On Montag, 3. Februar 2020 21:47:13 CET Marek Polacek wrote: > 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. Of course.
> > > 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. > Right thanks, that would explain why it worked consistently with the latest gcc versions. I guess it is more of a corner case to ask for it being warned about in --std=c++14 mode? 'Allan
