Additional reductions for and.

* regex.c (reg_optimize): If the empty regex is and-ed with
another regex, that other regex must be nullable, otherwise
the and matches nothing.  This is captured in some new
reductions for the and operator.

1 files changed, 6 insertions, 0 deletions

diff --git a/regex.c b/regex.c
index 3943d93a..823f0c4e 100644
--- a/regex.c
+++ b/regex.c
@@ -1945,6 +1945,12 @@ static val reg_optimize(val exp)
       if (arg1 == t || arg2 == t)
         return t;
 
+      if (arg1 == nil)
+        return null(reg_nullable(arg2));
+
+      if (arg2 == nil)
+        return null(reg_nullable(arg1));
+
       if (reg_matches_all(arg1))
         return arg2;