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PONeed help with BOOST_FOREACH/compiler bug
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  1. PONeed help with BOOST_FOREACH/compiler bug
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    copied!<p>I know that boost or compiler should be last to blame, but I can't see another explanation here. I'm using msvc 2008 SP1 and boost 1.43. </p> <p>In the following code snippet execution never leaves <strong>third</strong> BOOST_FOREACH loop</p> <pre><code>typedef Graph&lt;unsigned, unsigned&gt;::VertexIterator Iter; Graph&lt;unsigned, unsigned&gt; g; g.createVertex(0x66); // works fine Iter it = g.getVertices().first, end = g.getVertices().second; for(; it != end; ++it) ; // fine std::pair&lt;Iter, Iter&gt; p = g.getVertices(); BOOST_FOREACH(unsigned handle, p) ; // fine unsigned vertex_count = 0; BOOST_FOREACH(unsigned handle, g.getVertices()) vertex_count++; // oops, infinite loop vertex_count = 0; BOOST_FOREACH(unsigned handle, g.getVertices()) vertex_count++; vertex_count = 0; BOOST_FOREACH(unsigned handle, g.getVertices()) vertex_count++; // ... last block repeated 6 times </code></pre> <p>Iterator code:</p> <pre><code>class Iterator : public boost::iterator_facade&lt;Iterator, unsigned const, boost::bidirectional_traversal_tag&gt; { public: Iterator() : list(NULL), handle(INVALID_ELEMENT_HANDLE) {} explicit Iterator(const VectorElementsList &amp;list, unsigned handle = INVALID_ELEMENT_HANDLE) : list(&amp;list), handle(handle) {} friend std::ostream&amp; operator&lt;&lt;(std::ostream &amp;s, const Iterator &amp;it) { s &lt;&lt; "[list: " &lt;&lt; it.list &lt;&lt;", handle: " &lt;&lt; it.handle &lt;&lt; "]"; return s; } private: friend class boost::iterator_core_access; void increment() { handle = list-&gt;getNext(handle); } void decrement() { handle = list-&gt;getPrev(handle); } unsigned const&amp; dereference() const { return handle; } bool equal(Iterator const&amp; other) const { return handle == other.handle &amp;&amp; list == other.list; } const VectorElementsList&lt;T&gt; *list; unsigned handle; }; </code></pre> <p>Some ASM fun:</p> <pre><code> vertex_count = 0; BOOST_FOREACH(unsigned handle, g.getVertices()) // initialization 013E1369 mov edi,dword ptr [___defaultmatherr+8 (13E5034h)] // end iterator handle: 0xFFFFFFFF 013E136F mov ebp,dword ptr [esp+0ACh] // begin iterator handle: 0x0 013E1376 lea esi,[esp+0A8h] // begin iterator list pointer 013E137D mov ebx,esi 013E137F nop // forever loop begin 013E1380 cmp ebp,edi 013E1382 jne main+238h (13E1388h) 013E1384 cmp ebx,esi 013E1386 je main+244h (13E1394h) 013E1388 lea eax,[esp+18h] 013E138C push eax // here iterator is incremented in ram 013E138D call boost::iterator_facade&lt;detail::VectorElementsList&lt;Graph&lt;unsigned int,unsigned int&gt;::VertexWrapper&gt;::Iterator,unsigned int const ,boost::bidirectional_traversal_tag,unsigned int const &amp;,int&gt;::operator++ (13E18E0h) 013E1392 jmp main+230h (13E1380h) vertex_count++; // forever loop end </code></pre> <p>It's easy to see that iterator handle is cached in EBP and it never gets incremented despite of a call to iterator operator++() function.<br> I've replaced Itarator implmentation with one deriving from std::iterator and the issue persisted, so this is not iterator_facade fault. This problem exists only on msvc 2008 SP1 x86 and amd64 release builds. Debug builds on msvc 2008 and debug/release builds on msvc 2010 and gcc 4.4 (linux) works fine. Furthermore the BOOST_FOREACH block must be repeaded exacly 10 times. If it's repeaded 9 times, it's all OK. </p> <p>I guess that due to BOOST_FOREACH use of template trickery (const auto_any), compiler assumes that iterator handle is constant and never reads its real value again.</p> <p>I would be very happy to hear that my code is wrong, correct it and move on with BOOST_FOREACH, which I'm very found of (as opposed to BOOST_FOREVER :).</p> <p>May be related to: <a href="https://stackoverflow.com/questions/1275852/why-does-boost-foreach-not-work-sometimes-with-c-strings">Why does BOOST_FOREACH not work sometimes with C++ strings?</a></p> <p><strong>EDIT:</strong></p> <p>I've prepared simplified project reproducing the problem. No templates, no default params, no nothing. Get it here: <a href="http://yabcok.nazwa.pl/ugly3.zip" rel="nofollow noreferrer">http://yabcok.nazwa.pl/ugly3.zip</a></p>
 

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