Improve detection of long lines.

* src/buffer.h (struct buffer_text): New field.
(BUF_CHARS_UNCHANGED_MODIFIED, CHARS_UNCHANGED_MODIFIED): New macros.

* src/buffer.c (Fget_buffer_create): Initialize the new field.

* src/xdisp.c (mark_window_display_accurate_1): Set the new field.
(redisplay_window): Use it, together with CHARS_MODIFF, instead of
MODIFF and UNCHANGED_MODIFIED to decide whether to check for long
lines.

* src/pdumper.c (dump_buffer): Dump the new field.

1 files changed, 9 insertions, 0 deletions

diff --git a/src/buffer.h b/src/buffer.h
index 47b4bdf749b..77f9ea20afa 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -149,12 +149,18 @@ enum { BEG = 1, BEG_BYTE = BEG };
 #define BUF_BEG_UNCHANGED(buf) ((buf)->text->beg_unchanged)
 #define BUF_END_UNCHANGED(buf) ((buf)->text->end_unchanged)
 
+#define BUF_CHARS_UNCHANGED_MODIFIED(buf) \
+  ((buf)->text->chars_unchanged_modified)
+
 #define UNCHANGED_MODIFIED \
   BUF_UNCHANGED_MODIFIED (current_buffer)
 #define OVERLAY_UNCHANGED_MODIFIED \
   BUF_OVERLAY_UNCHANGED_MODIFIED (current_buffer)
 #define BEG_UNCHANGED BUF_BEG_UNCHANGED (current_buffer)
 #define END_UNCHANGED BUF_END_UNCHANGED (current_buffer)
+
+#define CHARS_UNCHANGED_MODIFIED \
+  BUF_CHARS_UNCHANGED_MODIFIED (current_buffer)
 
 /* Functions to set PT in the current buffer, or another buffer.  */
 
@@ -268,6 +274,9 @@ struct buffer_text
        end_unchanged contain no useful information.  */
     modiff_count overlay_unchanged_modified;
 
+    /* CHARS_MODIFF as of last redisplay that finished.  */
+    modiff_count chars_unchanged_modified;
+
     /* Properties of this buffer's text.  */
     INTERVAL intervals;