[Bug middle-end/38503] New: [4.4 regression] warnings from -isystem headers strikes back.

[Bug middle-end/38503] New: [4.4 regression] warnings from -isystem headers strikes back.

[pluto at agmk dot net]

/local/devel/toolchain44/x86_64-gnu-linux/bin/x86_64-gnu-linux-g++ -dumpversion
4.4.0
/local/devel/toolchain44/x86_64-gnu-linux/bin/x86_64-gnu-linux-g++ -c -Wall -O2
-g0 -fPIC --save-temps \
        -isystem ./buildenv/linux/gcc-4.4/64/boost-stlport-1.37.0/include \
        bug.cpp
bug.cpp: In function 'void foo()':
bug.cpp:6: warning: dereferencing pointer '<anonymous>' does break
strict-aliasing rules
./buildenv/linux/gcc-4.4/64/boost-stlport-1.37.0/include/boost/optional/optional.hpp:315:
note: initialized from here
bug.cpp:6: warning: dereferencing pointer '<anonymous>' does break
strict-aliasing rules
./buildenv/linux/gcc-4.4/64/boost-stlport-1.37.0/include/boost/optional/optional.hpp:594:
note: initialized from here

on 4.3.2 it compiles cleanly.


-- 
           Summary: [4.4 regression] warnings from -isystem headers strikes
                    back.
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pluto at agmk dot net
GCC target triplet: x86_64-gnu-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[pluto at agmk dot net]

------- Comment #1 from pluto at agmk dot net  2008-12-12 11:37 -------
Created an attachment (id=16897)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16897&action=view)
testcase.

to reproduce bug you also need the boost-1.37.0 headers.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2008-12-12 11:53 -------
Related to/dup of PR38477.  I'll leave this one for the system header issue
and PR38477 for the libstdc++/C++ alias problem.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org
OtherBugsDependingO|                            |38477
              nThis|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |diagnostic
           Priority|P3                          |P2
   Last reconfirmed|0000-00-00 00:00:00         |2009-01-05 11:24:29
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[jakub at gcc dot gnu dot org]

------- Comment #3 from jakub at gcc dot gnu dot org  2009-01-09 10:25 -------
Please preprocess the testcase.  Whether a header was a system header or not is
recorded in # <linenum> directives in the preprocessed output.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |WAITING


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[pluto at agmk dot net]

------- Comment #4 from pluto at agmk dot net  2009-01-09 19:52 -------
Created an attachment (id=17067)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17067&action=view)
preprocessed testcase.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 1139 bytes --]



------- Comment #5 from rguenth at gcc dot gnu dot org  2009-01-12 13:54 -------
I can't seem to compile the preprocessed source:

In file included from ./sys-headers/boost/mpl/int.hpp:21,
                 from
./sys-headers/boost/type_traits/detail/template_arity_spec
.hpp:11,
                 from
./sys-headers/boost/type_traits/detail/bool_trait_def.hpp:
15,
                 from ./sys-headers/boost/type_traits/is_same.hpp:32,
                 from ./sys-headers/boost/type_traits/intrinsics.hpp:131,
                 from ./sys-headers/boost/type_traits/alignment_of.hpp:16,
                 from ./sys-headers/boost/optional/optional.hpp:22,
                 from ./sys-headers/boost/optional.hpp:16,
                 from bug.cpp:2:
./sys-headers/boost/mpl/aux_/integral_wrapper.hpp:43: error: expected
unqualifie
d-id before ‘int’
./sys-headers/boost/mpl/aux_/integral_wrapper.hpp:43: error: expected ‘)’
before
 ‘int’
...

Note that the warning is from bug.cpp:6, not a system header anyway (the
_note_ is from a system header, do you want that to disappear?)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[pluto at agmk dot net]

------- Comment #6 from pluto at agmk dot net  2009-01-12 15:01 -------
Created an attachment (id=17077)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17077&action=view)
full testcase (src + .ii + mkefile)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[pluto at agmk dot net]

------- Comment #7 from pluto at agmk dot net  2009-01-12 15:10 -------
(In reply to comment #5)
> I can't seem to compile the preprocessed source:

i've attached a new full archive.

