Possible redisplay performance enhancements (revisited)

[YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>]

Before pretesting, I'd like to revisit some of redisplay performance
issues I've mentioned in this list:

  1. Excessive redraw of overlapping/overlapped rows?
     http://lists.gnu.org/archive/html/emacs-devel/2005-09/msg00705.html

     Possibly-positive response from Kim F. Storm, and
     possibly-negative response from David Kastrup.
     Now I don't think mode-line/header-line updates affect redraw of
     overlapped/overlapping rows, because mode-line/header-line does
     not overlap with the other parts.

  2. Need to check face_id < BASIC_FACE_ID_SENTINEL in get_*_face_and_encoding?
     http://lists.gnu.org/archive/html/emacs-devel/2006-02/msg00238.html

     No response, but I couldn't find any reason to distinguish 
     known faces from others with respect to encode_char.
     
I've been using the following patch for a few months, but couldn't
find any problems.  So I'd like to propose installing it to CVS and
see if any problems can be found (if no objections, of course).

They are modifications to the platform-independent part, and some of
you may not notice the difference in performace.  But text drawing
with ATSUI on the Mac Carbon port is sensitive to these changes.  I
think ATSUI support is ready to be enabled by default once these
issues are solved.

				     YAMAMOTO Mitsuharu
				mituharu@math.s.chiba-u.ac.jp

Index: src/dispnew.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/dispnew.c,v
retrieving revision 1.362
diff -c -r1.362 dispnew.c
*** src/dispnew.c	12 Apr 2006 06:23:11 -0000	1.362
--- src/dispnew.c	21 Apr 2006 08:47:15 -0000
***************
*** 4156,4162 ****
  	  update_window_line (w, MATRIX_ROW_VPOS (mode_line_row,
  						  desired_matrix),
  			      &mouse_face_overwritten_p);
- 	  changed_p = 1;
  	}
  
        /* Find first enabled row.  Optimizations in redisplay_internal
--- 4156,4161 ----
***************
*** 4226,4232 ****
  	{
  	  header_line_row->y = 0;
  	  update_window_line (w, 0, &mouse_face_overwritten_p);
- 	  changed_p = 1;
  	}
  
        /* Fix the appearance of overlapping/overlapped rows.  */
--- 4225,4230 ----
Index: src/xdisp.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/xdisp.c,v
retrieving revision 1.1089
diff -c -r1.1089 xdisp.c
*** src/xdisp.c	20 Apr 2006 23:03:03 -0000	1.1089
--- src/xdisp.c	21 Apr 2006 08:47:17 -0000
***************
*** 18495,18502 ****
  	 sure to use a face suitable for unibyte.  */
        STORE_XCHAR2B (char2b, 0, glyph->u.ch);
      }
!   else if (glyph->u.ch < 128
! 	   && glyph->face_id < BASIC_FACE_ID_SENTINEL)
      {
        /* Case of ASCII in a face known to fit ASCII.  */
        STORE_XCHAR2B (char2b, 0, glyph->u.ch);
--- 18495,18501 ----
  	 sure to use a face suitable for unibyte.  */
        STORE_XCHAR2B (char2b, 0, glyph->u.ch);
      }
!   else if (glyph->u.ch < 128)
      {
        /* Case of ASCII in a face known to fit ASCII.  */
        STORE_XCHAR2B (char2b, 0, glyph->u.ch);
***************
*** 18897,18903 ****
        face_id = FACE_FOR_CHAR (f, face, c);
        face = FACE_FROM_ID (f, face_id);
      }
!   else if (c < 128 && face_id < BASIC_FACE_ID_SENTINEL)
      {
        /* Case of ASCII in a face known to fit ASCII.  */
        STORE_XCHAR2B (char2b, 0, c);
--- 18896,18902 ----
        face_id = FACE_FOR_CHAR (f, face, c);
        face = FACE_FROM_ID (f, face_id);
      }
!   else if (c < 128)
      {
        /* Case of ASCII in a face known to fit ASCII.  */
        STORE_XCHAR2B (char2b, 0, c);