🚀 go-pugleaf

In article <danpop.839541415@news.cern.ch>, Dan Pop <Dan.Pop@cern.ch> wrote:
>In <vkohklaizj.fsf@atari.connectinc.com> bji@connectinc.com (Bryan Ischo) writes:
>
>>In article <danpop.839504721@news.cern.ch> Dan.Pop@cern.ch (Dan Pop) writes:
>>   In <4ubnat$75u@freeside.fc.net> mrbig@freeside.fc.net (Mike Big) writes:
>>
>>   >int *flag_pt;
>>   >
    [snip]
>>   >  while(flag){ /* does NOT exit when using gcc -O2 */
>>
>>[more skippage]
>>
>>   >    counter++;
>>   >    /* uncomenting the printf below will fix things. weird heh */
>>
>>Just out of curiosity ... why can't the compiler be sure that 'flag' won't be
>>modified by printf? 
>
>Because flag is accessible via the flag_pt pointer, which is a global
>variable, hence available to any function called by the program.
> 
>>Shouldn't the compiler be smart enough to know that flag can't be modified
>>even IF the printf is in the loop, given how smart it's been about everything
>>else?
>
>On the contrary, it is smart enough to know that flag CAN be modified by
>a function called within the loop.

... but not smart enough to know that flag can be manipulated by a
signal driven function while the loop is running.   Isn't optimization
fun?  My first reaction, if I was still writing compilers, to assigning
a variable's address to a global would be to treat the variable as a
volatile from there on in, but I'm sure I could independently come up
with pretty much the same reasons as the ANSI committee did for why
that's not necessarily a good thing.

                 ____
   david parsons \bi/ It's better to be a firewall hacker; the pay is better
                  \/   and you only have to deal with people trying to break
		                                                          in.