Conditionalize __builtin_prefetch() on it existing!!

You have to check that something that isn't standard C actually exists
before trying to use it...

Cc: Colin Ian King <colin.i.king@intel.com>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

configure.ac

@@ -278,6 +278,7 @@ dnl Some rather useful gcc extensions...
 dnl
 PA_HAVE_FUNC(__builtin_constant_p, (0))
 PA_HAVE_FUNC(__builtin_choose_expr, (0,1,2))
+PA_HAVE_FUNC(__builtin_prefetch, (NULL))
 
 dnl
 dnl Check for supported gcc attributes; some compilers (e.g. Sun CC)

include/compiler.h

@@ -320,7 +320,7 @@ static inline void *mempset(void *dst, int c, size_t n)
  * Hints to the compiler that a particular branch of code is more or
  * less likely to be taken.
  */
-#if HAVE___BUILTIN_EXPECT
+#ifdef HAVE___BUILTIN_EXPECT
 # define likely(x)	__builtin_expect(bool(x), true)
 # define unlikely(x)	__builtin_expect(bool(x), false)
 #else
@@ -328,6 +328,12 @@ static inline void *mempset(void *dst, int c, size_t n)
 # define unlikely(x)	bool(x)
 #endif
 
+#ifdef HAVE___BUILTIN_PREFETCH
+# define prefetch(x) __builtin_prefetch(x)
+#else
+# define prefetch(x) ((void)(x))
+#endif
+
 /*
  * Attributes
  */

nasmlib/hashtbl.c

@@ -80,7 +80,7 @@ void **hash_findb(struct hash_table *head, const void *key,
 void **hash_find(struct hash_table *head, const char *key,
                  struct hash_insert *insert)
 {
-    __builtin_prefetch(key);
+    prefetch(key);
 
     return hash_findb(head, key, strlen(key)+1, insert);
 }
@@ -126,7 +126,7 @@ void **hash_findib(struct hash_table *head, const void *key, size_t keylen,
 void **hash_findi(struct hash_table *head, const char *key,
                   struct hash_insert *insert)
 {
-    __builtin_prefetch(key);
+    prefetch(key);
 
     return hash_findib(head, key, strlen(key)+1, insert);
 }

nasmlib/strlist.c

@@ -48,7 +48,7 @@ strlist_add(struct strlist *list, const char *str)
 	struct hash_insert hi;
 	size_t size;
 
-	__builtin_prefetch(str);
+	prefetch(str);
 
 	if (!list)
 		return NULL;