Amend af784385: Avoid vtable overhead

When neither MSAN nor Valgrind are enabled, declare
Field::mark_unused_memory_as_defined() as an empty inline function,
instead of declaring it as a virtual function.

include/my_valgrind.h

-/* Copyright (C) 2010, 2019, MariaDB Corporation.
+/* Copyright (C) 2010, 2020, MariaDB Corporation.
 
    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
@@ -32,6 +32,7 @@
 
 #if defined(HAVE_VALGRIND_MEMCHECK_H) && defined(HAVE_valgrind)
 # include <valgrind/memcheck.h>
+# define HAVE_valgrind_or_MSAN
 # define MEM_UNDEFINED(a,len) VALGRIND_MAKE_MEM_UNDEFINED(a,len)
 # define MEM_MAKE_DEFINED(a,len) VALGRIND_MAKE_MEM_DEFINED(a,len)
 # define MEM_NOACCESS(a,len) VALGRIND_MAKE_MEM_NOACCESS(a,len)
@@ -50,6 +51,7 @@
 # define REDZONE_SIZE 8
 #elif __has_feature(memory_sanitizer)
 # include <sanitizer/msan_interface.h>
+# define HAVE_valgrind_or_MSAN
 # define MEM_UNDEFINED(a,len) __msan_allocated_memory(a,len)
 # define MEM_MAKE_DEFINED(a,len) __msan_unpoison(a,len)
 # define MEM_NOACCESS(a,len) ((void) 0)

sql/field.cc

 /*
    Copyright (c) 2000, 2017, Oracle and/or its affiliates.
-   Copyright (c) 2008, 2017, MariaDB
+   Copyright (c) 2008, 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
@@ -7772,11 +7772,14 @@ my_decimal *Field_varstring::val_decimal(my_decimal *decimal_value)
 
 }
 
+
+#ifdef HAVE_valgrind_or_MSAN
 void Field_varstring::mark_unused_memory_as_defined()
 {
-  uint used_length __attribute__((unused)) = get_length();
+  uint used_length= get_length();
   MEM_MAKE_DEFINED(get_data() + used_length, field_length - used_length);
 }
+#endif
 
 
 int Field_varstring::cmp_max(const uchar *a_ptr, const uchar *b_ptr,

sql/field.h

 #ifndef FIELD_INCLUDED
 #define FIELD_INCLUDED
 /* Copyright (c) 2000, 2015, Oracle and/or its affiliates.
-   Copyright (c) 2008, 2017, MariaDB Corporation.
+   Copyright (c) 2008, 2020, MariaDB Corporation.
 
    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
@@ -850,13 +850,17 @@ class Field: public Value_source
             enum_check_fields check_level);
   int store(const LEX_STRING *ls, CHARSET_INFO *cs)
   { return store(ls->str, (uint32) ls->length, cs); }
-  /*
+#ifdef HAVE_valgrind_or_MSAN
+  /**
     Mark unused memory in the field as defined. Mainly used to ensure
     that if we write full field to disk (for example in
     Count_distinct_field::add(), we don't write unitalized data to
     disk which would confuse valgrind or MSAN.
   */
   virtual void mark_unused_memory_as_defined() {}
+#else
+  void mark_unused_memory_as_defined() {}
+#endif
 
   virtual double val_real(void)=0;
   virtual longlong val_int(void)=0;
@@ -3250,7 +3254,9 @@ class Field_varstring :public Field_longstr {
   int  store(const char *to,uint length,CHARSET_INFO *charset);
   int  store(longlong nr, bool unsigned_val);
   int  store(double nr) { return Field_str::store(nr); } /* QQ: To be deleted */
+#ifdef HAVE_valgrind_or_MSAN
   void mark_unused_memory_as_defined();
+#endif /* HAVE_valgrind_or_MSAN */
   double val_real(void);
   longlong val_int(void);
   String *val_str(String*,String *);