dispatch_atomic_xchg.patch

Description:
 Prevent an invalid macro for dispatch_atomic_xchg() on some platforms.
 Credit to Joakim Johansson for reporting this bug as libdispatch Trac 
 ticket #35, and credit to Paolo Bonzini for identifying the fix.
 .
Author: Mark Heily <mark@heily.com>
Date: Sat, 24 Sep 2011 21:02:28 -0400

Index: hw_shims.h
===================================================================
--- hw_shims.h	(revision 197)
+++ hw_shims.h	(working copy)
@@ -36,7 +36,7 @@
 // GCC generates suboptimal register pressure
 // LLVM does better, but doesn't support tail calls
 // 6248590 __sync_*() intrinsics force a gratuitous "lea" instruction, with resulting register pressure
-#if 0 && defined(__i386__) || defined(__x86_64__)
+#if 0 && (defined(__i386__) || defined(__x86_64__))
 #define dispatch_atomic_xchg(p, n)	({ typeof(*(p)) _r; asm("xchg %0, %1" : "=r" (_r) : "m" (*(p)), "0" (n)); _r; })
 #else
 #define dispatch_atomic_xchg(p, n)	((typeof(*(p)))__sync_lock_test_and_set((p), (n)))