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* [Bug c++/110344] New: [C++26] P2738R1 - constexpr cast from void*
@ 2023-06-21 16:16 mpolacek at gcc dot gnu.org
2023-06-22 6:28 ` [Bug c++/110344] " pinskia at gcc dot gnu.org
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2023-06-21 16:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110344
Bug ID: 110344
Summary: [C++26] P2738R1 - constexpr cast from void*
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: mpolacek at gcc dot gnu.org
Target Milestone: ---
See <https://wg21.link/P2738R1>.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/110344] [C++26] P2738R1 - constexpr cast from void*
2023-06-21 16:16 [Bug c++/110344] New: [C++26] P2738R1 - constexpr cast from void* mpolacek at gcc dot gnu.org
@ 2023-06-22 6:28 ` pinskia at gcc dot gnu.org
2023-06-24 21:55 ` jason at gcc dot gnu.org
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-06-22 6:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110344
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2023-06-22
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/110344] [C++26] P2738R1 - constexpr cast from void*
2023-06-21 16:16 [Bug c++/110344] New: [C++26] P2738R1 - constexpr cast from void* mpolacek at gcc dot gnu.org
2023-06-22 6:28 ` [Bug c++/110344] " pinskia at gcc dot gnu.org
@ 2023-06-24 21:55 ` jason at gcc dot gnu.org
2023-06-24 21:57 ` jason at gcc dot gnu.org
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: jason at gcc dot gnu.org @ 2023-06-24 21:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110344
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jason at gcc dot gnu.org
--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Reduced version of the paper's testcase that we already (wrongly) accept:
class Doer {
private:
const void *ob;
int (*fn)(const void *);
public:
template <typename T>
constexpr Doer(const T &t)
: ob{&t},
fn{[](const void *p) { return static_cast<const T *>(p)->doit(); }}
{}
constexpr int operator()() const { return fn(ob); }
};
struct Thing { constexpr int doit() const { return 42; }; };
static_assert (Doer(Thing())() == 42);
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/110344] [C++26] P2738R1 - constexpr cast from void*
2023-06-21 16:16 [Bug c++/110344] New: [C++26] P2738R1 - constexpr cast from void* mpolacek at gcc dot gnu.org
2023-06-22 6:28 ` [Bug c++/110344] " pinskia at gcc dot gnu.org
2023-06-24 21:55 ` jason at gcc dot gnu.org
@ 2023-06-24 21:57 ` jason at gcc dot gnu.org
2023-06-27 19:03 ` jason at gcc dot gnu.org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: jason at gcc dot gnu.org @ 2023-06-24 21:57 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110344
--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
Version of the paper testcase that just adds constexpr, that we currently
reject:
#include <string_view>
struct Sheep {
constexpr std::string_view speak() const noexcept { return "Baaaaaa"; }
};
struct Cow {
constexpr std::string_view speak() const noexcept { return "Mooo"; }
};
class Animal_View {
private:
const void *animal;
std::string_view (*speak_function)(const void *);
public:
template <typename Animal>
constexpr Animal_View(const Animal &a)
: animal{&a}, speak_function{[](const void *object) {
return static_cast<const Animal
*>(object)->speak();
}} {}
constexpr std::string_view speak() const noexcept {
return speak_function(animal);
}
};
// This is the key bit here. This is a single concrete function
// that can take anything that happens to have the "Animal_View"
// interface
constexpr std::string_view do_speak(Animal_View av) { return av.speak(); }
int main() {
// A Cow is a cow. The only think that makes it special
// is that it has a "std::string_view speak() const" member
constexpr Cow cow;
constexpr auto result = do_speak(cow);
return static_cast<int>(result.size());
}
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/110344] [C++26] P2738R1 - constexpr cast from void*
2023-06-21 16:16 [Bug c++/110344] New: [C++26] P2738R1 - constexpr cast from void* mpolacek at gcc dot gnu.org
` (2 preceding siblings ...)
2023-06-24 21:57 ` jason at gcc dot gnu.org
@ 2023-06-27 19:03 ` jason at gcc dot gnu.org
2023-06-28 3:29 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: jason at gcc dot gnu.org @ 2023-06-27 19:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110344
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |jason at gcc dot gnu.org
Status|NEW |ASSIGNED
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/110344] [C++26] P2738R1 - constexpr cast from void*
2023-06-21 16:16 [Bug c++/110344] New: [C++26] P2738R1 - constexpr cast from void* mpolacek at gcc dot gnu.org
` (3 preceding siblings ...)
