Minor redisplay optimization when the region length is zero.

* xdisp.c (markpos_of_region): New function.
(init_iterator): Do not highlight the region of zero length.
(redisplay_window): Check whether the region is of non-zero length.
(try_cursor_movement): Allow if the region length is zero.
(try_window_reusing_current_matrix, try_window_id): Likewise.

2 files changed, 35 insertions, 21 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index b7bb772d266..f513e80408d 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,12 @@
+2012-12-13  Dmitry Antipov  <dmantipov@yandex.ru>
+
+        Minor redisplay optimization when the region length is zero.
+        * xdisp.c (markpos_of_region): New function.
+        (init_iterator): Do not highlight the region of zero length.
+        (redisplay_window): Check whether the region is of non-zero length.
+        (try_cursor_movement): Allow if the region length is zero.
+        (try_window_reusing_current_matrix, try_window_id): Likewise.
+
 2012-12-13  Eli Zaretskii  <eliz@gnu.org>
 
         * search.c (search_buffer): Check the inverse translations of each
diff --git a/src/xdisp.c b/src/xdisp.c
index aead10a7b9b..2801f3def10 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -2559,8 +2559,24 @@ check_window_end (struct window *w)
 
 #endif /* GLYPH_DEBUG and ENABLE_CHECKING */
 
+/* Return mark position if current buffer has the region of non-zero length,
+   or -1 otherwise.  */
+
+static ptrdiff_t
+markpos_of_region (void)
+{
+  if (!NILP (Vtransient_mark_mode)
+      && !NILP (BVAR (current_buffer, mark_active))
+      && XMARKER (BVAR (current_buffer, mark))->buffer != NULL)
+    {
+      ptrdiff_t markpos = XMARKER (BVAR (current_buffer, mark))->charpos;
+
+      if (markpos != PT)
+        return markpos;
+    }
+  return -1;
+}
 
-
 /***********************************************************************
                        Iterator initialization
  ***********************************************************************/
@@ -2589,7 +2605,7 @@ init_iterator (struct it *it, struct window *w,
                ptrdiff_t charpos, ptrdiff_t bytepos,
                struct glyph_row *row, enum face_id base_face_id)
 {
-  int highlight_region_p;
+  ptrdiff_t markpos;
   enum face_id remapped_base_face_id = base_face_id;
 
   /* Some precondition checks.  */
@@ -2692,16 +2708,10 @@ init_iterator (struct it *it, struct window *w,
   /* Are multibyte characters enabled in current_buffer?  */
   it->multibyte_p = !NILP (BVAR (current_buffer, enable_multibyte_characters));
 
-  /* Non-zero if we should highlight the region.  */
-  highlight_region_p
-    = (!NILP (Vtransient_mark_mode)
-       && !NILP (BVAR (current_buffer, mark_active))
-       && XMARKER (BVAR (current_buffer, mark))->buffer != 0);
-
-  /* Set IT->region_beg_charpos and IT->region_end_charpos to the
-     start and end of a visible region in window IT->w.  Set both to
-     -1 to indicate no region.  */
-  if (highlight_region_p
+  /* If visible region is of non-zero length, set IT->region_beg_charpos
+     and IT->region_end_charpos to the start and end of a visible region
+     in window IT->w.  Set both to -1 to indicate no region.  */
+  if ((markpos = markpos_of_region ()) != -1
       /* Maybe highlight only in selected window.  */
       && (/* Either show region everywhere.  */
           highlight_nonselected_windows
@@ -2713,7 +2723,6 @@ init_iterator (struct it *it, struct window *w,
               && WINDOWP (minibuf_selected_window)
               && w == XWINDOW (minibuf_selected_window))))
     {
-      ptrdiff_t markpos = marker_position (BVAR (current_buffer, mark));
       it->region_beg_charpos = min (PT, markpos);
       it->region_end_charpos = max (PT, markpos);
     }
@@ -15073,8 +15082,7 @@ try_cursor_movement (Lisp_Object window, struct text_pos startp, int *scroll_ste
       /* Can't use this case if highlighting a region.  When a
          region exists, cursor movement has to do more than just
          set the cursor.  */
-      && !(!NILP (Vtransient_mark_mode)
-           && !NILP (BVAR (current_buffer, mark_active)))
+      && (markpos_of_region () == -1)
       && NILP (w->region_showing)
       && NILP (Vshow_trailing_whitespace)
       /* This code is not used for mini-buffer for the sake of the case
@@ -15743,8 +15751,7 @@ redisplay_window (Lisp_Object window, int just_this_one_p)
 
           /* If we are highlighting the region, then we just changed
              the region, so redisplay to show it.  */
-          if (!NILP (Vtransient_mark_mode)
-              && !NILP (BVAR (current_buffer, mark_active)))
+          if (markpos_of_region () != -1)
             {
               clear_glyph_matrix (w->desired_matrix);
               if (!try_window (window, startp, 0))
@@ -16449,8 +16456,7 @@ try_window_reusing_current_matrix (struct window *w)
     return 0;
 
   /* Can't do this if region may have changed.  */
-  if ((!NILP (Vtransient_mark_mode)
-       && !NILP (BVAR (current_buffer, mark_active)))
+  if ((markpos_of_region () != -1)
       || !NILP (w->region_showing)
       || !NILP (Vshow_trailing_whitespace))
     return 0;
@@ -17282,8 +17288,7 @@ try_window_id (struct window *w)
 
   /* Can't use this if highlighting a region because a cursor movement
      will do more than just set the cursor.  */
-  if (!NILP (Vtransient_mark_mode)
-      && !NILP (BVAR (current_buffer, mark_active)))
+  if (markpos_of_region () != -1)
     GIVE_UP (9);
 
   /* Likewise if highlighting trailing whitespace.  */