On Mon, Feb 03, 2020 at 09:26:40PM +0100, Allan Sandfeld Jensen wrote: > Hello gcc > > I have now twice hit obscure bugs in Chromium that crashed on some compilers > but not on others, and didn't produce any warnings on any compiler. I would > like to know if this code is as undefined as I think it is, and if it would > make sense to have gcc warn about it. > > Both cases basically has this form: > > std::unique_ptr<A> a; > > a->b->callMethod(something, bind(callback, std::move(a))); > > This crashed with MSVC and gcc 5, but not with newer gcc or with clang.
You mean the application itself, not the compiler, presumably. > When it crashes it is because the arguments and the move therein have been > evaluated before a->b is resolved. > > I assume this is undefined behavior? So why isn't the warning for using and > modifying in the same expression triggered? This should be defined in C++17, with P0145 in particular: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0145r3.pdf which says that the expression that names the function is sequenced before every argument expression and every default argument. Marek