2023-06-27 19:03 ` jason at gcc dot gnu.org
@ 2023-06-28 3:29 ` cvs-commit at gcc dot gnu.org
2023-06-28 3:34 ` jason at gcc dot gnu.org
2023-07-14 22:38 ` cvs-commit at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-06-28 3:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110344
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Jason Merrill <jason@gcc.gnu.org>:
https://gcc.gnu.org/g:a1c6e9631ca33990a2b7411060ca4d18db081a7d
commit r14-2146-ga1c6e9631ca33990a2b7411060ca4d18db081a7d
Author: Jason Merrill <jason@redhat.com>
Date: Sat Jun 24 05:15:02 2023 -0400
c++: C++26 constexpr cast from void* [PR110344]
P2768 allows static_cast from void* to ob* in constant evaluation if the
pointer does in fact point to an object of the appropriate type.
cxx_fold_indirect_ref already does the work of finding such an object if it
happens to be a subobject rather than the outermost object at that address,
as in constexpr-voidptr2.C.
P2768
PR c++/110344
gcc/c-family/ChangeLog:
* c-cppbuiltin.cc (c_cpp_builtins): Update __cpp_constexpr.
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_constant_expression): In C++26, allow cast
from void* to the type of a pointed-to object.
gcc/testsuite/ChangeLog:
* g++.dg/cpp26/constexpr-voidptr1.C: New test.
* g++.dg/cpp26/constexpr-voidptr2.C: New test.
* g++.dg/cpp26/feat-cxx26.C: New test.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/110344] [C++26] P2738R1 - constexpr cast from void*
2023-06-21 16:16 [Bug c++/110344] New: [C++26] P2738R1 - constexpr cast from void* mpolacek at gcc dot gnu.org
` (4 preceding siblings ...)
2023-06-28 3:29 ` cvs-commit at gcc dot gnu.org
@ 2023-06-28 3:34 ` jason at gcc dot gnu.org
2023-07-14 22:38 ` cvs-commit at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: jason at gcc dot gnu.org @ 2023-06-28 3:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110344
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Target Milestone|--- |14.0
Resolution|--- |FIXED
--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Implemented for GCC 14.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/110344] [C++26] P2738R1 - constexpr cast from void*
2023-06-21 16:16 [Bug c++/110344] New: [C++26] P2738R1 - constexpr cast from void* mpolacek at gcc dot gnu.org
` (5 preceding siblings ...)
2023-06-28 3:34 ` jason at gcc dot gnu.org
@ 2023-07-14 22:38 ` cvs-commit at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-07-14 22:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110344
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Jason Merrill <jason@gcc.gnu.org>:
https://gcc.gnu.org/g:8d344146727da02eb5c62fbf6cee97a4e96d63db
commit r14-2535-g8d344146727da02eb5c62fbf6cee97a4e96d63db
Author: Jason Merrill <jason@redhat.com>
Date: Fri Jul 14 09:37:21 2023 -0400
c++: c++26 regression fixes
Apparently I wasn't actually running the testsuite in C++26 mode like I
thought I was, so there were some failures I wasn't seeing.
The constexpr hunk fixes regressions with the P2738 implementation; we
still
need to use the old handling for casting from void pointers to heap
variables.
PR c++/110344
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_constant_expression): Move P2738 handling
after heap handling.
* name-lookup.cc (get_cxx_dialect_name): Add C++26.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-cast2.C: Adjust for P2738.
* g++.dg/ipa/devirt-45.C: Handle -fimplicit-constexpr.
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2023-07-14 22:38 UTC | newest]
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2023-06-21 16:16 [Bug c++/110344] New: [C++26] P2738R1 - constexpr cast from void* mpolacek at gcc dot gnu.org
2023-06-22 6:28 ` [Bug c++/110344] " pinskia at gcc dot gnu.org
2023-06-24 21:55 ` jason at gcc dot gnu.org
2023-06-24 21:57 ` jason at gcc dot gnu.org
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