$ make
rm -f *.ii *.o *.s
/local/devel/toolchain44/x86_64-gnu-linux/bin/x86_64-gnu-linux-g++ -c -Wall -O2
-g0 -fPIC --save-temps -isystem ./sys-headers bug.cpp
bug.cpp: In function 'void foo()':
bug.cpp:6: warning: dereferencing pointer '<anonymous>' does break
strict-aliasing rules
./sys-headers/boost/optional/optional.hpp:315: note: initialized from here
bug.cpp:6: warning: dereferencing pointer '<anonymous>' does break
strict-aliasing rules
./sys-headers/boost/optional/optional.hpp:594: note: initialized from here

> Note that the warning is from bug.cpp:6, not a system header anyway

looks weird, because i can't see any dereferencing in bug.cpp:6
there's only trivial cctor which copies an enum.

for me it looks like the <warning> comes from boost::optional::
::aligned_storage::adress() manipulations inside boost system headers.

> (the _note_ is from a system header, do you want that to disappear?)

i want to disappear'em all :-)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenther at suse dot de]

------- Comment #8 from rguenther at suse dot de  2009-01-12 15:16 -------
Subject: Re:  [4.4 regression] warnings from -isystem
 headers strikes back.

On Mon, 12 Jan 2009, pluto at agmk dot net wrote:

> 
> 
> ------- Comment #7 from pluto at agmk dot net  2009-01-12 15:10 -------
> (In reply to comment #5)
> > I can't seem to compile the preprocessed source:
> 
> i've attached a new full archive.
> 
> $ make
> rm -f *.ii *.o *.s
> /local/devel/toolchain44/x86_64-gnu-linux/bin/x86_64-gnu-linux-g++ -c -Wall -O2
> -g0 -fPIC --save-temps -isystem ./sys-headers bug.cpp
> bug.cpp: In function 'void foo()':
> bug.cpp:6: warning: dereferencing pointer '<anonymous>' does break
> strict-aliasing rules
> ./sys-headers/boost/optional/optional.hpp:315: note: initialized from here
> bug.cpp:6: warning: dereferencing pointer '<anonymous>' does break
> strict-aliasing rules
> ./sys-headers/boost/optional/optional.hpp:594: note: initialized from here
> 
> > Note that the warning is from bug.cpp:6, not a system header anyway
> 
> looks weird, because i can't see any dereferencing in bug.cpp:6
> there's only trivial cctor which copies an enum.
> 
> for me it looks like the <warning> comes from boost::optional::
> ::aligned_storage::adress() manipulations inside boost system headers.
> 
> > (the _note_ is from a system header, do you want that to disappear?)
> 
> i want to disappear'em all :-)

Fair enough ;)  The compiler just warns that in a second it will remove
that dereference (ok, only on the alias-improvements branch).

Richard.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2009-01-14 16:48 -------
I just installed a fix - can you verify if all the annoying warnigns are gone? 
Thx!


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[pluto at agmk dot net]

------- Comment #10 from pluto at agmk dot net  2009-01-14 18:29 -------
(In reply to comment #9)
> I just installed a fix - can you verify if all the annoying warnigns are gone? 
> Thx!
> 

they are still there.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenther at suse dot de]

------- Comment #11 from rguenther at suse dot de  2009-01-14 20:50 -------
Subject: Re:  [4.4 regression] warnings from -isystem
 headers strikes back.

On Wed, 14 Jan 2009, pluto at agmk dot net wrote:

> ------- Comment #10 from pluto at agmk dot net  2009-01-14 18:29 -------
> (In reply to comment #9)
> > I just installed a fix - can you verify if all the annoying warnigns are gone? 
> > Thx!
> > 
> 
> they are still there.

Then they are either real bugs in the testcase or in PTA.

Richard.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

------- Comment #12 from rguenth at gcc dot gnu dot org  2009-01-23 16:52 -------
this is placement-new related.

