Date: Wed, 17 Mar 2004 01:28:48 +0200 From: Ruslan Ermilov <ru@freebsd.org> To: Dag-Erling Sm?rgrav <des@des.no> Cc: net@freebsd.org Subject: Re: libalias patch for review / testing Message-ID: <20040316232848.GR3462@ip.net.ua> In-Reply-To: <xzpllm0ie5z.fsf@dwp.des.no> References: <xzp7jxkjv98.fsf@dwp.des.no> <xzp3c88jv7k.fsf@dwp.des.no> <20040316225230.GO3462@ip.net.ua> <xzpllm0ie5z.fsf@dwp.des.no>
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--soWJpSPh+l8Y6Fy7 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Mar 17, 2004 at 12:07:52AM +0100, Dag-Erling Sm?rgrav wrote: > Ruslan Ermilov <ru@FreeBSD.org> writes: > > I know this code quite well. Where do you suspect could be a bug > > affecting -O2 compiles, or you just simply fixed -O2 and hope it > > will auto-fix the (possible) bugs in -O2? >=20 > Since there is no inline asm, the most likely suspect is aliasing, > which is what my patch tries to address. >=20 Hmm, read this again: : `-fstrict-aliasing' : Allows the compiler to assume the strictest aliasing rules : applicable to the language being compiled. For C (and C++), this : activates optimizations based on the type of expressions. In : particular, an object of one type is assumed never to reside at : the same address as an object of a different type, unless the : types are almost the same. For example, an `unsigned int' can : alias an `int', but not a `void*' or a `double'. A character type : may alias any other type. And asking myself a question: should those (void *)'s in your patch be (char *)'s instead, e.g., in twowords() and DifferentialChecksum(), or am I misreading the above? Also, the easiest way to check if strict aliasing is guilty for not working libalias compiled with -O2, is to compile the original code with -O2 -fno-strict-aliasing. You guys who have seen a problem, can you please check and confirm that? Cheers, --=20 Ruslan Ermilov FreeBSD committer ru@FreeBSD.org --soWJpSPh+l8Y6Fy7 Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (FreeBSD) iD8DBQFAV42wUkv4P6juNwoRAjfoAKCFmQfpsRXd7YlDm94ly3fatLaGgQCfb0kR H9QhpVVaijqCfWVt877nLd8= =UvNf -----END PGP SIGNATURE----- --soWJpSPh+l8Y6Fy7--
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