linux-kernel - [tip:x86/asm] x86/64: Adjust types of temporaries used by ffs()/ fls()/fls64()

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Message-ID: <tip-1edfbb4153bd29bcf8d2236676238d5237972be1@git.kernel.org>
Date:	Thu, 13 Sep 2012 23:22:30 -0700
From:	tip-bot for Jan Beulich <JBeulich@...e.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	torvalds@...ux-foundation.org, jbeulich@...e.com,
	JBeulich@...e.com, tglx@...utronix.de
Subject: [tip:x86/asm] x86/64: Adjust types of temporaries used by ffs()/
 fls()/fls64()

Commit-ID:  1edfbb4153bd29bcf8d2236676238d5237972be1
Gitweb:     http://git.kernel.org/tip/1edfbb4153bd29bcf8d2236676238d5237972be1
Author:     Jan Beulich <JBeulich@...e.com>
AuthorDate: Mon, 10 Sep 2012 12:04:16 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 13 Sep 2012 17:43:58 +0200

x86/64: Adjust types of temporaries used by ffs()/fls()/fls64()

The 64-bit special cases of the former two (the thrird one is
64-bit only anyway) don't need to use "long" temporaries, as the
result will always fit in a 32-bit variable, and the functions
return plain "int". This avoids a few REX prefixes, i.e.
minimally reduces code size.

Signed-off-by: Jan Beulich <jbeulich@...e.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/504DE550020000780009A258@nat28.tlf.novell.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/bitops.h |   10 ++++------
 1 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 72f5009..ebaee69 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -417,10 +417,9 @@ static inline int ffs(int x)
 	 * We cannot do this on 32 bits because at the very least some
 	 * 486 CPUs did not behave this way.
 	 */
-	long tmp = -1;
 	asm("bsfl %1,%0"
 	    : "=r" (r)
-	    : "rm" (x), "0" (tmp));
+	    : "rm" (x), "0" (-1));
 #elif defined(CONFIG_X86_CMOV)
 	asm("bsfl %1,%0\n\t"
 	    "cmovzl %2,%0"
@@ -459,10 +458,9 @@ static inline int fls(int x)
 	 * We cannot do this on 32 bits because at the very least some
 	 * 486 CPUs did not behave this way.
 	 */
-	long tmp = -1;
 	asm("bsrl %1,%0"
 	    : "=r" (r)
-	    : "rm" (x), "0" (tmp));
+	    : "rm" (x), "0" (-1));
 #elif defined(CONFIG_X86_CMOV)
 	asm("bsrl %1,%0\n\t"
 	    "cmovzl %2,%0"
@@ -490,13 +488,13 @@ static inline int fls(int x)
 #ifdef CONFIG_X86_64
 static __always_inline int fls64(__u64 x)
 {
-	long bitpos = -1;
+	int bitpos = -1;
 	/*
 	 * AMD64 says BSRQ won't clobber the dest reg if x==0; Intel64 says the
 	 * dest reg is undefined if x==0, but their CPU architect says its
 	 * value is written to set it to the same as before.
 	 */
-	asm("bsrq %1,%0"
+	asm("bsrq %1,%q0"
 	    : "+r" (bitpos)
 	    : "rm" (x));
 	return bitpos + 1;
--
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