endl;
}
void print(const auto& t) {
std::cout << t << std::endl;
}
int main() {
static_assert(SmallVar); // ok
static_assert(SmallVar); // ok
static_assert(!SmallVar); // ok
print("hello");
print('a'); // gcc 11.2 sees here ambiguity
print(6); // gcc 11.2 sees here ambiguity
}
Code:
https://godbolt.org/z/jq8edKM3E
[Bug c++/106094] New: Lifetime extension of temporary do not obey some rules of [class.temporary]
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106094
Bug ID: 106094
Summary: Lifetime extension of temporary do not obey some rules
of [class.temporary]
Product: gcc
Version: 12.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: kirshamir at gmail dot com
Target Milestone: ---
The simple cases of lifetime extension are working.
But all below do not obey the rules.
Lifetime should have been extended and it is not.
// casting (non user-defined) + member access
const auto& a1 = static_cast(A("a1")).ptr;
// casting (non user-defined) + member access
const auto& a2 = ((const A&&)A("a2")).arr;
// casting (non user-defined) + member access
const auto& a3 = const_cast(A("a3")).str;
// a pointer to a member + extending lifetime access
const auto& arr_member = &A::arr;
const auto& a4 = (A("a4").*arr_member)[0];
const auto& str_member = &A::str;
const auto& a5 = A("a5").*str_member;
const auto& ptr_member = &A::ptr;
const auto& a6 = A("a6").*ptr_member;
Code:
https://godbolt.org/z/jeeoefhPr
Rules:
https://timsong-cpp.github.io/cppwp/n4868/class.temporary#6
[Bug c++/117317] New: An internal compiler error on call to virtual constexpr function via comparison operator in CRTP with multiple inheritance
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117317
Bug ID: 117317
Summary: An internal compiler error on call to virtual
constexpr function via comparison operator in CRTP
with multiple inheritance
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: kirshamir at gmail dot com
Target Milestone: ---
The following code results with internal compiler error:
class Base {
public:
constexpr bool operator==(const Base& b) const {
return getIdentity() == b.getIdentity();
}
private:
constexpr virtual int getIdentity() const = 0;
};
template
class Comparable: public Base1, public AdditionalBases... {
public:
constexpr bool operator==(const Comparable&) const = default;
private:
constexpr int getIdentity() const override {
return 1;
}
};
class A: public Comparable {};
class B: public Comparable {};
class AB: public Comparable {};
int main() {
constexpr AB ab_1;
constexpr AB ab_2;
// internal compiler error :-(
static_assert(ab_1 == ab_2);
}
=
Error:
: In instantiation of 'constexpr int Comparable::getIdentity() const [with ActualType = AB; Base1 = A;
AdditionalBases = {B}]':
:4:27: required from here
4 | return getIdentity() == b.getIdentity();
|~~~^~
:31:24: in 'constexpr' expansion of 'ab_1.AB::Comparable.Comparable::operator==(ab_2.AB::Comparable)'
:13:20: in 'constexpr' expansion of '((const Comparable*)this)->Comparable::A.A::Comparable.Comparable::operator==(.Comparable::A.A::Comparable)'
:13:20: in 'constexpr' expansion of '((const Comparable*)this)->Comparable::Base.Base::operator==(.Comparable::Base)'
:17:5: internal compiler error: in use_thunk, at cp/method.cc:324
17 | }
| ^
0x287e175 diagnostic_context::diagnostic_impl(rich_location*,
diagnostic_metadata const*, diagnostic_option_id, char const*, __va_list_tag
(*) [1], diagnostic_t)
???:0
0x28945d5 internal_error(char const*, ...)
???:0
0xa90ace fancy_abort(char const*, int, char const*)
???:0
0xd1eb6b emit_associated_thunks(tree_node*)
???:0
0xd1ed0e expand_or_defer_fn(tree_node*)
???:0
0xcc60cd instantiate_decl(tree_node*, bool, bool)
???:0
0xb08a50 maybe_constant_value(tree_node*, tree_node*, mce_value)
???:0
0xd23df0 finish_static_assert(tree_node*, tree_node*, unsigned int, bool, bool)
???:0
0xc9e57a c_parse_file()
???:0
0xdf7f99 c_common_parse_file()
???:0
--
Notes:
1. Code compiles with clang: https://godbolt.org/z/j8oMxar8o
2. Removing the constexpr or the virtual from getIdentity() - code compiles:
https://godbolt.org/z/G5nMnWMd9 and https://godbolt.org/z/f3PWez1sb
3. Without CRTP code compiles: https://godbolt.org/z/56ah81n6h
[Bug c++/117317] An internal compiler error on call to virtual constexpr function via comparison operator in CRTP with multiple inheritance
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117317
--- Comment #1 from Amir Kirsh ---
A more simple example, same internal compiler error:
class Base {
public:
constexpr bool operator==(const Base& b) const {
return getIdentity() == b.getIdentity();
}
private:
constexpr virtual int getIdentity() const = 0;
};
template
class Comparable: public Base1, public Base2 {
public:
constexpr bool operator==(const Comparable&) const = default;
private:
constexpr int getIdentity() const override {
return 1;
}
};
class A: public Base {};
class B: public Base {};
class AB: public Comparable {};
int main() {
constexpr AB ab_1;
constexpr AB ab_2;
// internal compiler error :-(
static_assert(ab_1 == ab_2);
}
Error:
: In instantiation of 'constexpr int Comparable::getIdentity() const [with ActualType = AB; Base1 = A; Base2 = B]':
:4:27: required from here
4 | return getIdentity() == b.getIdentity();
|~~~^~
:31:24: in 'constexpr' expansion of 'ab_1.AB::Comparable.Comparable::operator==(ab_2.AB::Comparable)'
:13:20: in 'constexpr' expansion of '((const Comparable*)this)->Comparable::A.A::Base.Base::operator==(.Comparable::A.A::Base)'
:17:5: internal compiler error: in use_thunk, at cp/method.cc:324
17 | }
| ^
0x287e175 diagnostic_context::diagnostic_impl(rich_location*,
diagnostic_metadata const*, diagnostic_option_id, char const*, __va_list_tag
(*) [1], diagnostic_t)
???:0
0x28945d5 internal_error(char const*, ...)
???:0
0xa90ace fancy_abort(char const*, int, char const*)
???:0
0xd1eb6b emit_associated_thunks(tree_node*)
???:0
0xd1ed0e expand_or_defer_fn(tree_node*)
???:0
0xcc60cd instantiate_decl(tree_node*, bool, bool)
???:0
0xb08a50 maybe_constant_value(tree_node*, tree_node*, mce_value)
???:0
0xd23df0 finish_static_assert(tree_node*, tree_node*, unsigned int, bool, bool)
???:0
0xc9e57a c_parse_file()
???:0
0xdf7f99 c_common_parse_file()
???:0
Code:
https://godbolt.org/z/4x9bMYPhj
Compiles with clang
And still, it compiles without the template:
https://godbolt.org/z/Wecqz9YW1
