Fixed LP bug #684117.

A crash may happenin the cases when the range optimizer tried to OR
two index merge such that the second one contained less range trees
than the first one.
The bug was introduced by the patch of MWL#24: 
"index_merge: fair choice between index_merge union and range access".

mysql-test/r/range_vs_index_merge.result

@@ -1386,3 +1386,15 @@ WHERE c  = 'i'  OR b IN ( 'Arkansas' , 'd' , 'pdib' , 'can' )  OR
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	index_merge	PRIMARY,idx1,idx2,idx3	idx3,idx2,PRIMARY,idx1	67,13,4,3	NULL	8	Using sort_union(idx3,idx2,PRIMARY,idx1); Using where
 DROP TABLE t1;
+CREATE TABLE t1 (
+f1 int, f2 int, f3 int, f4 int, f5 int,
+PRIMARY KEY (f4), KEY (f1), KEY (f2), KEY (f3)
+) ;
+INSERT INTO t1 VALUES (0,0,NULL,9,5), (0,0,1,9425,NULL);
+SELECT f5 FROM t1
+WHERE f2 != 1 OR f1 IS NULL OR f4 = 4 OR
+f2 AND (f4 BETWEEN 6 AND 255 OR f3 IS NULL);
+f5
+5
+NULL
+DROP TABLE t1;

mysql-test/r/range_vs_index_merge_innodb.result

@@ -1387,4 +1387,16 @@ WHERE c  = 'i'  OR b IN ( 'Arkansas' , 'd' , 'pdib' , 'can' )  OR
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	index_merge	PRIMARY,idx1,idx2,idx3	idx3,idx2,idx1,PRIMARY	67,13,3,4	NULL	9	Using sort_union(idx3,idx2,idx1,PRIMARY); Using where
 DROP TABLE t1;
+CREATE TABLE t1 (
+f1 int, f2 int, f3 int, f4 int, f5 int,
+PRIMARY KEY (f4), KEY (f1), KEY (f2), KEY (f3)
+) ;
+INSERT INTO t1 VALUES (0,0,NULL,9,5), (0,0,1,9425,NULL);
+SELECT f5 FROM t1
+WHERE f2 != 1 OR f1 IS NULL OR f4 = 4 OR
+f2 AND (f4 BETWEEN 6 AND 255 OR f3 IS NULL);
+f5
+5
+NULL
+DROP TABLE t1;
 SET SESSION STORAGE_ENGINE=DEFAULT;

mysql-test/t/range_vs_index_merge.test

@@ -918,3 +918,20 @@ SELECT COUNT(*) FROM t1
   (pk BETWEEN 120 AND 79 + 255 OR a IN ( 4 , 179 , 1 ) ) AND a > 8 ;
 
 DROP TABLE t1;
+
+#
+# Bug #684117: ORing of two index merge that caused a crash
+#
+
+CREATE TABLE t1 (
+  f1 int, f2 int, f3 int, f4 int, f5 int,
+  PRIMARY KEY (f4), KEY (f1), KEY (f2), KEY (f3)
+) ;
+INSERT INTO t1 VALUES (0,0,NULL,9,5), (0,0,1,9425,NULL);
+
+SELECT f5 FROM t1
+  WHERE f2 != 1 OR f1 IS NULL OR f4 = 4 OR
+        f2 AND (f4 BETWEEN 6 AND 255 OR f3 IS NULL);
+
+DROP TABLE t1;
+ 

sql/opt_range.cc

@@ -1187,7 +1187,8 @@ int SEL_IMERGE::or_sel_imerge_with_checks(RANGE_OPT_PARAM *param,
 {
   *is_last_check_pass= TRUE;
   SEL_TREE** tree= imerge->trees;
-  for (uint i= 0; i < n_trees; i++, tree++)
+  SEL_TREE** tree_end= imerge->trees_next;
+  for ( ; tree < tree_end; tree++)
   {
     uint rc;
     bool is_last= TRUE;