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SubjectRe: [patch 4/21] fix ARCH_HAS_PREFETCH
On Tue, Aug 13, 2002 at 03:12:53PM -0700, H. Peter Anvin wrote:
> Followup to: <Pine.NEB.4.44.0208132322340.1351-100000@mimas.fachschaften.tu-muenchen.de>
> By author: Adrian Bunk <bunk@fs.tum.de>
> In newsgroup: linux.dev.kernel
> > >
> > > 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;

Right! But people are confusing "practise", "published interface", and
"spec" again.

Published interface in this case is that gcc will not optimize an empty
loop away, as it is often used to generate a timing loop.

Roger.

--
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2600998 **
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* There are also old, bald pilots.
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