powerpc: Don't use local named register variable in current_thread_info

LLVM doesn't support local named register variables and is unlikely
to. current_thread_info is using one, fix it by moving it out and
calling it __current_r1().

I gave it a bit of an obscure name because we don't want anyone else
using it - they should use current_stack_pointer(). This specific
case is performance critical and we can't afford to call a function
to get it. Furthermore it isn't important to know exactly where in
the stack we are since we mask the lower bits.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/thread_info.h

@@ -71,13 +71,12 @@ struct thread_info {
 #define THREAD_SIZE_ORDER	(THREAD_SHIFT - PAGE_SHIFT)
 
 /* how to get the thread information struct from C */
+register unsigned long __current_r1 asm("r1");
 static inline struct thread_info *current_thread_info(void)
 {
-	register unsigned long sp asm("r1");
-
 	/* gcc4, at least, is smart enough to turn this into a single
 	 * rlwinm for ppc32 and clrrdi for ppc64 */
-	return (struct thread_info *)(sp & ~(THREAD_SIZE-1));
+	return (struct thread_info *)(__current_r1 & ~(THREAD_SIZE-1));
 }
 
 #endif /* __ASSEMBLY__ */