MFC: r200938

- Don't check for a valid interrupt controller on every interrupt
  in intr_execute_handlers(). If we managed to get here without an
  associated interrupt controller we have way bigger problems.
  While at it predict stray vector interrupts as false as they are
  rather unlikely.
- Don't blindly call the clear function of an interrupt controller
  when adding a handler in inthand_add() as interrupt controllers
  like the one driven by upa(4) are auto-clearing and thus provide
  NULL instead.

sys/sparc64/sparc64/intr_machdep.c

@@ -276,7 +276,7 @@ intr_execute_handlers(void *cookie)
 	struct intr_vector *iv;
 
 	iv = cookie;
-	if (iv->iv_ic == NULL || intr_event_handle(iv->iv_event, NULL) != 0)
+	if (__predict_false(intr_event_handle(iv->iv_event, NULL) != 0))
 		intr_stray_vector(iv);
 }
 
@@ -377,7 +377,8 @@ inthand_add(const char *name, int vec, driver_filter_t *filt,
 #endif
 	ic->ic_enable(iv);
 	/* Ensure the interrupt is cleared, it might have triggered before. */
-	ic->ic_clear(iv);
+	if (ic->ic_clear != NULL)
+		ic->ic_clear(iv);
 	sx_xunlock(&intr_table_lock);
 	return (0);
 }