commit bf1ca14ff3f3faa9f7a018097b25aa0f66d068cd

Author: Sergei Golubchik <serg@mariadb.org>

Date:   Mon Mar 12 18:53:59 2018 +0100

    cleanup: Item_func_case

    reorder items in args[] array. Instead of

      when1,then1,when2,then2,...[,case][,else]

    sort them as

      [case,]when1,when2,...,then1,then2,...[,else]

    in this case all items used for comparison take a continuous part

    of the array and can be aggregated directly. and all items that

    can be returned take a continuous part of the array and can be

    aggregated directly. Old code had to copy them to a temporary

    array before aggreation, and then copy back (thd->change_item_tree)

    everything that was changed.

  /*

    Reorder args, to have at first the optional CASE expression, then all WHEN

    expressions, then all THEN expressions.  And the optional ELSE expression

    at the end.

  */

  const size_t size= sizeof(Item*)*nwhens*2;

  Item **arg_buffer= (Item **)my_safe_alloca(size);

  memcpy(arg_buffer, args + first_expr_num + 1, size);

  for (uint i= 0; i < nwhens ; i++)

  {

    args[first_expr_num + 1 + i]= arg_buffer[i*2];

    args[first_expr_num + 1 + i + nwhens] = arg_buffer[i*2 + 1];

  }

  my_safe_afree(arg_buffer, size);