Date: Wed, 17 Mar 2004 00:34:46 +0100 From: des@des.no (Dag-Erling =?iso-8859-1?q?Sm=F8rgrav?=) To: Ruslan Ermilov <ru@freebsd.org> Cc: net@freebsd.org Subject: Re: libalias patch for review / testing Message-ID: <xzpn06ggycp.fsf@dwp.des.no> In-Reply-To: <20040316232848.GR3462@ip.net.ua> (Ruslan Ermilov's message of "Wed, 17 Mar 2004 01:28:48 %2B0200") References: <xzp7jxkjv98.fsf@dwp.des.no> <xzp3c88jv7k.fsf@dwp.des.no> <20040316225230.GO3462@ip.net.ua> <xzpllm0ie5z.fsf@dwp.des.no> <20040316232848.GR3462@ip.net.ua>
next in thread | previous in thread | raw e-mail | index | archive | help
Ruslan Ermilov <ru@freebsd.org> writes: > : `-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? You're misreading, we're doing u_short * <-> void * (both pointers) but the man page speaks about int <-> void * (scalar vs pointer) Also, I doubt DifferentialChecksum() is a problem, since it's a function call. I think the problem may be in the code I've replaced with calls to twowords(). > 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. True, I didn't think of that. DES --=20 Dag-Erling Sm=C3=B8rgrav - des@des.no
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?xzpn06ggycp.fsf>