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* [Bug middle-end/104436] New: spurious -Wdangling-pointer assigning local address to a class passed by value
@ 2022-02-07 23:49 msebor at gcc dot gnu.org
2022-02-07 23:50 ` [Bug middle-end/104436] " msebor at gcc dot gnu.org
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: msebor at gcc dot gnu.org @ 2022-02-07 23:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104436
Bug ID: 104436
Summary: spurious -Wdangling-pointer assigning local address to
a class passed by value
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
The test case below, reduced from
https://bugzilla.redhat.com/show_bug.cgi?id=2051740, shows that
-Wdangling-pointer can be made to trigger by assigning an object of a C++ class
with a user-defined copy ctor that stores a pointer to a local in a function
that takes an argument of the class by value. GCC transforms the by-value
argument of the function to a by-reference, which is one of the use cases the
warning is designed to detect.
$ cat rhbz2051740.C && gcc -O1 -S -Wall -fdump-tree-optimized=/dev/stdout
rhbz2051740.C
struct S
{
S () = default;
S (const S &s): p (s.p) { }
void *p;
};
void foo (S s)
{
int a[3];
S t; t.p = a;
s = t;
}
rhbz2051740.C: In function ‘void foo(S)’:
rhbz2051740.C:13:5: warning: storing the address of local variable ‘a’ in
‘*s.S::p’ [-Wdangling-pointer=]
13 | s = t;
| ~~^~~
rhbz2051740.C:11:7: note: ‘a’ declared here
11 | int a[3];
| ^
rhbz2051740.C:11:7: note: ‘s’ declared here
;; Function foo (_Z3foo1S, funcdef_no=3, decl_uid=2396, cgraph_uid=4,
symbol_order=3)
void foo (struct S & s)
{
int a[3];
<bb 2> [local count: 1073741824]:
s_2(D)->p = &a;
a ={v} {CLOBBER};
return;
}
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/104436] spurious -Wdangling-pointer assigning local address to a class passed by value
2022-02-07 23:49 [Bug middle-end/104436] New: spurious -Wdangling-pointer assigning local address to a class passed by value msebor at gcc dot gnu.org
@ 2022-02-07 23:50 ` msebor at gcc dot gnu.org
2022-02-08 0:22 ` msebor at gcc dot gnu.org
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: msebor at gcc dot gnu.org @ 2022-02-07 23:50 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104436
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2022-02-07
URL| |https://bugzilla.redhat.com
| |/show_bug.cgi?id=2051740
Keywords| |diagnostic
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Blocks| |104077
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104077
[Bug 104077] bogus/missing -Wdangling-pointer
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/104436] spurious -Wdangling-pointer assigning local address to a class passed by value
2022-02-07 23:49 [Bug middle-end/104436] New: spurious -Wdangling-pointer assigning local address to a class passed by value msebor at gcc dot gnu.org
2022-02-07 23:50 ` [Bug middle-end/104436] " msebor at gcc dot gnu.org
@ 2022-02-08 0:22 ` msebor at gcc dot gnu.org
2022-02-08 9:08 ` rguenth at gcc dot gnu.org
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: msebor at gcc dot gnu.org @ 2022-02-08 0:22 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104436
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |msebor at gcc dot gnu.org
--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
It seems that DECL_BY_REFERENCE(fndecl) might be able to tell us if the
argument is a "fake reference" that the by-value argument is substituted for.
Let me see if that works.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/104436] spurious -Wdangling-pointer assigning local address to a class passed by value
2022-02-07 23:49 [Bug middle-end/104436] New: spurious -Wdangling-pointer assigning local address to a class passed by value msebor at gcc dot gnu.org
2022-02-07 23:50 ` [Bug middle-end/104436] " msebor at gcc dot gnu.org
2022-02-08 0:22 ` msebor at gcc dot gnu.org
@ 2022-02-08 9:08 ` rguenth at gcc dot gnu.org
2022-02-08 22:00 ` [Bug middle-end/104436] [12 Regression] " msebor at gcc dot gnu.org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-02-08 9:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104436
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
DECL_BY_REFERENCE on the PARM_DECL tells you that indeed (not on the fndecl).
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/104436] [12 Regression] spurious -Wdangling-pointer assigning local address to a class passed by value
2022-02-07 23:49 [Bug middle-end/104436] New: spurious -Wdangling-pointer assigning local address to a class passed by value msebor at gcc dot gnu.org
` (2 preceding siblings ...)
