Optimize 'set_vertical_scroll_bar' for long lines

* src/xdisp.c (set_vertical_scroll_bar): Don't bother
being accurate about window_end_pos if long-line shortcuts
are in effect in the current buffer.

diff --git a/src/xdisp.c b/src/xdisp.c
index c507d0caf2059654b86a1ee07b62c537bd9ef4ff..c73958854cd3d1f330abb06cfeabdd22f5b2f526 100644 (file)
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -18968,8 +18968,9 @@ set_vertical_scroll_bar (struct window *w)
       ptrdiff_t window_end_pos = w->window_end_pos;
 
       /* If w->window_end_pos cannot be trusted, recompute it "the
-        hard way".  */
-      if (!w->window_end_valid)
+        hard way".  But don't bother to be too accurate when
+        long-line shortcuts are in effect.  */
+      if (!w->window_end_valid && !buf->long_line_optimizations_p)
        {
          struct it it;
          struct text_pos start_pos;