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---- Original Message ----- From: "Al Viro" <viro@parcelfarce.linux.theplanet.co.uk> To: "Pekka J Enberg" <penberg@cs.helsinki.fi> Cc: "Anton Altaparmakov" <aia21@cam.ac.uk>; <linux-ntfs-dev@lists.sourceforge.net>; <linux-kernel@vger.kernel.org> Sent: Thursday, May 26, 2005 03:04 Subject: Re: ntfs: remove redundant assignments> On Thu, May 26, 2005 at 09:21:46AM +0300, Pekka J Enberg wrote: > > On Wed, 2005-05-25 at 22:10 +0100, Anton Altaparmakov wrote: > > >This is not. memset(0) is not the same as = NULL IMO. I don't care if > > >the compiler thinks it is the same. NULL does not have to be 0 so I > > >prefer to initialize pointers explicitly to NULL. Even more so since this > > >code is not performance critical at all so I prefer clarity here. FWIW, a series of explicit assignments to zero puffs up the code on x86. Several GCC releases using the default kernel -O2 build are too dumb to zero EAX, or some other reg, and assign using it, so you're looking at 4 bytes of immediate zero plus opcode ModRm/SIB. If the locations being assigned happened to be statics you can often wind up with a 10 byte instruction to zero a single dword somewhere. I have tried a few tricks trying to get GCC to not use this 4 byte immediate 0 in non speed critical areas all to no avail (ex. foo &= 0; the AND instruction can use a one byte sign extended operand, but GCC morphs something like " &= 0" into a straight up "MOV thing,imm32" instruction) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||
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