[Bug c++/103443] New: consteval function rejected as constant expression
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103443
Bug ID: 103443
Summary: consteval function rejected as constant expression
Product: gcc
Version: 11.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent.hamp at higaski dot at
Target Milestone: ---
Not really sure whether that's a frontend or a libstdc++ bug, but GCC 11.1.0
(and according to godbolt trunk as well) does not accept the following snippet.
#include
#include
#include
// #define QUALIFIER constexpr // compiles
#define QUALIFIER consteval// does not compile
template
QUALIFIER uint32_t index_sequence2mask(std::index_sequence) {
if constexpr (sizeof...(Is) == 0u)
return 0u;
else
return ((1u << Is) | ...);
}
template {})>
void use_mask() {
printf("%s\n", __PRETTY_FUNCTION__);
}
int main() { use_mask(); }
The code is rejected with the following error:
"expression 'std::make_index_sequence<1>{}' is not a constant expression"
[Bug c++/99059] New: Static inline variable can't refer to itself
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99059
Bug ID: 99059
Summary: Static inline variable can't refer to itself
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent.hamp at higaski dot at
Target Milestone: ---
Declaring a static inline member variable and initializing it with a pointer to
itself is currently impossible. The textbook example for such code would
probably be a linked list of some sort:
struct link {
link* next{nullptr};
link* prev{nullptr};
};
struct list {
static inline link tail{, };
};
list l;
Making the member just static and initializing it outside of the class works,
but this kinda breaks my mental model of "static inline" as just being
syntactic sugar. Is this an actual bug or just some overlooked thing in the
standard?
[Bug c++/95307] New: Compiler accepts reinterpret_cast in constexpr
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95307
Bug ID: 95307
Summary: Compiler accepts reinterpret_cast in constexpr
Product: gcc
Version: 10.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent.hamp at higaski dot at
Target Milestone: ---
The following snippet allows using reinterpret_casts inside a constexpr.
#include
uint64_t v;
constexpr auto p{reinterpret_cast() - 1u};
Compiled with GCC 10.1 and 9.3 with -std=c++2a
Interestingly subtracting 0u results in an error.
[Bug c++/94422] New: static_cast from std::array to enum class
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94422
Bug ID: 94422
Summary: static_cast from std::array to enum class
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent.hamp at higaski dot at
Target Milestone: ---
static_cast from std::array operator[] to an enum class inside a template class
produces an unexpected expression error. It seems that error is only present in
9.3, 9.2 and trunk work.
#include
#include
enum class EnumC : int8_t { Forward = 1, Backward = -1 };
std::array buf;
template
struct S {
void foo() { auto const cast_to_enum{static_cast(buf[0])}; }
};
S s;
[Bug c++/92134] New: static constinit members incorrectly compile
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92134
Bug ID: 92134
Summary: static constinit members incorrectly compile
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent.hamp at higaski dot at
Target Milestone: ---
The new C++20 constinit specifier currently doesn't seem to work with static
data members.
The following snippet compiles although the constructor of Value calls new.
struct Value {
Value() : v{new int{42}} {}
int* v;
};
struct S {
static constinit inline Value v{};
};
int main() { return *S::v.v; }
[Bug c++/92003] New: constexpr-ness of char const* doesn't propagate
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92003
Bug ID: 92003
Summary: constexpr-ness of char const* doesn't propagate
Product: gcc
Version: 9.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent.hamp at higaski dot at
Target Milestone: ---
For some reasons the compiler seems to differ between a constexpr char const*
which is directly initialized by a string literal and one which actually points
to a constexpr char array.
The last expression in the following code-snippet fails to compile on the
current trunk:
constexpr char const* get_c_str() { return "abc"; }
constexpr bool use_get_c_str_in_constexpr_context{get_c_str()}; // works
template
struct string {
static constexpr char const* c_str() { return [0]; }
private:
static constexpr char c[]{Cs..., '\0'};
};
constexpr char const* cstr{string<'a', 'b', 'c'>::c_str()};
constexpr bool use_cstr_in_constexpr_context{cstr}; // doesn't work
https://godbolt.org/z/k3TBUC
[Bug c++/89871] New: Wall + designated initializers
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89871 Bug ID: 89871 Summary: Wall + designated initializers Product: gcc Version: 8.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: vincent.hamp at higaski dot at Target Milestone: --- Created attachment 46050 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46050=edit Example fails to compile with -Wall Using a struct with an anonymous union and trying to assign to it using designated initializers does not compile with -Wall. So e.g. g++ -std=c++2a -Wall designated_init.cpp produces "internal compiler error: side-effects element in no-side-effects CONSTRUCTOR" The error can be reproduced on 8.1, 8.2 and 8.3. The current trunk however seems to work.
