A clean-up for MDEV-7950:

- Turning get_mm_tree_for_const() from a static function into
  a protected method in Item.
- Adding a new class Item_bool_func2_with_rev, for the functions and operators
  that have a reverse function and can use the range optimizer for
  to optimize "value OP field" as "field REV_OP value". Deriving
  Item_bool_rowready_func2 and Item_funt_spatial_rel from the new class.
- Removing Item_bool_func2::have_rev_func().

Author: Alexander Barkov

sql/item.h

@@ -656,6 +656,8 @@ class Item: public Value_source,
   */
   String str_value;
 
+  SEL_TREE *get_mm_tree_for_const(RANGE_OPT_PARAM *param);
+
 public:
   /*
     Cache val_str() into the own buffer, e.g. to evaluate constant

sql/item_cmpfunc.h

@@ -144,12 +144,42 @@ class Item_bool_func :public Item_int_func
   virtual SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param,
                                      Field *field, Item *value)
   {
-    DBUG_ENTER("Item_bool_func2::get_func_mm_tree");
+    DBUG_ENTER("Item_bool_func::get_func_mm_tree");
     DBUG_ASSERT(0);
     DBUG_RETURN(0);
   }
+  /*
+    Return the full select tree for "field_item" and "value":
+    - a single SEL_TREE if the field is not in a multiple equality, or
+    - a conjuction of all SEL_TREEs for all fields from
+      the same multiple equality with "field_item".
+  */
   SEL_TREE *get_full_func_mm_tree(RANGE_OPT_PARAM *param,
                                   Item_field *field_item, Item *value);
+  /**
+    Test if "item" and "value" are suitable for the range optimization
+    and get their full select tree.
+
+    "Suitable" means:
+    - "item" is a field or a field reference
+    - "value" is NULL                (e.g. WHERE field IS NULL), or
+      "value" is an unexpensive item (e.g. WHERE field OP value)
+
+    @param item  - the argument that is checked to be a field
+    @param value - the other argument
+    @returns - NULL if the arguments are not suitable for the range optimizer.
+    @returns - the full select tree if the arguments are suitable.
+  */
+  SEL_TREE *get_full_func_mm_tree_for_args(RANGE_OPT_PARAM *param,
+                                           Item *item, Item *value)
+  {
+    DBUG_ENTER("Item_bool_func::get_full_func_mm_tree_for_args");
+    Item *field= item->real_item();
+    if (field->type() == Item::FIELD_ITEM && !field->const_item() &&
+        (!value || !value->is_expensive()))
+      DBUG_RETURN(get_full_func_mm_tree(param, (Item_field *) field, value));
+    DBUG_RETURN(NULL);
+  }
   SEL_TREE *get_mm_parts(RANGE_OPT_PARAM *param, Field *field,
                          Item_func::Functype type, Item *value);
   SEL_TREE *get_ne_mm_tree(RANGE_OPT_PARAM *param,
@@ -324,33 +354,15 @@ class Item_in_optimizer: public Item_bool_func
 */
 class Item_bool_func2 :public Item_bool_func
 {                                              /* Bool with 2 string args */
-  bool have_rev_func() const { return rev_functype() != UNKNOWN_FUNC; }
 protected:
   void add_key_fields_optimize_op(JOIN *join, KEY_FIELD **key_fields,
                                   uint *and_level, table_map usable_tables,
                                   SARGABLE_PARAM **sargables, bool equal_func);
-  SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param,
-                             Field *field, Item *value)
-  {
-    DBUG_ENTER("Item_bool_func2::get_func_mm_tree");
-    /*
-       Here the function for the following predicates are processed:
-       <, <=, =, <=>, >=, >, LIKE, spatial relations
-       If the predicate is of the form (value op field) it is handled
-       as the equivalent predicate (field rev_op value), e.g.
-       2 <= a is handled as a >= 2.
-    */
-    Item_func::Functype func_type=
-      (value != arguments()[0]) ? functype() : rev_functype();
-    DBUG_RETURN(get_mm_parts(param, field, func_type, value));
-  }
 public:
   Item_bool_func2(THD *thd, Item *a, Item *b):
     Item_bool_func(thd, a, b) { }
-  virtual enum Functype rev_functype() const { return UNKNOWN_FUNC; }
 