D.20941_8 = &ox

ox = { } no-tbaa-pruning
D.20941_8 = { ox }

alias warning for D.20941_8

After alias:

  ox.D.20531.m_initialized = 0;
  D.20941_8 = (struct X *) &ox.D.20531.m_storage.dummy_.data[0];
  D.20941_8->e_ = 0;
  ox.D.20531.m_initialized = 1;
  D.20946_10 = ox.D.20531.m_initialized;

Before:

  ox.D.20531.m_initialized ={v} 0;
  <<<change_dynamic_type (struct X *) &ox.D.20531.m_storage.dummy_.data[0])>>>
  D.20941_8 = (struct X *) &ox.D.20531.m_storage.dummy_.data[0];
  D.20941_8->e_ ={v} 0;
  ox.D.20531.m_initialized ={v} 1;
  D.20946_10 = ox.D.20531.m_initialized;

so it looks like we do placement new on _parts_ of an object that
continues to live over that placement new.

Uh oh.  Is this even legal?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

------- Comment #13 from rguenth at gcc dot gnu dot org  2009-01-24 15:56 -------
Testcase:

inline void *operator new (__SIZE_TYPE__, void *__p) throw() { return __p; }

struct Y {
  Y() {}
  int i;
};

struct X {
  X() {}
  void construct(const Y& y)
  {
    new (&m_data[0]) Y(y);
  }
  bool initialized;
  char m_data[sizeof (Y)];
};

void bar(const X&);
void foo(Y& y)
{
  X x;
  x.construct(y);
  x.initialized = true;
  bar(x);
}


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW
   Last reconfirmed|2009-01-05 11:24:29         |2009-01-24 15:56:04
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

------- Comment #14 from rguenth at gcc dot gnu dot org  2009-01-24 17:00 -------
placement new handling is still completely broken.  And of course unfixable
without severely pessimizing TBAA.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
           Priority|P2                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

------- Comment #15 from rguenth at gcc dot gnu dot org  2009-01-24 17:50 -------
Mine.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2009-01-24 15:56:04         |2009-01-24 17:50:17
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

------- Comment #16 from rguenth at gcc dot gnu dot org  2009-01-27 10:43 -------
Subject: Bug 38503

Author: rguenth
Date: Tue Jan 27 10:42:59 2009
New Revision: 143700

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=143700
Log:
2009-01-27  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/38503
        * cfgexpand.c (expand_gimple_basic_block): Ignore
        GIMPLE_CHANGE_DYNAMIC_TYPE during expansion.
        * tree-ssa-structalias.c (set_uids_in_ptset): Do not prune
        variables that cannot have TBAA applied.
        (compute_points_to_sets): Do not remove GIMPLE_CHANGE_DYNAMIC_TYPE
        statements.

        * g++.dg/warn/Wstrict-aliasing-bogus-placement-new.C: New testcase.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-placement-new.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/cfgexpand.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-structalias.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

------- Comment #17 from rguenth at gcc dot gnu dot org  2009-01-27 10:43 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[hjl at gcc dot gnu dot org]

------- Comment #18 from hjl at gcc dot gnu dot org  2009-01-30 17:32 -------
Subject: Bug 38503

Author: hjl
Date: Fri Jan 30 17:31:24 2009
New Revision: 143798

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=143798
Log:
2009-01-30  H.J. Lu  <hongjiu.lu@intel.com>

        2009-01-27  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/38503
        * g++.dg/warn/Wstrict-aliasing-bogus-placement-new.C: New testcase.

        2009-01-26  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/38745
        * g++.dg/torture/pr38745.C: New testcase.

        2009-01-26  Richard Guenther  <rguenther@suse.de>

        PR middle-end/38851
        * g++.dg/warn/Wuninitialized-1.C: New testcase.

        2009-01-20  Andrew Pinski  <andrew_pinski@playstation.sony.com>
                    Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/38747
        PR tree-optimization/38748
        * gcc.dg/tree-ssa/struct-aliasing-1.c: New test.
        * gcc.c-torture/execute/struct-aliasing-1.c: Likewise.

