Dave Korn writes:
> On 07 November 2006 16:33, Andrew Haley wrote:
>
> > Ricardo FERNANDEZ PASCUAL writes:
>
> > > I have done some experiments to try to understand what is happening, and
> > > I am a bit confused by the bahavior of GCC. Consider the following C
> > > function:
> > >
> > > static struct { int w; } s;
> > >
> > > void wait (void) {
> > > int t;
> > > loop:
> > > t = *((volatile int *) &s.w);
> > > if (t > 0) goto loop;
> > > }
> > >
> > >
> > > The code generated by "cc1 -O3" on x86 is:
> > >
> > > wait:
> > > movl s, %eax
> > > pushl %ebp
> > > movl %esp, %ebp
> > > testl %eax, %eax
> > > jg .L6
> > > popl %ebp
> > > ret
> > > .L3:
> > > .L6:
> > > jmp .L6
> > >
> > >
> > > Which does not seem to respect the semantics of volatile. Is this the
> > > expected behavior or is this a bug?
> >
> > I think it's a bug.
>
> > > FWIW, the folowing function:
>
> > which looks right. A temporary shouldn't make any difference here.
>
> Can I just remind everyone we had a huge long thread with this discussion
> last year and it might be worth reviewing. Look for the thread titled
> "volatile semantics" running from Tue 03/05/2005 09:42 to Tue 26/07/2005
> 00:09. (We should try not to repeat too much of a three-month long debate!)
Yeah it was, and there was a decision:
http://gcc.gnu.org/ml/gcc/2005-07/msg00731.html
So no, we don't have to revisit it.
Paolo Bonzini has come up with a simple fix.
Andrew.
