On Wed, Mar 30, 2005 at 10:29:43AM -0800, Shankar Unni wrote: > Jean Delvare wrote: > > > v = p->field; > > if (!p) return; > > > >can be seen as equivalent to > > > > if (!p) return; > > v = p->field; > > Heck, no. > > You're missing the side-effect of a null pointer dereference crash (for > p->field) (even though v is unused before the return). The optimizer is > not allowed to make exceptions go away as a result of the hoisting.
Actually it is. Dereferencing a null pointer is either undefined or implementation-dependant in the standard (don't remember which), and as such the compiler can do whatever it wants, be it starting nethack or not doing the dereference in the first place. The principle of least surprise makes doing such an "optimisation" not so smart in practice. A compiler capable of detecting that situation would be better off spitting a warning in red blinking letter. OG. - 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/
