Don't use a redisplay optimization in a certain case on ttys

* src/dispnew.c (is_tty_root_frame_with_visible_child): New function.
* src/dispextern.h: Declare it.
* src/xdisp.c (redisplay_internal): Don't use optimization 1 for tty root
frames with a visible child frame.

src/dispextern.h

@@ -3953,6 +3953,7 @@ Lisp_Object frames_in_reverse_z_order (struct frame *f, bool visible);
 bool is_tty_frame (struct frame *f);
 bool is_tty_child_frame (struct frame *f);
 bool is_tty_root_frame (struct frame *f);
+bool is_tty_root_frame_with_visible_child (struct frame *f);
 void combine_updates (Lisp_Object root_frames);
 void combine_updates_for_frame (struct frame *f, bool inhibit_id_p);
 void tty_raise_lower_frame (struct frame *f, bool raise);

src/dispnew.c

@@ -3479,6 +3479,18 @@ is_tty_root_frame (struct frame *f)
   return !FRAME_PARENT_FRAME (f) && is_tty_frame (f);
 }
 
+/* Return true if frame F is a tty root frame that has a visible child
+   frame..  */
+
+bool
+is_tty_root_frame_with_visible_child (struct frame *f)
+{
+  if (!is_tty_root_frame (f))
+    return false;
+  Lisp_Object z_order = frames_in_reverse_z_order (f, true);
+  return CONSP (XCDR (z_order));
+}
+
 /* Return the index of the first enabled row in MATRIX, or -1 if there
    is none.  */
 

src/xdisp.c

@@ -17279,7 +17279,11 @@ redisplay_internal (void)
 		 line and this line is the current one, because
 		 display_line above is not informed about the
 		 current-line's vpos, and cannot DTRT in that case.  */
-	      && !hscrolling_current_line_p (w))
+	      && !hscrolling_current_line_p (w)
+	      /* A root frame may have visible children displayed in its
+		 current matrix, so that we can't do the below with its
+		 current matrix.  */
+	      && !is_tty_root_frame_with_visible_child (it.f))
 	    {
  	      /* If this is not the window's last line, we must adjust
  		 the charstarts of the lines below.  */