Date: Fri, 8 Apr 2005 21:51:01 -0400 From: David Schultz <das@FreeBSD.ORG> To: Alan Cox <alc@cs.rice.edu> Cc: cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/lib/libc/amd64/string Makefile.inc bcmp.S memcmp.S Message-ID: <20050409015101.GA40551@VARK.MIT.EDU> In-Reply-To: <20050408164716.GI20275@cs.rice.edu> References: <200504080515.j385FtbX016388@repoman.freebsd.org> <20050408061426.GH20275@cs.rice.edu> <20050408160358.GA37897@VARK.MIT.EDU> <20050408164716.GI20275@cs.rice.edu>
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On Fri, Apr 08, 2005, Alan Cox wrote: > On Fri, Apr 08, 2005 at 12:03:58PM -0400, David Schultz wrote: > > On Fri, Apr 08, 2005, Alan Cox wrote: > > > On Fri, Apr 08, 2005 at 05:15:55AM +0000, Alan Cox wrote: > > > > alc 2005-04-08 05:15:55 UTC > > > > > > > > FreeBSD src repository > > > > > > > > Modified files: > > > > lib/libc/amd64/string Makefile.inc > > > > Added files: > > > > lib/libc/amd64/string bcmp.S memcmp.S > > > > Log: > > > > Add machine-specific, optimized implementations of bcmp and memcmp. > > > > > > > > PR: 73111 > > > > Submitted by: Ville-Pertti Keinonen <will@iki.fi> (taken from NetBSD) > > > > MFC after: 3 weeks > > > > > > > > Revision Changes Path > > > > 1.2 +1 -1 src/lib/libc/amd64/string/Makefile.inc > > > > 1.1 +25 -0 src/lib/libc/amd64/string/bcmp.S (new) > > > > 1.1 +41 -0 src/lib/libc/amd64/string/memcmp.S (new) > > > > > > It is worth noting that by default the current version of gcc > > > automatically inlines its own implementation of these functions. That > > > implementation is slower than this new libc implementation for strings > > > of non-trivial length. > > > > IIRC, gcc only inlines these in special cases, e.g. if it knows > > the length or contents of one of the strings. But this may have > > changed. > > Yes, however, for bcmp and memcmp the length is given as a parameter > and thus is always known. The surprising fact is that the length does > not have to be a constant for inlining to occur. Arguably gcc's > heuristic for inlining these functions should require the length to be > a small constant. Ah, right, I was thinking of strcmp(). Perhaps this should be filed as a gcc bug.
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