When I compile the following code with gcc-4.4.0 with "-O3 -Wall" flags I get the messages below. Testcase has 'union' between Z and char types therefore such type conversion should be allowed by aliasing rules.
--- error message --- pr.C: In member function Z& X::get(): pr.C:12: warning: dereferencing type-punned pointer will break strict-aliasing rules --- testcase --- struct Z {int ii;}; struct X { union { Z objs[1]; char bb[20]; }; Z& get() { return (*(Z*)&bb[0]); // <--- error message here } }; -- Summary: Erroneous aliasing rules message Product: gcc Version: 4.4.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: yuri at tsoft dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40560