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[Bug libc/1262] Use larger-block comparisons for memcmp on x86?
- From: "greenrd at greenrd dot org" <sourceware-bugzilla at sources dot redhat dot com>
- To: glibc-bugs at sources dot redhat dot com
- Date: 29 Aug 2005 15:25:22 -0000
- Subject: [Bug libc/1262] Use larger-block comparisons for memcmp on x86?
- References: <20050829003224.1262.greenrd@greenrd.org>
- Reply-to: sourceware-bugzilla at sources dot redhat dot com
------- Additional Comments From greenrd at greenrd dot org 2005-08-29 15:25 -------
Created an attachment (id=627)
--> (http://sources.redhat.com/bugzilla/attachment.cgi?id=627&action=view)
test case
(In reply to comment #3)
> glibc configured for i686+ is not comparing 8 bits at a time, but 32; see
> sysdeps/i386/i686/memcmp.S
Oh. But on my rawhide system, sysdeps/i386/i686/memcmp.S is not being used.
Rather you just get "repz cmpsb" in the generated assembly code. See attached
test case and compile with -S. I don't know why this happens. (Strangely, the
file sysdeps/i386/i686/memcmp.S doesn't appear in glibc-debuginfo.)
Maybe gcc is inlining a dumb i386 version - but if so, how to tell it not to?
Or maybe the file sysdeps/i386/i686/memcmp.S has been deleted from fedora glibc
for some reason (hence its absence in -debuginfo)?
--
http://sources.redhat.com/bugzilla/show_bug.cgi?id=1262
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