src/xdisp.c: Use same test in `redisplay_window` and `prepare_menu_bars`

This consolidates the test made in those two functions so as to make
sure they agree whether a window needs to be redisplayed.
At the same time, change this test so it uses the window's point
rather than the buffer's point when comparing to `w->last_point`.

* src/xdisp.c (needs_no_redisplay): New function, extracted from
`redisplay_window`.
(redisplay_window, prepare_menu_bars): Use it.

* src/window.c (window_point): New function, extracted from `Fwindow_point`.
(Fwindow_point): Use it.
* src/window.h (window_point): Declare it.

1 files changed, 9 insertions, 6 deletions

diff --git a/src/window.c b/src/window.c
index 4cca60e23d9..48da7839314 100644
--- a/src/window.c
+++ b/src/window.c
@@ -1692,6 +1692,14 @@ column 0.  */)
 				  0, false, false);
 }
 
+ptrdiff_t
+window_point (struct window *w)
+{
+  return (w == XWINDOW (selected_window)
+          ? BUF_PT (XBUFFER (w->contents))
+          : XMARKER (w->pointm)->charpos);
+}
+
 DEFUN ("window-point", Fwindow_point, Swindow_point, 0, 1, 0,
        doc: /* Return current value of point in WINDOW.
 WINDOW must be a live window and defaults to the selected one.
@@ -1705,12 +1713,7 @@ correct to return the top-level value of `point', outside of any
 `save-excursion' forms.  But that is hard to define.  */)
   (Lisp_Object window)
 {
-  register struct window *w = decode_live_window (window);
-
-  if (w == XWINDOW (selected_window))
-    return make_fixnum (BUF_PT (XBUFFER (w->contents)));
-  else
-    return Fmarker_position (w->pointm);
+  return make_fixnum (window_point (decode_live_window (window)));
 }
 
 DEFUN ("window-old-point", Fwindow_old_point, Swindow_old_point, 0, 1, 0,