MDEV-19740: Fix GCC 9.2.1 -Wmaybe-uninitialized on AMD64

For CMAKE_BUILD_TYPE=Debug, the default MYSQL_MAINTAINER_MODE=AUTO
implies -Werror along with other flags in cmake/maintainer.cmake,
which would break the debug builds when CMAKE_CXX_FLAGS include -O2.

This fix includes a backport of 6dd3f240
from MariaDB 10.3.

sql/item_cmpfunc.cc

@@ -428,11 +428,9 @@ static bool convert_const_to_int(THD *thd, Item_field *field_item,
     TABLE *table= field->table;
     sql_mode_t orig_sql_mode= thd->variables.sql_mode;
     enum_check_fields orig_count_cuted_fields= thd->count_cuted_fields;
-    my_bitmap_map *old_maps[2];
+    my_bitmap_map *old_maps[2] = { NULL, NULL };
     ulonglong UNINIT_VAR(orig_field_val); /* original field value if valid */
 
-    LINT_INIT_STRUCT(old_maps);
-
     /* table->read_set may not be set if we come here from a CREATE TABLE */
     if (table && table->read_set)
       dbug_tmp_use_all_columns(table, old_maps, 

sql/opt_subselect.h

 /*
-   Copyright (c) 2010, 2015, MariaDB
+   Copyright (c) 2010, 2019, MariaDB
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -92,19 +92,15 @@ class Loose_scan_opt
 
 public:
   Loose_scan_opt():
-    try_loosescan(FALSE),
+    try_loosescan(false),
     bound_sj_equalities(0),
-    quick_uses_applicable_index(FALSE)
+    quick_uses_applicable_index(FALSE), quick_max_loose_keypart(0),
+    best_loose_scan_key(0), best_loose_scan_records(0.0),
+    best_loose_scan_start_key(NULL),
+    best_max_loose_keypart(0), best_ref_depend_map(0)
   {
-    /* Protected by quick_uses_applicable_index */
-    LINT_INIT(quick_max_loose_keypart);
-    /* The following are protected by best_loose_scan_cost!= DBL_MAX */
-    LINT_INIT(best_loose_scan_key);
-    LINT_INIT(best_loose_scan_records);
-    LINT_INIT(best_max_loose_keypart);
-    LINT_INIT(best_loose_scan_start_key);
   }
-  
+
   void init(JOIN *join, JOIN_TAB *s, table_map remaining_tables)
   {
     /*

sql/sql_statistics.cc

@@ -1814,16 +1814,13 @@ class Index_prefix_calc: public Sql_alloc
   bool is_partial_fields_present;
 
   Index_prefix_calc(THD *thd, TABLE *table, KEY *key_info)
-    : index_table(table), index_info(key_info)
+    : index_table(table), index_info(key_info), prefixes(0), empty(true),
+    calc_state(NULL), is_single_comp_pk(false), is_partial_fields_present(false)
   {
     uint i;
     Prefix_calc_state *state;
     uint key_parts= table->actual_n_key_parts(key_info);
-    empty= TRUE;
-    prefixes= 0;
-    LINT_INIT_STRUCT(calc_state);
 
-    is_partial_fields_present= is_single_comp_pk= FALSE;
     uint pk= table->s->primary_key;
     if ((uint) (table->key_info - key_info) == pk &&
         table->key_info[pk].user_defined_key_parts == 1)

storage/maria/ma_ft_nlq_search.c

@@ -83,13 +83,13 @@ static int walk_and_match(FT_WORD *word, uint32 count, ALL_IN_ONE *aio)
 #error
 #endif
   DBUG_ENTER("walk_and_match");
-  LINT_INIT_STRUCT(subkeys);
 
   word->weight=LWS_FOR_QUERY;
 
   _ma_ft_make_key(info, &key, aio->keynr, keybuff, word, 0);
   key.data_length-= HA_FT_WLEN;
   doc_cnt=0;
+  subkeys.i= 0;
 
   if (share->lock_key_trees)
     mysql_rwlock_rdlock(&share->keyinfo[aio->keynr].root_lock);

storage/myisam/ft_nlq_search.c

@@ -81,13 +81,13 @@ static int walk_and_match(FT_WORD *word, uint32 count, ALL_IN_ONE *aio)
 #error
 #endif
   DBUG_ENTER("walk_and_match");
-  LINT_INIT_STRUCT(subkeys);
 
   word->weight=LWS_FOR_QUERY;
 
   keylen=_ft_make_key(info,aio->keynr,keybuff,word,0);
   keylen-=HA_FT_WLEN;
   doc_cnt=0;
+  subkeys.i= 0;
 
   if (share->concurrent_insert)
     mysql_rwlock_rdlock(&share->key_root_lock[aio->keynr]);

storage/myisam/mi_create.c

@@ -47,7 +47,7 @@ int mi_create(const char *name,uint keys,MI_KEYDEF *keydefs,
   uint internal_table= flags & HA_CREATE_INTERNAL_TABLE;
   ulong reclength, real_reclength,min_pack_length;
   char kfilename[FN_REFLEN],klinkname[FN_REFLEN], *klinkname_ptr;
-  char dfilename[FN_REFLEN],dlinkname[FN_REFLEN], *dlinkname_ptr;
+  char dfilename[FN_REFLEN],dlinkname[FN_REFLEN], *dlinkname_ptr= 0;
   ulong pack_reclength;
   ulonglong tot_length,max_rows, tmp;
   enum en_fieldtype type;