Few simple performance fixes found with sysbench oltp.lua and Oprofile:

 - Avoid needless load/stores in my_hash_sort_simple due to possible aliasing
 - Avoid expensive Join_plan_state constructor in choose_subquery_plan when no subquery
 - Avoid calling update_virtual_fields for every row when no virtual fields.

1 files changed, 3 insertions, 1 deletions

diff --git a/sql/opt_subselect.cc b/sql/opt_subselect.cc
index dcb5181acc3..1f6524e5afa 100644
--- a/sql/opt_subselect.cc
+++ b/sql/opt_subselect.cc
@@ -4950,7 +4950,6 @@ bool setup_jtbm_semi_joins(JOIN *join, List<TABLE_LIST> *join_list,
 
 bool JOIN::choose_subquery_plan(table_map join_tables)
 {
-  Join_plan_state save_qep; /* The original QEP of the subquery. */
   enum_reopt_result reopt_result= REOPT_NONE;
   Item_in_subselect *in_subs;
 
@@ -4969,12 +4968,15 @@ bool JOIN::choose_subquery_plan(table_map join_tables)
   }
   else
     return false;
+
   /* A strategy must be chosen earlier. */
   DBUG_ASSERT(in_subs->has_strategy());
   DBUG_ASSERT(in_to_exists_where || in_to_exists_having);
   DBUG_ASSERT(!in_to_exists_where || in_to_exists_where->fixed);
   DBUG_ASSERT(!in_to_exists_having || in_to_exists_having->fixed);
 
+  Join_plan_state save_qep; /* The original QEP of the subquery. */
+
   /*
     Compute and compare the costs of materialization and in-exists if both
     strategies are possible and allowed by the user (checked during the prepare