Use _mm_pause() for win64 spin_delay(), per note from Tsutomu Yamada.

src/include/storage/s_lock.h

@@ -66,7 +66,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	  $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.170 2010/01/04 17:10:24 mha Exp $
+ *	  $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.171 2010/01/05 11:06:28 mha Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -837,13 +837,13 @@ typedef LONG slock_t;
 #define SPIN_DELAY() spin_delay()
 
 /* If using Visual C++ on Win64, inline assembly is unavailable.
- * Use a __nop instrinsic instead of rep nop.
+ * Use a _mm_pause instrinsic instead of rep nop.
  */
 #if defined(_WIN64)
 static __forceinline void
 spin_delay(void)
 {
-	__nop();
+	_mm_pause();
 }
 #else
 static __forceinline void