MWL#17: Table elimination

Address review feedback: 
- Change from Wave-based approach (a-la const table detection) to 
  building and walking functional dependency graph.
- Change from piggy-backing on ref-access code and KEYUSE structures
  to using our own expression analyzer.


sql/item.cc:
  MWL#17: Table elimination
  - Move from C-ish Field_processor_info to C++ ish and generic Field_enumerator
sql/item.h:
  MWL#17: Table elimination
  - Move from C-ish Field_processor_info to C++ ish and generic Field_enumerator
sql/sql_bitmap.h:
  MWL#17: Table elimination
  - Backport of Table_map_iterator from 6.0

sql/item.cc

@@ -1918,30 +1918,8 @@ void Item_field::reset_field(Field *f)
 
 bool Item_field::check_column_usage_processor(uchar *arg)
 {
-  Field_processor_info* info=(Field_processor_info*)arg;
-
-  if (field->table == info->table)
-  {
-    /* It is not ok to use columns that are not part of the key of interest: */
-    if (!(field->part_of_key.is_set(info->keyno)))
-       return TRUE;
-
-    /* Find which key part we're using and mark it in needed_key_parts */
-    KEY *key= &field->table->key_info[info->keyno];
-    for (uint part= 0; part < key->key_parts; part++)
-    {
-      if (field->field_index == key->key_part[part].field->field_index)
-      {
-        if (part == info->forbidden_part)
-          return TRUE;
-        info->needed_key_parts |= key_part_map(1) << part;
-        break;
-      }
-    }
-    return FALSE;
-  }
-  else
-    info->used_tables |= this->used_tables();
+  Field_enumerator *fe= (Field_enumerator*)arg;
+  fe->see_field(field);
   return FALSE;
 }
 

sql/item.h

@@ -1017,7 +1017,7 @@ public:
   bool eq_by_collation(Item *item, bool binary_cmp, CHARSET_INFO *cs); 
 };
 
-/* Data for Item::check_column_usage_processor */
+#if 0
 typedef struct 
 {
   TABLE *table;         /* Table of interest */
@@ -1028,7 +1028,15 @@ typedef struct
   /* [Set by processor] Parts of index of interest that expression refers to */
   uint needed_key_parts;
 } Field_processor_info;
+#endif 
 
+/* Data for Item::check_column_usage_processor */
+class Field_enumerator
+{
+public:
+  virtual void see_field(Field *field)= 0;
+  virtual ~Field_enumerator() {}; /* Shut up compiler warning */
+};
 
 class sp_head;
 

sql/sql_bitmap.h

@@ -93,6 +93,34 @@ public:
   }
 };
 
+/* An iterator to quickly walk over bits in unlonglong bitmap. */
+class Table_map_iterator
+{
+  ulonglong bmp;
+  uint no;
+public:
+  Table_map_iterator(ulonglong t) : bmp(t), no(0) {}
+  int next_bit()
+  {
+    static const char last_bit[16]= {32, 0, 1, 0, 
+                                      2, 0, 1, 0, 
+                                      3, 0, 1, 0,
+                                      2, 0, 1, 0};
+    uint bit;
+    while ((bit= last_bit[bmp & 0xF]) == 32)
+    {
+      no += 4;
+      bmp= bmp >> 4;
+      if (!bmp)
+        return BITMAP_END;
+    }
+    bmp &= ~(1LL << bit);
+    return no + bit;
+  }
+  int operator++(int) { return next_bit(); }
+  enum { BITMAP_END= 64 };
+};
+
 template <> class Bitmap<64>
 {
   ulonglong map;
@@ -136,5 +164,10 @@ public:
   my_bool operator==(const Bitmap<64>& map2) const { return map == map2.map; }
   char *print(char *buf) const { longlong2str(map,buf,16); return buf; }
   ulonglong to_ulonglong() const { return map; }
+  class Iterator : public Table_map_iterator
+  {
+  public:
+    Iterator(Bitmap<64> &bmp) : Table_map_iterator(bmp.map) {}
+  };
 };