feature/long-lines-and-font-locking 350e97d78e: Speed up redisplay of long truncated lines

[Eli Zaretskii]

branch: feature/long-lines-and-font-locking
commit 350e97d78e7803650c6dd2bf46fcfece8e2b4b32
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Speed up redisplay of long truncated lines
    
    * src/xdisp.c (forward_to_next_line_start): Fix logic of
    interpreting the result of Fnext_single_property_change.
    (reseat_at_next_visible_line_start): When ON_NEWLINE_P is zero,
    pass NULL to 'forward_to_next_line_start', to avoid costly bidi
    iteration when none is needed.  This speeds up redisplay of very
    long lines under 'truncate-lines'.
---
 src/xdisp.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index 215a6d561e..690f10b840 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -7153,10 +7153,10 @@ forward_to_next_line_start (struct it *it, bool 
*skipped_p,
          || ((pos = Fnext_single_property_change (make_fixnum (start),
                                                   Qdisplay, Qnil,
                                                   make_fixnum (limit)),
-              NILP (pos))
+              (NILP (pos) || XFIXNAT (pos) == limit))
              && next_overlay_change (start) == ZV))
        {
-         if (!it->bidi_p)
+         if (!it->bidi_p || !bidi_it_prev)
            {
              IT_CHARPOS (*it) = limit;
              IT_BYTEPOS (*it) = bytepos;
@@ -7319,7 +7319,8 @@ reseat_at_next_visible_line_start (struct it *it, bool 
on_newline_p)
   bool skipped_p = false;
   struct bidi_it bidi_it_prev;
   bool newline_found_p
-    = forward_to_next_line_start (it, &skipped_p, &bidi_it_prev);
+    = forward_to_next_line_start (it, &skipped_p,
+                                 on_newline_p ? &bidi_it_prev : NULL);
 
   /* Skip over lines that are invisible because they are indented
      more than the value of IT->selective.  */
@@ -7331,7 +7332,8 @@ reseat_at_next_visible_line_start (struct it *it, bool 
on_newline_p)
        eassert (IT_BYTEPOS (*it) == BEGV
                 || FETCH_BYTE (IT_BYTEPOS (*it) - 1) == '\n');
        newline_found_p =
-         forward_to_next_line_start (it, &skipped_p, &bidi_it_prev);
+         forward_to_next_line_start (it, &skipped_p,
+                                     on_newline_p ? &bidi_it_prev : NULL);
       }
 
   /* Position on the newline if that's what's requested.  */