From 53b43f30781fb26bf8a9764e4d852ac581edd964 Mon Sep 17 00:00:00 2001
From: Monty <monty@mariadb.org>
Date: Fri, 14 Aug 2020 21:11:30 +0300
Subject: [PATCH] Added full_name_cstring()

This returns a LEX_CSTRING and allows one to avoid strlen() calls.
---
 sql/item.cc           | 36 ++++++++++++++++++++----------------
 sql/item.h            | 13 ++++++++++---
 sql/item_subselect.cc |  3 +--
 sql/sql_test.cc       |  3 +--
 4 files changed, 32 insertions(+), 23 deletions(-)

diff --git a/sql/item.cc b/sql/item.cc
index 5afad7eef14..d90747bb12c 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -501,8 +501,7 @@ void Item::print_parenthesised(String *str, enum_query_type query_type,
 
 void Item::print(String *str, enum_query_type query_type)
 {
-  const char *name= full_name();
-  str->append(name, strlen(name));
+  str->append(full_name_cstring());
 }
 
 
@@ -3146,32 +3145,37 @@ bool Item_field::switch_to_nullable_fields_processor(void *arg)
   return 0;
 }
 
-const char *Item_ident::full_name() const
+LEX_CSTRING Item_ident::full_name_cstring() const
 {
   char *tmp;
+  size_t length;
   if (!table_name.str || !field_name.str)
-    return field_name.str ? field_name.str : name.str ? name.str : "tmp_field";
-
+  {
+    if (field_name.str)
+      return field_name;
+    if (name.str)
+      return name;
+    return { STRING_WITH_LEN("tmp_field") };
+  }
   if (db_name.str && db_name.str[0])
   {
     THD *thd= current_thd;
     tmp=(char*) thd->alloc((uint) db_name.length+ (uint) table_name.length +
 			   (uint) field_name.length+3);
-    strxmov(tmp,db_name.str,".",table_name.str,".",field_name.str,NullS);
+    length= (strxmov(tmp,db_name.str,".",table_name.str,".",field_name.str,
+                     NullS) - tmp);
   }
   else
   {
-    if (table_name.str[0])
-    {
-      THD *thd= current_thd;
-      tmp= (char*) thd->alloc((uint) table_name.length +
-			      field_name.length + 2);
-      strxmov(tmp, table_name.str, ".", field_name.str, NullS);
-    }
-    else
-      return field_name.str;
+    if (!table_name.str[0])
+      return field_name;
+
+    THD *thd= current_thd;
+    tmp= (char*) thd->alloc((uint) table_name.length +
+                            field_name.length + 2);
+    length= (strxmov(tmp, table_name.str, ".", field_name.str, NullS) - tmp);
   }
-  return tmp;
+  return {tmp, length};
 }
 
 void Item_ident::print(String *str, enum_query_type query_type)
diff --git a/sql/item.h b/sql/item.h
index bf49546b60f..62a3204a257 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -1697,7 +1697,13 @@ public:
 
   virtual Field *get_tmp_table_field() { return 0; }
   virtual Field *create_field_for_create_select(MEM_ROOT *root, TABLE *table);
-  virtual const char *full_name() const { return name.str ? name.str : "???"; }
+  inline const char *full_name() const { return full_name_cstring().str; }
+  virtual LEX_CSTRING full_name_cstring() const
+  {
+    if (name.str)
+      return name;
+    return { STRING_WITH_LEN("???") };
+  }
   const char *field_name_or_null()
   { return real_item()->type() == Item::FIELD_ITEM ? name.str : NULL; }
   const TABLE_SHARE *field_table_or_null();
@@ -3439,7 +3445,7 @@ public:
              const LEX_CSTRING &field_name_arg);
   Item_ident(THD *thd, Item_ident *item);
   Item_ident(THD *thd, TABLE_LIST *view_arg, const LEX_CSTRING &field_name_arg);
-  const char *full_name() const override;
+  LEX_CSTRING full_name_cstring() const override;
   void cleanup() override;
   st_select_lex *get_depended_from() const;
   bool remove_dependence_processor(void * arg) override;
@@ -5845,7 +5851,8 @@ public:
   /* Following methods make this item transparent as much as possible */
 
   void print(String *str, enum_query_type query_type) override;
-  const char *full_name() const override { return orig_item->full_name(); }
+  LEX_CSTRING full_name_cstring() const override
+  { return orig_item->full_name_cstring(); }
   void make_send_field(THD *thd, Send_field *field) override
   { orig_item->make_send_field(thd, field); }
   bool eq(const Item *item, bool binary_cmp) const override
diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index 580e67a11da..b77cb1d701e 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -2307,8 +2307,7 @@ Item_in_subselect::create_single_in_to_exists_cond(JOIN *join,
   if (join_having || select_lex->with_sum_func ||
       select_lex->group_list.elements)
   {
-    const char *tmp= this->full_name();
-    LEX_CSTRING field_name= {tmp, safe_strlen(tmp)};
+    LEX_CSTRING field_name= this->full_name_cstring();
     Item *item= func->create(thd, expr,
                              new (thd->mem_root) Item_ref_null_helper(
                                                       thd,
diff --git a/sql/sql_test.cc b/sql/sql_test.cc
index e29bb3188f5..e06600700bb 100644
--- a/sql/sql_test.cc
+++ b/sql/sql_test.cc
@@ -189,8 +189,7 @@ TEST_join(JOIN *join)
       JOIN_TAB *tab= jt_range->start + i;
       for (ref= 0; ref < tab->ref.key_parts; ref++)
       {
-        const char *full_name=(tab->ref.items[ref]->full_name());
-        ref_key_parts[i].append(full_name, strlen(full_name));
+        ref_key_parts[i].append(tab->ref.items[ref]->full_name_cstring());
         ref_key_parts[i].append(STRING_WITH_LEN("  "));
       }
     }