Adrian Bunk wrote:
> It can be a performance regression, but there are also cases where it
> can improve performance. If gcc produces lower performance code that
> would be a bug in gcc that should be reported, but using a division is
> not generally wrong.
>
> A more clearer example might be:
>
> <-- snip -->
>
> void foo(u64 ns)
> {
> if (ns < 10000)
> return;
>
> while(ns >= 3) {
> ns -= 3;
> #ifdef DEBUG
> bar(ns);
> #endif
> }
> }
>
> <-- snip -->
>
> With DEBUG not defined you can hardly argue gcc should be fixed to not
> use a division for performance reasons.
Absent any clear information about the possible values of ns, IMO this
is a case where the compiler should just assume that the programmer
knows best whether to use a loop or a division. Principle of least
surprise, and all that...
Bernd
--
This footer brought to you by insane German lawmakers.
Analog Devices GmbH Wilhelm-Wagenfeld-Str. 6 80807 Muenchen
Sitz der Gesellschaft Muenchen, Registergericht Muenchen HRB 40368
Geschaeftsfuehrer Thomas Wessel, William A. Martin, Margaret Seif
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
