Small Windows specific performance fixes:

- Use native memcmp() supplied with C runtime instead of hand-unrolled loop ptr_compare_N loop
Prior to fix  ptr_compare_0()  has  3.7% samples in OLTP-RO in-memory. 
Fix brings this down to 1.8% (all memcmp samples)

- Innodb : fix UT_RELAX_CPU to  be defined  as YieldProcessor, as  was also originally intended 
(but intention was lost in the #ifdef maze

This reduces number of ut_delay() samples in profile from 1.5% to 0.5%

mysys/ptr_cmp.c

@@ -21,17 +21,23 @@
 
 #include "mysys_priv.h"
 #include <myisampack.h>
-
-#ifdef __sun
 /*
- * On Solaris, memcmp() is normally faster than the unrolled ptr_compare_N
+ * On some platforms, memcmp() is faster than the unrolled ptr_compare_N
  * functions, as memcmp() is usually a platform-specific implementation
- * written in assembler, provided in /usr/lib/libc/libc_hwcap*.so.1.
- * This implementation is also usually faster than the built-in memcmp
- * supplied by GCC, so it is recommended to build with "-fno-builtin-memcmp"
- * in CFLAGS if building with GCC on Solaris.
+ * written in assembler. for example one in /usr/lib/libc/libc_hwcap*.so.1.
+ * on Solaris, or on Windows inside C runtime linrary.
+ *
+ * On Solaris, native implementation is also usually faster than the 
+ * built-in memcmp supplied by GCC, so it is recommended to build 
+ * with "-fno-builtin-memcmp"in CFLAGS if building with GCC on Solaris.
  */
 
+#if defined (__sun) || defined (_WIN32)
+#define USE_NATIVE_MEMCMP 1
+#endif
+
+#ifdef USE_NATIVE_MEMCMP
+
 #include <string.h>
 
 static int native_compare(size_t *length, unsigned char **a, unsigned char **b)
@@ -39,7 +45,7 @@ static int native_compare(size_t *length, unsigned char **a, unsigned char **b)
   return memcmp(*a, *b, *length);
 }
 
-#else	/* __sun */
+#else	/* USE_NATIVE_MEMCMP */
 
 static int ptr_compare(size_t *compare_length, uchar **a, uchar **b);
 static int ptr_compare_0(size_t *compare_length, uchar **a, uchar **b);
@@ -50,7 +56,7 @@ static int ptr_compare_3(size_t *compare_length, uchar **a, uchar **b);
 
 	/* Get a pointer to a optimal byte-compare function for a given size */
 
-#ifdef __sun
+#ifdef USE_NATIVE_MEMCMP
 qsort2_cmp get_ptr_compare (size_t size __attribute__((unused)))
 {
   return (qsort2_cmp) native_compare;
@@ -68,7 +74,7 @@ qsort2_cmp get_ptr_compare (size_t size)
     }
   return 0;					/* Impossible */
 }
-#endif /* __sun */
+#endif /* USE_NATIVE_MEMCMP */
 
 
 	/*
@@ -78,7 +84,7 @@ qsort2_cmp get_ptr_compare (size_t size)
 
 #define cmp(N) if (first[N] != last[N]) return (int) first[N] - (int) last[N]
 
-#ifndef __sun
+#ifndef USE_NATIVE_MEMCMP
 
 static int ptr_compare(size_t *compare_length, uchar **a, uchar **b)
 {

storage/innobase/include/ut0ut.h

@@ -63,16 +63,16 @@ typedef time_t	ib_time_t;
 #  define UT_RELAX_CPU() __asm__ __volatile__ ("pause")
 #elif defined(HAVE_FAKE_PAUSE_INSTRUCTION)
 #  define UT_RELAX_CPU() __asm__ __volatile__ ("rep; nop")
-#elif defined(HAVE_ATOMIC_BUILTINS)
-#  define UT_RELAX_CPU() do { \
-     volatile lint	volatile_var; \
-     os_compare_and_swap_lint(&volatile_var, 0, 1); \
-   } while (0)
 #elif defined(HAVE_WINDOWS_ATOMICS)
    /* In the Win32 API, the x86 PAUSE instruction is executed by calling
    the YieldProcessor macro defined in WinNT.h. It is a CPU architecture-
    independent way by using YieldProcessor. */
 #  define UT_RELAX_CPU() YieldProcessor()
+#elif defined(HAVE_ATOMIC_BUILTINS)
+#  define UT_RELAX_CPU() do { \
+     volatile lint	volatile_var; \
+     os_compare_and_swap_lint(&volatile_var, 0, 1); \
+   } while (0)
 #else
 #  define UT_RELAX_CPU() ((void)0) /* avoid warning for an empty statement */
 #endif

storage/xtradb/include/ut0ut.h

@@ -63,16 +63,16 @@ typedef time_t	ib_time_t;
 #  define UT_RELAX_CPU() __asm__ __volatile__ ("pause")
 #elif defined(HAVE_FAKE_PAUSE_INSTRUCTION)
 #  define UT_RELAX_CPU() __asm__ __volatile__ ("rep; nop")
-#elif defined(HAVE_ATOMIC_BUILTINS)
-#  define UT_RELAX_CPU() do { \
-     volatile lint	volatile_var; \
-     os_compare_and_swap_lint(&volatile_var, 0, 1); \
-   } while (0)
 #elif defined(HAVE_WINDOWS_ATOMICS)
    /* In the Win32 API, the x86 PAUSE instruction is executed by calling
    the YieldProcessor macro defined in WinNT.h. It is a CPU architecture-
    independent way by using YieldProcessor. */
 #  define UT_RELAX_CPU() YieldProcessor()
+#elif defined(HAVE_ATOMIC_BUILTINS)
+#  define UT_RELAX_CPU() do { \
+     volatile lint	volatile_var; \
+     os_compare_and_swap_lint(&volatile_var, 0, 1); \
+   } while (0)
 #else
 #  define UT_RELAX_CPU() ((void)0) /* avoid warning for an empty statement */
 #endif