Date: Sun, 17 May 2009 18:41:13 +0200 From: Christoph Mallon <christoph.mallon@gmx.de> To: Stanislav Sedov <stas@FreeBSD.org> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: C99: Suggestions for style(9) Message-ID: <4A103E29.4040309@gmx.de> In-Reply-To: <20090517200456.cefa04fb.stas@FreeBSD.org> References: <49F4070C.2000108@gmx.de> <20090428114754.GB89235@server.vk2pj.dyndns.org> <49FAE4EA.1010205@gmx.de> <20090517144516.331b01a8.stas@FreeBSD.org> <4A1004B3.5040805@gmx.de> <20090517200456.cefa04fb.stas@FreeBSD.org>
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Stanislav Sedov schrieb: > On Sun, 17 May 2009 14:36:03 +0200 > Christoph Mallon <christoph.mallon@gmx.de> mentioned: > >>> Aliasing behavior is stritcly described in >>> ISO C99 standard, so there's a good point to enforcing strict-aliasing clear >>> code in our kernel. >> If you like this addition because of this reason, I have to disappoint >> you: This addition has absolutly *nothing* to do with strict-aliasing. >> > > I didn't meant I like this change only from aliasing point of view: certianly, > the code readability argument is very important. But this change also > works towards the strict aliasing problem solving too: there's just > a less chance someone will reuse a variable, address of which was > previously taken. Something like this would violate strict-aliasing: int i; short* p = (short*)&i; A short pointer may never point at an int object (ISO/IEC 9899:1999 (E) §6.5:7). The suggested paragraph has nothing to do with strict-aliasing. It's "just" about reusing the same variable in different contexts. Reusing the same variable in different contexts is bad, because it's harder for a human reader to identify the def-use-chains and additionally if the address of the variable has escaped (just a "normal" alias problem, nothing about type-punning and strict-aliasing) the generated code will be worse. Please, can we stop this now? It was already rejected. It's a pity, but maintaining status quo for style(9) seems to be too holy. *sigh* Christoph
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