   bool is_null() { return MY_TEST(args[0]->is_null() || args[1]->is_null()); }
-  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr);
   COND *remove_eq_conds(THD *thd, Item::cond_result *cond_value,
                         bool top_level);
   bool count_sargable_conds(uchar *arg);
@@ -368,15 +380,87 @@ class Item_bool_func2 :public Item_bool_func
     */
     return STRING_RESULT;
   }
+  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
+  {
+    DBUG_ENTER("Item_bool_func2::get_mm_tree");
+    DBUG_ASSERT(arg_count == 2);
+    SEL_TREE *ftree= get_full_func_mm_tree_for_args(param, args[0], args[1]);
+    if (!ftree)
+      ftree= Item_func::get_mm_tree(param, cond_ptr);
+    DBUG_RETURN(ftree);
+  }
+};
+
+
+/**
+  A class for functions and operators that can use the range optimizer and
+  have a reverse function/operator that can also use the range optimizer,
+  so this condition:
+    WHERE value OP field
+  can be optimized as equivalent to:
+    WHERE field REV_OP value
+
+  This class covers:
+  - scalar comparison predicates:  <, <=, =, <=>, >=, >
+  - MBR and precise spatial relation predicates (e.g. SP_TOUCHES(x,y))
+
+  For example:
+    WHERE 10 > field
+  can be optimized as:
+    WHERE field < 10
+*/
+class Item_bool_func2_with_rev :public Item_bool_func2
+{
+protected:
+  SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param,
+                             Field *field, Item *value)
+  {
+    DBUG_ENTER("Item_bool_func2_with_rev::get_func_mm_tree");
+    Item_func::Functype func_type=
+      (value != arguments()[0]) ? functype() : rev_functype();
+    DBUG_RETURN(get_mm_parts(param, field, func_type, value));
+  }
+public:
+  Item_bool_func2_with_rev(THD *thd, Item *a, Item *b):
+    Item_bool_func2(thd, a, b) { }
+  virtual enum Functype rev_functype() const= 0;
+  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
+  {
+    DBUG_ENTER("Item_bool_func2_with_rev::get_mm_tree");
+    DBUG_ASSERT(arg_count == 2);
+    SEL_TREE *ftree;
+    /*
+      Even if get_full_func_mm_tree_for_args(param, args[0], args[1]) will not
+      return a range predicate it may still be possible to create one
+      by reversing the order of the operands. Note that this only
+      applies to predicates where both operands are fields. Example: A
+      query of the form
+
+         WHERE t1.a OP t2.b
+
+      In this case, args[0] == t1.a and args[1] == t2.b.
+      When creating range predicates for t2,
+      get_full_func_mm_tree_for_args(param, args[0], args[1])
+      will return NULL because 'field' belongs to t1 and only
+      predicates that applies to t2 are of interest. In this case a
+      call to get_full_func_mm_tree_for_args() with reversed operands
+      may succeed.
+    */
+    if (!(ftree= get_full_func_mm_tree_for_args(param, args[0], args[1])) &&
+        !(ftree= get_full_func_mm_tree_for_args(param, args[1], args[0])))
+      ftree= Item_func::get_mm_tree(param, cond_ptr);
+    DBUG_RETURN(ftree);
+  }
 };
 
-class Item_bool_rowready_func2 :public Item_bool_func2
+
+class Item_bool_rowready_func2 :public Item_bool_func2_with_rev
 {
 protected:
   Arg_comparator cmp;
 public:
   Item_bool_rowready_func2(THD *thd, Item *a, Item *b):
-    Item_bool_func2(thd, a, b), cmp(tmp_arg, tmp_arg + 1)
+    Item_bool_func2_with_rev(thd, a, b), cmp(tmp_arg, tmp_arg + 1)
   {
     allowed_arg_cols= 0;  // Fetch this value from first argument
   }
@@ -1495,7 +1579,14 @@ class Item_func_null_predicate :public Item_bool_func
   Item_func_null_predicate(THD *thd, Item *a): Item_bool_func(thd, a) { }
   void add_key_fields(JOIN *join, KEY_FIELD **key_fields, uint *and_level,
                       table_map usable_tables, SARGABLE_PARAM **sargables);
-  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr);
+  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
+  {
+    DBUG_ENTER("Item_func_null_predicate::get_mm_tree");
+    SEL_TREE *ftree= get_full_func_mm_tree_for_args(param, args[0], NULL);
+    if (!ftree)
+      ftree= Item_func::get_mm_tree(param, cond_ptr);
+    DBUG_RETURN(ftree);
+  }
   CHARSET_INFO *compare_collation() const
   { return args[0]->collation.collation; }
   void fix_length_and_dec() { decimals=0; max_length=1; maybe_null=0; }
@@ -1608,6 +1699,12 @@ class Item_func_like :public Item_bool_func2
   String cmp_value1, cmp_value2;
   bool with_sargable_pattern() const;
 protected:
+  SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param,
+                             Field *field, Item *value)
+  {
+    DBUG_ENTER("Item_func_like::get_func_mm_tree");
+    DBUG_RETURN(get_mm_parts(param, field, LIKE_FUNC, value));
+  }
   SEL_ARG *get_mm_leaf(RANGE_OPT_PARAM *param, Field *field,
                        KEY_PART *key_part,
                        Item_func::Functype type, Item *value);

