- implement inheritance of sp_instr: public Query_arena.

  We need every instruction to have its own arena, because we want to
  track instruction's state (INITIALIZED_FOR_SP -> EXECUTED). Because of 
  `if' statements and other conditional instructions used in stored 
  procedures, not every instruction of a stored procedure gets executed 
  during the first (or even subsequent) execution of the procedure. 
  So it's better if we track the execution state of every instruction 
  independently.
  All instructions of a given procedure now also share sp_head's 
  mem_root, but keep their own free_list.
  This simplifies juggling with free Item lists in sp_head::execute.
- free_items() moved to be a member of Query_arena. 
- logic of 'backup_arena' debug member of Query_arena has been
  changed to support
  multi-backups. Until now, TRUE 'backup_arena' meant that there is
  exactly one active backup of the THD arena. Now it means simply that
  the arena is used for backup, so that we can't accidentally overwrite an 
  existing backup. This allows doing multiple backups, e.g. in
  sp_head::execute and Cursor::fetch, when THD arena is already backed up
  but we want to set yet another arena (usually the 'permanent' arena,
  to save permanent transformations/optimizations of a parsed tree).


sql/sp_head.cc:
  - use Query_arena support in sp_head::execute() as now sp_instr inherites
    from it.
sql/sp_head.h:
  - inherite sp_instr from Query_arena
sql/sql_class.cc:
  - changed the principle of Query_arena::backup_arena; free_items is now
    a member of Query_arena.
sql/sql_class.h:
  - changed the principle of Query_arena::backup_arena; free_items is now
    a member of Query_arena.
sql/sql_prepare.cc:
  free_items() is now a member of Query_arena.
sql/sql_select.cc:
  free_items() now automatically sets free_list to zero.

1 files changed, 3 insertions, 4 deletions

diff --git a/sql/sp_head.h b/sql/sp_head.h
index 2c75a320f30..aaef5a3d50e 100644
--- a/sql/sp_head.h
+++ b/sql/sp_head.h
@@ -274,7 +274,7 @@ private:
 // "Instructions"...
 //
 
-class sp_instr : public Sql_alloc
+class sp_instr :public Query_arena, public Sql_alloc
 {
   sp_instr(const sp_instr &);	/* Prevent use of these */
   void operator=(sp_instr &);
@@ -282,17 +282,16 @@ class sp_instr : public Sql_alloc
 public:
 
   uint marked;
-  Item *free_list;              // My Items
   uint m_ip;			// My index
   sp_pcontext *m_ctx;		// My parse context
 
   // Should give each a name or type code for debugging purposes?
   sp_instr(uint ip, sp_pcontext *ctx)
-    :Sql_alloc(), marked(0), free_list(0), m_ip(ip), m_ctx(ctx)
+    :Query_arena(0, INITIALIZED_FOR_SP), marked(0), m_ip(ip), m_ctx(ctx)
   {}
 
   virtual ~sp_instr()
-  { free_items(free_list); }
+  { free_items(); }
 
   // Execute this instrution. '*nextp' will be set to the index of the next
   // instruction to execute. (For most instruction this will be the