regex: add case to complement optimization.

* regex.c (reg_optimize): Based on the reasoning in the
previous commit, we can also statically optimize a
complement whose argument is the t regex: match nothing.
We convert that to match everything: the .* regex.
Now (regex-compile "~[]") -> #/.*/.

1 files changed, 2 insertions, 0 deletions

diff --git a/regex.c b/regex.c
index 61416fb0..24caca48 100644
--- a/regex.c
+++ b/regex.c
@@ -1897,6 +1897,8 @@ static val reg_optimize(val exp)
         return t;
       if (arg == nil)
         return cons(oneplus_s, cons(wild_s, nil));
+      if (arg == t)
+        return cons(zeroplus_s, cons(wild_s, nil));
       if (reg_single_char_p(arg))
         return list(or_s,
                     list(optional_s, invert_single(arg), nao),