Added:
    branches/gcc-4_3-branch/gcc/testsuite/g++.dg/torture/pr38745.C
      - copied unchanged from r143797,
trunk/gcc/testsuite/g++.dg/torture/pr38745.C
   
branches/gcc-4_3-branch/gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-placement-new.C
      - copied unchanged from r143797,
trunk/gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-placement-new.C
    branches/gcc-4_3-branch/gcc/testsuite/g++.dg/warn/Wuninitialized-1.C
      - copied unchanged from r143797,
trunk/gcc/testsuite/g++.dg/warn/Wuninitialized-1.C
   
branches/gcc-4_3-branch/gcc/testsuite/gcc.c-torture/execute/struct-aliasing-1.c
      - copied unchanged from r143797,
trunk/gcc/testsuite/gcc.c-torture/execute/struct-aliasing-1.c
    branches/gcc-4_3-branch/gcc/testsuite/gcc.dg/tree-ssa/struct-aliasing-1.c
      - copied unchanged from r143797,
trunk/gcc/testsuite/gcc.dg/tree-ssa/struct-aliasing-1.c
Modified:
    branches/gcc-4_3-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[pluto at agmk dot net]

------- Comment #19 from pluto at agmk dot net  2009-02-02 08:55 -------
(In reply to comment #16)
> Subject: Bug 38503
> 
> Author: rguenth
> Date: Tue Jan 27 10:42:59 2009
> New Revision: 143700

this patch doesn't fix testcase that i found yesterday.

i found another testcase for gcc-4.4.0-20090130 not covered
by patch commited on january, the 27.

$ cat bug2.cpp
#include <boost/optional.hpp>
#include <string>
struct X
{
        std::string s;
        bool f;
};
extern boost::optional< X > x;
void foo( std::string const& );
bool bar()
{
        if ( !x )
                return false;
        if ( x->f )
                foo( x->s );
        return false;
}

$ make
rm -f *.ii *.o *.s
/local/devel/toolchain44/x86_64-gnu-linux/bin/x86_64-gnu-linux-g++ -c -Wall -O2
-g0 -fPIC --save-temps -isystem ./sys-headers bug2.cpp
bug2.cpp: In function 'bool bar()':
bug2.cpp:14: warning: dereferencing pointer '<anonymous>' does break
strict-aliasing rules
bug2.cpp:14: note: initialized from here


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

------- Comment #20 from rguenth at gcc dot gnu dot org  2009-02-02 10:23 -------
Same issue.  Only possible fix is to not apply TBAA pruning to escaped
symbols, which will - well - basically disable TBAA.  Testcase:

inline void *operator new (__SIZE_TYPE__, void *__p) throw() { return __p; }

struct Y {
  Y() {}
  int i;
};

struct X {
  X() {}
  void construct(const Y& y)
  {
    new (&m_data[0]) Y(y);
  }
  template <class T>
  Y& get() { return reinterpret_cast<Y&>(m_data); }
  bool initialized;
  char m_data[sizeof (Y)];
};

X x;

void bar(const X&);
void foo(Y& y)
{
  x.get<Y>() = y;
  x.initialized = true;
  bar(x);
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[pluto at agmk dot net]

------- Comment #21 from pluto at agmk dot net  2009-02-27 10:29 -------
(In reply to comment #20)
> Same issue.  Only possible fix is to not apply TBAA pruning to escaped
> symbols, which will - well - basically disable TBAA.  Testcase:

waht about this testcase?
the bug is marked as fixed but warnings are still present?

