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* [Bug c++/94923] New: False positive -Wclass-memaccess with trivially copyable std::optional
@ 2020-05-02 13:46 dawid_jurek at vp dot pl
2020-05-02 15:38 ` [Bug c++/94923] " daniel.kruegler at googlemail dot com
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: dawid_jurek at vp dot pl @ 2020-05-02 13:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94923
Bug ID: 94923
Summary: False positive -Wclass-memaccess with trivially
copyable std::optional
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dawid_jurek at vp dot pl
Target Milestone: ---
Consider following C++ snippet:
static_assert(std::is_trivially_copyable_v<std::optional<char>>);
static void not_ok() {
std::optional<char> value;
std::byte buf[128;
std::memcpy(&buf[0], &value, sizeof value);
std::memcpy(&value, &buf[0], sizeof value);
}
With above snippet fresh x86-64 gcc trunk reports following warning:
source>: In function 'void not_ok()':
<source>:27:46: warning: 'void* memcpy(void*, const void*, size_t)' copying an
object of non-trivial type 'class std::optional<char>' from an array of 'enum
class std::byte' [-Wclass-memaccess]
27 | std::memcpy(&value, &buf[0], sizeof value);
[basic.types]/2 explicitly permits for such round trip for every trivially
copyable T via std::memcpy even if T is not trivial.
Also clang accept such code without complains (take a look at link below).
Changing std::byte buf[128; to char buf[128]; suppress the warning so seems
that std::byte is relevant.
You can find full source code here https://godbolt.org/z/JrcnS5
Regards,
Dawid
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/94923] False positive -Wclass-memaccess with trivially copyable std::optional
2020-05-02 13:46 [Bug c++/94923] New: False positive -Wclass-memaccess with trivially copyable std::optional dawid_jurek at vp dot pl
@ 2020-05-02 15:38 ` daniel.kruegler at googlemail dot com
2020-05-02 17:59 ` dawid_jurek at vp dot pl
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: daniel.kruegler at googlemail dot com @ 2020-05-02 15:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94923
Daniel Krügler <daniel.kruegler at googlemail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |daniel.kruegler@googlemail.
| |com
--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
Corrected code without typos and including the necessary header files:
```
#include <type_traits>
#include <optional>
#include <cstddef>
#include <cstring>
static_assert(std::is_trivially_copyable_v<std::optional<char>>);
void not_ok() {
std::optional<char> value;
std::byte buf[128];
std::memcpy(&buf[0], &value, sizeof value);
std::memcpy(&value, &buf[0], sizeof value);
}
int main() {}
```
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/94923] False positive -Wclass-memaccess with trivially copyable std::optional
2020-05-02 13:46 [Bug c++/94923] New: False positive -Wclass-memaccess with trivially copyable std::optional dawid_jurek at vp dot pl
2020-05-02 15:38 ` [Bug c++/94923] " daniel.kruegler at googlemail dot com
@ 2020-05-02 17:59 ` dawid_jurek at vp dot pl
2020-05-02 22:34 ` msebor at gcc dot gnu.org
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: dawid_jurek at vp dot pl @ 2020-05-02 17:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94923
--- Comment #2 from dawid_jurek at vp dot pl ---
Yeah, that's the correct reproducer of issue I reported.
I noticed missing bracket after pasting it from godbolt but unfortunately
couldn't edit my comment after posting.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/94923] False positive -Wclass-memaccess with trivially copyable std::optional
2020-05-02 13:46 [Bug c++/94923] New: False positive -Wclass-memaccess with trivially copyable std::optional dawid_jurek at vp dot pl
2020-05-02 15:38 ` [Bug c++/94923] " daniel.kruegler at googlemail dot com
2020-05-02 17:59 ` dawid_jurek at vp dot pl
@ 2020-05-02 22:34 ` msebor at gcc dot gnu.org
2020-05-02 22:36 ` msebor at gcc dot gnu.org
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: msebor at gcc dot gnu.org @ 2020-05-02 22:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94923
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |diagnostic
Status|UNCONFIRMED |NEW
Last reconfirmed| |2020-05-02
Ever confirmed|0 |1
CC| |msebor at gcc dot gnu.org
--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
The warning code treats character types as special in this context but there's
no such handling for std::byte. It probably makes sense to extend the same
treatment to it.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/94923] False positive -Wclass-memaccess with trivially copyable std::optional
2020-05-02 13:46 [Bug c++/94923] New: False positive -Wclass-memaccess with trivially copyable std::optional dawid_jurek at vp dot pl
` (2 preceding siblings ...)
