Compile the following with the C and C++ front-end and you will get different assembly, the C front- end does not do NVR at all while the C++ front-end will change the a decl to be the return_decl before so we the vectorizer cannot do the vectorization because it does not hanndle RETURN_DECLs at all.
struct A { int x[4]; }; struct A foo() { struct A a; for (int i=0; i<4; ++i) a.x[i] = 0; return a; } -- Summary: tree vectorizer does not understand RETURN_DECL Product: gcc Version: 4.0.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: enhancement Priority: P2 Component: tree-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: pinskia at gcc dot gnu dot org CC: gcc-bugs at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18546