> inline void *operator new (__SIZE_TYPE__, void *__p) throw() { return __p; }
> 
> struct Y {
>   Y() {}
>   int i;
> };
> 
> struct X {
>   X() {}
>   void construct(const Y& y)
>   {
>     new (&m_data[0]) Y(y);
>   }
>   template <class T>
>   Y& get() { return reinterpret_cast<Y&>(m_data); }
>   bool initialized;
>   char m_data[sizeof (Y)];
> };
> 
> X x;
> 
> void bar(const X&);
> void foo(Y& y)
> {
>   x.get<Y>() = y;
>   x.initialized = true;
>   bar(x);
> }
> 

t.cpp: In member function 'Y& X::get() [with T = Y]':
t.cpp:25:   instantiated from here
t.cpp:15: warning: dereferencing type-punned pointer will break strict-aliasing
rules
t.cpp: In function 'void foo(Y&)':
t.cpp:25: warning: dereferencing pointer '<anonymous>' does break
strict-aliasing rules
t.cpp:25: note: initialized from here


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenther at suse dot de]

------- Comment #22 from rguenther at suse dot de  2009-02-27 10:33 -------
Subject: Re:  [4.4 regression] warnings from -isystem
 headers strikes back.

On Fri, 27 Feb 2009, pluto at agmk dot net wrote:

> ------- Comment #21 from pluto at agmk dot net  2009-02-27 10:29 -------
> (In reply to comment #20)
> > Same issue.  Only possible fix is to not apply TBAA pruning to escaped
> > symbols, which will - well - basically disable TBAA.  Testcase:
> 
> waht about this testcase?
> the bug is marked as fixed but warnings are still present?

The original reported problem is gone.  The testcase below is unfixable.

> > inline void *operator new (__SIZE_TYPE__, void *__p) throw() { return __p; }
> > 
> > struct Y {
> >   Y() {}
> >   int i;
> > };
> > 
> > struct X {
> >   X() {}
> >   void construct(const Y& y)
> >   {
> >     new (&m_data[0]) Y(y);
> >   }
> >   template <class T>
> >   Y& get() { return reinterpret_cast<Y&>(m_data); }
> >   bool initialized;
> >   char m_data[sizeof (Y)];
> > };
> > 
> > X x;
> > 
> > void bar(const X&);
> > void foo(Y& y)
> > {
> >   x.get<Y>() = y;
> >   x.initialized = true;
> >   bar(x);
> > }
> > 
> 
> t.cpp: In member function 'Y& X::get() [with T = Y]':
> t.cpp:25:   instantiated from here
> t.cpp:15: warning: dereferencing type-punned pointer will break strict-aliasing
> rules
> t.cpp: In function 'void foo(Y&)':
> t.cpp:25: warning: dereferencing pointer '<anonymous>' does break
> strict-aliasing rules
> t.cpp:25: note: initialized from here
> 
> 
> 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[pluto at agmk dot net]

------- Comment #23 from pluto at agmk dot net  2009-02-27 11:04 -------
(In reply to comment #22)

> The original reported problem is gone.  The testcase below is unfixable.

so what users can do now?
the -isystem feature doesn't work as expected with this unfixable diagnostics.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenth at gcc dot gnu dot org]

------- Comment #24 from rguenth at gcc dot gnu dot org  2009-02-27 11:07 -------
The user can use -Wno-strict-aliasing.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[pluto at agmk dot net]

------- Comment #25 from pluto at agmk dot net  2009-02-27 11:22 -------
(In reply to comment #24)
> The user can use -Wno-strict-aliasing.
> 

naturally, but -O2 turns on -fstrict-aliasing, so using strict-aliasing
without warnings about aliasing violations is a bit horrible :)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503

[Bug middle-end/38503] [4.4 regression] warnings from -isystem headers strikes back.

[rguenther at suse dot de]

------- Comment #26 from rguenther at suse dot de  2009-02-27 12:04 -------
Subject: Re:  [4.4 regression] warnings from -isystem
 headers strikes back.

On Fri, 27 Feb 2009, pluto at agmk dot net wrote:

> ------- Comment #25 from pluto at agmk dot net  2009-02-27 11:22 -------
> (In reply to comment #24)
> > The user can use -Wno-strict-aliasing.
> > 
> 
> naturally, but -O2 turns on -fstrict-aliasing, so using strict-aliasing
> without warnings about aliasing violations is a bit horrible :)

On IRC we agreed that turning strict-aliasing warnings off for 
system-headers is not a good idea.

So -Wno-strict-aliasing is the only thing I can offer.

Richard.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38503