GitLab

(struct buffer): Add prevent_redisplay_optimizations_p.
(BUF_UNCHANGED_MODIFIED, UNCHANGED_MODIFIED,
BUF_OVERLAY_UNCHANGED_MODIFIED, OVERLAY_UNCHANGED_MODIFIED,
BUF_BEG_UNCHANGED, BEG_UNCHANGED, BUF_END_UNCHANGED,
END_UNCHANGED): New.
(struct buffer_text):  Add beg_unchanged, end_unchanged,
unchanged_modified, overlay_unchanged_modified.