x86: atomic64: Improve cmpxchg8b()

Rewrite cmpxchg8b() to not use %edi register but a generic "+m" constraint, to increase compiler freedom in code generation and possibly better code. Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Mike Galbraith <[email protected]> Cc: Paul Mackerras <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Frederic Weisbecker <[email protected]> Cc: David Howells <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Arnd Bergmann <[email protected]> LKML-Reference: <[email protected]> Signed-off-by: Ingo Molnar <[email protected]>
jadonk · Jul 3, 2009 · 69237f9 · 69237f9
1 parent aacf682
commit 69237f9
Showing 1 changed file with 7 additions and 12 deletions.
diff --git a/arch/x86/lib/atomic64_32.c b/arch/x86/lib/atomic64_32.c
@@ -6,19 +6,14 @@
 
 static inline u64 cmpxchg8b(u64 *ptr, u64 old, u64 new)
 {
-	asm volatile(
-
-		LOCK_PREFIX "cmpxchg8b (%[ptr])\n"
-
-		     :		"=A" (old)
-
-		     : [ptr]	"D" (ptr),
-				"A" (old),
-				"b" (ll_low(new)),
-				"c" (ll_high(new))
-
-		     : "memory");
+	u32 low = new;
+	u32 high = new >> 32;
 
+	asm volatile(
+		LOCK_PREFIX "cmpxchg8b %1\n"
+		     : "+A" (old), "+m" (*ptr)
+		     :  "b" (low),  "c" (high)
+		     );
 	return old;
 }