Code that uses BOOST_THROW_EXCEPTION produces a lot of "result may be used uninitialized (...)" warnings in certain conditions

[Adam Romanek <romanek.adam@…>]

The problem appears when using g++ with -Wuninitialized -fno-exceptions -O3 flags.

Given a simple test:

#include <boost/lexical_cast.hpp>

int main() {
  return boost::lexical_cast<int>("");
}

when compiled using g++ v4.6.3 produces the following output:

$ g++ test.cpp -Iboost -fno-exceptions -Wuninitialized -O3 -c

In file included from test.cpp:1:0:
boost/boost/lexical_cast.hpp: In static member function ‘static Target boost::detail::lexical_cast_do_cast<Target, Source>::lexical_cast_impl(const Source&) [with Target = int, Source = const char*]’:
boost/boost/lexical_cast.hpp:2353:24: warning: ‘result’ may be used uninitialized in this function [-Wuninitialized]

Please note that this problem appears only when using -O3 optimization level.

One way of fixing this issue is to add BOOST_ATTRIBUTE_NORETURN to boost::throw_exception() declaration in boost/throw_exception.hpp, as shown in the attached patch.

It should be safe to do so, as the documentation of boost::throw_exception() says that:

(...) Callers of throw_exception are allowed to assume that the function never returns (...)

This solves the issue completely.