[Boost-bugs] [Boost C++ Libraries] #11169: boost::optional triggers -Wmaybe-uninitialized errors in g++

Subject: [Boost-bugs] [Boost C++ Libraries] #11169: boost::optional triggers -Wmaybe-uninitialized errors in g++
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-04-06 16:24:34

#11169: boost::optional triggers -Wmaybe-uninitialized errors in g++
---------------------------------------------+-----------------------
 Reporter:  Mathias Stearn <redbeard0531@…>  |      Owner:  fcacciola
     Type:  Bugs                             |     Status:  new
Milestone:  To Be Determined                 |  Component:  optional
  Version:  Boost 1.57.0                     |   Severity:  Problem
 Keywords:                                   |
---------------------------------------------+-----------------------
 Example taken from StackOverflow question 21755206*

 {{{
 #include <boost/optional.hpp>

 ::boost::optional<int> getitem();

 int go(int nr)
 {
   boost::optional<int> a = getitem();
   boost::optional<int> b;

   if (nr > 0)
     b = nr;

   if (a != b)
     return 1;

   return 0;
 }
 }}}


 {{{
 g++ -c -O2 -Wall /tmp/test.cpp
 /tmp/test.cpp: In function ‘int go(int)’
 /tmp/test.cpp:13:3: warning: ‘*((void*)& b +4)’ may be used uninitialized
 in this function [-Wmaybe-uninitialized]
    if (a != b)
    ^
 }}}


 This has been reported as gcc bug 47679*.

 Two workarounds that seem to work in my testing are value-initializing
 dummy_ in the aligned_storage default constructor or adding an empty asm
 statement that lists dummy_ as an output. Would it be possible to include
 a fix in mainline boost?

 * Sorry, but trac flags this as spam if I include direct links.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/11169>
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