Fix for bug#37337: Function returns different results

Problem: REGEXP in functions/PSs may return wrong results
due to improper initialization.

Fix: initialize required REGEXP params.

mysql-test/r/func_regexp.result

@@ -115,3 +115,21 @@ SELECT 1 REGEXP NULL;
 1 REGEXP NULL
 NULL
 End of 5.0 tests
+CREATE TABLE t1(a INT, b CHAR(4));
+INSERT INTO t1 VALUES (1, '6.1'), (1, '7.0'), (1, '8.0');
+PREPARE stmt1 FROM "SELECT a FROM t1 WHERE a=1 AND '7.0' REGEXP b LIMIT 1";
+EXECUTE stmt1;
+a
+1
+EXECUTE stmt1;
+a
+1
+EXECUTE stmt1;
+a
+1
+EXECUTE stmt1;
+a
+1
+DEALLOCATE PREPARE stmt1;
+DROP TABLE t1;
+End of 5.1 tests

mysql-test/t/func_regexp.test

@@ -65,3 +65,20 @@ drop table t1;
 SELECT 1 REGEXP NULL;
 
 --echo End of 5.0 tests
+
+
+#
+# Bug #37337: Function returns different results
+#
+CREATE TABLE t1(a INT, b CHAR(4));
+INSERT INTO t1 VALUES (1, '6.1'), (1, '7.0'), (1, '8.0');
+PREPARE stmt1 FROM "SELECT a FROM t1 WHERE a=1 AND '7.0' REGEXP b LIMIT 1";
+EXECUTE stmt1;
+EXECUTE stmt1;
+EXECUTE stmt1;
+EXECUTE stmt1;
+DEALLOCATE PREPARE stmt1;
+DROP TABLE t1;
+
+
+--echo End of 5.1 tests

sql/item_cmpfunc.cc

@@ -4592,6 +4592,7 @@ void Item_func_regex::cleanup()
   {
     my_regfree(&preg);
     regex_compiled=0;
+    prev_regexp.length(0);
   }
   DBUG_VOID_RETURN;
 }