id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
11169	boost::optional triggers -Wmaybe-uninitialized errors in g++	Mathias Stearn <redbeard0531@…>	Fernando Cacciola	"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."	Bugs	new	To Be Determined	optional	Boost 1.57.0	Problem