=== modified file 'src/xdisp.c'
--- src/xdisp.c	2012-12-13 16:55:28 +0000
+++ src/xdisp.c	2012-12-14 13:43:30 +0000
@@ -2559,8 +2559,8 @@
 
 #endif /* GLYPH_DEBUG and ENABLE_CHECKING */
 
-/* Return mark position if current buffer has the region of non-zero length,
-   or -1 otherwise.  */
+/* Return mark position if current buffer has the region of non-zero
+   length, zero if mark and point are the same, or -1 otherwise.  */
 
 static ptrdiff_t
 markpos_of_region (void)
@@ -2571,8 +2571,7 @@
     {
       ptrdiff_t markpos = XMARKER (BVAR (current_buffer, mark))->charpos;
 
-      if (markpos != PT)
-	return markpos;
+      return markpos == PT ? 0 : markpos;
     }
   return -1;
 }
@@ -2712,7 +2711,7 @@
      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.  */
   markpos = markpos_of_region ();
-  if (0 <= markpos
+  if (0 < markpos
       /* Maybe highlight only in selected window.  */
       && (/* Either show region everywhere.  */
 	  highlight_nonselected_windows
@@ -13244,18 +13243,6 @@
       clear_garbaged_frames ();
     }
 
-
-  /* If showing the region, and mark has changed, we must redisplay
-     the whole window.  The assignment to this_line_start_pos prevents
-     the optimization directly below this if-statement.  */
-  if (((!NILP (Vtransient_mark_mode)
-	&& !NILP (BVAR (XBUFFER (w->buffer), mark_active)))
-       != !NILP (w->region_showing))
-      || (!NILP (w->region_showing)
-	  && !EQ (w->region_showing,
-		  Fmarker_position (BVAR (XBUFFER (w->buffer), mark)))))
-    CHARPOS (this_line_start_pos) = 0;
-
   /* Optimize the case that only the line containing the cursor in the
      selected window has changed.  Variables starting with this_ are
      set in display_line and record information about the line
@@ -13288,7 +13275,8 @@
 	      || FETCH_BYTE (BYTEPOS (tlbufpos)) == '\n'))
 	/* Former continuation line has disappeared by becoming empty.  */
 	goto cancel;
-      else if (window_outdated (w) || MINI_WINDOW_P (w))
+      else if (window_outdated (w) || MINI_WINDOW_P (w)
+	       || 0 <= markpos_of_region ())
 	{
 	  /* We have to handle the case of continuation around a
 	     wide-column character (see the comment in indent.c around
@@ -13410,6 +13398,10 @@
 	      if (w->cursor_off_p == w->last_cursor_off_p)
 		goto end_of_redisplay;
 	    }
+#ifdef GLYPH_DEBUG
+	      *w->desired_matrix->method = 0;
+	      debug_method_add (w, "optimization 2");
+#endif
 	  goto update;
 	}
       /* If highlighting the region, or if the cursor is in the echo area,
@@ -15083,7 +15075,7 @@
       /* Can't use this case if highlighting a region.  When a
          region exists, cursor movement has to do more than just
          set the cursor.  */
-      && markpos_of_region () < 0
+      && markpos_of_region () <= 0
       && NILP (w->region_showing)
       && NILP (Vshow_trailing_whitespace)
       /* This code is not used for mini-buffer for the sake of the case
@@ -15752,7 +15744,7 @@
 
 	  /* If we are highlighting the region, then we just changed
 	     the region, so redisplay to show it.  */
-	  if (0 <= markpos_of_region ())
+	  if (0 < markpos_of_region ())
 	    {
 	      clear_glyph_matrix (w->desired_matrix);
 	      if (!try_window (window, startp, 0))
@@ -16457,7 +16449,7 @@
     return 0;
 
   /* Can't do this if region may have changed.  */
-  if (0 <= markpos_of_region ()
+  if (0 < markpos_of_region ()
       || !NILP (w->region_showing)
       || !NILP (Vshow_trailing_whitespace))
     return 0;
@@ -17289,7 +17281,7 @@
 
   /* Can't use this if highlighting a region because a cursor movement
      will do more than just set the cursor.  */
-  if (0 <= markpos_of_region ())
+  if (0 < markpos_of_region ())
     GIVE_UP (9);
 
   /* Likewise if highlighting trailing whitespace.  */