Re: [patch 4/21] fix ARCH_HAS_PREFETCH

[Adrian Bunk]

On 13 Aug 2002, H. Peter Anvin wrote:

>...
> > > Because the compiler sees:
> > >
> > > 	for (i = 0; i < N; i++)
> > > 		;
> > >
> > > and it says "ah ha.  A busy wait delay loop" and leaves it alone.
> > >
> > > It's actually a special-case inside the compiler to not optimise
> > > away such constructs.
> >
> > Why is this a special case? As long as a compiler can't prove that the
> > computed value of i isn't used later it mustn't optimize it away.
>
> Bullsh*t.  It can legitimately transform it into:
>
> 	   i = N;
>...

Ah, my misunderstanding:
"optimize away" didn't mean "completely remove it" but "transform it to
something semantically equivalent".

> 	-hpa

Thanks
Adrian

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