[Bug c++/51231] New: g++ remove placement new with -O1

[Bug c++/51231] New: g++ remove placement new with -O1

[dushistov at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51231

             Bug #: 51231
           Summary: g++ remove placement new with -O1
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: dushistov@mail.ru


If code bellow compile with -O1 it prints '0', while with '-O0' it prints
deadbeaf.

The problem in   allocator.construct (allocator.address (at), value);
In boost_1_46_1/boost/interprocess/allocators/allocator.hpp it looks like:
void construct(const pointer &ptr, const_reference v)
   {  new((void*)detail::get_pointer(ptr)) value_type(v);  }

if rewrite it for example in such way:
 void construct(const pointer &ptr, const_reference v)
   {
        static volatile value_type *myp;
        myp = detail::get_pointer(ptr);
        ::new((void *)myp) value_type(v);
   }

the code print expected value: deadbeaf.

#include <iostream>
#include <boost/interprocess/allocators/allocator.hpp>
#include <boost/interprocess/managed_shared_memory.hpp>

namespace interp = boost::interprocess;

struct interp_memory_chunk
{
  interp::managed_shared_memory  chunk;

  interp_memory_chunk ()
  {
    interp::shared_memory_object::remove ("GCC_interprocess_test");
    chunk = interp::managed_shared_memory (interp::create_only,
"GCC_interprocess_test", 0x10000);
  }

  ~interp_memory_chunk ()
  {
    interp::shared_memory_object::remove ("GCC_interprocess_test");
  }
};

typedef  interp::allocator <int,
interp::managed_shared_memory::segment_manager>  allocator_type;

inline  void
create (allocator_type& allocator, allocator_type::value_type& at, int value)
{
  allocator.construct (allocator.address (at), value);
}

int
main ()
{
  interp_memory_chunk      memory;
  allocator_type           allocator (memory.chunk.get_segment_manager ());
  allocator_type::pointer  data = allocator.allocate (1);

  create (allocator, *data, 0xdeadbeef);
  std::cout << std::hex << *data << "\n";
}

[Bug c++/51231] g++ remove placement new with -O1

[dushistov at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51231

--- Comment #1 from Evgeniy Dushistov <dushistov at mail dot ru> 2011-11-19 21:49:33 UTC ---
The code works as expected for 4.4.5,
and show buggy behaviour with 4.5.3 and 4.6.2.

[Bug c++/51231] g++ remove placement new with -O1

[dushistov at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51231

--- Comment #2 from Evgeniy Dushistov <dushistov at mail dot ru> 2011-11-19 22:03:49 UTC ---
Created attachment 25862
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25862
the preprocessed test case

generate from source with command:
g++ -ggdb -c -save-temps -O1  -Wall -Wextra boost_interp_alloc.cpp,
you still need -lboost_thread to create executable.

[Bug c++/51231] g++ remove placement new with -O1

[dushistov at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51231

--- Comment #3 from Evgeniy Dushistov <dushistov at mail dot ru> 2011-11-19 22:07:40 UTC ---
To build test case you need use command:
g++ -ggdb -O1  -Wall -Wextra boost_interp_alloc.cpp  -lboost_thread

I use boost 1.46.1.

Or you can use preprocessed attachment to look at generated assembler.
Tested on x86_64.

[Bug c++/51231] g++ remove placement new with -O1

[dushistov at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51231

Evgeniy Dushistov <dushistov at mail dot ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.4.5
      Known to fail|                            |4.5.3, 4.6.2
           Severity|normal                      |major

[Bug regression/51231] g++ remove placement new with -O1

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51231

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|major                       |normal

[Bug middle-end/51231] [4.5/4.6/4.7 Regression] g++ remove placement new with -O1

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51231

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
          Component|regression                  |middle-end
   Target Milestone|---                         |4.5.4
            Summary|g++ remove placement new    |[4.5/4.6/4.7 Regression]
                   |with -O1                    |g++ remove placement new
                   |                            |with -O1

[Bug middle-end/51231] [4.5/4.6/4.7 Regression] g++ remove placement new with -O1

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51231

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-02-07 11:45:31 UTC ---
Confirmed.  The store of 0xdeadbeef is gone:

void create(allocator_type&, boost::interprocess::allocator<int,
boost::interprocess::segment_manager<char,
boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family>,
boost::interprocess::iset_index> >::value_type&, int) (struct allocator_type &
allocator, value_type & at, int value)
{
  value_type * myp;
  const ptrdiff_t D.99202;
  sizetype D.99201;
  struct pointer D.83867;

<bb 2>:
  # USE = nonlocal { D.83867 }
  # CLB = nonlocal { D.83867 }
  D.83867 = boost::interprocess::allocator<int,
boost::interprocess::segment_manager<char,
boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family>,
boost::interprocess::iset_index> >::address (allocator_1(D), at_2(D)); [return
slot optimization]
  D.99202_7 = D.83867.internal.m_offset;
  if (D.99202_7 != 1)
    goto <bb 3>;
  else
    goto <bb 4>;

<bb 3>:
  D.99201_8 = (sizetype) D.99202_7;
  # PT = { D.83867 }
  myp_9 = &D.83867 + D.99201_8;

<bb 4>:
  # PT = null { D.83867 }

  # myp_10 = PHI <0B(2), myp_9(3)>
  if (myp_10 != 0B)
    goto <bb 5>;
  else
    goto <bb 6>;

<bb 5>:
  value_11 = value_14(D);
  *myp_10 = value_11;

<bb 6>:
  D.83867 ={v} {CLOBBER};
  return;

}

in ealias.  Note that Boost invokes undefined behavior here as it
computes &D.83867 + D.83867.internal.m_offset which supposedly
points to an object that is not D.83867 obviously, as that is
automatic in function create() and the store would be dead anyway.