Created attachment 1345261 [details] Preprocessed multidelta output Description of problem: Unexpected -Wmaybe-uninitialized warning with gcc7 that doesn't appear to me to match any upstream bug. Version-Release number of selected component (if applicable): gcc-7.2.1-2.fc26.x86_64 How reproducible: 100% Steps to Reproduce: $ cat<<EOF>minimal.cpp #include <boost/variant.hpp> #include <string> struct A { A() {} A(int64_t _x, std::string _y) : x(_x), y(_y) {} int64_t x = 0; std::string y; }; struct B { B() {} }; typedef boost::variant<A, B> BV; struct D { D() {} BV bv; void f(); }; void D::f() { bv = B(); } EOF $ g++ -Wuninitialized -O1 -c minimal.cpp Actual results: minimal.cpp: In member function ‘void D::f()’: minimal.cpp:4:8: warning: ‘*((void*)(& temp)+8).A::x’ may be used uninitialized in this function [-Wmaybe-uninitialized] struct A { Expected results: No warnings generated. Additional info: Moving the definition of 'f' inside the declaration of 'D' resolves the warning as does swapping the order of 'x' and 'y'. Attaching group_pool.ii which is preprocessed source which has been run through multidelta to try and reduce the size with limited success.
Changing 'typedef boost::variant<A, B> BV;' to 'typedef boost::variant<B, A> BV;' also eliminates the warning.
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