Avoid calling 'current_column' in buffers with long lines.

* src/xdisp.c (decode_mode_spec, redisplay_window)
(mode_line_update_needed):
* src/indent.c (Fcurrent_column): In a buffer with long-line
optimizations enabled, avoid calling 'current_column', which is
very slow in that case.

2 files changed, 10 insertions, 2 deletions

diff --git a/src/indent.c b/src/indent.c
index d4ef075f001..e90e3fde203 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -306,6 +306,8 @@ and point (e.g., control characters will have a width of 2 or 4, tabs
 will have a variable width).
 Ignores finite width of frame, which means that this function may return
 values greater than (frame-width).
+In a buffer with very long lines, the value can be zero, because calculating
+the exact number is very expensive.
 Whether the line is visible (if `selective-display' is t) has no effect;
 however, ^M is treated as end of line when `selective-display' is t.
 Text that has an invisible property is considered as having width 0, unless
@@ -313,6 +315,9 @@ Text that has an invisible property is considered as having width 0, unless
   (void)
 {
   Lisp_Object temp;
+
+  if (current_buffer->long_line_optimizations_p)
+    return make_fixnum (0);
   XSETFASTINT (temp, current_column ());
   return temp;
 }
diff --git a/src/xdisp.c b/src/xdisp.c
index 690f10b8403..c507d0caf20 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -12998,7 +12998,8 @@ mode_line_update_needed (struct window *w)
 {
   return (w->column_number_displayed != -1
           && !(PT == w->last_point && !window_outdated (w))
-          && (w->column_number_displayed != current_column ()));
+          && (!current_buffer->long_line_optimizations_p
+              && w->column_number_displayed != current_column ()));
 }
 
 /* True if window start of W is frozen and may not be changed during
@@ -20116,6 +20117,7 @@ redisplay_window (Lisp_Object window, bool just_this_one_p)
        || w->base_line_pos > 0
        /* Column number is displayed and different from the one displayed.  */
        || (w->column_number_displayed != -1
+           && !current_buffer->long_line_optimizations_p
            && (w->column_number_displayed != current_column ())))
       /* This means that the window has a mode line.  */
       && (window_wants_mode_line (w)
@@ -27619,7 +27621,8 @@ decode_mode_spec (struct window *w, register int c, int field_width,
         return "";
       else
         {
-          ptrdiff_t col = current_column ();
+          ptrdiff_t col =
+            b->long_line_optimizations_p ? 0 : current_column ();
           int disp_col = (c == 'C') ? col + 1 : col;
           w->column_number_displayed = col;
           pint2str (decode_mode_spec_buf, width, disp_col);