[Boost-bugs] [Boost C++ Libraries] #12806: flat_map.hpp function force_copy break strict-aliasing on gcc < 4.4

Subject: [Boost-bugs] [Boost C++ Libraries] #12806: flat_map.hpp function force_copy break strict-aliasing on gcc < 4.4
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2017-02-02 16:38:59

#12806: flat_map.hpp function force_copy break strict-aliasing on gcc < 4.4
----------------------------------+-------------------------
 Reporter:  Vladislav <phprus@…>  |      Owner:  igaztanaga
     Type:  Bugs                  |     Status:  new
Milestone:  To Be Determined      |  Component:  container
  Version:  Boost 1.63.0          |   Severity:  Showstopper
 Keywords:                        |
----------------------------------+-------------------------
 Hello!

 On function
 ([https://github.com/boostorg/container/blob/develop/include/boost/container/flat_map.hpp#L61]):

 {{{
 template<class D, class S>
 BOOST_CONTAINER_FORCEINLINE static D force_copy(S s)
 {
    D *vp = reinterpret_cast<D *>(&s);
    return D(*vp);
 }
 }}}

 gcc 4.3.4 (SLE 11) produced wrong code.
 It seems that the compiler does not create a copy of an object "s" and
 returns an object of D().

 If I change the signature of function on "BOOST_CONTAINER_FORCEINLINE
 static D force_copy(const S& s)" the code works and the tests pass. But
 then does not create a copy of an object "s" in a function call.

 I'm not sure that this change is correct.
 Is there any other workaround for this problem with a compiler gcc 4.3 or
 better disable strict-aliasing?

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/12806>
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