From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752121Ab1LKSN3 (ORCPT ); Sun, 11 Dec 2011 13:13:29 -0500 Received: from mail-bw0-f46.google.com ([209.85.214.46]:60233 "EHLO mail-bw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751986Ab1LKSN1 (ORCPT ); Sun, 11 Dec 2011 13:13:27 -0500 Date: Sun, 11 Dec 2011 21:13:19 +0300 From: Alexey Dobriyan To: tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com Cc: x86@kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] i386: less assembly in strlen() Message-ID: <20111211181319.GA17097@p183.telecom.by> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Current i386 strlen() hardcodes NOT/DEC sequence. DEC is mentioned to be suboptimal on Core2. So, put only REPNE SCASB sequence in assembly, compiler can do the rest. The difference in generated code is like below (MCORE2=y): : push %edi mov $0xffffffff,%ecx mov %eax,%edi xor %eax,%eax repnz scas %es:(%edi),%al not %ecx - dec %ecx - mov %ecx,%eax + lea -0x1(%ecx),%eax pop %edi ret Signed-off-by: Alexey Dobriyan --- arch/x86/lib/string_32.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) --- a/arch/x86/lib/string_32.c +++ b/arch/x86/lib/string_32.c @@ -164,15 +164,13 @@ EXPORT_SYMBOL(strchr); size_t strlen(const char *s) { int d0; - int res; + size_t res; asm volatile("repne\n\t" - "scasb\n\t" - "notl %0\n\t" - "decl %0" + "scasb" : "=c" (res), "=&D" (d0) : "1" (s), "a" (0), "0" (0xffffffffu) : "memory"); - return res; + return ~res - 1; } EXPORT_SYMBOL(strlen); #endif