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* [Bug libstdc++/100470] New: std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members
@ 2021-05-07 11:16 oleksandr.koval.dev at gmail dot com
2021-09-06 15:54 ` [Bug c++/100470] " redi at gcc dot gnu.org
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: oleksandr.koval.dev at gmail dot com @ 2021-05-07 11:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100470
Bug ID: 100470
Summary: std::is_nothrow_move_constructible incorrect behavior
for explicitly defaulted members
Product: gcc
Version: 11.1.0
URL: https://godbolt.org/z/hqeh4E3M8
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: oleksandr.koval.dev at gmail dot com
Target Milestone: ---
Explicit exception specification should be the actual one, hence, S2 should NOT
be nothrow-constructible.
#include <type_traits>
struct S1{
S1(S1&&) noexcept(false);
};
struct S2{
S2(S2&&) noexcept(false) = default;
};
struct S3{
S3(S3&&) noexcept(false){}
};
struct S4{
S4(S4&&) = default;
};
static_assert(!std::is_nothrow_move_constructible_v<S1>); // OK
static_assert(!std::is_nothrow_move_constructible_v<S2>); // failed
static_assert(!std::is_nothrow_move_constructible_v<S3>); // OK
static_assert(std::is_nothrow_move_constructible_v<S4>); // OK
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100470] std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members
2021-05-07 11:16 [Bug libstdc++/100470] New: std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members oleksandr.koval.dev at gmail dot com
@ 2021-09-06 15:54 ` redi at gcc dot gnu.org
2022-09-20 9:23 ` redi at gcc dot gnu.org
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: redi at gcc dot gnu.org @ 2021-09-06 15:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100470
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|libstdc++ |c++
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This is a compiler bug, the library trait just asks the compiler.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100470] std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members
2021-05-07 11:16 [Bug libstdc++/100470] New: std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members oleksandr.koval.dev at gmail dot com
2021-09-06 15:54 ` [Bug c++/100470] " redi at gcc dot gnu.org
@ 2022-09-20 9:23 ` redi at gcc dot gnu.org
2022-09-20 9:43 ` redi at gcc dot gnu.org
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: redi at gcc dot gnu.org @ 2022-09-20 9:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100470
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |fchelnokov at gmail dot com
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
*** Bug 106968 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100470] std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members
2021-05-07 11:16 [Bug libstdc++/100470] New: std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members oleksandr.koval.dev at gmail dot com
2021-09-06 15:54 ` [Bug c++/100470] " redi at gcc dot gnu.org
2022-09-20 9:23 ` redi at gcc dot gnu.org
@ 2022-09-20 9:43 ` redi at gcc dot gnu.org
2022-09-20 9:50 ` redi at gcc dot gnu.org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: redi at gcc dot gnu.org @ 2022-09-20 9:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100470
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Keywords| |wrong-code
Last reconfirmed| |2022-09-20
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1286r2.html says that
S" has a potentially-throwing move constructor.
It looks like the __is_nothrow_constructible built-in gets this wrong:
using size_t = decltype(sizeof(0));
void* operator new(size_t, void* p) noexcept { return p; }
namespace std {
template<typename T> T&& declval() noexcept;
template<typename T>
constexpr bool is_nothrow_move_constructible_v
= noexcept(new (declval<void*>()) T(declval<T>()));
}
struct S1{
S1(S1&&) noexcept(false);
};
struct S2{
S2(S2&&) noexcept(false) = default;
};
struct S3{
S3(S3&&) noexcept(false){}
};
struct S4{
S4(S4&&) = default;
};
static_assert(!std::is_nothrow_move_constructible_v<S1>); // OK
static_assert(!std::is_nothrow_move_constructible_v<S2>); // OK
static_assert(!std::is_nothrow_move_constructible_v<S3>); // OK
static_assert( std::is_nothrow_move_constructible_v<S4>); // OK
static_assert(!__is_nothrow_constructible(S1, S1)); // OK
static_assert(!__is_nothrow_constructible(S2, S2)); // failed
static_assert(!__is_nothrow_constructible(S3, S3)); // OK
static_assert( __is_nothrow_constructible(S4, S4)); // OK
This makes it a libstdc++ regression in GCC 11.1 and later, because we use
__is_nothrow_construcitble now, instead of a pure library implementation for
the traits.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100470] std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members
2021-05-07 11:16 [Bug libstdc++/100470] New: std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members oleksandr.koval.dev at gmail dot com
` (2 preceding siblings ...)
