(move_it_vertically_backward): At the end of the

function, when moving forward by lines, treat terminal frames
specially.

1 files changed, 16 insertions, 4 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index b1b2fd6bc59..4760893d284 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -5404,12 +5404,24 @@ move_it_vertically_backward (it, dy)
       else if (target_y >= it->current_y + line_height
                && IT_CHARPOS (*it) < ZV)
         {
-          /* Should move forward by at least one line, maybe more.  */
-          do
+          /* Should move forward by at least one line, maybe more.
+             
+             Note: Calling move_it_by_lines can be expensive on
+             terminal frames, where compute_motion is used (via
+             vmotion) to do the job, when there are very long lines
+             and truncate-lines is nil.  That's the reason for
+             treating terminal frames specially here.  */
+          
+          if (!FRAME_WINDOW_P (it->f))
+            move_it_vertically (it, target_y - (it->current_y + line_height));
+          else
             {
-              move_it_by_lines (it, 1, 1);
+              do
+                {
+                  move_it_by_lines (it, 1, 1);
+                }
+              while (target_y >= line_bottom_y (it) && IT_CHARPOS (*it) < ZV);
             }
-          while (target_y >= line_bottom_y (it) && IT_CHARPOS (*it) < ZV);
 
           xassert (IT_CHARPOS (*it) >= BEGV);
         }