Fix for bug#4912 "mysqld crashs in case a statement is executed

 a second time". The bug was caused by incompatibility of
negations elimination algorithm and PS: during first statement 
execute a subtree with negation was replaced with equivalent 
subtree without NOTs.
The problem was that although this transformation was permanent, 
items of the new subtree were created in execute-local memory.
The patch adds means to check if it is the first execute of a
prepared statement, and if this is the case, to allocate items
in memory of the prepared statement.
The implementation:
- backports Item_arena from 5.0
- adds Item_arena::is_stmt_prepare(), 
  Item_arena::is_first_stmt_execute().
- deletes THD::allocate_temporary_pool_for_ps_preparing(),
  THD::free_temporary_pool_for_ps_preparing(); they
  were redundant.
and adds a few invariants:
- thd->free_list never contains junk (= freed items)
- thd->current_arena is never null. If there is no
  prepared statement, it points at the thd. 
The rest of the patch contains mainly mechanical changes and
cleanups.


mysql-test/r/ps.result:
  Test results updated (test case for Bug#4912)
mysql-test/t/ps.test:
  A test case for Bug#4912 "mysqld crashs in case a statement is 
  executed a second time"
sql/item_cmpfunc.cc:
  current_statement -> current_arena
sql/item_subselect.cc:
  Statement -> Item_arena, current_statement -> current_arena
sql/item_subselect.h:
  Item_subselect does not need to save thd->current_statement.
sql/item_sum.cc:
  Statement -> Item_arena
sql/item_sum.h:
  Statement -> Item_arena
sql/mysql_priv.h:
  Statement -> Item_arena
sql/sql_base.cc:
  current_statement -> current_arena
sql/sql_class.cc:
  - Item_arena
  - convenient set_n_backup_statement, restore_backup_statement
  (nice idea, Sanja)
sql/sql_class.h:
  - Item_arena: backport from 5.0
  - allocate_temporary_pool_for_ps_preparing,
    free_temporary_pool_for_ps_preparing removed.
sql/sql_derived.cc:
  current_statement -> current_arena
sql/sql_lex.cc:
  current_statement -> current_arena
sql/sql_parse.cc:
  Deploy invariant that thd->free_list never contains junk items
  (backport from 5.0).
sql/sql_prepare.cc:
  - backporting Item_arena
  - no need to allocate_temporary_pool_for_ps_preparing().
sql/sql_select.cc:
  Fix for bug#4912 "mysqld crashs in case a statement is 
  executed a second time": if this is the first execute of
  a prepared statement, negation elimination is
  done in memory of the prepared statement.
sql/sql_union.cc:
  Backporting Item_arena from 5.0.

1 files changed, 26 insertions, 24 deletions

diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index 8c4dae92ddc..68bc144d518 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -125,7 +125,6 @@ bool Item_subselect::fix_fields(THD *thd_param, TABLE_LIST *tables, Item **ref)
 {
   DBUG_ASSERT(fixed == 0);
   engine->set_thd((thd= thd_param));
-  stmt= thd->current_statement;
 
   char const *save_where= thd->where;
   int res;
@@ -306,7 +305,10 @@ Item_singlerow_subselect::select_transformer(JOIN *join)
     return RES_OK;
 
   SELECT_LEX *select_lex= join->select_lex;
-  Statement backup;
+
+  /* Juggle with current arena only if we're in prepared statement prepare */
+  Item_arena *arena= join->thd->current_arena;
+  Item_arena backup;
 
   if (!select_lex->master_unit()->first_select()->next_select() &&
       !select_lex->table_list.elements &&
@@ -341,8 +343,8 @@ Item_singlerow_subselect::select_transformer(JOIN *join)
     if (join->conds || join->having)
     {
       Item *cond;
-      if (stmt)
-	thd->set_n_backup_item_arena(stmt, &backup);
+      if (arena->is_stmt_prepare())
+	thd->set_n_backup_item_arena(arena, &backup);
 
       if (!join->having)
 	cond= join->conds;
@@ -355,15 +357,15 @@ Item_singlerow_subselect::select_transformer(JOIN *join)
 					   new Item_null())))
 	goto err;
     }
-    if (stmt)
-      thd->restore_backup_item_arena(stmt, &backup);
+    if (arena->is_stmt_prepare())
+      thd->restore_backup_item_arena(arena, &backup);
     return RES_REDUCE;
   }
   return RES_OK;
 
 err:
-  if (stmt)
-    thd->restore_backup_item_arena(stmt, &backup);
+  if (arena->is_stmt_prepare())
+    thd->restore_backup_item_arena(arena, &backup);
   return RES_ERROR;
 }
 
@@ -640,11 +642,11 @@ Item_in_subselect::single_value_transformer(JOIN *join,
   }
 
   SELECT_LEX *select_lex= join->select_lex;
-  Statement backup;
+  Item_arena *arena= join->thd->current_arena, backup;
 
   thd->where= "scalar IN/ALL/ANY subquery";
-  if (stmt)
-    thd->set_n_backup_item_arena(stmt, &backup);
+  if (arena->is_stmt_prepare())
+    thd->set_n_backup_item_arena(arena, &backup);
 
   if (select_lex->item_list.elements > 1)
   {
@@ -857,21 +859,21 @@ Item_in_subselect::single_value_transformer(JOIN *join,
 	  push_warning(thd, MYSQL_ERROR::WARN_LEVEL_NOTE,
 		       ER_SELECT_REDUCED, warn_buff);
 	}
-	if (stmt)
-	  thd->restore_backup_item_arena(stmt, &backup);
+	if (arena->is_stmt_prepare())
+	  thd->restore_backup_item_arena(arena, &backup);
 	DBUG_RETURN(RES_REDUCE);
       }
     }
   }
 
 ok:
-  if (stmt)
-    thd->restore_backup_item_arena(stmt, &backup);
+  if (arena->is_stmt_prepare())
+    thd->restore_backup_item_arena(arena, &backup);
   DBUG_RETURN(RES_OK);
 
 err:
-  if (stmt)
-    thd->restore_backup_item_arena(stmt, &backup);
+  if (arena->is_stmt_prepare())
+    thd->restore_backup_item_arena(arena, &backup);
   DBUG_RETURN(RES_ERROR);
 }
 
@@ -885,12 +887,12 @@ Item_in_subselect::row_value_transformer(JOIN *join)
   {
     DBUG_RETURN(RES_OK);
   }
-  Statement backup;
+  Item_arena *arena= join->thd->current_arena, backup;
   Item *item= 0;
 
   thd->where= "row IN/ALL/ANY subquery";
-  if (stmt)
-    thd->set_n_backup_item_arena(stmt, &backup);
+  if (arena->is_stmt_prepare())
+    thd->set_n_backup_item_arena(arena, &backup);
 
   SELECT_LEX *select_lex= join->select_lex;
 
@@ -974,13 +976,13 @@ Item_in_subselect::row_value_transformer(JOIN *join)
     if (join->conds->fix_fields(thd, join->tables_list, 0))
       goto err;
   }
-  if (stmt)
-    thd->restore_backup_item_arena(stmt, &backup);
+  if (arena->is_stmt_prepare())
+    thd->restore_backup_item_arena(arena, &backup);
   DBUG_RETURN(RES_OK);
 
 err:
-  if (stmt)
-    thd->restore_backup_item_arena(stmt, &backup);
+  if (arena->is_stmt_prepare())
+    thd->restore_backup_item_arena(arena, &backup);
   DBUG_RETURN(RES_ERROR);
 }