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Re: Use assert()s for optimization?
Ross Smith <r-smith@ihug.co.nz> writes:
> On Friday 7 November 2003 11:01, Falk Hueffner wrote:
> > Richard Guenther <rguenth@tat.physik.uni-tuebingen.de> writes:
> > > Is there a way to turn an assert() into optimization hints for gcc?
> > > Like in
> > >
> > > double mysqrt(double x)
> > > {
> > > assert(x >= 0.0);
> > > return sqrt(x);
> > > }
> >
> > Interestingly, Toon Moene just asked for the same thing on
> > gcc-patches :) I don't think it's currently possible. Maybe we could
> > have
> > something similar to Microsoft's __assume(), which would then feed
> > the nonnegative_p etc. functions and the VRP to come. I'm not sure
> > how to represent it best in the intermediary representation, though.
>
> Doesn't __builtin_expect() already do this?
No. It only means "feel free to waste cycles should x not be true",
not "feel free to produce undefined behaviour should x not be true".
--
Falk