http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51392
Richard Guenther <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution| |INVALID --- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-12-04 15:50:40 UTC --- __attribute__((__const__)) Vector3f pie_SurfaceNormal3fv(Vector3f a, Vector3f b) { return Vector3f(a.y*b.z - a.z*b.y, a.z*b.x - a.x*b.z, a.x*b.y - a.y*b.x); } I think it is illegal to use the const attribute when the C++ frontend may elide the return value copy to being passed by invisible reference. That way the middle-end sees a store to global memory which is a side-effect that the const attribute does not allow (similar for pure btw.). Note that the Vector3f() constructors are not const either but they are both called from pie_SurfaceNormal3fv.