sql/item_func.h

@@ -130,7 +130,11 @@ class Item_func :public Item_func_or_sum, public Used_tables_and_const_cache
   COND *build_equal_items(THD *thd, COND_EQUAL *inherited,
                           bool link_item_fields,
                           COND_EQUAL **cond_equal_ref);
-  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr);
+  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
+  {
+    DBUG_ENTER("Item_func::get_mm_tree");
+    DBUG_RETURN(const_item() ? get_mm_tree_for_const(param) : NULL);
+  }
   bool eq(const Item *item, bool binary_cmp) const;
   virtual Item *key_item() const { return args[0]; }
   virtual bool const_item() const { return const_item_cache; }

sql/item_geofunc.h

@@ -275,7 +275,7 @@ class Item_func_spatial_collection: public Item_geometry_func
   Spatial relations
 */
 
-class Item_func_spatial_rel: public Item_bool_func2
+class Item_func_spatial_rel: public Item_bool_func2_with_rev
 {
 protected:
   enum Functype spatial_rel;
@@ -285,7 +285,7 @@ class Item_func_spatial_rel: public Item_bool_func2
                        Item_func::Functype type, Item *value);
 public:
   Item_func_spatial_rel(THD *thd, Item *a, Item *b, enum Functype sp_rel):
-    Item_bool_func2(thd, a, b), spatial_rel(sp_rel)
+    Item_bool_func2_with_rev(thd, a, b), spatial_rel(sp_rel)
   {
     maybe_null= true;
   }

sql/opt_range.cc

@@ -7423,10 +7423,10 @@ SEL_TREE *Item_cond::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
 }
 
 
-static SEL_TREE *get_mm_tree_for_const(RANGE_OPT_PARAM *param, Item *cond)
+SEL_TREE *Item::get_mm_tree_for_const(RANGE_OPT_PARAM *param)
 {
   DBUG_ENTER("get_mm_tree_for_const");
-  if (cond->is_expensive())
+  if (is_expensive())
     DBUG_RETURN(0);
   /*
     During the cond->val_int() evaluation we can come across a subselect
@@ -7437,8 +7437,8 @@ static SEL_TREE *get_mm_tree_for_const(RANGE_OPT_PARAM *param, Item *cond)
   MEM_ROOT *tmp_root= param->mem_root;
   param->thd->mem_root= param->old_root;
   SEL_TREE *tree;
-  tree= cond->val_int() ? new(tmp_root) SEL_TREE(SEL_TREE::ALWAYS) :
-                          new(tmp_root) SEL_TREE(SEL_TREE::IMPOSSIBLE);
+  tree= val_int() ? new(tmp_root) SEL_TREE(SEL_TREE::ALWAYS) :
+                    new(tmp_root) SEL_TREE(SEL_TREE::IMPOSSIBLE);
   param->thd->mem_root= tmp_root;
   DBUG_RETURN(tree);
 }
@@ -7448,7 +7448,7 @@ SEL_TREE *Item::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
 {
   DBUG_ENTER("Item::get_mm_tree");
   if (const_item())
-    DBUG_RETURN(get_mm_tree_for_const(param, this));
+    DBUG_RETURN(get_mm_tree_for_const(param));
 
