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* [Bug c++/44186] New: Wrong code generated with -O2 and above
@ 2010-05-18 3:37 eyakubovich at gmail dot com
2010-05-18 3:50 ` Andrew Pinski
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: eyakubovich at gmail dot com @ 2010-05-18 3:37 UTC (permalink / raw)
To: gcc-bugs
This is a stripped down code from proposed Boost.Move library. Asserts don't
fire with -O0 and -O1 but do with -O2 and -O3
#include <assert.h>
template <class T>
class rv : public T
{
rv();
~rv();
rv(rv const&);
void operator=(rv const&);
};
template <class T>
rv<T>& move(T& x)
{
return *static_cast<rv<T>* >(&x);
}
//A movable class
class movable
{
movable(movable &);
movable& operator=(movable&);
public:
operator rv<movable>&()
{ return *reinterpret_cast< rv<movable>* >(this); }
operator const rv<movable>&() const
{ return *reinterpret_cast<const rv<movable>* >(this); }
private:
int value_;
public:
movable() : value_(1){}
//Move constructor and assignment
movable(rv<movable>& m)
{ value_ = m.value_; m.value_ = 0; }
movable & operator=(rv<movable>& m)
{ value_ = m.value_; m.value_ = 0; return *this; }
bool moved() const //Observer
{ return value_ == 0; }
};
movable function(movable m)
{
return movable(move(m));
}
int main()
{
{
movable m;
movable m2(move(m));
assert(m.moved());
assert(!m2.moved());
}
{
movable m;
movable m3(function(movable(move(m))));
assert(m.moved());
assert(!m3.moved());
}
{
movable m;
movable m4(function(move(m)));
assert(m.moved());
assert(!m4.moved());
}
return 0;
}
--
Summary: Wrong code generated with -O2 and above
Product: gcc
Version: 4.4.4
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: eyakubovich at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44186
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [Bug c++/44186] New: Wrong code generated with -O2 and above
2010-05-18 3:37 [Bug c++/44186] New: Wrong code generated with -O2 and above eyakubovich at gmail dot com
@ 2010-05-18 3:50 ` Andrew Pinski
2010-05-18 3:50 ` [Bug c++/44186] " pinskia at gmail dot com
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: Andrew Pinski @ 2010-05-18 3:50 UTC (permalink / raw)
To: gcc-bugzilla; +Cc: gcc-bugs
Sent from my iPhone
On May 17, 2010, at 8:37 PM, "eyakubovich at gmail dot com" <gcc-bugzilla@gcc.gnu.org
> wrote:
> This is a stripped down code from proposed Boost.Move library.
> Asserts don't
> fire with -O0 and -O1 but do with -O2 and -O3
>
> #include <assert.h>
>
> template <class T>
> class rv : public T
> {
> rv();
> ~rv();
> rv(rv const&);
> void operator=(rv const&);
> };
>
> template <class T>
> rv<T>& move(T& x)
> {
> return *static_cast<rv<T>* >(&x);
> }
>
> //A movable class
> class movable
> {
> movable(movable &);
> movable& operator=(movable&);
> public:
> operator rv<movable>&()
> { return *reinterpret_cast< rv<movable>* >(this); }
> operator const rv<movable>&() const
> { return *reinterpret_cast<const rv<movable>* >(this); }
>
> private:
> int value_;
>
> public:
> movable() : value_(1){}
>
> //Move constructor and assignment
> movable(rv<movable>& m)
> { value_ = m.value_; m.value_ = 0; }
>
> movable & operator=(rv<movable>& m)
> { value_ = m.value_; m.value_ = 0; return *this; }
>
> bool moved() const //Observer
> { return value_ == 0; }
> };
>
> movable function(movable m)
> {
> return movable(move(m));
> }
>
> int main()
> {
> {
> movable m;
> movable m2(move(m));
The above code cause aliasing violations because you acess a movable
object via a rv<movable> (from now on just refered to as rv for short)
one. So you have a type rv who's base type is movable. note both rv
and movable are non pods which I think removes the case for upcasting
and then accessing the first member.
> assert(m.moved());
> assert(!m2.moved());
> }
>
> {
> movable m;
> movable m3(function(movable(move(m))));
> assert(m.moved());
> assert(!m3.moved());
> }
>
> {
> movable m;
> movable m4(function(move(m)));
> assert(m.moved());
> assert(!m4.moved());
> }
>
> return 0;
> }
>
>
> --
> Summary: Wrong code generated with -O2 and above
> Product: gcc
> Version: 4.4.4
> Status: UNCONFIRMED
> Severity: normal
> Priority: P3
> Component: c++
> AssignedTo: unassigned at gcc dot gnu dot org
> ReportedBy: eyakubovich at gmail dot com
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44186
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/44186] Wrong code generated with -O2 and above
2010-05-18 3:37 [Bug c++/44186] New: Wrong code generated with -O2 and above eyakubovich at gmail dot com
2010-05-18 3:50 ` Andrew Pinski
@ 2010-05-18 3:50 ` pinskia at gmail dot com
2010-05-18 6:31 ` pinskia at gcc dot gnu dot org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gmail dot com @ 2010-05-18 3:50 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from pinskia at gmail dot com 2010-05-18 03:50 -------
Subject: Re: New: Wrong code generated with -O2 and above
Sent from my iPhone
On May 17, 2010, at 8:37 PM, "eyakubovich at gmail dot com"
<gcc-bugzilla@gcc.gnu.org
> wrote:
> This is a stripped down code from proposed Boost.Move library.
