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From: "manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/39121] strange behavior in chained operations
Date: Thu, 25 Jun 2015 20:08:00 -0000 [thread overview]
Message-ID: <bug-39121-4-KvPWpXYF2v@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-39121-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=39121
Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |manu at gcc dot gnu.org
--- Comment #8 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to joe.carnuccio from comment #7)
> *a ^= *b ^= *a ^= *b should work the same way, but it does not (unless you
> compile with -Os).
https://gcc.gnu.org/wiki/FAQ#undefinedbut
>From gcc-bugs-return-490228-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Jun 25 20:19:11 2015
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From: "manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/66673] warning missing for undefined behavior when swapping variables via chained xor
Date: Thu, 25 Jun 2015 20:19:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66673
Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |REOPENED
Last reconfirmed| |2015-06-25
CC| |manu at gcc dot gnu.org
Resolution|INVALID |---
Summary|swapping variables via |warning missing for
|chained xor fails |undefined behavior when
| |swapping variables via
| |chained xor
Ever confirmed|0 |1
--- Comment #7 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #6)
> (In reply to joe.carnuccio from comment #2)
> > -Wall produces no warnings...
>
> Oh, you're using too old GCC. Please try a newer version.
To be fair, GCC 5.1 does not generate a warning either with -Wall -Wextra.
Neither does clang 3.7.
For this testcase:
void swap(int *a, int *b) {
*a ^= *b ^= *a ^= *b;
}
int main() {
int a = 5;
int b = 8;
printf("%d, %d\n", a, b);
a ^= b ^= a ^= b;
__builtin_printf("%d, %d\n", a, b);
swap(&a, &b);
__builtin_printf("%d, %d\n", a, b);
}
Clang warns:
20 : warning: unsequenced modification and access to 'a' [-Wunsequenced]
a ^= b ^= a ^= b;
but gcc is silent.
>From gcc-bugs-return-490229-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Jun 25 20:23:41 2015
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From: "manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/66673] Wsequence-point warning missing when swapping variables via chained xor
Date: Thu, 25 Jun 2015 20:23:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66673
Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |diagnostic
Version|4.4.6 |6.0
Summary|warning missing for |Wsequence-point warning
|undefined behavior when |missing when swapping
|swapping variables via |variables via chained xor
|chained xor |
Severity|major |enhancement
--- Comment #8 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
It seems a missing feature to me. There are several open PRs about
Wsequence-point but this one does not seem to be one of them.
>From gcc-bugs-return-490230-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Jun 25 20:26:23 2015
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From: "manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/66673] Wsequence-point warning missing when swapping variables via chained xor
Date: Thu, 25 Jun 2015 20:26:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66673
Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|REOPENED |RESOLVED
Resolution|--- |FIXED
--- Comment #9 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
Ops, this may have been added recently, it does warn with my GCC 6 build:
test.c:2:6: warning: operation on ‘*a’ may be undefined [-Wsequence-point]
*a ^= *b ^= *a ^= *b;
^
test.c:9:5: warning: operation on ‘a’ may be undefined [-Wsequence-point]
a ^= b ^= a ^= b;
^
Oh, well, then this is INVALID. Sorry for the noise.
>From gcc-bugs-return-490231-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Jun 25 20:35:30 2015
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From: "scovich at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/65656] __builtin_constant_p should always be constexpr
Date: Thu, 25 Jun 2015 20:35:00 -0000
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--- Comment #3 from Ryan Johnson <scovich at gmail dot com> ---
(In reply to Jason Merrill from comment #2)
> Author: jason
> Date: Tue Apr 28 14:43:59 2015
> New Revision: 222531
>
> URL: https://gcc.gnu.org/viewcvs?rev=222531&root=gcc&view=rev
> Log:
> PR c++/65656
> * constexpr.c (cxx_eval_builtin_function_call): Fix
> __builtin_constant_p.
>
> Added:
> trunk/gcc/testsuite/g++.dg/cpp0x/constexpr-builtin3.C
> Modified:
> trunk/gcc/cp/ChangeLog
> trunk/gcc/cp/constexpr.c
Any reason this bug should not be closed as 'fixed' ?
>From gcc-bugs-return-490232-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Jun 25 20:47:32 2015
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From: "huili80 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/66674] New: name lookup failure in lambda construction in a member function of a template class
Date: Thu, 25 Jun 2015 20:47:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idf674
Bug ID: 66674
Summary: name lookup failure in lambda construction in a member
function of a template class
Product: gcc
Version: 4.8.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: huili80 at gmail dot com
Target Milestone: ---
The following causes internal compiler error with gcc4.8.2.
struct base
{
void foo(){};
};
template < typename >
struct derived : base
{
void foo()
{
auto l = [this](){base::foo();};
// workaround:
// auto l = [this](){this->base::foo();};
};
};
int main()
{
derived<int> d;
d.foo();
}
next prev parent reply other threads:[~2015-06-25 20:08 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-39121-4@http.gcc.gnu.org/bugzilla/>
2015-06-25 18:51 ` joe.carnuccio at qlogic dot com
2015-06-25 19:10 ` pinskia at gcc dot gnu.org
2015-06-25 19:40 ` joe.carnuccio at qlogic dot com
2015-06-25 20:08 ` manu at gcc dot gnu.org [this message]
2015-08-10 3:38 ` frankhb1989 at gmail dot com
2009-02-06 19:40 [Bug c/39121] New: strange behavior of a chain of operations nospam at pamies dot cat
2009-02-06 20:10 ` [Bug c/39121] strange behavior in chained operations pinskia at gcc dot gnu dot org
2009-02-06 21:07 ` nospam at pamies dot cat
2009-02-06 21:22 ` rguenth at gcc dot gnu dot org
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