[Bug target/69789] g++ -O2 is removing tests against a variable that can be changed

[tmark at isc dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69789

--- Comment #3 from Thomas Markwalder <tmark at isc dot org> ---
After further analysis we've discovered that the optimizer does not remove the
tests, it alters the comparison of (ec == enumerated value).   If one replaces
the "ec" with "ec.value()" in the expressions, such that you are explicitly
comparing the interger error value the code works correctly when optimized:

{{{
     :

    // Retry operation if interrupted by signal.
    if (ec.value() == boost::asio::error::interrupted)
      continue;

    // Check if we need to run the operation again.
    if (ec.value() == boost::asio::error::would_block
        || ec == boost::asio::error::try_again)
      return false;

     :
}}}

Alternatively, adding an inline operator:

{{{
      inline friend bool operator==( const error_code & lhs,
                                     const int & rhs ) BOOST_SYSTEM_NOEXCEPT
      {
        return lhs.m_val == rhs;
      }
}}}

to error_code class also avoids the issue.