This is the mail archive of the
mailing list for the GCC project.
Re: Empty loop elimination in 4.0 ?
Michael Veksler wrote:-
> Maybe in C, but not in C++ when you may have generic code
> that is translated to empty loops.
> When you pass a generic visitor (visitor in the old GTL sense), it has a
> of callbacks. These callbacks are inline functions, some of them are empty.
> template <class V>
> f(V v)
> for(....) v.Do1();
> for(....) v.Do2();
> Whoever defines 'f' does not care if V::Do1() is empty. Morever,
> nobody wants to write special code for the case when V::Do1() is
> empty. It is assumed that the compiler is smart enough to get
> rid of the loop.
To the front end these are not empty loops. Such warnings belong
in the front end not the optimizers.
> Another example, with C macros. I assume that with -DNDEBUG
> assert(x) is empty:
> for (p: iterates over elements)
> assert(p->value != NULL); /* Will warn with -DNDEBUG */
> /* Should I add "#ifndef NDEBUG" to protect the loop? */
Any warning can be triggered by certain uses of macro expansions.
That is not usually used as an argument to suppress them.