From owner-freebsd-hackers@FreeBSD.ORG  Fri Jan 28 09:54:50 2005
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To: Jacques Fourie <jf@trispen.com>
References: <41F90140.3020705@trispen.com>
	<20050127160914.GA72454@VARK.MIT.EDU>
From: des@des.no (=?iso-8859-1?q?Dag-Erling_Sm=F8rgrav?=)
Date: Fri, 28 Jan 2005 10:54:24 +0100
In-Reply-To: <20050127160914.GA72454@VARK.MIT.EDU> (David Schultz's message
 of "Thu, 27 Jan 2005 11:09:14 -0500")
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cc: freebsd-hackers@FreeBSD.ORG
Subject: Re: kernel vm question
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David Schultz <das@FreeBSD.ORG> writes:
> On Thu, Jan 27, 2005, Jacques Fourie wrote:
> > unsigned char *p =3D NULL;
> > unsigned char v =3D 0x55;
> > /* ... */
> > p =3D (unsigned char *)ip_output;
> > /* ... */
> > v =3D p[0];
> > p[0] =3D v;
> > /* ... */
> When the line is there, the compiler is probably smart enough to
> realize that 'x=3Dy; y=3Dx' is (usually) a no-op, so it optimizes away
> both statements.

Wrong.  The compiler is free to optimize away the second statement
provided that neither x nor y is declared volatile, but it cannot
optimize away the first statement.

DES
--=20
Dag-Erling Sm=F8rgrav - des@des.no