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* [Bug c/105585] New: [12/13 Regression] Spurious stringop-overflow warning with <atomic>
@ 2022-05-12 16:58 ed at catmur dot uk
2022-05-12 16:59 ` [Bug c/105585] " ed at catmur dot uk
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: ed at catmur dot uk @ 2022-05-12 16:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105585
Bug ID: 105585
Summary: [12/13 Regression] Spurious stringop-overflow warning
with <atomic>
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: ed at catmur dot uk
Target Milestone: ---
Reduced (from code in abseil-cpp):
#include <atomic>
struct S {
int i;
std::atomic<int> a;
};
S* q();
void f();
void g(bool b) {
auto p = b ? q() : nullptr;
++p->a;
if (p)
f();
}
In file included from atomic:41,
from <source>:1:
In member function 'std::__atomic_base<_IntTp>::__int_type
std::__atomic_base<_IntTp>::operator++() [with _ITp = int]',
inlined from 'void g(bool)' at <source>:10:3:
bits/atomic_base.h:385:34: warning: 'unsigned int __atomic_add_fetch_4(volatile
void*, unsigned int, int)' writing 4 bytes into a region of size 0 overflows
the destination [-Wstringop-overflow=]
385 | { return __atomic_add_fetch(&_M_i, 1, int(memory_order_seq_cst));
}
| ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/105585] [12/13 Regression] Spurious stringop-overflow warning with <atomic>
2022-05-12 16:58 [Bug c/105585] New: [12/13 Regression] Spurious stringop-overflow warning with <atomic> ed at catmur dot uk
@ 2022-05-12 16:59 ` ed at catmur dot uk
2022-05-12 17:50 ` ed at catmur dot uk
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: ed at catmur dot uk @ 2022-05-12 16:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105585
--- Comment #1 from Ed Catmur <ed at catmur dot uk> ---
Flags: -O1 -Wstringop-overflow=1
https://godbolt.org/z/8r8roz7Pa
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c/105585] [12/13 Regression] Spurious stringop-overflow warning with <atomic>
2022-05-12 16:58 [Bug c/105585] New: [12/13 Regression] Spurious stringop-overflow warning with <atomic> ed at catmur dot uk
2022-05-12 16:59 ` [Bug c/105585] " ed at catmur dot uk
@ 2022-05-12 17:50 ` ed at catmur dot uk
2022-05-13 7:55 ` [Bug tree-optimization/105585] " rguenth at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: ed at catmur dot uk @ 2022-05-12 17:50 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105585
--- Comment #2 from Ed Catmur <ed at catmur dot uk> ---
Affected code: https://github.com/abseil/abseil-cpp/issues/1175
The proposed patch to abseil-cpp corresponds to adding an assumption that `b`
is true above.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105585] [12/13 Regression] Spurious stringop-overflow warning with <atomic>
2022-05-12 16:58 [Bug c/105585] New: [12/13 Regression] Spurious stringop-overflow warning with <atomic> ed at catmur dot uk
2022-05-12 16:59 ` [Bug c/105585] " ed at catmur dot uk
2022-05-12 17:50 ` ed at catmur dot uk
@ 2022-05-13 7:55 ` rguenth at gcc dot gnu.org
2022-05-13 12:02 ` [Bug tree-optimization/105585] [12/13 Regression] Spurious stringop-overflow warning with <atomic> since r12-4725-g88b504b7a8c5affb marxin at gcc dot gnu.org
2022-05-17 14:15 ` msebor at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-05-13 7:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105585
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |12.2
Keywords| |diagnostic
Component|c |tree-optimization
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105585] [12/13 Regression] Spurious stringop-overflow warning with <atomic> since r12-4725-g88b504b7a8c5affb
2022-05-12 16:58 [Bug c/105585] New: [12/13 Regression] Spurious stringop-overflow warning with <atomic> ed at catmur dot uk
` (2 preceding siblings ...)
2022-05-13 7:55 ` [Bug tree-optimization/105585] " rguenth at gcc dot gnu.org
@ 2022-05-13 12:02 ` marxin at gcc dot gnu.org
2022-05-17 14:15 ` msebor at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: marxin at gcc dot gnu.org @ 2022-05-13 12:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105585
Martin Liška <marxin at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|[12/13 Regression] Spurious |[12/13 Regression] Spurious
|stringop-overflow warning |stringop-overflow warning
|with <atomic> |with <atomic> since
| |r12-4725-g88b504b7a8c5affb
Status|UNCONFIRMED |NEW
Last reconfirmed| |2022-05-13
CC| |marxin at gcc dot gnu.org,
| |msebor at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> ---
Started with r12-4725-g88b504b7a8c5affb.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105585] [12/13 Regression] Spurious stringop-overflow warning with <atomic> since r12-4725-g88b504b7a8c5affb
2022-05-12 16:58 [Bug c/105585] New: [12/13 Regression] Spurious stringop-overflow warning with <atomic> ed at catmur dot uk
` (3 preceding siblings ...)
2022-05-13 12:02 ` [Bug tree-optimization/105585] [12/13 Regression] Spurious stringop-overflow warning with <atomic> since r12-4725-g88b504b7a8c5affb marxin at gcc dot gnu.org
@ 2022-05-17 14:15 ` msebor at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: msebor at gcc dot gnu.org @ 2022-05-17 14:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105585
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|NEW |RESOLVED
--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
The warning is caused by the if statement: if p is null, accessing the p->a
member is undefined. It triggers because the GCC optimizer splits the code
into two branches: one with a nonnull p and another with a null p. The second
one triggers the warning.
If p can be null then moving the increment to the body of the if statement
avoids the undefined behavior (and the warning). If p cannot be null then
making the if statement unconditional also avoids the warning.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2022-05-17 14:15 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2022-05-12 16:58 [Bug c/105585] New: [12/13 Regression] Spurious stringop-overflow warning with <atomic> ed at catmur dot uk
2022-05-12 16:59 ` [Bug c/105585] " ed at catmur dot uk
2022-05-12 17:50 ` ed at catmur dot uk
2022-05-13 7:55 ` [Bug tree-optimization/105585] " rguenth at gcc dot gnu.org
2022-05-13 12:02 ` [Bug tree-optimization/105585] [12/13 Regression] Spurious stringop-overflow warning with <atomic> since r12-4725-g88b504b7a8c5affb marxin at gcc dot gnu.org
2022-05-17 14:15 ` msebor at gcc dot gnu.org
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