> Asserts don't
> fire with -O0 and -O1 but do with -O2 and -O3
>
> #include <assert.h>
>
> template <class T>
> class rv : public T
> {
> rv();
> ~rv();
> rv(rv const&);
> void operator=(rv const&);
> };
>
> template <class T>
> rv<T>& move(T& x)
> {
> return *static_cast<rv<T>* >(&x);
> }
>
> //A movable class
> class movable
> {
> movable(movable &);
> movable& operator=(movable&);
> public:
> operator rv<movable>&()
> { return *reinterpret_cast< rv<movable>* >(this); }
> operator const rv<movable>&() const
> { return *reinterpret_cast<const rv<movable>* >(this); }
>
> private:
> int value_;
>
> public:
> movable() : value_(1){}
>
> //Move constructor and assignment
> movable(rv<movable>& m)
> { value_ = m.value_; m.value_ = 0; }
>
> movable & operator=(rv<movable>& m)
> { value_ = m.value_; m.value_ = 0; return *this; }
>
> bool moved() const //Observer
> { return value_ == 0; }
> };
>
> movable function(movable m)
> {
> return movable(move(m));
> }
>
> int main()
> {
> {
> movable m;
> movable m2(move(m));
The above code cause aliasing violations because you acess a movable
object via a rv<movable> (from now on just refered to as rv for short)
one. So you have a type rv who's base type is movable. note both rv
and movable are non pods which I think removes the case for upcasting
and then accessing the first member.
> assert(m.moved());
> assert(!m2.moved());
> }
>
> {
> movable m;
> movable m3(function(movable(move(m))));
> assert(m.moved());
> assert(!m3.moved());
> }
>
> {
> movable m;
> movable m4(function(move(m)));
> assert(m.moved());
> assert(!m4.moved());
> }
>
> return 0;
> }
>
>
> --
> Summary: Wrong code generated with -O2 and above
> Product: gcc
> Version: 4.4.4
> Status: UNCONFIRMED
> Severity: normal
> Priority: P3
> Component: c++
> AssignedTo: unassigned at gcc dot gnu dot org
> ReportedBy: eyakubovich at gmail dot com
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44186
>
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44186
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/44186] Wrong code generated with -O2 and above
2010-05-18 3:37 [Bug c++/44186] New: Wrong code generated with -O2 and above eyakubovich at gmail dot com
2010-05-18 3:50 ` Andrew Pinski
2010-05-18 3:50 ` [Bug c++/44186] " pinskia at gmail dot com
@ 2010-05-18 6:31 ` pinskia at gcc dot gnu dot org
2010-05-18 9:26 ` paolo dot carlini at oracle dot com
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2010-05-18 6:31 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from pinskia at gcc dot gnu dot org 2010-05-18 06:31 -------
*** Bug 44187 has been marked as a duplicate of this bug. ***
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44186
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/44186] Wrong code generated with -O2 and above
2010-05-18 3:37 [Bug c++/44186] New: Wrong code generated with -O2 and above eyakubovich at gmail dot com
` (2 preceding siblings ...)
2010-05-18 6:31 ` pinskia at gcc dot gnu dot org
@ 2010-05-18 9:26 ` paolo dot carlini at oracle dot com
2010-05-18 9:53 ` rguenth at gcc dot gnu dot org
2010-05-18 10:08 ` paolo dot carlini at oracle dot com
5 siblings, 0 replies; 7+ messages in thread
From: paolo dot carlini at oracle dot com @ 2010-05-18 9:26 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from paolo dot carlini at oracle dot com 2010-05-18 09:25 -------
Note however, that both the warning and the miscompilation do not happen with
current 4_5-branch and mainline...
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44186
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/44186] Wrong code generated with -O2 and above
2010-05-18 3:37 [Bug c++/44186] New: Wrong code generated with -O2 and above eyakubovich at gmail dot com
` (3 preceding siblings ...)
2010-05-18 9:26 ` paolo dot carlini at oracle dot com
@ 2010-05-18 9:53 ` rguenth at gcc dot gnu dot org
2010-05-18 10:08 ` paolo dot carlini at oracle dot com
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2010-05-18 9:53 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from rguenth at gcc dot gnu dot org 2010-05-18 09:53 -------
(In reply to comment #3)
> Note however, that both the warning and the miscompilation do not happen with
> current 4_5-branch and mainline...
Which is because we see the must-alias and punt. After all this just
invokes undefined behavior which includes "works" and "does not work".
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44186
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/44186] Wrong code generated with -O2 and above
2010-05-18 3:37 [Bug c++/44186] New: Wrong code generated with -O2 and above eyakubovich at gmail dot com
` (4 preceding siblings ...)
2010-05-18 9:53 ` rguenth at gcc dot gnu dot org
@ 2010-05-18 10:08 ` paolo dot carlini at oracle dot com
5 siblings, 0 replies; 7+ messages in thread
From: paolo dot carlini at oracle dot com @ 2010-05-18 10:08 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from paolo dot carlini at oracle dot com 2010-05-18 10:08 -------
Ok ;)
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44186
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2010-05-18 10:08 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2010-05-18 3:37 [Bug c++/44186] New: Wrong code generated with -O2 and above eyakubovich at gmail dot com
2010-05-18 3:50 ` Andrew Pinski
2010-05-18 3:50 ` [Bug c++/44186] " pinskia at gmail dot com
2010-05-18 6:31 ` pinskia at gcc dot gnu dot org
2010-05-18 9:26 ` paolo dot carlini at oracle dot com
2010-05-18 9:53 ` rguenth at gcc dot gnu dot org
2010-05-18 10:08 ` paolo dot carlini at oracle dot com
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