[S390] use compiler builtin versions of strlen/strcpy/strcat

Use builtin variants if gcc 4 or newer is used to compile the kernel.
Generates better code than the asm variants.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/string.h

@@ -100,6 +100,7 @@ static inline char *strcat(char *dst, const char *src)
 
 static inline char *strcpy(char *dst, const char *src)
 {
+#if __GNUC__ < 4
 	register int r0 asm("0") = 0;
 	char *ret = dst;
 
@@ -109,10 +110,14 @@ static inline char *strcpy(char *dst, const char *src)
 		: "+&a" (dst), "+&a" (src) : "d" (r0)
 		: "cc", "memory");
 	return ret;
+#else
+	return __builtin_strcpy(dst, src);
+#endif
 }
 
 static inline size_t strlen(const char *s)
 {
+#if __GNUC__ < 4
 	register unsigned long r0 asm("0") = 0;
 	const char *tmp = s;
 
@@ -121,6 +126,9 @@ static inline size_t strlen(const char *s)
 		"	jo	0b"
 		: "+d" (r0), "+a" (tmp) :  : "cc");
 	return r0 - (unsigned long) s;
+#else
+	return __builtin_strlen(s);
+#endif
 }
 
 static inline size_t strnlen(const char * s, size_t n)

arch/s390/lib/string.c

@@ -44,7 +44,11 @@ static inline char *__strnend(const char *s, size_t n)
  */
 size_t strlen(const char *s)
 {
+#if __GNUC__ < 4
 	return __strend(s) - s;
+#else
+	return __builtin_strlen(s);
+#endif
 }
 EXPORT_SYMBOL(strlen);
 
@@ -70,6 +74,7 @@ EXPORT_SYMBOL(strnlen);
  */
 char *strcpy(char *dest, const char *src)
 {
+#if __GNUC__ < 4
 	register int r0 asm("0") = 0;
 	char *ret = dest;
 
@@ -78,6 +83,9 @@ char *strcpy(char *dest, const char *src)
 		      : "+&a" (dest), "+&a" (src) : "d" (r0)
 		      : "cc", "memory" );
 	return ret;
+#else
+	return __builtin_strcpy(dest, src);
+#endif
 }
 EXPORT_SYMBOL(strcpy);