Re: [xml] A long URL causes SEGV

[Sander Vesik <Sander Vesik Sun COM>]

Igor Zlatkovic wrote:
> Daniel Veillard wrote:
>
> >   The C spec itself.
> >   There is an awful lot of code relying on the order of such compound
> > test, like for example
> >    if ((p != NULL) && (*p != 0))
> > you have the right to expect that if p is NULL the dereference will 
> > not occur.
> > It's the same for the test you pointed out, and in a lot of places in 
> > libxml2
> > code.
>
>
> For reasons not even known to me, I have lived under assumption that the 
> compiler might perhaps take the freedom to reorder the execution of 
> those tests. Doing so would not affect the logic of the whole expression 
> and the compiler just might think it would help some of its mysterious 
> and aggressive optimisation steps. Those were my thoughts. It was never 
> really important, somehow. Now, thinking of it, for years I made code 
> which leaves the compiler a freedom the compiler would never take :-)

It might do such reordings - but only *IF* such would not have any user 
visible side effects. Such are more likely on machines that have 
predicated instructions, non-faulting loads and other such "goodies" for 
high performance.

> See, I know what the compiler does. I just never knew wether the 
> compiler must do it, or it just happen to do it.
>
> Hm, instead of rereading some official info, I have believed another 
> urban myth which I created for myself without ever noticing. So read the 
> docs, folks, or you'll end up like me. :-) :-)
>
> Thanks for the answer, all of you.
>
> Ciao,
> Igor
>
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