Chris Lattner <clattner@xxxxxxxxx> writes:
> > union
> > {
> > vectortype v;
> > float af[4];
> > } u;
> > u.v = v;
> > return u.af[0];
> >
> > Ian
>
> Or, alternatively:
>
> vectortype v;
>
> elementtype e = ((elementtype*)&v)[1]
Well, I don't recommend that in general. gcc currently has an
exception to the aliasing rules, and treats vectortype* and
elementtype* as being in the same alias set. But at my previous
company, we got significantly better generated code in some cases by
breaking that aliasing. In particular this aliasing forces a pointer
to a vector of char to alias char* and therefore alias everything.
But if the compiler breaks that aliasing, then your suggestion of
using a cast will fail in some cases.
Ian