2020-05-02 22:34 ` msebor at gcc dot gnu.org
@ 2020-05-02 22:36 ` msebor at gcc dot gnu.org
2020-05-08 18:58 ` msebor at gcc dot gnu.org
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: msebor at gcc dot gnu.org @ 2020-05-02 22:36 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94923
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Known to fail| |10.0, 8.4.0, 9.3.0
Assignee|unassigned at gcc dot gnu.org |msebor at gcc dot gnu.org
Status|NEW |ASSIGNED
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/94923] False positive -Wclass-memaccess with trivially copyable std::optional
2020-05-02 13:46 [Bug c++/94923] New: False positive -Wclass-memaccess with trivially copyable std::optional dawid_jurek at vp dot pl
` (3 preceding siblings ...)
2020-05-02 22:36 ` msebor at gcc dot gnu.org
@ 2020-05-08 18:58 ` msebor at gcc dot gnu.org
2020-05-19 19:09 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: msebor at gcc dot gnu.org @ 2020-05-08 18:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94923
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |patch
--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
Patch: https://gcc.gnu.org/pipermail/gcc-patches/2020-May/545421.html
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/94923] False positive -Wclass-memaccess with trivially copyable std::optional
2020-05-02 13:46 [Bug c++/94923] New: False positive -Wclass-memaccess with trivially copyable std::optional dawid_jurek at vp dot pl
` (4 preceding siblings ...)
2020-05-08 18:58 ` msebor at gcc dot gnu.org
@ 2020-05-19 19:09 ` cvs-commit at gcc dot gnu.org
2020-05-21 8:31 ` dawid_jurek at vp dot pl
2022-03-17 19:53 ` msebor at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2020-05-19 19:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94923
--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Sebor <msebor@gcc.gnu.org>:
https://gcc.gnu.org/g:c0d8623ce5aa6d92c2e6c62e1bee66272a011f59
commit r11-499-gc0d8623ce5aa6d92c2e6c62e1bee66272a011f59
Author: Martin Sebor <msebor@redhat.com>
Date: Tue May 19 12:46:37 2020 -0600
PR c++/94923 - False positive -Wclass-memaccess with trivially copyable
std::optional
gcc/cp/ChangeLog:
PR c++/94923
* call.c ((maybe_warn_class_memaccess): Use is_byte_access_type.
* cp-tree.h (is_dummy_object): Return bool.
(is_byte_access_type): Declare new function.
* tree.c (is_dummy_object): Return bool.
(is_byte_access_type): Define new function.
gcc/testsuite/ChangeLog:
PR c++/94923
* g++.dg/Wclass-memaccess.C: Add tests for std::byte.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/94923] False positive -Wclass-memaccess with trivially copyable std::optional
2020-05-02 13:46 [Bug c++/94923] New: False positive -Wclass-memaccess with trivially copyable std::optional dawid_jurek at vp dot pl
` (5 preceding siblings ...)
2020-05-19 19:09 ` cvs-commit at gcc dot gnu.org
@ 2020-05-21 8:31 ` dawid_jurek at vp dot pl
2022-03-17 19:53 ` msebor at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: dawid_jurek at vp dot pl @ 2020-05-21 8:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94923
--- Comment #6 from dawid_jurek at vp dot pl ---
I quickly tried trunk and all false positive warnings vanished.
Thanks Martin.
Regards,
Dawid
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/94923] False positive -Wclass-memaccess with trivially copyable std::optional
2020-05-02 13:46 [Bug c++/94923] New: False positive -Wclass-memaccess with trivially copyable std::optional dawid_jurek at vp dot pl
` (6 preceding siblings ...)
2020-05-21 8:31 ` dawid_jurek at vp dot pl
@ 2022-03-17 19:53 ` msebor at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: msebor at gcc dot gnu.org @ 2022-03-17 19:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94923
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
--- Comment #7 from Martin Sebor <msebor at gcc dot gnu.org> ---
Fixed per comment #6.
^ permalink raw reply [flat|nested] 9+ messages in thread
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2020-05-02 13:46 [Bug c++/94923] New: False positive -Wclass-memaccess with trivially copyable std::optional dawid_jurek at vp dot pl
2020-05-02 15:38 ` [Bug c++/94923] " daniel.kruegler at googlemail dot com
2020-05-02 17:59 ` dawid_jurek at vp dot pl
2020-05-02 22:34 ` msebor at gcc dot gnu.org
2020-05-02 22:36 ` msebor at gcc dot gnu.org
2020-05-08 18:58 ` msebor at gcc dot gnu.org
2020-05-19 19:09 ` cvs-commit at gcc dot gnu.org
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2022-03-17 19:53 ` msebor at gcc dot gnu.org
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