Fix bug MDEV-4895 Valgrind warnings (Conditional jump or move depends on uninitialised value) in Field_datetime::get_date on GREATEST(..) IS NULL

Analysis:
The cause of the valgrind warning was an attempt to evaluate a Field that was not yet read.
The reason was that on one hand Item_func_isnotnull was marked as constant by
Item_func_isnotnull::update_used_tables, and this allowed eval_const_cond() to be called.
On the other hand Item_func_isnotnull::val_int() evaluated its argument as if it was not
constant.

Solution:
The fix make sure that Item_func_isnotnull::val_int() doesn't evaluate its argument when
it is constant and cannot be NULL, because the result is known in this case. 

1 files changed, 28 insertions, 0 deletions

diff --git a/mysql-test/t/null.test b/mysql-test/t/null.test
index 2878b54c357..4a45240ec68 100644
--- a/mysql-test/t/null.test
+++ b/mysql-test/t/null.test
@@ -255,3 +255,31 @@ DESCRIBE t2;
 DROP TABLE t1, t2;
 
 --echo # End of 5.0 tests
+
+--echo #
+--echo # MDEV-4895 Valgrind warnings (Conditional jump or move depends on uninitialised value) in Field_datetime::get_date on GREATEST(..) IS NULL
+--echo #
+
+CREATE TABLE t1 (dt DATETIME NOT NULL);
+INSERT INTO t1 VALUES (NOW()),(NOW());
+
+EXPLAIN
+SELECT * FROM t1 WHERE concat( dt, '2012-12-21 12:12:12' ) IS NULL;
+SELECT * FROM t1 WHERE concat( dt, '2012-12-21 12:12:12' ) IS NULL;
+
+DROP TABLE t1;
+CREATE TABLE t1 (dt INT NOT NULL);
+INSERT INTO t1 VALUES (1),(2);
+EXPLAIN
+SELECT * FROM t1 WHERE concat( dt, '1' ) IS NULL;
+SELECT * FROM t1 WHERE concat( dt, '1' ) IS NULL;
+
+DROP TABLE t1;
+CREATE TABLE t1 (dt INT NOT NULL);
+INSERT INTO t1 VALUES (1),(2);
+
+EXPLAIN
+SELECT * FROM t1 WHERE NOT (concat( dt, '1' ) IS NOT NULL); 
+SELECT * FROM t1 WHERE NOT (concat( dt, '1' ) IS NOT NULL); 
+
+DROP TABLE t1;