2022-02-08 9:08 ` rguenth at gcc dot gnu.org
@ 2022-02-08 22:00 ` msebor at gcc dot gnu.org
2022-03-09 13:18 ` rguenth at gcc dot gnu.org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: msebor at gcc dot gnu.org @ 2022-02-08 22:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104436
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |12.0
Summary|spurious -Wdangling-pointer |[12 Regression] spurious
|assigning local address to |-Wdangling-pointer
|a class passed by value |assigning local address to
| |a class passed by value
Keywords| |patch
--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
Patch: https://gcc.gnu.org/pipermail/gcc-patches/2022-February/590046.html
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/104436] [12 Regression] spurious -Wdangling-pointer assigning local address to a class passed by value
2022-02-07 23:49 [Bug middle-end/104436] New: spurious -Wdangling-pointer assigning local address to a class passed by value msebor at gcc dot gnu.org
` (3 preceding siblings ...)
2022-02-08 22:00 ` [Bug middle-end/104436] [12 Regression] " msebor at gcc dot gnu.org
@ 2022-03-09 13:18 ` rguenth at gcc dot gnu.org
2022-03-15 0:27 ` cvs-commit at gcc dot gnu.org
2022-03-15 0:27 ` msebor at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-03-09 13:18 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104436
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P1
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/104436] [12 Regression] spurious -Wdangling-pointer assigning local address to a class passed by value
2022-02-07 23:49 [Bug middle-end/104436] New: spurious -Wdangling-pointer assigning local address to a class passed by value msebor at gcc dot gnu.org
` (4 preceding siblings ...)
2022-03-09 13:18 ` rguenth at gcc dot gnu.org
@ 2022-03-15 0:27 ` cvs-commit at gcc dot gnu.org
2022-03-15 0:27 ` msebor at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-03-15 0:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104436
--- Comment #4 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:373a2dc2be0089ae59b61202a6023458aaaf63d8
commit r12-7650-g373a2dc2be0089ae59b61202a6023458aaaf63d8
Author: Martin Sebor <msebor@redhat.com>
Date: Mon Mar 14 18:23:08 2022 -0600
Avoid -Wdangling-pointer for by-transparent-reference arguments [PR104436].
This change avoids -Wdangling-pointer for by-value arguments transformed
into by-transparent-reference.
Resolves:
PR middle-end/104436 - spurious -Wdangling-pointer assigning local address
to a class passed by value
gcc/ChangeLog:
PR middle-end/104436
* gimple-ssa-warn-access.cc (pass_waccess::check_dangling_stores):
Check for warning suppression. Avoid by-value arguments
transformed
into by-transparent-reference.
gcc/testsuite/ChangeLog:
PR middle-end/104436
* c-c++-common/Wdangling-pointer-8.c: New test.
* g++.dg/warn/Wdangling-pointer-5.C: New test.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/104436] [12 Regression] spurious -Wdangling-pointer assigning local address to a class passed by value
2022-02-07 23:49 [Bug middle-end/104436] New: spurious -Wdangling-pointer assigning local address to a class passed by value msebor at gcc dot gnu.org
` (5 preceding siblings ...)
2022-03-15 0:27 ` cvs-commit at gcc dot gnu.org
@ 2022-03-15 0:27 ` msebor at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: msebor at gcc dot gnu.org @ 2022-03-15 0:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104436
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|ASSIGNED |RESOLVED
--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
Fixed in r12-7650.
^ permalink raw reply [flat|nested] 8+ messages in thread
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2022-02-07 23:49 [Bug middle-end/104436] New: spurious -Wdangling-pointer assigning local address to a class passed by value msebor at gcc dot gnu.org
2022-02-07 23:50 ` [Bug middle-end/104436] " msebor at gcc dot gnu.org
2022-02-08 0:22 ` msebor at gcc dot gnu.org
2022-02-08 9:08 ` rguenth at gcc dot gnu.org
2022-02-08 22:00 ` [Bug middle-end/104436] [12 Regression] " msebor at gcc dot gnu.org
2022-03-09 13:18 ` rguenth at gcc dot gnu.org
2022-03-15 0:27 ` cvs-commit at gcc dot gnu.org
2022-03-15 0:27 ` msebor at gcc dot gnu.org
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