   /*
     Here we have a not-constant non-function Item.
@@ -7474,7 +7474,7 @@ Item_func_between::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
 {
   DBUG_ENTER("Item_func_between::get_mm_tree");
   if (const_item())
-    DBUG_RETURN(get_mm_tree_for_const(param, this));
+    DBUG_RETURN(get_mm_tree_for_const(param));
 
   SEL_TREE *tree= 0;
   SEL_TREE *ftree= 0;
@@ -7521,7 +7521,7 @@ SEL_TREE *Item_func_in::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
 {
   DBUG_ENTER("Item_func_in::get_mm_tree");
   if (const_item())
-    DBUG_RETURN(get_mm_tree_for_const(param, this));
+    DBUG_RETURN(get_mm_tree_for_const(param));
 
   if (key_item()->real_item()->type() != Item::FIELD_ITEM)
     DBUG_RETURN(0);
@@ -7535,7 +7535,7 @@ SEL_TREE *Item_equal::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
 {
   DBUG_ENTER("Item_equal::get_mm_tree");
   if (const_item())
-    DBUG_RETURN(get_mm_tree_for_const(param, this));
+    DBUG_RETURN(get_mm_tree_for_const(param));
 
   SEL_TREE *tree= 0;
   SEL_TREE *ftree= 0;
@@ -7562,77 +7562,6 @@ SEL_TREE *Item_equal::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
 }
 
 
-SEL_TREE *Item_func::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
-{
-  DBUG_ENTER("Item_func::get_mm_tree");
-  DBUG_RETURN(const_item() ? get_mm_tree_for_const(param, this) : NULL);
-}
-
-
-SEL_TREE *Item_func_null_predicate::get_mm_tree(RANGE_OPT_PARAM *param,
-                                                Item **cond_ptr)
-{
-  DBUG_ENTER("Item_func_null_predicate::get_mm_tree");
-  if (const_item())
-    DBUG_RETURN(get_mm_tree_for_const(param, this));
-  if (args[0]->real_item()->type() == Item::FIELD_ITEM)
-  {
-    Item_field *field_item= (Item_field*) args[0]->real_item();
-    if (!field_item->const_item())
-      DBUG_RETURN(get_full_func_mm_tree(param, field_item, NULL));
-  }
-  DBUG_RETURN(NULL);
-}
-
-
-SEL_TREE *Item_bool_func2::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
-{
-  DBUG_ENTER("Item_bool_func2::get_mm_tree");
-  if (const_item())
-    DBUG_RETURN(get_mm_tree_for_const(param, this));
-
-  SEL_TREE *ftree= 0;
-  DBUG_ASSERT(arg_count == 2);
-  if (arguments()[0]->real_item()->type() == Item::FIELD_ITEM)
-  {
-    Item_field *field_item= (Item_field*) (arguments()[0]->real_item());
-    Item *value= arguments()[1];
-    if (value && value->is_expensive())
-      DBUG_RETURN(0);
-    if (!arguments()[0]->real_item()->const_item())
-      ftree= get_full_func_mm_tree(param, field_item, value);
-  }
-  /*
-    Even if get_full_func_mm_tree() was executed above and did not
-    return a range predicate it may still be possible to create one
-    by reversing the order of the operands. Note that this only
-    applies to predicates where both operands are fields. Example: A
-    query of the form
-
-       WHERE t1.a OP t2.b
-
-    In this case, arguments()[0] == t1.a and arguments()[1] == t2.b.
-    When creating range predicates for t2, get_full_func_mm_tree()
-    above will return NULL because 'field' belongs to t1 and only
-    predicates that applies to t2 are of interest. In this case a
-    call to get_full_func_mm_tree() with reversed operands (see
-    below) may succeed.
-  */
-  if (!ftree && have_rev_func() &&
-      arguments()[1]->real_item()->type() == Item::FIELD_ITEM)
-  {
-    Item_field *field_item= (Item_field*) (arguments()[1]->real_item());
-    Item *value= arguments()[0];
-    if (value && value->is_expensive())
-      DBUG_RETURN(0);
-    if (!arguments()[1]->real_item()->const_item())
-      ftree= get_full_func_mm_tree(param, field_item, value);
-  }
-
-  DBUG_RETURN(ftree);
-}
-
-
 SEL_TREE *
 Item_bool_func::get_mm_parts(RANGE_OPT_PARAM *param, Field *field,
 	                     Item_func::Functype type, Item *value)