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* [Bug c++/105571] New: Spurious "set but not used" on static constexpr local, used in lambda
@ 2022-05-11 19:06 cuzdav at gmail dot com
2022-05-26 18:38 ` [Bug c++/105571] " johelegp at gmail dot com
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: cuzdav at gmail dot com @ 2022-05-11 19:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105571
Bug ID: 105571
Summary: Spurious "set but not used" on static constexpr local,
used in lambda
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: cuzdav at gmail dot com
Target Milestone: ---
With -Wall, in every c++ language level on virtually every version of g++ as
far back as 4.9, g++ warns ("variable 'THIS_IS_USED' set but not used") on the
following complete code:
template <typename IterT, typename FuncT>
void for_each(IterT b, IterT e, FuncT f) {
while (b != e) {
f(*b++);
}
}
volatile int sink;
void xxx(int x) {
sink = x;
}
void foo() {
static constexpr auto THIS_IS_USED = 1;
int arr[10]{1,2,3,4,5,6,7,8,9,10};
for_each(arr, arr+10, [](auto v) {
xxx(THIS_IS_USED + v);
});
}
<source>: In function 'void foo()':
<source>:15:27: warning: variable 'THIS_IS_USED' set but not used
[-Wunused-but-set-variable]
15 | static constexpr auto THIS_IS_USED = 1;
| ^~~~~~~~~~~~
Compiler returned: 0
https://godbolt.org/z/b1s5Yqb3r
This appears to be related to the "auto" parameter in the lambda. Changing it
to 'int' makes the problem go away.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/105571] Spurious "set but not used" on static constexpr local, used in lambda
2022-05-11 19:06 [Bug c++/105571] New: Spurious "set but not used" on static constexpr local, used in lambda cuzdav at gmail dot com
@ 2022-05-26 18:38 ` johelegp at gmail dot com
2022-05-26 18:39 ` johelegp at gmail dot com
2022-09-23 16:25 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: johelegp at gmail dot com @ 2022-05-26 18:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105571
Johel Ernesto Guerrero Peña <johelegp at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |johelegp at gmail dot com
--- Comment #1 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
*** Bug 105743 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/105571] Spurious "set but not used" on static constexpr local, used in lambda
2022-05-11 19:06 [Bug c++/105571] New: Spurious "set but not used" on static constexpr local, used in lambda cuzdav at gmail dot com
2022-05-26 18:38 ` [Bug c++/105571] " johelegp at gmail dot com
@ 2022-05-26 18:39 ` johelegp at gmail dot com
2022-09-23 16:25 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: johelegp at gmail dot com @ 2022-05-26 18:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105571
--- Comment #2 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Simplified reproducer from Bug 105743:
See https://godbolt.org/z/xq16xac15.
```C++
void f(auto x) { x(0); }
void g() {
static constexpr auto h = [](...) { };
f([](auto x) { h(x); });
}
```
```
<source>: In function 'void g()':
<source>:3:25: warning: variable 'h' set but not used
[-Wunused-but-set-variable]
3 | static constexpr auto h = [](...) { };
| ^
```
Arguably, `h(x)` could perform ADL on `x`. But perhaps it'd be better to stay
silent, like the other compilers.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/105571] Spurious "set but not used" on static constexpr local, used in lambda
2022-05-11 19:06 [Bug c++/105571] New: Spurious "set but not used" on static constexpr local, used in lambda cuzdav at gmail dot com
2022-05-26 18:38 ` [Bug c++/105571] " johelegp at gmail dot com
2022-05-26 18:39 ` johelegp at gmail dot com
@ 2022-09-23 16:25 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-09-23 16:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105571
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |DUPLICATE
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 88804. The problem is with templated lambdas (auto param is really a
templated lambda).
*** This bug has been marked as a duplicate of bug 88804 ***
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-09-23 16:25 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2022-05-11 19:06 [Bug c++/105571] New: Spurious "set but not used" on static constexpr local, used in lambda cuzdav at gmail dot com
2022-05-26 18:38 ` [Bug c++/105571] " johelegp at gmail dot com
2022-05-26 18:39 ` johelegp at gmail dot com
2022-09-23 16:25 ` pinskia at gcc dot gnu.org
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