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.

sql/filesort.cc

@@ -589,7 +589,7 @@ static ha_rows find_all_keys(SORTPARAM *param, SQL_SELECT *select,
     {
       if ((error= select->quick->get_next()))
         break;
-      if (!error)
+      if (!error && sort_form->vfield)
         update_virtual_fields(thd, sort_form);
       file->position(sort_form->record[0]);
       DBUG_EXECUTE_IF("debug_filesort", dbug_print_record(sort_form, TRUE););
@@ -608,7 +608,7 @@ static ha_rows find_all_keys(SORTPARAM *param, SQL_SELECT *select,
       else
       {
 	error=file->ha_rnd_next(sort_form->record[0]);
-	if (!error)
+	if (!error && sort_form->vfield)
 	  update_virtual_fields(thd, sort_form);
 	if (!flag)
 	{

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

sql/records.cc

@@ -344,7 +344,8 @@ static int rr_quick(READ_RECORD *info)
       break;
     }
   }
-  update_virtual_fields(info->thd, info->table);
+  if (info->table->vfield)
+    update_virtual_fields(info->thd, info->table);
   return tmp;
 }
 

sql/sql_select.cc

@@ -15828,7 +15828,8 @@ evaluate_join_record(JOIN *join, JOIN_TAB *join_tab,
     DBUG_RETURN(NESTED_LOOP_KILLED);            /* purecov: inspected */
   }
 
-  update_virtual_fields(join->thd, join_tab->table);
+  if (join_tab->table->vfield)
+    update_virtual_fields(join->thd, join_tab->table);
 
   if (select_cond)
   {

sql/table.cc

@@ -2466,30 +2466,35 @@ int open_table_from_share(THD *thd, TABLE_SHARE *share, const char *alias,
   /*
     Process virtual columns, if any.
   */
-  if (!(vfield_ptr = (Field **) alloc_root(&outparam->mem_root,
-                                          (uint) ((share->vfields+1)*
-                                                  sizeof(Field*)))))
-    goto err;
-
-  outparam->vfield= vfield_ptr;
-  
-  for (field_ptr= outparam->field; *field_ptr; field_ptr++)
+  if (!share->vfields)
+    outparam->vfield= NULL;
+  else
   {
-    if ((*field_ptr)->vcol_info)
+    if (!(vfield_ptr = (Field **) alloc_root(&outparam->mem_root,
+                                             (uint) ((share->vfields+1)*
+                                                     sizeof(Field*)))))
+      goto err;
+
+    outparam->vfield= vfield_ptr;
+
+    for (field_ptr= outparam->field; *field_ptr; field_ptr++)
     {
-      if (unpack_vcol_info_from_frm(thd,
-                                    outparam,
-                                    *field_ptr,
-                                    &(*field_ptr)->vcol_info->expr_str,
-                                    &error_reported))
+      if ((*field_ptr)->vcol_info)
       {
-        error= 4; // in case no error is reported
-        goto err;
+        if (unpack_vcol_info_from_frm(thd,
+                                      outparam,
+                                      *field_ptr,
+                                      &(*field_ptr)->vcol_info->expr_str,
+                                      &error_reported))
+        {
+          error= 4; // in case no error is reported
+          goto err;
+        }
+        *(vfield_ptr++)= *field_ptr;
       }
-      *(vfield_ptr++)= *field_ptr;
     }
+    *vfield_ptr= 0;                              // End marker
   }
-  *vfield_ptr= 0;                              // End marker
 
 #ifdef WITH_PARTITION_STORAGE_ENGINE
   if (share->partition_info_str_len && outparam->file)

strings/ctype-simple.c

@@ -306,19 +306,24 @@ void my_hash_sort_simple(CHARSET_INFO *cs,
 {
   register const uchar *sort_order=cs->sort_order;
   const uchar *end;
+  ulong n1, n2;
 
   /*
     Remove end space. We have to do this to be able to compare
     'A ' and 'A' as identical
   */
   end= skip_trailing_space(key, len);
-  
+
+  n1= *nr1;
+  n2= *nr2;
   for (; key < (uchar*) end ; key++)
   {
-    nr1[0]^=(ulong) ((((uint) nr1[0] & 63)+nr2[0]) * 
-	     ((uint) sort_order[(uint) *key])) + (nr1[0] << 8);
-    nr2[0]+=3;
+    n1^=(ulong) ((((uint) n1 & 63)+n2) *
+	     ((uint) sort_order[(uint) *key])) + (n1 << 8);
+    n2+=3;
   }
+  *nr1= n1;
+  *nr2= n2;
 }