Minor additional fix in the wake of bugs #13623 and 13626.

 src/xdisp.c (redisplay_internal): Don't set w->region_showing to the
 marker's position.
 (display_line): Set w->region_showing to the value of
 it->region_beg_charpos, not to -1.  This fixes redisplay
 optimization when cursor is moved up after M->.
 src/window.h (struct window): region_showing can no longer be negative.

1 files changed, 1 insertions, 2 deletions

diff --git a/src/window.h b/src/window.h
index 0f4f242641e..dcef37abb4c 100644
--- a/src/window.h
+++ b/src/window.h
@@ -338,8 +338,7 @@ struct window
     int vscroll;
 
     /* If we have highlighted the region (or any part of it), the mark
-       position or -1 (the latter is used by the iterator for internal
-       purposes); otherwise zero.  */
+       (region start) position; otherwise zero.  */
     ptrdiff_t region_showing;
 
     /* Z_BYTE - buffer position of the last glyph in the current matrix of W.