2022-09-20 9:43 ` redi at gcc dot gnu.org
@ 2022-09-20 9:50 ` redi at gcc dot gnu.org
2023-08-08 21:45 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: redi at gcc dot gnu.org @ 2022-09-20 9:50 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100470
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
My guess is that either is_nothrow_xible or check_noexcept_r assumes that a
trivial special member is always non-throwing, but that fails to consider the
P1206 rule that says if there's an explicit noexcept-specifier, that overrides
the implicit one.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100470] std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members
2021-05-07 11:16 [Bug libstdc++/100470] New: std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members oleksandr.koval.dev at gmail dot com
` (3 preceding siblings ...)
2022-09-20 9:50 ` redi at gcc dot gnu.org
@ 2023-08-08 21:45 ` pinskia at gcc dot gnu.org
2023-10-26 16:07 ` johelegp at gmail dot com
2023-12-11 2:34 ` cvs-commit at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-08-08 21:45 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100470
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |nikolasklauser at berlin dot de
--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 106611 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100470] std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members
2021-05-07 11:16 [Bug libstdc++/100470] New: std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members oleksandr.koval.dev at gmail dot com
` (4 preceding siblings ...)
2023-08-08 21:45 ` pinskia at gcc dot gnu.org
@ 2023-10-26 16:07 ` johelegp at gmail dot com
2023-12-11 2:34 ` cvs-commit at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: johelegp at gmail dot com @ 2023-10-26 16:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100470
Johel Ernesto Guerrero Peña <johelegp at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |johelegp at gmail dot com
--- Comment #6 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Is this a duplicate of Bug 96090?
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/100470] std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members
2021-05-07 11:16 [Bug libstdc++/100470] New: std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members oleksandr.koval.dev at gmail dot com
` (5 preceding siblings ...)
2023-10-26 16:07 ` johelegp at gmail dot com
@ 2023-12-11 2:34 ` cvs-commit at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-12-11 2:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100470
--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Nathaniel Shead <nshead@gcc.gnu.org>:
https://gcc.gnu.org/g:4719b6f5ae4d758f193a17bbd5fb6cbacd702a23
commit r14-6395-g4719b6f5ae4d758f193a17bbd5fb6cbacd702a23
Author: Nathaniel Shead <nathanieloshead@gmail.com>
Date: Sat Oct 28 16:04:52 2023 +1100
c++: Fix noexcept checking for trivial operations [PR96090]
This patch stops eager folding of trivial operations (construction and
assignment) from occurring when checking for noexceptness. This was
previously done in PR c++/53025, but only for copy/move construction,
and the __is_nothrow_xible builtins did not receive the same treatment
when they were added.
To handle `is_nothrow_default_constructible`, the patch also ensures
that when no parameters are passed we do value initialisation instead of
just building the constructor call: in particular, value-initialisation
doesn't necessarily actually invoke the constructor for trivial default
constructors, and so we need to handle this case as well.
This is contrary to the proposed resolution of CWG2820; for now we just
ensure it matches the behaviour of the `noexcept` operator and create
testcases formalising this, and if that issue gets accepted we can
revisit.
PR c++/96090
PR c++/100470
gcc/cp/ChangeLog:
* call.cc (build_over_call): Prevent folding of trivial special
members when checking for noexcept.
* method.cc (constructible_expr): Perform value-initialisation
for empty parameter lists.
(is_nothrow_xible): Treat as noexcept operator.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/noexcept81.C: New test.
* g++.dg/ext/is_nothrow_constructible7.C: New test.
* g++.dg/ext/is_nothrow_constructible8.C: New test.
Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
^ permalink raw reply [flat|nested] 8+ messages in thread
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2021-05-07 11:16 [Bug libstdc++/100470] New: std::is_nothrow_move_constructible incorrect behavior for explicitly defaulted members oleksandr.koval.dev at gmail dot com
2021-09-06 15:54 ` [Bug c++/100470] " redi at gcc dot gnu.org
2022-09-20 9:23 ` redi at gcc dot gnu.org
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