compile.c: remove unreferred label

* compile.c (remove_unreachable_chunk): remove unreferred label
  to optimize away unreachable chunk.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53402 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Fri Jan  1 12:05:53 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* compile.c (remove_unreachable_chunk): remove unreferred label
+	  to optimize away unreachable chunk.
+
 Fri Jan  1 11:42:57 2016  James Edward Gray II  <james@graysoftinc.com>
 
 	* lib/csv.rb (CSV): Add a liberal_parsing option.

compile.c

@@ -1968,6 +1968,9 @@ remove_unreachable_chunk(LINK_ELEMENT *i)
 		break;
 	    }
 	}
+	else if (i->type == ISEQ_ELEMENT_LABEL) {
+	    if (((LABEL *)i)->refcnt > 0) break;
+	}
 	else break;
 	REMOVE_ELEM(i);
 	removed = 1;