patch 7.4.783
Problem:    copy_chars() and copy_spaces() are inefficient.
Solution:   Use memset() instead. (Dominique Pelle)
diff --git a/src/screen.c b/src/screen.c
index 379b0f4..3efce5f 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -2833,7 +2833,7 @@
     int		fdc = compute_foldcolumn(wp, 0);
 
     /* Init to all spaces. */
-    copy_spaces(p, (size_t)fdc);
+    vim_memset(p, ' ', (size_t)fdc);
 
     level = win_foldinfo.fi_level;
     if (level > 0)