Fix GCC 10.2.0 -Og -fsanitize=undefined -Wmaybe-uninitialized

For some reason, adding -fsanitize=undefined (cmake -DWITH_UBSAN=ON)
to the compilation flags will cause even more warnings to be emitted.
The warnings do look bogus, but the code can be simplified.

sql/item_geofunc.cc

 /* Copyright (c) 2003, 2016, Oracle and/or its affiliates.
-   Copyright (c) 2011, 2016, MariaDB
+   Copyright (c) 2011, 2020, 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
@@ -456,14 +456,16 @@ String *Item_func_boundary::val_str(String *str_value)
   DBUG_ASSERT(fixed == 1);
   String arg_val;
   String *swkb= args[0]->val_str(&arg_val);
+
+  if ((null_value= args[0]->null_value))
+    DBUG_RETURN(0);
+
   Geometry_buffer buffer;
-  Geometry *g;
   uint32 srid= 0;
   Transporter trn(&res_receiver);
 
-  if ((null_value=
-       args[0]->null_value ||
-       !(g= Geometry::construct(&buffer, swkb->ptr(), swkb->length()))))
+  Geometry *g= Geometry::construct(&buffer, swkb->ptr(), swkb->length());
+  if (!g)
     DBUG_RETURN(0);
 
   if (g->store_shapes(&trn))

sql/opt_subselect.cc

 /*
-   Copyright (c) 2010, 2019, MariaDB
+   Copyright (c) 2010, 2020, 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
@@ -2634,16 +2634,11 @@ bool find_eq_ref_candidate(TABLE *table, table_map sj_inner_tables)
     do
     {
       uint key= keyuse->key;
-      KEY *keyinfo;
       key_part_map bound_parts= 0;
-      bool is_excluded_key= keyuse->is_for_hash_join(); 
-      if (!is_excluded_key)
-      {
-        keyinfo= table->key_info + key;
-        is_excluded_key= !MY_TEST(keyinfo->flags & HA_NOSAME);
-      }
-      if (!is_excluded_key)
+      if (!keyuse->is_for_hash_join() &&
+          (table->key_info[key].flags & HA_NOSAME))
       {
+        KEY *keyinfo= table->key_info + key;
         do  /* For all equalities on all key parts */
         {
           /*

storage/innobase/btr/btr0sea.cc

@@ -1731,7 +1731,6 @@ btr_search_update_hash_node_on_insert(btr_cur_t* cursor)
 void
 btr_search_update_hash_on_insert(btr_cur_t* cursor)
 {
-	hash_table_t*	table;
 	buf_block_t*	block;
 	dict_index_t*	index;
 	const rec_t*	rec;
@@ -1798,6 +1797,7 @@ btr_search_update_hash_on_insert(btr_cur_t* cursor)
 	}
 
 	rw_lock_t* const latch = btr_get_search_latch(index);
+	hash_table_t* const table = btr_get_search_table(index);
 	bool locked = false;
 
 	if (!page_rec_is_infimum(rec)) {
@@ -1814,7 +1814,6 @@ btr_search_update_hash_on_insert(btr_cur_t* cursor)
 				goto function_exit;
 			}
 
-			table = btr_get_search_table(index);
 			ha_insert_for_fold(table, ins_fold, block, ins_rec);
 		}
 
@@ -1830,7 +1829,6 @@ btr_search_update_hash_on_insert(btr_cur_t* cursor)
 			if (!btr_search_enabled || !block->index) {
 				goto function_exit;
 			}
-			table = btr_get_search_table(index);
 		}
 
 		if (!left_side) {
@@ -1851,7 +1849,6 @@ btr_search_update_hash_on_insert(btr_cur_t* cursor)
 				if (!btr_search_enabled || !block->index) {
 					goto function_exit;
 				}
-				table = btr_get_search_table(index);
 			}
 
 			ha_insert_for_fold(table, ins_fold, block, ins_rec);
@@ -1868,7 +1865,6 @@ btr_search_update_hash_on_insert(btr_cur_t* cursor)
 			if (!btr_search_enabled || !block->index) {
 				goto function_exit;
 			}
-			table = btr_get_search_table(index);
 		}
 
 		if (!left_side) {