Re: no-op delay loops

[yalin wang]

> On Nov 27, 2015, at 16:53, Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> wrote:
> 
> Hi,
> 
> It seems that gcc happily compiles
> 
> for (i = 0; i < 1000000000; ++i) ;
> 
> into simply
> 
> i = 1000000000;
> 
> (which is then usually eliminated as a dead store). At least at -O2, and
> when i is not declared volatile. So it would seem that the loops at
> 
> arch/mips/pci/pci-rt2880.c:235
> arch/mips/pmcs-msp71xx/msp_setup.c:80
> arch/mips/sni/reset.c:35
> 
> actually don't do anything. (In the middle one, i is 'register', but
> that doesn't change anything.) Is mips compiled with some special flags
> that would make gcc actually emit code for the above?
> 
you can try to declare i as  volatile int i;
may gcc will not optimize it .

Thanks

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/